2008

Ages and Lengths of Yellow Perch Perca flavescens, White Perch Morone americana, and Lake Whitefish Coregonus clupeaformis in Commercial Trap Nets in Western Lake Erie (PDF file - 76 KB)

We collected samples of yellow perch (Perca flavescens) and white perch (Morone americana) in spring, and of lake whitefish (Coregonus clupeaformis) in autumn, from commercial trap nets set in western Lake Erie in 2008. The yellow perch sample (N = 153) was dominated (72%, of the total sample) by the 2003 year class, followed by the 2005 year class (12%). The white perch sample (N = 201) was dominated by the 2005 year class (39% of the total sample), followed by the 2003 year class (23%). The lake whitefish (N = 99) sample was dominated by the 2003 year class (75%) followed by the 2001 year class (10%). For yellow perch (both sexes in spring, analyzed separately) and lake whitefish (males in autumn), mean total length at age 5 was the same for the 2001 year class (calculated from historical data) and the 2003 year class.

Great Lakes Prey Fish Populations: A Cross-Basin View of Status and Trends in 2008 (PDF file - 162 KB)

Assessments of prey fishes in the Great Lakes have been conducted annually since the 1970s by the Great Lakes Science Center, sometimes assisted by partner agencies. Prey fish assessments differ among lakes in the proportion of a lake covered, seasonal timing, bottom trawl gear used, sampling design, and the manner in which the trawl is towed (across or along bottom contours). Because each assessment is unique in one or more important aspects, a direct comparison of prey fish catches among lakes is problematic. All of the assessments, however, produce indices of abundance or biomass that can be standardized to facilitate comparisons of trends among lakes and to illustrate present status of the populations. We present indices of abundance for important prey fishes in the Great Lakes standardized to the highest value for a time series within each lake: cisco (Coregonus artedi), bloater (C. hoyi), rainbow smelt (Osmerus mordax), and alewife (Alosa pseudoharengus). We also provide indices for round goby (Neogobius melanostomus), an invasive fish presently spreading throughout the basin. Our intent is to provide a short, informal report emphasizing data presentation rather than synthesis; for this reason we intentionally avoid use of tables and cited references.

For each lake, standardized relative indices for annual biomass and density estimates of important prey fishes were calculated as the fraction relative to the largest value observed in the times series. To determine whether basin-wide trends were apparent for each species, we first ranked standardized index values within each lake. When comparing ranked index values from three or more lakes, we calculated the Kendall coefficient of concordance (W), which can range from 0 (complete discordance or disagreement among trends) to 1 (complete concordance or agreement among trends). The P-value for W provides the probability of agreement across the lakes. When comparing ranked index values from two lakes, we calculated the Kendall correlation coefficient (τ), which ranges from -1 (inverse association, perfect disagreement) to 1 (direct association, perfect agreement). Here, the P-value for τ provides the probability of either inverse or direct association between the lakes. First, we present trends in relative biomass of age-1 and older prey fishes to show changes in populations within each lake. Then, we present standardized indices of numerical abundance of a single age class to show changes in relative year-class strength within each lake. Indices of year-class strength reliably reflect the magnitude of the cohort size at subsequent ages. However, because of differences in survey timing across lakes, the age class that is used for each species to index year-class strength varies across lakes and, just as surveys differ among lakes, methods for determining fish age-class differ also. For Lake Superior cisco, bloater, smelt, and Lake Michigan alewife, year- class strengths are based on aged fish and age-length keys, and for all other combinations of lakes and species, age-classes are assigned based on fish length cut-offs. Our intent with this report is to provide a cross-lakes view of population trends but not to propose reasons for those trends.

Lake Trout Rehabilitation in Lake Ontario, 2008 (PDF file - 162 KB)

Each year we report on the progress toward rehabilitation of the Lake Ontario lake trout Salvelinus namaycush population, including the results of stocking, annual assessment surveys, creel surveys, and evidence of natural reproduction observed from all standard surveys performed by USGS and NYSDEC. During 2008, the number of yearling lake trout stocked in May (500,908) was at the target level of 500,000. The adjusted catch of age-2 lake trout with bottom trawls during the juvenile lake trout survey remained low and was 88% below the mean for the 1983-1989 year classes. Adult lake trout catch per unit effort from the gill net survey was 70% below the 1986-1998 average. The rate of wounding by sea lamprey Petromyzon marinus on lake trout caught in gill nets was 1.47 fresh (A1) wounds per 100 lake trout and was below target for the first time in six years. Estimates from the NYSDEC fishing boat survey indicated that, for the third consecutive year, angler catch, harvest, and harvest rate of lake trout remained near record lows. The condition of adult lake trout, indexed from annual length–weight regressions, increased from the reduced levels observed during 2004-2006 to a level equivalent to the high levels observed during 1996-1999. The improved condition for juvenile lake trout observed in 2006 and 2007 continued in 2008 and remained above the mean for the data series. Reproductive potential for the adult stock in 2008, determined from the annual egg deposition index, fell to a level 76% below the 1993-1998 mean. One age-2 naturally produced lake trout was collected in survey catches providing evidence of a 2006 year class, but age-1s were absent for the fourth consecutive year.

Plasma levels of estradiol, testosterone, and vitellogenin in lake sturgeon (Acipenser fulvescens) to determine their sex ratio in the St. Clair River (PDF file - 523 KB)

Very little is known about remnant lake sturgeon stocks and the consequences of fishery management options on those stocks. Since 1997, assessment surveys by the Michigan Department of Natural Resources (MDNR) have characterized the St. Clair River (SCR) lake sturgeon population as relatively young with steady or increasing recruitment. However, researchers have not been able to determine effectively the sex or maturity for most of the sturgeon they capture because few fish caught during surveys were releasing gametes. Consequently, data are sparse or lacking for sex ratio, maturity schedule, and sex-specific growth rates and age composition. As a result, MDNR sport fishing regulations designed to protect reproductively mature females are based on minimal data and may not provide adequate protection of mature females from harvest. Sex ratio, age at first maturity, and spawning frequency data are needed to assist in managing the population for sustainable sport and commercial harvest. Available techniques for sexing sturgeon range from very invasive surgery to a simple blood draw and laboratory assays. This study focused on identifying the sex of mature and immature lake sturgeon by measuring the sex hormones estradiol (E2) and testosterone (T) and the phosphoprotein vitellogenin (Vtg) in blood plasma by radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA), and evaluating this technique as a tool in lake sturgeon population management. A total of 115 lake sturgeon were sampled from May through June in 2004 and 2005 from the SCR, Michigan, USA. Twelve fish were releasing gametes at the time of capture. Due to the reproductive biology of lake sturgeon, we were able to assign a sex designation to 56% of the captured sturgeon based on hormone levels, resulting in a sex ratio of 1 female to 2.7 males. Considering that lake sturgeon are threatened with extinction in Michigan, advantages to using blood plasma assays were that fish were not harmed, and sample collection was quick, simple, and inexpensive. On the other hand, turnaround time, cost, and specialized equipment and training for the laboratory hormone assays make the technique far less than ideal for MDNR needs. Alternative options may include using other non-destructive field methods presented in the literature (e.g., ultrasound and fiber-optic endoscope) in conjunction with plasma hormone assays both to provide immediate sex identification and to support research and development of plasma hormone assays designed for the field. Determining the sex ratio of the SCR lake sturgeon population is an important component of a management program so that sturgeon restoration measures can be taken. This research supports the ‘Restoration ecology of native species and their habitats’ theme of the Huron-Erie Corridor Initiative www.huron-erie.org).

Spring and Autumn Fish Density, Biomass, and Diets in Michigan and Ontario Waters of the Western Basin of Lake Erie (PDF file - 156 KB)

The Lake Erie Biological Station completed its fifth consecutive year of a collaborative, multi-agency assessment of forage fish populations throughout the western basin of Lake Erie in 2008. The objectives of this evaluation were to provide estimates of densities and biomasses of forage fishes throughout the western basin of Lake Erie to the interagency database for assessing seasonal and spatial distributions of forage fishes and to assess year class strength of key forage and predator species. We sampled 25 stations in Ontario and Michigan waters of the western basin of Lake Erie with bottom trawls in June and September 2008. We calculated density (number/ha) and biomass (kg/ha) of all forage fishes. We also examined stomach contents from white perch Morone americana and yellow perch Perca flavescens. Most species had strong year classes in 2008 following several consecutive weaker year classes. Freshwater drum Aplodinotus grunniens and rainbow smelt Osmerus mordax had the strongest year classes of the time series. We captured several individuals of the invasive tubenose goby Proterorhinus marmoratus at four sites near the mouth of the Detroit River, which may signal a range expansion. Diets of yearling and older yellow perch in 2008 were dominated by macroinvertebrates in both spring and autumn. White perch diets were dominated by zooplankton in June and macroinvertebrates and fish equally in September. Unlike the trend exhibited during 2005-2007, autumn diets of both species exhibited a decrease in the proportion of fish and an increase in the proportion of zooplankton during 2008. Recent analyses of other USGS data sets have underscored the value of nighttime sampling for indices of abundance of yellow perch and walleye. We will explore the possibility of adding nighttime sampling to our western basin program in the future.

Status and Trends of the Lake Huron Deepwater Demersal Fish Community, 2008 (PDF file - 310 KB)

The U.S.Geological Survey Great Lakes Science Center has conducted trawl surveys to assess annual changes in the deepwater demersal fish community of Lake Huron since 1973. Since 1992, surveys have been carried out using a 21 m wing trawl towed on-contour at depths ranging from 9 to 110 m on fixed transects. Sample sites include five ports in U.S. waters with less frequent sampling near Goderich, Ontario. The 2008 fall bottom trawl survey was carried out between October 24 and November 20, 2008 and sampled only the three northern U.S. ports at DeTour, Hammond Bay, and Alpena due to mechanical problems with the research vessel and prolonged periods of bad weather. Therefore, all data presented for 2008 are based on samples collected from these ports. Compared to previous years, alewife populations in Lake Huron remain at low levels after collapsing in 2004. Age-0 alewife density and biomass appears to have increased slightly but overall levels remain near the nadir observed in 2004. Density and biomass of adult and juvenile rainbow smelt showed a decrease from 2007 despite record-high abundance of juveniles observed in 2005, suggesting recruitment was low. Numbers of adult and juvenile bloater were low despite recent high year-classes. Abundances for most other prey species were similar to the low levels observed in 2005 - 2007. We captured one wild juvenile lake trout in 2008 representing the fifth consecutive year that wild lake trout were captured in the survey. Based on pairwise graphical comparisons and nonparametric correlation analyses, dynamics of prey abundance at the three northern ports followed lakewide trends since 1992. Density of benthic macroinvertebrates was at an all-time low in 2008 since sampling began in 2001. The decline in abundance was due to decreases in all taxonomic groups and a large reduction in recruitment of quagga mussels. Density of Diporeia at northern ports in 2008 was the lowest observed. Diporeia were found only at 73-m sites of three ports sampled in northern Lake Huron. While no lakewide estimate of prey biomass was calculated due to the limited spatial scope of the 2008 survey, existing data suggest prey biomass remains depressed. Prey available to salmonids during 2009 will likely be small alewives, small rainbow smelt and small bloaters. Predators in Lake Huron will continue to face potential prey shortages.

Status and Trends of Pelagic Prey Fishes in Lake Huron, 2008 (PDF file - 178 KB)

The USGS Great Lakes Science Center conducted acoustic/midwater trawl surveys of Lake Huron during 2004-2008. The 2008 survey was conducted during September and October, and included transects in Lake Huron’s Main Basin, Georgian Bay, and North Channel. Main Basin estimates of pelagic fish density and biomass were higher in 2008 compared to surveys in 2004-2007 because of increases in both age-0 and adult bloater. Native species now comprise the majority of the Main Basin biomass. We also observed substantial increase in the abundance of threespine and ninespine sticklebacks, although they contributed little to total community biomass increase due to small size. Rainbow smelt densities and biomass appeared similar to other years, and both alewife and emerald shiner were scarce. Also notably absent was cisco which historically were an important pelagic prey fish in Lake Huron. Unlike previous surveys, we did not observe differences in fish density or biomass among Lake Huron’s basins; during 2008 both density and biomass in the North Channel, Georgian Bay, and Main Basin were similar. This appeared to be a result of increases in the Main Basin and not declines in other areas. Main Basin prey availability for salmonids will depend largely on the extent of their predation on bloater which now comprise the majority of the prey biomass there. The Georgian Bay prey biomass had almost equal proportions of bloaters and rainbow smelt, while the North Channel pelagic biomass remained dominated by rainbow smelt. The present situation in Lake Huron where bloater is relatively abundant but alewife and other prey are scarce may result in dependence on bloater as the primary prey for salmonids.

Status and Trends of Prey Fish Populations in Lake Superior, 2008 (PDF file - 221 KB)

The Great Lakes Science Center has conducted annual daytime bottom trawl surveys of the Lake Superior nearshore (15-80 m bathymetric depth zone) every spring since 1978 to provide a long-term index of relative abundance and biomass of the fish community. Between May 5 and June 14, 2008, 58 stations were sampled around the perimeter of the lake with 12-m wide bottom trawls. Trawls were deployed cross-contour at median start and end depths of 17 and 55 m, respectively. The lakewide mean relative biomass estimate for the entire fish community was 4.61 kg/ha which was similar to that measured in 2007, 4.81 kg/ha. Dominant species in the catch were lake whitefish, rainbow smelt, longnose sucker and cisco, which represented 49, 18, 11, and 7 % of the total community biomass, respectively. Compared to 2007 levels, lake whitefish and cisco biomass increased 35% and 55%, respectively, while bloater and rainbow smelt biomass declined 69% and 41%, respectively. Increased biomass of lake whitefish and decreased biomass in bloater represent trends observed since 2007; however, reversed trends in biomass were observed for cisco and rainbow smelt. Year-class strength for the 2007 cisco cohort (0.20 fish/ha) was below the long-term (1977-2007) average (73.31 fish/ha), as was year-class strength for the 2007 bloater cohort (0.33 fish/ha) compared to the long-term average (11.11 fish/ha). Smelt year class strength (226.26 fish/ha) continues a trend of increasing strength from a 31-year low of 56.75 fish/ha in 2001 and was above the long-term average of 193.81 fish/ha. The 2008 cisco age structure was dominated by age 5 and older fish, which accounted for 82% of the mean relative density. Wisconsin waters continue to be the most productive (mean total community biomass of 17.09 kg/ha), followed by western Ontario (5.40 kg/ha), eastern Ontario (3.08 kg/ha), Michigan (2.82 kg/ha), and Minnesota (0.89 kg/ha).

Densities of small (< 226 mm), intermediate (226-400 mm) and large (>400 mm) hatchery lake trout continued a pattern of decline observed since 1993-1996 to 0.04, 0.03 and 0.01 fish/ha in 2008, respectively. Densities of small and large wild (lean) lake trout continued a decreasing trend observed since 1996-1998. From 2007 to 2008, density of small lean lake trout declined from 0.29 to 0.15 fish/ha, the lowest value since 1978. Density of large lean lake trout has been relatively stable since 1986 but more recently density declined from 0.43 fish/ha in 2006 to 0.10 fish/ha in 2008. Density of intermediate size lean lake trout showed a small increase from 0.31 in 2007 to 0.41 fish/ha in 2008. Siscowet lake trout have shown a pattern of variable but increasing density since 1980. Since 2006, densities of small and intermediate size siscowet lake trout have increased from 0.10 to 0.12 and 0.08 to 0.15 fish/ha, respectively. Densities of large siscowet lake trout have fluctuated between 0.10 and 0.07 fish/ha since 2000. In 2008 the proportions of total lake trout density that were hatchery, lean and siscowet were 8, 60, and 32%, respectively.

Status of Important Prey Fishes in the U.S. Waters of Lake Ontario, 2008 (PDF file - 343 KB)

The U.S. Geological Survey (USGS) and New York State Department of Environmental Conservation (NYSDEC) have cooperatively assessed Lake Ontario prey fishes each year since 1978. Bottom trawling has been conducted during spring to assess alewife Alosa pseudoharengus, summer to assess rainbow smelt Osmerus mordax, and autumn to assess slimy sculpin Cottus cognatus. Timing of the surveys was selected to correspond with the season in which bottom trawl catches of the target species peaked during May to October trawling conducted in 1972 (Owens et al. 2003). Twelve transects were established at roughly 25-km (15.5 mile) intervals along the U.S. shoreline (Figure 1). Bottom trawling was generally conducted at all transects to assess alewife, at all transects except Fair Haven to assess rainbow smelt, and at six transects to assess slimy sculpin. Although each survey targets one species of fish, catches of non-target fishes are also tracked and they provide information on ecologically important changes in the fish community such as the resurgence of once abundant native species like deepwater sculpin Myoxocephalus thompsonii (Lantry et al. 2007) or increasing abundance of recently introduced invasive species like round goby Neogobius melanostomus (Walsh et al. 2007a).

The underlying principle of our original sampling plan was to concentrate sampling effort in the depth zone where the target species was most abundant by using our knowledge of each fish species’ unique bathymetric distribution. At each transect, we typically made trawl hauls at 10-m depth intervals through the range of depths occupied by the target species. In 1997, however, we modified the number and range of depths fished at each transect, as well as the trawling gear, in response to the invasion of zebra and quagga mussels (Dreissena polymorpha and D. bugensis, respectively, hereafter referred to collectively as dreissenids) which changed fish distribution in the early 1990s (O’Gorman et al. 2000) and resulted in bottom trawls clogged with shells. Fixed station sampling designs, such as ours, are commonly used for assessing fish populations in the Great Lakes and in northern Europe (ICES 2004). The underlying assumption is that changes in relative abundance at the fixed stations are representative of changes in the whole population. Mean abundance from fixed station surveys will not be biased if the fish are randomly distributed. We have always assumed that the fish are randomly distributed in the geographic area in which a transect is located, and because we have numerous transects spaced at regular intervals around the shore, that our abundance indices are unbiased. Acoustic sampling conducted during the 2004-2006 alewife bottom trawl assessments confirmed our assumption of random distribution within geographic areas. Furthermore, differences among geographic areas in densities of alewife-strength targets measured with acoustics were reflected in the densities of alewife measured by bottom trawl. However, there is no assurance that this has always been true given the large scale shifts in fish distribution since dreissenids proliferated. Although random sampling is preferable for estimating precision, the systematic, fixed-station sampling that we employ in Lake Ontario will often be optimal for generating the most precise estimate of relative abundance even though the variance of the estimated relative abundance will be biased (ICES 2004).

Status of Pelagic Prey Fishes and Pelagic Macroinvertebrates in Lake Michigan, 2008 (PDF file - 465 KB)

Acoustic surveys were conducted in late summer/early fall during the years 1992-1996 and 2001-2008 to estimate pelagic prey fish biomass in Lake Michigan. Midwater trawling during the surveys provided a measure of species and size composition of the fish community for use in scaling acoustic data and providing species-specific abundance estimates. In 2005, we began sampling Mysis diluviana during the survey. The 2008 survey provided data from 24 acoustic transects (734 km), 33 midwater tows, and 39 mysid tows. Mean total prey fish biomass was 15.3 kg/ha (relative standard error, RSE = 7.6%) or ~82 kilotonnes (kt, 1,000 metric tons), which was 1.9 times higher than the estimate for 2007 but 78% lower than the long-term mean. The increase from 2007 was because of increased biomass of age-1 and age-3 alewife. The 2008 alewife year-class contributed ~12% of total alewife biomass (11.0 kg/ha, RSE = 9.0%), while the 2007 and 2005 alewife year-classes contributed ~33% and 35%, respectively. In 2008, alewife comprised 72% of total biomass, while rainbow smelt and bloater were 11 and 17% of total biomass, respectively. Rainbow smelt biomass in 2008 (1.6 kg/ha, RSE = 10.6%) was identical to the biomass in 2007 (1.6 kg/ha). Bloater biomass was again much lower (2.6 kg/ha, RSE = 15.2%) than in the 1990s, but mean density of small bloater in 2008 (534 fish/ha, RSE = 10.9) was the highest observed in any acoustic survey on record. Prey fish biomass remained well below the Fish Community Objectives target of 500-800 kt and only alewife and small bloater are above or near long-term mean biomass levels. Mysis diluviana remains relatively abundant. Mean density ranged from 185 ind./m² (RSE = 6.8%) in 2005 to 112 ind./m² (RSE = 5.1%) in 2007, but there was not a statistically significant difference among years.

Status and Trends of Prey Fish Populations in Lake Michigan, 2008 (PDF file - 297 KB)

The Great Lakes Science Center (GLSC) has conducted lake-wide surveys of the fish community in Lake Michigan each fall since 1973 using standard 12-m bottom trawls towed along contour at depths of 9 to 110 m at each of seven index transects. The resulting data on relative abundance, size structure, and condition of individual fishes are used to estimate various population parameters that are in turn used by state and tribal agencies in managing Lake Michigan fish stocks. All seven established index transects of the survey were completed in 2008. The survey provides relative abundance and biomass estimates between the 5-m and 114-m depth contours of the lake (herein, lake-wide) for prey fish populations, as well as burbot, yellow perch, and the introduced dreissenid mussels. Lake-wide biomass of alewives in 2008 was estimated at 8.27 kilotonnes (kt) (1 kt = 1000 metric tons), which was the smallest biomass estimate in the entire time series and 29% lower than the 2007 estimate. Lake-wide biomass of bloater in 2008 was estimated at 3.33 kt, which was the lowest estimate since 1977 and 38% lower than the 2007 estimate. Rainbow smelt lake-wide biomass equaled 0.89 kt, which was only 0.01 kt higher than 2007, which is the lowest estimate in the time series. Deepwater sculpin lake-wide biomass equaled 5.23 kt, which is the fourth straight year of declining biomass. The 2008 estimate is the second smallest in the time series, and 39% lower than the 2007 estimate. Slimy sculpin lake-wide biomass remained relatively high in 2008 (2.75 kt), increasing 25% over 2007. Ninespine stickleback lake-wide biomass equaled only 0.50 kt in 2008, which was 79% lower than the 2007 estimate. The final prey fish, exotic round goby, increased two orders of magnitude between 2007 and 2008, from 0.02 to 4.65 kt. Round gobies now represent 18% of the prey fish biomass. Burbot lake-wide biomass (0.91 kt in 2008) has remained fairly constant since 2002. Numeric density of age-0 yellow perch (i.e., < 100 mm) equaled 0.7 fish per ha, which is indicative of a relatively poor year-class. Lake-wide biomass of dreissenid mussels dropped precipitously in 2008, down to 9.47 kt, and a 96% decline from the 2007 biomass estimate. Overall, the total lake-wide prey fish biomass estimate (sum of alewife, bloater, rainbow smelt, deepwater sculpin, slimy sculpin, round goby, and ninespine stickleback) in 2008 was 25.62 kt, which was the lowest observed since the survey began in 1973.

Surveillance and Status of Fish Stocks in Western Lake Erie, 2008

The Lake Erie Biological Station has conducted bottom trawl assessments of fish populations in western Lake Erie near East Harbor State Park, Ohio each summer and autumn since 1961. The catches of most age-0 forage fishes in 2008 were less than their 15-year means. Mean densities for five species exceeded the long term mean. Mean density of age-0 white perch Morone americana was more than double last year’s mean and the long-term mean. Densities of both yellow perch Perca flavescens and walleye Sander vitreus were at or above their long term mean. Catches of round goby Neogobius melanostomus (all ages combined) exceeded the previous five years, but were substantially below the species’ 13-year (1996-2008) mean. For five species, mean total lengths of age-0 individuals captured in 2008 were greater than their respective 20-year means. During 1988-2007, the frequency of occurrence for yellow perch diet items was highest for benthic invertebrates and zooplankton during the summer and benthic invertebrates in autumn. During summer zooplankton and benthic invertebrates were frequently consumed by white perch. Benthic prey for white perch occurred more frequently in the last 5-10 years.

2007

Ages and Lengths of Yellow Perch Perca flavescens in Commercial Trap Nets in Western Lake Erie (PDF file - 71.7 KB)

We collected samples of yellow perch (Perca flavescens) in spring and autumn 2007 from commercial trap nets set in western Lake Erie. The spring sample (N = 86) was dominated (63.9% of the total sample) by the 2003 year class, followed by the 2001 year class (26.7%). This result was similar to commercial samples collected in spring 2006. Similarly, the autumn 2007 sample (N = 95) was also dominated (66.3% of the total sample) by the 2003 year class. This result was similar to the commercial samples collected in autumn 2006 and autumn 2005. Mean total length at age 4 in spring was greater for the 2003 year class than for the 2001 year class for both sexes. Similarly, mean total length at age 4 in autumn was greater for females from the 2003 year class than for females from the 2001 year class.

Comparison of Spring and Autumn Bottom Trawl Sampling in the Western Basin of Lake Erie (PDF file - 190 KB)

The Lake Erie Biological Station completed its fourth consecutive year of a collaborative, multi-agency assessment of forage fish populations throughout the western basin of Lake Erie in 2007. The objectives of this evaluation are to determine the best time of year for sampling in order to estimate year-class strength, to examine seasonal distributions of forage fishes, to examine relationships between abundance indices among seasons, and to improve estimates of basin-wide density and biomass of forage fishes. We sampled 25 stations in Ontario and Michigan waters of the western basin of Lake Erie with bottom trawls in June and September 2007. We calculated density (number per hectare) and biomass (kilograms per hectare) of all forage fishes and compared species diversity across seasons and depth strata. We also examined stomach contents from white perch Morone americana and yellow perch Perca flavescens to describe diets of these two species. Several species, including yellow perch and walleye Sander vitreus had stronger year classes in 2007 following three consecutive weaker year classes. Several important forage species also had stronger year classes in 2007 and were abundant throughout the western basin. Fish densities differed among shallow (≤ 6 m) and deep (> 6 m) sites, which supports the two-strata sampling approach recommended by the Lake Erie Forage Task Group. Diets of age-2 and older yellow perch and white perch in 2007 were dominated by zooplankton in June and shifted to benthos in September. Autumn diets of both species exhibited a decrease in the proportion of zooplankton and an increase in the proportion of fish during 2005-2007. Recent analyses of other USGS data sets have underscored the value of nighttime sampling for indices of abundance of yellow perch and walleye. We will explore the possibility of adding nighttime sampling to our western basin program in the future.

Diet Composition and Fish Consumption of Double-Crested Cormorants from the Little Galloo Island Colony of Eastern Lake Ontario in 2007 (PDF file - 63.4 KB)

Since the early 1990's increasing populations of double crested cormorants (Phalacrocorax auritus) in the eastern basin of Lake Ontario have concerned both members of the public and the New York State Department of Environmental Conservation (NYSDEC) in regards to impacts on fish populations. Although the number and size of cormorant colonies in the eastern basin has not increased for several years, the cormorant population in the area remains high, at levels where depletions of local fish populations may occur. Because it supports the largest cormorant colony in the eastern basin, Little Galloo Island (LGI) has received the most attention regarding cormorant-fish interactions with annual diet studies dating back 16 years. These studies (Johnson et al. 2002a,b) together with other studies which examined the status of fish populations surrounding Little Galloo Island (Burnett et al. 2002, Lantry et al. 2002) have shown a significant relationship between increased cormorant numbers and decreased numbers of yellow perch and smallmouth bass.

The year 2007 marked the sixteenth year of study of the food habits and fish consumption of LGI cormorants. Johnson et al. (2002a) characterized these studies as minimal (1995 - 1997), moderate (1992-1994), and comprehensive (1998 - 2001). This paper reports the findings of work carried out in 2007, the tenth consecutive year of comprehensive work on diet composition and fish consumption of the LGI cormorant colony.

Diet Composition and Fish Consumption of Double-Crested Cormorants from the Pigeon and Snake Island Colonies of Eastern Lake Ontario in 2007 (PDF file - 154 KB)

Pigeon Island (PI) and Snake Island (SI) are home to intermediate-sized colonies of double-crested cormorants (Phalacrocorax auritus) in the Eastern Basin of Lake Ontario. The proliferation of cormorant colonies in this area has created concern as to the effects that these piscivorous birds may have on local fish populations (Schneider et al. 1999). This year (2007) represents the 9^th consecutive year of diet sampling of the nesting cormorants on PI and SI, based on regurgitated digestive pellets for prey enumeration. Since 1999 over 11,000 cormorant pellets have been collected on PI (5,649) and SI (6,062), while some 15,600 were examined at a neighboring island, Little Galloo (LGI). This paper reports on the diet composition and fish consumption of cormorants from PI and SI colonies in 2007. We also estimate the size of important species of fish consumed by cormorants. Our goal is to not only quantify these aspects of cormorant diet, but also to identify changes from previous years.

Diet Composition and Fish Consumption of Double-Crested Cormorants from Three St. Lawrence River Colonies in 2007 (PDF file - 3.95 MB)

Double-crested cormorants (Phalacrocorax auritus) were first observed nesting in the upper St. Lawrence River at Strachan Island in 1992. Cormorants now nest at a number of islands in the Thousand Islands section on the river. The three largest colonies in the upper river are at Griswold, McNair, and Strachan islands where nest counts have remained relatively stable, ranging from 200 to 400 nests per colony. Although the size of cormorant colonies in the upper St. Lawrence River is smaller than those in the eastern basin of Lake Ontario, the close proximity of islands in the Thousand Islands region that have colonies may cause a cumulative fish consumption effect similar to a larger colony.

Because of increasing numbers of double-crested cormorants in the upper St. Lawrence River and the possible impacts on fish populations, studies were initiated in 1999 to quantify cormorant diet and fish consumption at the three largest colonies. From 1999 to 2006 these studies have shown that cormorants consumed about 49.5 million fish including 23.2 million yellow perch, 8.2 million rock bass and 0.48 million smallmouth bass (Johnson et al. 2007). During this same time period fish assessment studies near some of these islands have shown a major decrease in yellow perch populations (Klindt 2007). This occurrence is known as the halo effect and happens when piscivorous birds deplete local fish populations in areas immediately surrounding the colony (Ashmole 1963). This paper describes the diet and fish consumption of cormorants in the upper St. Lawrence River in 2007.

Great Lakes Prey Fish Populations: A Cross-Basin View of Status and Trends in 2007 (PDF file - 260 KB)

Assessments of prey fishes in the Great Lakes have been conducted annually since the 1970s by the Great Lakes Science Center, sometimes assisted by partner agencies. Prey fish assessments differ among lakes in the proportion of a lake covered, seasonal timing, bottom trawl gear used, sampling design, and manner in which the trawl is towed (across or along bottom contours). Because each assessment is unique in one or more important aspect, a direct comparison of prey fish catches among lakes is problematic. All of the assessments, however, produce indices of abundance or biomass that can be standardized to facilitate comparisons of trends among lakes and to illustrate present status of the populations. Herein we present indices of abundance, standardized to the highest value for a time series within each lake, for important prey fishes in the various Great Lakes: lake herring (Coregonus artedi), bloater (C. hoyi), rainbow smelt (Osmerus mordax), and alewife (Alosa pseudoharengus). We also provide indices for round goby (Neogobius melanostomus), a new invasive fish presently spreading throughout the basin.

Lake Trout Rehabilitation in Lake Ontario, 2007 (PDF file - 225 KB)

Each year we report on the progress toward rehabilitation of the Lake Ontario lake trout Salvelinus namaycush population, including the results of stocking, annual assessment surveys, creel surveys, and evidence of natural reproduction observed from all standard surveys performed by USGS and NYSDEC. During 2007, the number of yearling lake trout stocked in May (453,156) was only 9.4% below the target level of 500,000. The adjusted catch of age-2 lake trout with bottom trawls during the juvenile lake trout survey remained low and was 87% below the mean for the 1983-1989 year classes. Adult lake trout catch per unit effort from the gill net survey was 80% below the 1986-1998 average. The rate of wounding by sea lamprey Petromyzon marinus on lake trout caught in gill nets was 2.4 times the target level, suggesting that host density was continuing to affect wounding rates. Estimates from the NYSDEC fishing boat census indicated that, for the third consecutive year, angler catch, harvest, and harvest rate of lake trout were record lows. The condition of adult lake trout, indexed from annual length–weight regressions, increased from the reduced levels observed during 2004-2006 and approached the high level observed during 1996-1999. The improved condition for juvenile lake trout observed in 2006 continued in 2007 and remained above the mean for the data series. Reproductive potential for the adult stock in 2007, determined from the annual egg deposition index, fell to a level 85% below the 1993-1998 mean. Three age-2 naturally produced lake trout were present in survey catches providing evidence of a 2005 year class, but age-1s were absent for the third consecutive year.

Spawning Cisco Investigation in Canada Waters of Lake Superior During 2007 (PDF file - 249 KB)

The purpose of this report is to summarize results of year one of a three-year study of spawning ciscoes in Canada waters of Lake Superior. During November 2007, we conducted two temporally-distinct acoustic and midwater trawl surveys of Thunder Bay, Ontario, spanning the nights of 14-18 (Survey 1) and 24-27 November (Survey 2). Densities of spawning-size (> 250 mm) ciscoes did not vary significantly (P = 0.69) across the two surveys, averaging 142.0/ha (95% CI = 119.8 – 164.5/ha; Table 2) during survey 1 and 134.2/ha (95% CI = 117.3-151.9/ha) during survey 2. Both 2007 estimates exceeded the estimate generated during a November 2005 survey (78.4/ha). The increase in spawner abundance is consistent with a strong 2003 year-class growing in size and joining the spawning stock. During Survey 1, the ratio of spawning-size females to males was close to 1:1 (females = 52%; males = 48%), while females outnumbered males during Survey 2 (females = 68%, males = 32%).The estimated exploitation rates of 350-399 mm ciscoes (the size-class supporting the bulk of the 2007 harvest) averaged 11.99% for males and 8.38% for females, generally lower than the safe-harvest level currently recommended by the Lake Superior Technical Committee (10-15%). Survey results suggest that the year-classes that followed the 2003 cohort have been comparatively weak. If recruitment continues to be low over the next few years, we may encounter a situation whereby the fishery is only being supported by two strong year classes that recruited in 1998 and 2003. If such a scenario transpires, managers may wish to consider ways to protect spawners from harvest (such as reducing the total allowable catch) until another strong year-class is realized.

Status and Trends of the Lake Huron Deepwater Demersal Fish Community, 2007 (PDF file - 252 KB)

The U.S.G.S. Great Lakes Science Center has conducted trawl surveys to assess annual changes in the fish community of Lake Huron since 1973. Since 1992, surveys have been carried out using a 21 m wing trawl towed on-contour at depths ranging from 9 to 110 m on fixed transects. Sample sites include five ports in U.S. waters with less frequent sampling near Goderich, Ontario. The 2007 fall prey fish survey was carried out between October 15 and November 4, 2007 and sampled all five U.S. ports and Goderich, Ontario. The alewife population remained at low levels after collapsing in 2004. Adult and age-0 alewife density and biomass declined from 2006 levels and remain near the historical low observed in 2004. Density and biomass of adult and juvenile rainbow smelt showed only a slight increase from 2006 levels despite record-high abundance of juveniles observed in 2005 suggesting recruitment was limited. Juvenile rainbow smelt abundance in 2007 remained slightly higher than the long-term mean for the time series since 1992. Numbers of adult bloater increased in 2007 approaching the high levels observed in the early 1990s showing evidence of recruitment, but biomass remains low due the small size distribution of the new recruits. Juvenile bloaters remained ubiquitous with abundance surpassing the previous record high observed in 2005. Abundances for most other prey species were similar to the low levels observed in 2005 and 2006. We captured 11 wild juvenile lake trout in 2007; this represents the fourth consecutive year that substantial numbers of wild lake trout were captured in the survey. Benthic macroinvertebrates have been sampled during the fall survey since 2001. Density of benthic macroinvertebrates showed an increase from 2005-2006 values due largely to increases in oligochaete and quagga mussel densities. Prey biomass available to the bottom trawl increased slightly from 2006 levels due to increases in bloater and rainbow smelt biomass. However, total prey biomass remains near the all-time low observed in 2006. The prey available to salmonids during 2008 will be small rainbow smelt and small bloaters. Predators in Lake Huron will continue to face potential prey shortages.

Status and Trends of Pelagic Prey Fish in Lake Huron, 2007 (PDF file - 173 KB)

The USGS Great Lakes Science Center conducted annual acoustic/midwater trawl surveys of Lake Huron from 2004-2007. The 2007 survey was conducted during September and October, and included transects in Lake Huron’s main basin, Georgian Bay, and North Channel. Main basin estimates of pelagic fish density were similar during all four years. Biomass estimates were significantly lower during 2006 compared to other years, but all annual estimates ranged between 3.5 and 8.8 kg/ha. During 2004-2007 alewife were virtually absent, and rainbow smelt and bloaters comprised the majority of pelagic biomass. However, emerald shiners Notropis atherinoides were prominent in 2006, while cisco Coregonous artedi were prominent in 2007. Ciscoes were absent in trawl catches in 2004-2006, but comprised about 30% of main basin pelagic fish biomass in 2007 due to their large size compared to other species. As with previous surveys during 2004 and 2005, pelagic fish density and biomass in the North Channel was significantly higher than Georgian Bay and the main basin. Native species now comprise the majority of the main basin biomass.

Status and Trends of Prey Fish Populations in Lake Michigan, 2007 (PDF file - 280 KB)

The Great Lakes Science Center (GLSC) has conducted lake-wide surveys of the fish community in Lake Michigan each fall since 1973 using standard 12-m bottom trawls towed along contour at depths of 9 to 110 m at each of seven index transects. The resulting data on relative abundance, size structure, and condition of individual fishes are used to estimate various population parameters that are in turn used by state and tribal agencies in managing Lake Michigan fish stocks. All seven established index transects of the survey were completed in 2007. The survey provides relative abundance and biomass estimates between the 5-m and 114-m depth contours of the lake (herein, lake-wide) for prey fish populations, as well as burbot, yellow perch, and the introduced dreissenid mussels and round gobies. Lake-wide biomass of alewives in 2007 was estimated at 11.67 kilotonnes (kt) (1 kt = 1000 metric tons), which was 18% higher than in 2006. Lake-wide biomass estimates of bloater (5.39 kt) and rainbow smelt (0.88 kt) in 2007 were 59% and 63%, respectively, lower than in 2006. Bloater biomass has declined drastically since 1989, and the 2007 estimate was the lowest since 1978. The 2007 rainbow smelt lake-wide biomass estimate was the lowest biomass estimate for rainbow smelt on record. Deepwater sculpin lake-wide biomass had shown neither an increasing nor decreasing trend during 1990-2006, but then decreased from 22.86 kt in 2006 to 8.53 kt in 2007. Slimy sculpin lake-wide biomass had been steadily increasing since 2001, but then decreased from 8.16 kt in 2006 to 2.20 kt in 2007. Ninespine stickleback lake-wide biomass remained relatively high in 2007 (2.37 kt), as the species has generally increased in abundance from 1996-present compared to 1973-1995. Burbot lake-wide biomass (1.91 kt in 2007) has remained fairly constant since 2002. After a record-high 2005 year-class, numeric density of age-0 yellow perch (i.e., < 100 mm) remained relatively high (4.7 fish per ha) in 2007 compared with the 1996-2004 period. Lake-wide biomass of dreissenid mussels appeared to be leveling off in 2007 at 245.51 kt, after increasing exponentially during 2003-2006. Round goby abundance decreased from 27.7 fish per ha in 2006 to 1.0 fish per ha in 2007. Overall, the total lake-wide prey fish biomass estimate (sum of alewife, bloater, rainbow smelt, deepwater sculpin, slimy sculpin, and ninespine stickleback) in 2007 was 31.04 kt, which was the lowest observed since the survey began in 1973.

Status and Trends of Prey Fish Populations in Lake Superior, 2007 (PDF file - 352 KB)

The Great Lakes Science Center has conducted annual daytime bottom trawl surveys of the Lake Superior nearshore (15-80 m depth zone) every spring since 1978 to provide a long-term index of relative abundance and biomass of the fish community. Between April 24 and June 19, 2007, 54 stations were sampled around the perimeter of the lake with 12-m wide bottom trawls. Trawls were deployed cross-contour at median start and end depths of 17 and 56 m, respectively. The lakewide mean relative biomass estimate for the entire fish community declined 29% from 6.80 kg/ha in 2006 to 4.81 kg/ha in 2007. Most of this decline was a result of decreased biomass estimates for cisco (89%) and bloater (55%). However, rainbow smelt and lake whitefish biomass increased by 61% and 13% from 2005 to 2006, respectively. Lake whitefish represented the highest percentage of biomass for the entire community (31%), followed by rainbow smelt (27%), bloater (13%), and cisco (4%). Year-class strength for the 2006 cisco cohort (0.3 fish/ha) was well below the long-term (1977- 2006) average (76 fish/ha), as was year-class strength for the 2006 bloater cohort (0.3 fish/ha) compared to the long-term average (12 fish/ha). The 2007 cisco age structure was dominated by the strong 2003 year class, which accounted for 42% of the mean relative density. Wisconsin waters continue to be the most productive (mean total community biomass of 12.60 kg/ha), followed by western Ontario (6.60 kg/ha), eastern Ontario (2.88 kg/ha), Michigan (1.98 kg/ha), and Minnesota (0.06 kg/ha).

For the first time, we examined lake trout densities from the bottom trawl series by size classes to detect population trends. Our analysis showed a strong recovery of adult lake trout in the mid-1980s preceded by increasing densities of small and intermediate size classes. Periods of increased recruitment of small (< 226 mm) and intermediate (226-400 mm) size fish followed the appearance and growth of large year classes of native prey fishes (cisco, bloater) in 1984-1989 and 1992-1999. After 2000, recruitment and growth of small and intermediate size wild lake trout declined and this is the primary reason for a declining trend in total wild lake trout biomass since 1998. Densities of large (> 400 mm) adult wild lake trout have remained relatively steady since 1986, indicative of a recovered adult spawning population for 20+ years.

As a follow-up to fall 2005 cisco spawning surveys and spring 2006 larval cisco surveys in Thunder and Black bays, we conducted additional day bottom trawls in these bays during May 2007 to characterize age-1 densities and thereby assess survival from egg to larval to age-1 life stages. Based on these surveys, we estimated survival of eggs to larvae at 0.29% and 0.46%, and larvae to age-1 at 0.16% and 0.52% in Thunder and Black bays, respectively.

In May 2007 we conducted a study of diel variation in depth distribution of the principal prey fishes. We observed that prey species have discrete habitat distributions that shift from demersal or lower pelagic during day to pelagic at night (rainbow smelt, cisco, bloater, kiyi), or shift from deeper to shallower demersal habitat from day to night (lake whitefish). These patterns reveal the potential for Lake Superior prey fishes to couple resource use in nearshore and offshore zones by movement across habitats.

Status of Important Prey Fishes in the U.S. Waters of Lake Ontario, 2007 (PDF file - 772 KB)

The U.S. Geological Survey (USGS) and New York State Department of Environmental Conservation (NYSDEC) have cooperatively assessed Lake Ontario prey fishes each year since 1978. Bottom trawling has been conducted during spring to assess alewife Alosa pseudoharengus, summer to assess rainbow smelt Osmerus mordax, and autumn to assess slimy sculpin Cottus cognatus. Timing of the surveys was selected to correspond with the season in which bottom trawl catches of the target species peaked during May to October trawling conducted in 1972 (Owens et al. 2003). Twelve transects were established at roughly 25-km (15.5 mile) intervals along the U.S. shoreline (Figure 1). Bottom trawling was generally conducted at all transects to assess alewife, at all transects except Fair Haven to assess rainbow smelt, and at six transects to assess slimy sculpin. Although each of the three surveys targets one species of fish, catches of non-target fishes are also tracked and they provide information on ecologically important changes in the fish community such as resurgence of once abundant native species like deepwater sculpin Myoxocephalus thompsonii (Lantry et al. 2007) or increasing abundance of recently introduced invasive species like round goby Neogobius melanostomus (Walsh et al. 2007a).

The underlying principle of our original sampling plan was to concentrate sampling effort in the depth zone where the target species was most abundant by using our knowledge of each fish species’ unique bathymetric distribution. At each transect, we typically made trawl hauls at 10-m depth intervals through the range of depths occupied by the target species. In 1997, however, we modified the number and range of depths fished at each transect, as well as the trawling gear in response to the invasion of zebra and quagga mussels (Dreissena polymorpha and D. bugensis, respectively, hereafter referred to collectively as dreissenids) which changed fish distribution in the early 1990s (O’Gorman et al. 2000) and resulted in bottom trawls clogged with shells. Fixed station sampling designs, such as ours, are commonly used for assessing fish populations in the Great Lakes and in northern Europe (ICES 2004). The underlying assumption is that changes in relative abundance at the fixed stations are representative of changes in the whole population. Mean abundance from fixed station surveys will not be biased if the fish are randomly distributed. We have always assumed that the fish are randomly distributed in the geographic area in which a transect is located and, because we have numerous transects spaced at regular intervals around the shore, that our abundance indices are unbiased. Acoustic sampling conducted during the 2004-2006 alewife assessments confirmed our assumption of random distribution within geographic areas and differences among geographic areas in acoustically measured density of alewife-strength targets were reflected in the densities of alewife measured by bottom trawl. However, there is no assurance that this has always been true given the large scale shifts in fish distribution since dreissenids proliferated. Although random sampling is preferable for estimating precision, the systematic, fixed-station sampling that we employ in Lake Ontario will often be optimal for getting the most precise estimate of relative abundance even though the variance of the estimated relative abundance will be biased (ICES 2004).

Status of Pelagic Prey Fishes in Lake Michigan, 1992-2007 (PDF file - 555 KB)

Acoustic surveys were conducted in late summer/early fall during the years 1992-1996 and 2001-2007 to estimate pelagic prey fish biomass in Lake Michigan. Midwater trawling during the surveys provided a measure of species and size composition of the fish community for use in scaling acoustic data and providing species-specific abundance estimates. The 2007 survey provided data from 21 acoustic transects and 41 midwater tows. Mean total prey biomass was 8.2 kg/ha (RSE = 6.4%) or ~40 kilotonnes (kt) (or 1,000 metric tons), which was 32% lower than the estimate for 2006 and, largely a result of decreased rainbow smelt biomass. Total biomass in 2007 was 47% lower than in 2005, largely a result of decreased biomass of alewife and rainbow smelt. The 2007 alewife year-class contributed ~33% of total alewife biomass (4.7 kg/ha, RSE = 10.7%), while the 2005 alewife year-class contributed ~47% of alewife biomass. The remaining 20% of alewife biomass consisted of the 2000, 2002, 2003, 2004, and 2006 year-classes. In 2007, alewife comprised 57% of total biomass, while rainbow smelt and bloater were 19 and 23% of total biomass, respectively. Rainbow smelt biomass exhibited an increasing trend from 2002-2006 with the population consisting primarily of larger fish (≥ 90 mm), but rainbow smelt biomass was much lower in 2007 (1.6 kg/ha, RSE = 15.8%) than in 2006. Bloater biomass was again much lower (1.9 kg/ha, RSE = 24.0%) than in the 1990s, but mean density of small bloater in 2007 (320 fish/ha, RSE = 14.2) was the highest observed in any acoustic survey on record. Although acoustic and midwater trawl data suggest that the preyfish community is somewhat more diverse than in the previous five years, preyfish biomass remained well below the Fish Community Objectives target of 500-800 kt.

Surveillance and Status of Fish Stocks in Western Lake Erie, 2007 (PDF file - 365 KB)

Each summer and autumn since 1961, the Lake Erie Biological Station has conducted assessments of fish populations in western Lake Erie near East Harbor State Park, Ohio, and more recently has included assessments of fish diets, zooplankton, and benthic macroinvertebrates. The catches of all major age-0 forage fishes in autumn 2007 were less than their 15-year (1993-2007) means. Catches of round goby Neogobius melanostomus (all ages combined) were similar to the previous four years, but substantially below the species’ 12-year (1996-2007) mean. For five species examined, mean total lengths for age-0 individuals in 2007 were greater than their respective 20-year means; for four species the reverse was true. Yellow perch Perca flavescens and white perch Morone americana adults (age-2 and older) consumed predominately benthic macroinvertebrates in summer and fall. Although the autumn diet of white perch was dominated by benthic macroinvertebrates, fish accounted for a relatively large proportion (41.3% by wet weight). The proportion of benthic macroinvertebrates in the summer diet of yellow perch was the highest since 2004, and dominated the autumn diet. The proportion of benthic macroinvertebrates in the summer diet of white perch has increased since 2004. Dreissena spp. dominated the benthic macroinvertebrates collected in 2007, followed by Chironomidae. Veligers of Dreissena spp. was the most abundant taxon in the summer zooplankton samples

The Effects of Egg Oiling on Fish Consumption by Double-Crested Cormorants On Little Galloo Island, Lake Ontario, in 2007 (PDF file - 61.9 KB)

For over a decade Little Galloo Island (LGI) has supported the largest colony of double-crested cormorants (Phalacrocorax auritus) in the eastern basin of Lake Ontario. Cormorant nest counts on the island since the early 1990's have averaged about 5,125 per year reaching a high of 8,400 in 1996. Since 1992, Johnson et al. (2007) estimate that cormorants from LGI alone have consumed 385 million fish. The proliferation of cormorants in the eastern basin of Lake Ontario has coincided with declines in two important recreational fish species, smallmouth bass and yellow perch. Lantry et al. (2002) and Burnett et al. (2002) provide convincing evidence linking cormorant population increases to declining eastern basin smallmouth bass and yellow perch stocks. Decline of these fish stocks is evident only in the eastern basin, suggesting a localized problem which is consistent with the halo effect where large piscivorous waterbird colonies may deplete local fish stocks (Birt et al. 1987).

In 1999, the New York State Department of Environmental Conservation (NYSDEC) initiated an experimental program to control the reproductive success of cormorants nesting on LGI. The program consists of spraying cormorant eggs with corn oil. Here we report on the effectiveness of the nine years of control measures that were carried out through 2007 with regard to fish consumption.

2006

Age Composition of Yellow Perch (Perca flavescens) and Lake Whitefish (Coregonus clupeaformis) in Commercial Trap Nets in Western Lake Erie (PDF file - 130 KB)

We collected samples of yellow perch (Perca flavescens) in spring and autumn 2006, and lake whitefish (Coregonus clupeaformis) in autumn 2006, from commercial trap nets set in western Lake Erie. The spring yellow perch sample (N = 85) was dominated (70.6% of the total sample) by the 2001 year class. These results were similar to the spring commercial samples collected in 2004 and 2005. The autumn yellow perch sample (N = 106) was dominated by the 2003 year class (58.5% of the total sample) and the 2001 year class (34.9%). These results were similar to the autumn 2005 commercial sample, in which the 2001 and 2003 year classes collectively accounted for 88.2% of the individuals collected. Similarly, the 2001 year class dominated the autumn 2004 commercial sample of yellow perch. The lake whitefish sample (N = 205) was dominated by the 2003 and 2001 year classes, which respectively accounted for 62% and 17.6% of the sample. No sample of lake whitefish was collected in 2005. However, the 2000 year class, which dominated the autumn 2004 commercial sample, was nearly absent in 2006.

Comparison of Commercial Landings of Cisco to Acoustic Estimates of Abundance in Thunder Bay and Black Bay, Ontario. (PDF file - 312 KB)

The two largest remaining cisco Coregonus artedi commercial fisheries on Lake Superior are supported by the Thunder and Black Bay, Ontario, stocks. The sustainability of these fisheries relies on con rolling the harvest in relation to the size of the populations. During mid-November 2005 we conducted acoustic and midwater trawl surveys of both bays to assess abundances of various year-classes at-large which we compared to commercial catches to estimate exploitation levels. At present, the cisco population in Thunder Bay is dominated by the 2003, 1998, 1990, 1989 and 1988 yearclasses. These five strong year-classes were caught previously during an annual USGS spring bottom trawl survey as age-1 fish, while the remaining year-classes were largely absent from trawl catches as yearlings. Using acoustic methods, we estimate the numbers of large (> 250 mm) ciscoes in Thunder and Black bays at 5.2 million (95% CI = 4.3 – 6.2 million) and 244,000 (95% CI = 32,000 – 456,000), respectively. We estimate that commercial fishers harvested 2.49% of males older than age-6 and 8.46% of age-6 and older females from Thunder Bay. Plots of catch-per-unit-effort (CPUE) of commercial nets versus landing date showed that our survey of Thunder Bay occurred when CPUE was high, indicating most spawners were present. The CPUE of ciscoes in Black Bay increased rapidly after our survey, suggesting our acoustic abundance estimate is conservative. Given the 1998 and 2003 year-classes are both strong and well established, we conclude that present commercial harvest quotas will not jeopardize the persistence of the Thunder Bay stock into the foreseeable future (i.e., next 5-10 years). Given that our abundance estimate from Black Bay is conservative and the estimate suffers from poorprecision, we can not comment on the sustainability of the current Black Bay harvest quota.

Comparison of Spring and Autumn Bottom Trawl Sampling in the Western Basin of Lake Erie (PDF file - 283 KB)

In 2006, the Lake Erie Biological Station participated for the third consecutive year in a collaborative, multi-agency effort to evaluate forage fish populations throughout the western basin of Lake Erie. The objectives of this evaluation are to determine the best time of year for sampling in order to estimate year-class strength and to develop a method for estimating basin-wide density and biomass of forage fishes. We sampled 25 stations in Ontario and Michigan waters of the western basin of Lake Erie with bottom trawls in June and September 2006. We calculated density (number per hectare) and biomass (kilograms per hectare) of all forage fishes and compared species diversity across political jurisdictions, seasons, and depth strata. We also examined stomach contents from white perch Morone americana and yellow perch Perca flavescens to describe diets of these two species. Compared to previous years, density and biomass estimates were lower for coolwater species and higher for warmwater species. The outbreak of viral hemorrhagic septicemia that resulted in mass mortality of several species in spring and early summer may have negatively affected recruitment of freshwater drum Aplodinotus grunniens. Species diversity was higher in autumn, higher in Ontario waters, and generally increased with depth. Average water depth in Ontario waters is deeper than in Michigan and likely accounts for some of the difference in species diversity across political jurisdictions. We recommend adding night sampling in a subset of the sites sampled during daylight to examine whether time of day sampled affects estimates of density, biomass, and species diversity.

Evaluation of Methods to Estimate Lake Herring Spawner Abundance in Lake Superior (PDF file - 337 KB)

Historically, commercial fishers harvested Lake Superior lake herring Coregonus artedi for their flesh, but recently operators have targeted lake herring for roe. Because no surveys have estimated spawning female abundance, direct estimates of fishing mortality are lacking. The primary objective of this study was to determine the feasibility of using acoustic techniques in combination with midwater trawling to estimate spawning female lake herring densities in a Lake Superior statistical grid (i.e., a 10' latitude x 10' longitude area over which annual commercial harvest statistics are compiled). Midwater trawling showed that mature female lake herring were largely pelagic during the night in late November, accounting for 94.5% of all fish caught exceeding 250 mm total length. When calculating acoustic estimates of mature female lake herring, we excluded backscattering from smaller pelagic fishes like immature lake herring and rainbow smelt Osmerus mordax by applying an empirically derived threshold of – 35.6 dB. We estimated the average density of mature females in statistical grid 1409 at 13.3 fish/ha and the total number of spawning females at 227,600 (95% confidence interval = 172,500–282,700). Using information on mature female densities, size structure, and fecundity, we estimate that females deposited 3.027 billion (109) eggs in grid 1409 (95% confidence interval = 2.356–3.778 billion). The relative estimation error of the mature female density estimate derived using a geostatistical model – based approach was low (12.3%), suggesting that the employed method was robust. Fishing mortality rates of all mature females and their eggs were estimated at 2.3% and 3.8%, respectively. The techniques described for enumerating spawning female lake herring could be used to develop a more accurate stock–recruitment model for Lake Superior lake herring.

Great Lakes Prey Fish Populations: A Cross-Basin View of Status and Trends in 2006 (PDF file - 153 KB)

Assessments of prey fishes in the Great Lakes have been conducted annually since the 1970s by the Great Lakes Science Center, sometimes assisted by partner agencies. Prey fish assessments differ among lakes in the proportion of a lake covered, seasonal timing, bottom trawl gear used, sampling design, and manner in which the trawl is towed (across or along bottom contours). Because each assessment is unique in one or more important aspect, a direct comparison of prey fish catches among lakes is problematic. All of the assessments, however, produce indices of abundance or biomass that can be standardized to facilitate comparisons of trends among lakes and to illustrate present status of the populations. Herein we present indices of abundance, standardized to the highest value for a time series within each lake, for important prey fishes in the various Great Lakes: lake herring (Coregonus artedii), bloater (C. hoyi), rainbow smelt (Osmerus mordax), and alewife (Alosa pseudoharengus). We also provide indices for round goby (Neogobius melanostomus), a new invasive fish presently spreading throughout the basin.

Prey Fish Consumption by Double-crested Cormorants in Western Lake Erie Near West Sister Island, Ohio (PDF file - 258 KB)

The objectives for this study were to: 1) determine the diet of Double-crested Cormorant (Phalacrocorax auritus, hereafter: cormorants) in western Lake Erie; 2) to determine if yellow perch (Perca flavescens) or walleye (Sander vitreus) were a noteworthy prey item; and 3) to determine if the invasive round goby (Neogobius melanostomus) are consumed. Diet of cormorants was determined from stomach contents of 228 birds collected in western Lake Erie. Cormorants consumed 16 different fish species and one benthic invertebrate, Dreissena spp. Although white perch (Morone americana) composed the largest percent of the biomass consumed by cormorants during April - June, gizzard shad (Dorosoma cepedianum) dominated from July - September and, by weight, was the fish consumed most over the entire study period. Emerald shiner (Notropis atherinoides) was the most frequently consumed prey but the species accounted for a very small percent of the total diet biomass. Round goby, white perch, white bass (M. chrysops), and yellow perch were consumed most frequently by cormorants in May. Mean individual prey fish weights for major species were generally greatest during April and May. The frequency of empty stomachs was extremely high from the end of July through early September.

Status and Trends of Pelagic Prey Fish in Lake Huron's Main Basin, 2006 (PDF file - 234 KB)

The USGS Great Lakes Science Center conducted acoustic and midwater trawl surveys of Lake Huron in 1997, 2004, 2005, and 2006. The 2006 survey was conducted during August and was comprised of Lake Huron’s main basin. Main basin estimates of pelagic fish density were higher in 2006, primarily due to increased age-0 rainbow smelt Osmerus mordax abundance. However, biomass estimates were lower than in 2004 and 2005 due to lower abundance of adult rainbow smelt and adult bloaters Coregonus hoyi. Alewife Alosa pseudoharengus density and biomass remained low; alewife densities were 56 fish·ha-1 and all alewives captured in trawls were age-0’s. Emerald shiner Notropis atherinoides density and biomass increased substantially throughout the main basin in 2006, and they comprised about 25% of pelagic biomass. Increased emerald shiner biomass did not offset decreases in other species, and total pelagic fish biomass estimates during 2006 were 69% lower compared with 2004. Results of the acoustic survey were consistent with observations of low prey abundance in bottom trawl surveys, and suggest that overall prey availability in the main basin may be at an all time low since inception of annual surveys in 1973.

Status and Trends of Prey Fish Populations in Lake Michigan, 2006 (PDF file - 500 KB)

The Great Lakes Science Center (GLSC) has conducted lake-wide surveys of the fish community in Lake Michigan each fall since 1973 using standard 12-m bottom trawls towed along contour at depths of 9 to 110 m at each of seven index transects. The resulting data on relative abundance, size structure, and condition of individual fishes are used to estimate various population parameters that are in turn used by state and tribal agencies in managing Lake Michigan fish stocks. All seven established index transects of the survey were completed in 2006. The survey provides relative abundance and biomass estimates between the 5-m and 114-m depth contours of the lake (herein, lake-wide) for prey fish populations, as well as burbot, yellow perch, and the introduced dreissenid mussels and round gobies. Lake-wide biomass of alewives in 2006 was estimated at 9.86 kilotonnes (kt) (1 kt = 1000 metric tons), which was 26% lower than 2005. Lake-wide biomass estimates of bloater (13.30 kt) and rainbow smelt (2.39 kt) in 2006 were 46% and 69%, respectively, lower than in 2005. Bloater biomass has declined drastically since 1989 and the 2006 estimate is the lowest since 1978. Abundance of age-0 bloaters (< 120 mm) in 2004-2006, however, has been higher than in the previous 10-year period, perhaps signaling a bloater recovery. The 2006 rainbow smelt lake-wide biomass estimate was similar to the previous 10-year period; the 2005 estimate was the highest since 1993. Deepwater sculpin lake-wide biomass (22.86 kt in 2006) has not shown a pronounced temporal trend during 1990-2006. Slimy sculpin lake-wide biomass has been increasing since 2001, and biomass in 2006 (8.16 kt) was the highest in the overall time series. Ninespine stickleback lake-wide biomass remained relatively high in 2006 (4.05 kt), as the species has generally increased in abundance from 1996-present compared to 1973-1995. Burbot lake-wide biomass (2.05 kt in 2006) has remained fairly constant since 2002. After a record-high 2005 year-class, numeric density of age-0 yellow perch (i.e., < 100 mm) remained relatively high (5.2 fish per ha) compared to the 1996-2004 period. Lake-wide biomass of dreissenid mussels has been increasing since 2003, and the 2006 estimate (212.27 kt) was a nearly 3-fold increase over the 2005 estimate. Round goby were first captured in 2003 and have since been increasing in abundance. Round goby abundance in 2006 (27.7 fish per ha) was a 16-fold increase over the 2005 estimate. Overall, the total lake-wide prey fish biomass estimate (sum of alewife, bloater, rainbow smelt, deepwater sculpin, slimy sculpin, and ninespine stickleback) was 60.62 kt, which was the lowest observed since the survey began in 1973.

Status and Trends of Prey Fish Populations in Lake Superior, 2006 (PDF file - 1.18 MB)

The Great Lakes Science Center conducts an annual daytime bottom trawl survey of the Lake Superior fish community every spring to provide a long-term index of relative abundance and biomass. The survey began in 1978 for U.S. waters and was expanded in 1989 to include Canadian waters. Currently, 86 fixed stations are distributed around the perimeter of Lake Superior. In 2005, a total of 51 stations were sampled with 12-m bottom trawls between April 27 and June 15. Trawls were deployed cross-contour at median start and end depths of 21 and 55 m, respectively. The lakewide mean relative biomass estimate for all species combined increased from 6.29 kg/ha in 2004 to 9.13 kg/ha in 2005. Most of this increase was a result of increased biomass estimates for lake whitefish, rainbow smelt, and lake trout. Lake whitefish made up the highest percent of the total mean biomass for any species (34%), followed by lake herring (21%), bloater (14%), and rainbow smelt (12%). Lake herring and bloater biomass remained at similar levels from 2004 to 2005. We predict that biomass estimates for lake herring in 2006 will drop as the moderately strong 2003 cohort matures and becomes less susceptible to day bottom trawling. Biomass of siscowets decreased in 2005, while wild and hatchery lake trout biomass increased by 5x and 42x, respectively. The increases were a result of increased catch of large (> 500 mm) lake trout (wild and hatchery) and higher frequency of non-zero catches in the trawls (wild lake trout). Year-class strengths for the 2004 lake herring (1 fish/ha) and bloater (< 1 fish/ha) cohorts were below their long-term (1977-2004) averages (76 and 11 fish/ha, respectively). Wisconsin waters continue to be the most productive (mean total biomass of 26.78 kg/ha), followed by western Ontario (10.96 kg/ha), eastern Ontario (2.29 kg/ha), Michigan (1.61 kg/ha), and Minnesota (0.02 kg/ha). Estimates of mean relative density from the spring survey indicate the biological impossibility of increased densities of age-2 lake herring in 2005 compared to age-1 lake herring in 2004. Age-2 rainbow smelt density in 2005 was also greater than age-1 density in 2004. These results suggest improvements to our sampling strategy and survey design should be considered. Additionally, qualitative comparisons of relative biomass estimates based on all stations versus a subset of stations reveal similar trends in biomass dynamics at the community and species levels. These results suggest reduced effort could provide similar information. Any savings in reduced effort could be directed at improving assessment strategies and/or adding new ecological investigations.

Status and Trends of the Lake Huron Deepwater Demersal Fish Community, 2006 (PDF file - 656 KB)

The U.S.G.S. Great Lakes Science Center has conducted trawl surveys to assess annual changes in the fish community of Lake Huron since 1973. Since 1992, surveys have been carried out using a 21 m wing trawl towed on-contour at depths ranging from 9 to 110 m on fixed transects. Sample sites include five ports in U.S. waters with less frequent sampling near Goderich, Ontario. The 2006 fall prey fish survey was carried out between October 17 and November 7, 2006 and sampled all five U.S. ports and Goderich, Ontario. The alewife population remained at low levels after collapsing in 2004 due to four consecutive years of poor recruitment. Adult and age-0 alewife density and biomass declined from 2005 levels and remain near the historical low observed in 2004. Density and biomass of adult rainbow smelt continued to decline from 2004 levels and juvenile rainbow smelt declined from the record-high abundance observed in 2005. Juvenile rainbow smelt abundance in 2006 is slightly higher than the long-term mean for the time series since 1992. Adult bloater abundance increased slightly showing some recruitment, but juvenile bloaters remained ubiquitous with abundance levels second to the record high for the time series observed in 2005. Abundances for most other prey species were similar to the low levels observed in 2005. We captured 15 wild age-0 lake trout in 2006; this represents the third consecutive year that substantial numbers of wild fish were captured in the survey. Benthic macroinvertebrates have been sampled during the fall survey since 2001 and the six-year time series shows a general declining trend. Density of benthic macroinvertebrates showed a slight increase from 2005 values due largely to increases in oligochaete and quagga mussel densities. However, macroinvertebrate densities remain about half of that observed in 2002. Prey biomass available to the bottom trawl decreased slightly from 2005 levels due to declines in alewife and rainbow smelt biomass. Total prey biomass remains near the all-time low observed in 2004. The prey available to salmonids during 2007 will be small rainbow smelt and small bloaters. Predators in Lake Huron will continue to face potential prey shortages.

Status of Pelagic Prey Fishes in Lake Michigan, 1992-2006 (PDF file - 654 KB)

Acoustic surveys were conducted in late summer/fall during the years 1992-1996 and 2001-2006 to estimate prey fish biomass in Lake Michigan. Midwater trawling during the surveys provided a measure of species and size composition of the fish community for use in scaling acoustic data and providing species-specific abundance estimates. The 2006 survey provided data from 13 acoustic transects and 23 midwater tows. Mean total prey biomass was 10.1 kg/ha (RSE=8.9%), similar to the estimate for 2005 (12.7 kg/ha, RSE=9.7%). The 2006 alewife year-class contributed ~10% of alewife biomass, while the 2005 alewife year-class contributed ~46% of alewife biomass. Another 36% of alewife biomass consisted of similar contributions (11-13%) of the 2002-2004 year-classes. The 1998 year-class was still present and made up 1% of biomass. In 2006, alewife and rainbow smelt biomass were similar (4.6 and 4.2 kg/ha, respectively), whereas in the previous five years rainbow smelt biomass was only 2-36% of alewife biomass. Rainbow smelt biomass has exhibited an increasing trend since 2002 and in 2006 consisted primarily of larger fish (=90 mm, 92% of rainbow smelt biomass). Bloater biomass was again much lower (1.4 kg/ha, RSE=7.1%) than in the 1990s, but mean density of small bloater in 2006 (50.0 fish/ha, RSE=16.7) was the fourth highest observed since 1992. Although acoustic and midwater trawl data suggest that the preyfish community is somewhat more diverse than in the previous five years, preyfish biomass remained well below the Fish Community Objectives target of 500-800 kt. Without recovery of the bloater population to levels in the 1980s and early 1990s, it seems likely that preyfish biomass will remain below the target level.

Surveillance and Status of Fish Stocks in Western Lake Erie, 2006 (PDF file - 420 KB)

Each summer and autumn since 1961, the Lake Erie Biological Station has conducted assessments of fish populations in western Lake Erie near East Harbor State Park, Ohio, and more recently has included assessments of fish diets, zooplankton, and benthic macroinvertebrates. The catches of nearly all major age-0 forage fishes in autumn 2006 were considerably less than their 15-year (1992-2006) means. Rainbow smelt (Osmerus mordax), was an exception, as catches were higher than the 15-year mean by nearly 50%. Catches of all age-0 spiny-rayed fishes caught in 2006 were less than 25% of their 15-year means. In particular, no age-0 walleye (Sander vitreus) were captured 2006. Catches of round goby (Neogobius melanostomus) (all ages combined) were similar to the previous three years and substantially below the species’ 11-year (1996-2006) mean. For most species examined, mean total lengths for age-0 individuals in 2006 were similar to their respective 15-year means. Yellow perch (Perca flavescens) and white perch (Morone americana) adults (age-2 and older) consumed predominately zooplankton and benthic macroinvertebrates in summer. The proportions of zooplankton in the diet of yellow perch and of benthic macroinvertebrates in the diet of white perch have increased since 2004. Although the autumn diet of white perch was dominated by benthic macroinvertebrates, fish composed a relatively large proportion (25.3% by wet weight). Dreissena spp. dominated the benthic macroinvertebrates collected in 2006, followed by Chironomidae. Chironomid density was the highest recorded on this survey since the first benthic samples were collected in 1997. Cyclopoid copepods were the most abundant zooplankton taxon detected during summer sampling, and Bosminidae was the most abundant zooplankton taxon detected in the autumn.

2005

Evaluation of Offshore Stocking to Mitigate Piscivore Predation on Newly Stocked Lake Trout in Lake Ontario (PDF file - 163 KB)

Great Lakes Prey Fish Populations: A Cross-Basin View of Status and Trends in 2005 (PDF file - 160 KB)

Lake Trout Rehabilitation in Lake Ontario, 2005 (PDF file - 109 KB)

Each year we report on the progress toward rehabilitation of the Lake Ontario lake trout population covering the results of stocking, annual assessment surveys, creel surveys, and evidence of natural reproduction observed from all standard surveys performed by USGS and NYSDEC. During 2005, the number of yearling lake trout stocked in May was 45% below the target level of 500,000. During the juvenile lake trout bottom trawling survey the total catch of age-2 lake trout declined by 87% from 2004 and was the second lowest catch on record. During the adult lake trout gill net survey CPUE was 47% lower than in 2004 and 73% below the 1986-98 average. The rate of wounding by sea lampreys on lake trout caught in gill nets was above the target level suggesting that host density was affecting wounding rates. Estimates from the NYSDEC fishing boat census indicated that while effort aimed at trout and salmon increased by 23% from the low set in 2003, angler harvest of lake trout reached a new record low. The condition of adult lake trout, indexed from annual length – weight regressions, was the lowest observed in 14 years. Despite continued low abundance of age-2 lake trout, the condition of juvenile lake trout remained low and was similar to values observed through the 1980’s. Reproductive potential for the adult stock from the annual egg deposition index declined by 40% from the 2001-2004 mean and was 64% below the average for 1993 to 1998. Age-2 naturally produced lake trout were present in survey catches, but for the first time in seven years age-1s were not suggesting little or no natural reproduction during 2004.

Mapping Potential Lake Sturgeon Habitat in the Lower Bad River Complex. (PDF file - 2.21 MB)

To assist in identifying potential lake sturgeon (Acipenser fulvescens) habitat in the lower Bad River complex, we used a digital sonar system combined with a global positioning system to provide georeferenced data, and specialized sonar, bottom typing, GIS and statistical software to acoustically map bottom substrate types, locations and bathymetry. Ground truth data were developed from both petite Ponar bottom samples and associated acoustic data which were processed with bottom typing software. These data were used to produce substrate models in statistical software with a recursive partitioning method. Models were applied to survey data toclassify it into substrate categories. Data were imported into GIS software to produce substrate maps. The lower Bad River had clay predominating at 45.82% (30.01 ha) of the total area (65.49 ha), followed by sand/clay at 32.07% (21.00 ha) and sand at 22.11% (14.48 ha). The open lake portion had sand/silt predominating at 75.74% (575.09 ha) of the total area (759.30 ha), followed by sand at 19.94% (151.40 ha), coarse sand/ medium pebbles at 2.33% (17.73 ha), clay at 1.94% (14.70 ha), and cobble /boulder at 0.05% (0.38 ha).

Pilot Study to Estimate Lake Herring Spawner Abundance and Number of Eggs Deposited in a Lake Superior Statistical Grid. (PDF file - 648 KB)

Predation on walleyes Sander vitreus by Double-crested Cormorants Phalacrocorax auritus at the West Sister Island colony in 2005 (PDF file - 84 KB)

Double-crested Cormorants Phalacrocorax auritus (hereafter cormorants) first nested in Lake Erie in the mid 1900s and have established numerous successful nesting colonies. Concerns by commercial and recreational fishermen about potential negative effects of this piscivorous species on populations of fishes in Lake Erie, especially walleyes Sander vitreus, prompted us to conduct two pilot investigations of consumption of walleyes by cormorants. We examined stomach contents undigested regurgitant of cormorants from the West Sister Island colony, the largest colony in Ohio waters of the western basin of Lake Erie. Examination of stomach contents revealed no walleyes were consumed, but half of all regurgitants examined contained remains of walleyes of at least 2 different year classes. These pilot studies confirmed that cormorants at the West Sister colony consume walleyes. Our methods were qualitative and we examined only one colony; thus we cannot estimate total consumption of walleyes and we cannot estimate basin-wide effects of cormorant predation on the walleye population. A quantitative study involving all 3 colonies will be required to determine if walleyes are consumed by cormorants throughout the western basin and to quantify the potential effects of cormorants on the walleye population.

Regional and local factors affecting patterins of E. coli distribution in southern Lake Michigan (PDF file - 3.98 MB)

Status and Trends of Pelagic Prey Fish in Lake Huron, 2005: Results From a Lake-Wide Acoustic Survey (PDF file - 186 KB)

The USGS Great Lakes Science Center conducted acoustic/midwater trawl surveys of Lake Huron in 1997, 2004, and 2005. The 2005 survey was conducted during September-October, and included transects in Lake Huron’s main basin, Georgian Bay, and the North Channel. Estimates of pelagic fish density were higher in 2005 than 2004, primarily due to increased rainbow smelt abundance in the North Channel and a lake-wide increase in age-0 bloater abundance. However, biomass estimates did not differ significantly between the two years, and were lower than estimates from the initial survey in 1997. Alewife density and biomass remained low; alewife density in 2005 was about 1 fish per hectare, compared with a density of 580 fish per hectare in 1997. Slight increases in the density of sticklebacks and emerald shiners during 2005 did not contribute substantially to pelagic fish biomass. Between 1997 and 2004-05, Lake Huron’s pelagic fish biomass decreased from about 150 kg per hectare to 10-20 kg hectare. This was due to almost complete disappearance of alewife and a change in age and size structure in the bloater population from dominance by adults to increased prevalence of smaller or younger bloaters. Rainbow smelt density varied among regions and North Channel density and biomass may have been higher than overall lake-wide densities observed during 1997. Lake Huron appears to have lost a substantial amount of pelagic fish biomass between 1997 and 2004-05. Results of the acoustic survey support observations of lower prey abundance observed in bottom trawl surveys, but suggest that overall prey availability remains higher in Georgian Bay and the North Channel than in the main basin.

Status and Trends of Prey Fish Populations in Lake Michigan, 2005 (PDF file - 276 KB)

The Great Lakes Science Center (GLSC) has conducted lake-wide surveys of the fish community in Lake Michigan each fall since 1973 using standard 12-m bottom trawls towed along contour at depths of 9 to 110 m at each of seven index transects. The resulting data on relative abundance, size structure, and condition of individual fishes are used to estimate various population parameters that are in turn used by state and tribal agencies in managing Lake Michigan fish stocks. All seven established index transects of the lake-wide survey were completed in 2005. Lake-wide biomass of alewives in 2005 was estimated at 13.401 kilotonnes (kt) (1 kt = 1000 metric tons), which was very similar to the lake-wide biomass estimate of 13.721 kt for alewives in 2004. Catch of adult alewives in 2005 was dominated by the 2002 year-class. Lake-wide biomasses of deepwater sculpin, bloater, rainbow smelt, and slimy sculpin in 2005 were estimated at 32.030 kt, 24.546 kt, 7.816 kt, and 5.474 kt, respectively. Bloater biomass drastically declined between 1989 and 2005. Abundance of juvenile bloaters steadily increased during 2003-2005, perhaps signaling the start of a bloater recovery. Rainbow smelt biomass increased substantially from 1.854 kt in 2004 to 7.816 kt in 2005. Deepwater sculpin biomass has not shown a pronounced temporal trend during 1990-2005. Burbot abundance showed a slight decrease during the early 2000s. Slimy sculpin abundance showed an increasing trend during 1985-2005. Yellow perch year-class strength in 2005 was the highest on record dating back to 1973. The lake-wide biomass estimate of dreissenid mussels was relatively high in 2005. Total catch of round gobies in 2005 was 37 fish, compared with 26 fish in 2004.

Status and Trends of Prey Fish Populations in Lake Superior, 2005 (PDF file - 257 KB)

The Great Lakes Science Center conducts an annual daytime bottom trawl survey of the Lake Superior fish community every spring to provide a long-term index of relative abundance and biomass. The survey began in 1978 for U.S. waters and was expanded in 1989 to include Canadian waters. Currently, 86 fixed stations are distributed around the perimeter of Lake Superior. In 2005, a total of 51 stations were sampled with 12-m bottom trawls between April 27 and June 15. Trawls were deployed cross-contour at median start and end depths of 21 and 55 m, respectively. The lakewide mean relative biomass estimate for all species combined increased from 6.29 kg/ha in 2004 to 9.13 kg/ha in 2005. Most of this increase was a result of increased biomass estimates for lake whitefish, rainbow smelt, and lake trout. Lake whitefish made up the highest percent of the total mean biomass for any species (34%), followed by lake herring (21%), bloater (14%), and rainbow smelt (12%). Lake herring and bloater biomass remained at similar levels from 2004 to 2005. We predict that biomass estimates for lake herring in 2006 will drop as the moderately strong 2003 cohort matures and becomes less susceptible to day bottom trawling. Biomass of siscowets decreased in 2005, while wild and hatchery lake trout biomass increased by 5x and 42x, respectively. The increases were a result of increased catch of large (> 500 mm) lake trout (wild and hatchery) and higher frequency of non-zero catches in the trawls (wild lake trout). Year-class strengths for the 2004 lake herring (1 fish/ha) and bloater (< 1 fish/ha) cohorts were below their long-term (1977-2004) averages (76 and 11 fish/ha, respectively). Wisconsin waters continue to be the most productive (mean total biomass of 26.78 kg/ha), followed by western Ontario (10.96 kg/ha), eastern Ontario (2.29 kg/ha), Michigan (1.61 kg/ha), and Minnesota (0.02 kg/ha). Estimates of mean relative density from the spring survey indicate the biological impossibility of increased densities of age-2 lake herring in 2005 compared to age-1 lake herring in 2004. Age-2 rainbow smelt density in 2005 was also greater than age-1 density in 2004. These results suggest improvements to our sampling strategy and survey design should be considered. Additionally, qualitative comparisons of relative biomass estimates based on all stations versus a subset of stations reveal similar trends in biomass dynamics at the community and species levels. These results suggest reduced effort could provide similar information. Any savings in reduced effort could be directed at improving assessment strategies and/or adding new ecological investigations.

Status and Trends of the Lake Huron Deepwater Demersal Fish Community, 2005 (PDF file - 266 KB)

The Great Lakes Science Center has conducted trawl surveys to assess annual changes in the fish community of Lake Huron since 1973. Since 1992, surveys have been carried out using a 21 m wing trawl towed on-contour at depths ranging from 9 to 110 m on fixed transects. Sample sites include five ports in U.S. waters with less frequent sampling near Goderich, Ontario. The 2005 fall prey fish survey was carried out between October 18 and November 7, 2005 and sampled all five US ports and Goderich, Ontario. The alewife population remained at low levels after collapsing in 2004 due to three consecutive years of poor recruitment. Adult alewife density and biomass remained near the historical low observed in 2004. Age-0 alewife showed a slight increase in abundance over 2004 estimates, but remain below the long-term mean for the time series. Density and biomass of adult rainbow smelt decreased from 2004 levels but juvenile rainbow smelt were at a record-high abundance in 2005. Adult bloater abundance decreased slightly, but juvenile bloaters remained ubiquitous with record high abundance for the time series. Abundances for most other prey species were lower than 2004. We captured 11 wild age-0 lake trout in 2005; this represents the second consecutive year that substantial numbers of wild fish were captured in the survey. Density of benthic macroinvertebrates was the lowest observed since collections began in 2001 due to declines in abundance of oligochaetes, Diporeia spp., and quagga mussels while sphaerid clams and chironomids increased slightly over 2004 levels. Prey biomass available to the trawl increased slightly over 2004 levels due to increases in age-0 alewife and rainbow smelt biomass. However, total prey biomass remains near the all-time low observed in 2004. The prey available to salmonids during 2006 will be small rainbow smelt and small bloaters. Predators in Lake Huron face potential prey shortages; estimates of predatory demand are now similar to estimates of prey biomass, and nearly all the remaining prey species are smaller than the adult alewives traditionally consumed.

Status of Important Prey Fishes in the U.S. Waters of Lake Ontario, 2005 (PDF file - 818 KB)

Status of Pelagic Prey Fishes in Lake Michigan, 1992-2005 (PDF file - 285 KB)

Acoustic surveys were conducted in the fall during the years 1992-1996 and 2001-2005 to estimate prey fish biomass in Lake Michigan. Midwater trawling during the surveys provided a measure of species and size composition of the fish community for use in scaling acoustic data and providing species-specific abundance estimates. The 2005 survey included 31 transects and 62 midwater tows. Alewives were the dominant species in the 2005 trawl catch by mass, followed by rainbow smelt then bloater. Alewife, rainbow smelt, bloater, and yellow perch all produced abundant young in 2005, with YOY alewife density highest since 1995. Bloater and yellow perch YOY were more abundant in 2005 than in any other year of the survey. Numeric density of YOY alewife in 2001-2005 was positively correlated with May-August surface water temperature (r²=0.95). Total prey biomass (alewife, rainbow smelt, bloater, sticklebacks, and yellow perch) was 2.2x higher in 2005 (69 kt) than in 2004, but was only ~40% of 2001 biomass. Of the lakewide prey fish total of 69 kt, 49% was alewife. In 2005, there was evidence of spatial structure at multiple scales, with small-scale autocorrelation in density occurring up to ~5 km accompanied by large-scale (regional) differences in distribution. The regional differences consisted of spatial segregation among species and between size groups within species in 2004-2005. Numeric fish density was again highest in offshore regions (north and south offshore), but biomass density was highest in nearshore areas (depths <100 m).

Surveillance and Status of Fish Stocks in Western Lake Erie, 2005 (PDF file - 504 KB)

Each summer and autumn since 1961, the Lake Erie Biological Station (LEBS) has conducted assessments of fish populations in western Lake Erie near East Harbor State Park, Ohio, and more recently has included assessments of fish diets, zooplankton, and benthic macroinvertebrates. The catches of major age-0 forage fishes (gizzard shad, [Dorosoma cepedianum], alewife [Alosa pseudoharengus] and emerald shiner [Notropis atherinoides]) fell below their 15-year (1991-2005) means. In contrast, the catches of spottail shiner (Notropis hudsonius) and trout-perch (Percopsis omiscomaycus), were higher than the long-term means. Catches of all major age-0 spiny-rayed fishes (yellow perch [Perca flavescens], walleye [Sander vitreus], white perch [Morone americana], white bass [Morone chrysops], and freshwater drum [Aplodinotus grunniens]) in 2005 were lower than the 15-year means. Catches of round goby (Neogobius melanostomus) (all ages combined) were lower than in any year since the species was first captured (1996). Mean lengths of emerald shiner, spottail shiner, yellow perch, walleye, white perch, and white bass were greater than their respective long-term means. In summer 2005, yellow perch diets were dominated by crustacean zooplankton and benthic macroinvertebrates, whereas white perch diets were dominated by zooplankton. Autumn 2005 diets for yellow perch consisted mostly of benthic macroinvertebrates and fish, while white perch consumed higher proportions of fish and zooplankton. Hexagenia sp. nymphs were the dominant taxonomic group in the fall diet of yellow perch. Zooplankton have contributed a higher mean percent weight of the diet in the past three years for both yellow perch and white perch. Benthic macroinvertebrates made up the largest proportion of the autumn diets for yellow perch during 2001-2004 and for white perch during 2003-2004. Dreissena sp. made up the largest portion of the benthic community near East Harbor State Park (mean = 62%), followed by Gastropoda. Calanoid copepods were the most abundant zooplankton taxon detected during both summer and fall sampling. The spring and autumn samples of yellow perch from commercial trap nets in 2005 were dominated by individuals from the 2001 year class, similar to last year.

In 2004, LEBS began an assessment of fish populations in the Ontario and Michigan waters of the western basin. Species diversity in 2005 was greater in autumn than in spring. Autumn densities of most age-0 forage fishes were higher in 2005 than in 2004. Both yellow perch and white perch consumed mainly zooplankton in spring and benthic macroinvertebrates in fall.

2004

Great Lakes Prey Fish Populations: A Cross-Basin View of Status and Trends in 2004 (PDF file - 504 KB)

Lake Report: Status and Trends of Prey Fish Populations in Lake Michigan, 2004 (PDF file - 265 KB)

The Great Lakes Science Center (GLSC) has conducted lake-wide surveys of the fish community in Lake Michigan each fall since 1973 using standard 12-m bottom trawls towed along contour at depths of 9 to 110 m at each of seven to nine index transects. The resulting data on relative abundance, size structure, and condition of individual fishes are used to estimate various population parameters that are in turn used by state and tribal agencies in managing Lake Michigan fish stocks. All seven established index transects of the lake-wide survey were completed in 2004. Alewife abundance decreased substantially between 2003 and 2004, as estimated lake-wide biomass dropped from 43.234 kilotonnes (kt) (1 kt = 1000 metric tons) in 2003 to 13.721 kt in 2004. Catch of adult alewives in 2004 was dominated by the 1998 yearclass. Lake-wide biomasses of bloater, deepwater sculpin, slimy sculpin, and rainbow smelt in 2004 were estimated at 34.321 kt, 26.519 kt, 3.658 kt, and 1.854 kt, respectively. Bloater biomass drastically declined between 1989 and 2004. Abundance of juvenile bloaters in 2004 was the highest juvenile bloater abundance observed since 1991. Rainbow smelt biomass declined during 1992-1997, and has remained low since 1997. Deepwater sculpin biomass has shown neither an increasing nor decreasing trend from 1990 to 2004. Burbot abundance decreased during 2001-2003, but increased in 2004. Slimy sculpin abundance appeared to be leveling off during 1999-2004, following an increase during the 1990s. Yellow perch year-class strength was poor in 2004. Lake-wide biomass estimates of dreissenid mussels trended neither upward nor downward during 1999-2004. Total catch of round gobies in 2004 (26 fish) was similar to that in 2003 (23 fish), and catches were again limited to the Manistique and Saugatuck transects.

Lake Report: Status and Trends of Prey Fish Populations in Lake Superior, 2004 (PDF file - 286 KB)

The Great Lakes Science Center conducts an annual daytime bottom trawl survey of the Lake Superior fish community every spring to provide a long-term index of relative abundance and biomass. The survey began in 1978 for U.S. waters and was expanded in 1989 to include Canadian waters. Currently, 87 fixed stations are distributed around the perimeter of Lake Superior. In 2004, a total of 75 stations were sampled with 12-m bottom trawls between May 10 and June 19. Trawls were deployed cross-contour at median start and end depths of 15 and 65 m, respectively. Acoustic data were also collected concurrently at 70 of the 75 stations to test the assumption that fish are primarily demersal during the day and thus susceptible to bottom trawls. The mean lakewide biomass estimate for all species combined increased from 4.71 kg/ha in 2003 to 6.29 kg/ha in 2004, halting the downward trend that began in the early 1990s. Most of this increase was a result of recruitment of the 2003 lake herring year-class, which was the seventh highest during the 27-year survey. Bloater, burbot, and longnose suckers also made minor contributions to the increase in biomass. Lake whitefish made up the highest percent of the total mean biomass for any species (30%), followed by lake herring (29%), bloater (18%), longnose sucker (7%), and rainbow smelt (5%). Lake whitefish and rainbow smelt biomass remained at similar levels from 2003 to 2004, in spite of a moderate 2003 year-class of rainbow smelt. Biomass of lean lake trout and siscowets decreased in 2004, with siscowet biomass exceeding wild lake trout biomass for the first time and hatchery lake trout reaching their lowest biomass over the time series. The 2002 and 2003 lake herring yearclasses were the largest consecutive cohorts since the 1988-1990 cohorts, though much smaller in magnitude. Bloater year-class strength increased for a second consecutive year, but still remains below the 1978-2004 average. Wisconsin waters continue to be the most productive (mean total biomass of 19.75 kg/ha), followed by western Ontario (5.33 kg/ha), Michigan (3.01 kg/ha), eastern Ontario (1.91 kg/ha), and Minnesota (0.75 kg/ha). Comparisons between acoustic techniques and bottom trawls indicate that, at a lakewide scale, mean fish biomass in the water column above the trawl path was 70% of the mean estimate derived from the bottom trawl data. Comparing estimates from both gears at western Lake Superior stations sampled concurrently in 2001, 2003, and 2004 shows high year-to-year and site-to-site variability in pelagic fish biomass during the day. The assumption that fish are primarily demersal during the day in the spring appears to be incorrect. These results suggest that fish behavior can have an impact on biomass estimates when daytime bottom trawling is the sole gear, and that relative differences in our spring survey indices may result from changes in fish behavior as well as actual changes in abundance. If absolute fish biomass estimates are a long-term goal for Lake Superior management agencies, consideration of a comprehensive lakewide survey that integrates multiple gears will be necessary.

Lake Report: Status and Trends of the Lake Huron Deepwater Fish Community, 2004 (PDF file - 300 KB)

The Great Lakes Science Center has conducted trawl surveys to assess annual changes in the fish community of Lake Huron since 1973. Since 1992, surveys have been carried out using a 21 m wing trawl towed on-contour at depths ranging from 9 to 110 m on fixed transects at five ports in U.S. waters with less frequent sampling near Goderich, Ontario. The 2004 fall prey fish survey was carried out during October and sampled all five US ports and Goderich, Ontario. The alewife population collapsed during 2004, due to three consecutive years of poor recruitment. Both adult and age-0 alewife density and biomass were at historical lows for the time series. Density and biomass of adult rainbow smelt abundance increased from 2003 levels due to strong year classes in both 2003 and 2004. Adult bloater abundance decreased slightly, but juvenile bloaters remained ubiquitous. Density of small bloaters increased during 2004 due to continued abundance of the exceptionally strong 2003 year class combined with substantial numbers of age-0 fish produced during 2004. Abundances for most other prey species were lower than 2003. We captured 22 wild age-0 lake trout in 2004; this represents the first time that substantial numbers of wild fish were captured in the survey. Prey biomass available to the trawl decreased by 65 % during 2001-2004; nearly all the decrease was due to reduced alewife biomass, and no other species has increased in abundance enough to compensate for their loss. The primary source of food for salmonids during 2005 will be small rainbow smelt. Predators in Lake Huron face potential prey shortages; estimates of predatory demand are now similar to estimates of prey biomass, and nearly all the remaining prey species are smaller than the adult alewives consumed traditionally.

Lake Report: Status Of Major Prey Fish Stocks in the U.S. Waters of Lake Ontario, 2004 (PDF file - 488 KB)

We began a comprehensive re-analysis of our bottom trawl assessments, conducted annually since 1978, with a re-evaluation of the alewife Alosa pseudoharengus assessment. Although, the re-evaluation resulted in numerous changes to the calculation of alewife abundance, the new indices showed the same trends as the historical indices (Spearman rank correlation, P < 0.0001, r = 0.95). Numerical and weight abundance indices for adult (age-2 and older) alewives in U.S. waters of Lake Ontario during spring 2004 were similar to those in spring 2002-2003 and were well below the long-term averages. The numerical abundance index for yearling alewives (2003 year class) was about 25% smaller in 2004 than in 2002-2003 and was below the long-term average for the fourth consecutive year. Wet weight condition of adult alewife in fall 2004 was higher than in any year since 1980 suggesting that the alewife population was more in balance with the productive capacity of the lake in 2004 than in any of the previous 23 years. Numerical and weight abundance indices for age-1 and older rainbow smelt Osmerus mordax in 2004 were markedly higher than the record lows recorded in 2003. The increase was due entirely to a strong 2003 year class and not to a decrease in mortality rates of adult rainbow smelt -- age-2 and older smelt remain scarce. We have lost the ability to track abundance of slimy sculpin Cottus cognatus along the south shore -- dreissenid numbers now preclude towing the trawl gear historically used to assess sculpins, and trawling with other gear produced inconsistent results. One deepwater sculpin Myoxocephalus thompsonii was collected in spring 2004.

Lake Report: Status of Pelagic Prey Fish in Lake Huron in 1997 and 2004 (PDF file - 405 KB)

To provide annual estimates of prey fish biomass in Lake Huron, acoustic surveys were conducted in the fall during the years 1997 and 2004. The survey conducted in 1997 was limited to areas <150 m deep, but in 2004 a more extensive survey was conducted. Midwater trawling during the surveys provided measures of species and size composition of the fish community for use in scaling acoustic data and providing species-specific abundance estimates. Bloaters (Coregonus hoyi) were the dominant component of acoustic biomass in both years, but rainbow smelt (Osmerus mordax) were numerically dominant in both years. Alewives (Alosa pseudoharengus) made up ~5% of biomass in 1997 and less than 0.05% in 2004 Acoustic estimates of total biomass, rainbow smelt biomass, and bloater biomass were significantly higher in 1997 than in 2004. This difference was not the result of limited spatial coverage. Total biomass estimated from the acoustic survey in 2004 was similar to the USGS bottom trawl survey estimate. The decline in biomass between 1997 and 2004 was of similar magnitude for both surveys. The Lake Huron preyfish community continues to be dominated by the native bloater. Density and biomass did not vary significantly among regions in 1997. In 2004, significant regional variation in rainbow smelt and YOY bloater density and biomass was observed; decreased abundance may have contributed to greater patchiness. It is unclear how biomass estimates presented here compare to recent salmonine consumption rates, but it is evident that preferred prey (alewife) is not abundant enough to support predator demand.

Lake Report: Status of Pelagic Prey Fish in Lake Michigan 2001-2004 (PDF file - 518 KB)

Acoustic surveys were conducted in the fall during the years 2001-2004 to estimate prey fish biomass in Lake Michigan. Surveys conducted in 2001-2003 were limited in coverage, but regions included in the 2004 lakewide survey represented ~94% of the lake area. Midwater trawling during the surveys provided measures of species and size composition of the fish community for use in scaling acoustic data and providing species-specific abundance estimates. Alewives (Alosa pseudoharengus) were the largest proportion of the catch in all years but 2003. No trends were observed in the proportion (by weight) of any species in the trawl catch, but acoustic estimates of total biomass and alewife biomass exhibited a decreasing trend across years. The decrease in total biomass was driven primarily by a decline in alewife biomass. Alewife biomass and variance estimates from the acoustic surveys were similar to estimates derived from the USGS fall bottom trawl survey. The decline in alewife biomass over time was of similar magnitude for both the acoustic and bottom trawl surveys, suggesting that the decrease in the acoustic estimates of biomass was not an artifact of the limited spatial coverage in 2001- 2003. Two alewife year classes (2002 and 2003) made up a large portion of the midwater catch of yearling-and-older alewives at age one. Even though the highest young-of-the-year alewife biomass occurred in 2002, only the 2003 year class made up a significant portion of the total catch beyond age 0, suggesting the 2003 year class may dominate the alewife population for the next several years. The 95% confidence interval for lakewide biomass of alewives in 2004 was 18-32 kt, with a mean of 25 kt.

Lake Report: Surveillance and Status of Fish Stocks in Western Lake Erie, 2004 (PDF file - 218 KB)

Each summer and autumn since 1961, the Lake Erie Biological Station (LEBS) has conducted assessments of fish populations in western Lake Erie near East Harbor State Park, Ohio, and more recently has included assessments of fish diets, zooplankton, and benthic macroinvertebrates. The catches of major age-0 forage fishes (gizzard shad, [Dorosoma cepedianum], alewife [Alosa pseudoharengus] and emerald shiner [Notropis atherinoides]) fell below their 15-year (1991-2005) means. In contrast, the catches of spottail shiner (Notropis hudsonius) and trout-perch (Percopsis omiscomaycus), were higher than the long-term means. Catches of all major age-0 spiny-rayed fishes (yellow perch [Perca flavescens], walleye [Sander vitreus], white perch [Morone americana], white bass [Morone chrysops], and freshwater drum [Aplodinotus grunniens]) in 2005 were lower than the 15-year means. Catches of round goby (Neogobius melanostomus) (all ages combined) were lower than in any year since the species was first captured (1996). Mean lengths of emerald shiner, spottail shiner, yellow perch, walleye, white perch, and white bass were greater than their respective long-term means. In summer 2005, yellow perch diets were dominated by crustacean zooplankton and benthic macroinvertebrates, whereas white perch diets were dominated by zooplankton. Autumn 2005 diets for yellow perch consisted mostly of benthic macroinvertebrates and fish, while white perch consumed higher proportions of fish and zooplankton. Hexagenia sp. nymphs were the dominant taxonomic group in the fall diet of yellow perch. Zooplankton have contributed a higher mean percent weight of the diet in the past three years for both yellow perch and white perch. Benthic macroinvertebrates made up the largest proportion of the autumn diets for yellow perch during 2001-2004 and for white perch during 2003-2004. Dreissena sp. made up the largest portion of the benthic community near East Harbor State Park (mean = 62%), followed by Gastropoda. Calanoid copepods were the most abundant zooplankton taxon detected during both summer and fall sampling. The spring and autumn samples of yellow perch from commercial trap nets in 2005 were dominated by individuals from the 2001 year class, similar to last year.

In 2004, LEBS began an assessment of fish populations in the Ontario and Michigan waters of the western basin. Species diversity in 2005 was greater in autumn than in spring. Autumn densities of most age-0 forage fishes were higher in 2005 than in 2004. Both yellow perch and white perch consumed mainly zooplankton in spring and benthic macroinvertebrates in fall.

Status of Freshwater Unionid Populations at Sleeping Bear Dunes National Lakeshore, 2000-2003. (PDF file - 3.38 MB)

2003

Status of Freshwater Unionid Populations at Indiana Dunes National Lakeshore. (PDF file - 617 KB)

2002

Ecological Characterization of Long Lake, Porter and Lake Counties, Indiana (PDF file - 538 KB)

The purpose of this report is to characterize the west side of Long Lake. Because very little data is available on this section of Long Lake, data from the east section of Long Lake, as well as from other similar water bodies, will be used to extrapolate what possible conditions exist in the west section. This information is presented to offer an information base upon which to make decisions related to future hydrologic management decisions. This survey will characterize the physical, chemical, and biological characteristics of Long Lake and will attempt to compare differences between the basins east and west of County Line Road, Lake and Porter Counties, Indiana. Historical descriptions of the lake and its natural history will be presented to provide background of the area and evidence of the lake’s significance to the ecosystem.

Status and Trends of Selected Inland Lakes in the Great Lakes National Parks (PDF file - 10.3 MB)

The objective of this study was to inventory reference locations at selected lakes in the National Parks Services Great Lakes Cluster Parks and to install uniform, scientifically defendable biomonitoring programs that could detect long-term ecological trends.

Zooplankton as a Bioassessment Tool in the Great Lakes (PDF file - 1.4 MB)

This study explores the usefulness of using zooplankton in the Great Lakes region as a monitoring tool for the health of inland lakes. Based on research done on Sleeping Bear Dunes National Lakeshore zooplankton.

2001

Characterization of E. coli levels at 63rd Street Beach (PDF file - 2.73 MB)

The purpose of this report is to characterize the distribution and possible sources of E. coli at 63rd Street Beach, Chicago, an intensive study was undertaken between April and September 2000. Swimmability has been affected by high concentrations of E. coli in the past several years and in particular during the summer of 1999. Beach closures are enforced to protect the public from possible harmful illness associated with contamination. Most strains of E. coli are harmless, but it is typically associated with more harmful bacteria that can cause illness. The City of Chicago wanted to eliminate E. coli contamination at the beach in order to increase swimming safety and reduce beach closures. In order to accomplish this, sources of E. coli and the movement of E. coli within the system had to be determined.

Genetic Profiles of Selected Brook Trout Salvelinus fontinalis Populations from Lake Superior, Lake Huron and Selected Hatcheries. (PDF file - 952 KB)

In the Lake Superior drainage basin, brook trout are the only extant indigenous stream salmonid since the loss of several populations of river-run lake trout in the last century. Recent field investigations have shown evidence that brook trout populations in some Lake Superior tributaries are self-sustaining, and in some populations significant genetic diversity is still present. Some Lake Superior tributaries contained populations of “coaster” brook trout, a form of brook trout which spends a majority of its adult life in the open water of Lake Superior and returns to shoreline reefs or some upstream sites to spawn. Populations of coasters throughout the Lake Superior basin have suffered severe declines, and only a few streams are thought to still harbor remnant stocks. From throughout the Lake Superior basin, brook trout populations were sampled that represented suspected remnant wild populations, historical “coaster” populations, and populations with counterparts in above-barrier sections of streams. Much of the genetic diversity present among Lake Superior brook trout is partitioned among individual populations. Populations of brook trout in the Lake Superior basin show levels of genetic variability in the mitochondrial DNA genome that suggest that some populations are still sustained by wild fish. The combined effects of population declines and hatchery supplementation are reflected in the mtDNA profiles of several populations in this survey for which only the most common mtDNA haplotype was detected. No unique genetic markers were found in the mitochondrial DNA to correlate with samples identified as coasters, but sample sizes of known coasters were small. Further work with more known coasters and nuclear markers such as microsatellite DNA loci may shed more light on how the coaster phenotype is produced.

Status of Freshwater Unionid Populations at Isle Royale National Park, 1999-2001 (PDF file - 2.84 MB)

Status of Freshwater Unionid Populations at Pictured Rocks National Lakeshore, 1999-2000 (PDF file - 10.9 MB)

1998

An Integrated Acoustic and Trawl Based Prey Fish Assessment Strategy for Lake Michigan (PDF file - 31.7 MB)

1990

Chrionomidae of the southeastern United States (PDF file - 5 MB)

We provide a current listing of the species of midges (Diptera:Chironomidae) in the southeastern United States (Alabama, Florida, Georgia, North Carolina, South Carolina, and Tennessee). This checklist should aid in research on this group of insects, which have often proved useful in the assessment of water quality. We document each species' distribution and general habitat and provide the best taxonomic reference to facilitate the identification or description of species in that genus. Changes in nomenclature, unique ecological traits, bibliographic sources, or other items of information are summarized in a paragraph on each genus. Of the 10 subfamilies currently recognized in the Chironomidae, 7 occur in the Southeast. The chironomid fauna of the six southeastern States now consist of 164 described genera and 479 described species. In addition, we have listed 14 genera and 245 species that are tentatively noted as undescribed or that have been illustrated but not officially described. Regional distribution of the principal subfamilies indicated that the species of Chironominae and Tanypodinae were concentrated in the coastal region, whereas the Orthocladiinae were evenly distributed from the coast to the mountains. Considering the major habitats (lakes, rivers, and streams), Tanypodinae were about evenly distributed; Orthocladiinae were more predominant in streams and Chironominae in lakes.

1989

Effects of Altered Water Levels and Flows on Fish in the Great Lakes Connecting Channels (PDF file - 26.5 MB)

1988

The Detroit River, Michigan: An ecological profile (PDF file - 13.9 MB)

This monograph is part of a series of publications about current issues facing the Nation’s coastal environments. It synthesizes existing information describing the ecological structure and function of the Detroit River, which flow between Lakes Huron and Erie and forms the border between the United States (Michigan) and Canada (Ontario). Other reports in this series present information about two similar rivers between these countries, the St. Marys River (Duffy et al. 1987), and the St. Clair River and St. Clair (Edsall et al. 1987).

In gathering the available information on the Detroit River, especially that pertinent to managing its biological resources, we found gaps in the information needed to protect and enhance these resources; they are identified in the report. Wherever possible, the river is treated as a distinct but integrated unit of the Great Lakes ecosystem.

In recent years, the Detroit River has received considerable attention because its fishery resources move freely across the boundary between two nations and represent millions of dollars in revenue each year to each nation. Use of these same waters for navigation as well as for disposal of municipal and industrial wastes, coupled with rapid industrial and residential development of the shoreline, has focused concern on preparation of an action plan to control pollution by toxic substances, identify study needs, and develop management strategies. This report encompasses these needs and should be useful in these important efforts.

The St. Clair River and Lake St. Clair, Michigan: An ecological profile (PDF file - 21.8 MB)

This monograph on the St. Clair River and Lake St. Clair is one of an ongoing series of publications concerning current issues facing the Nation’s inland and estuarine waters. It purpose is to synthesize existing information describing the ecological structure and function of the St. Clair River and Lake St. Clair ecosystems, which, together with the Detroit River, compose the channel connecting Lakes Huron and Eirie and form the border between the U.S. (Michigan) and Canada (Ontario).

The St. Clair system is an extremely valuable resource that provides quality recreational opportunities to many people in southeast Michigan and the bordering areas of Ontario. Much of the St. Clair Delta remains in its natural state and more than 42,000 acres of wetlands in the delta support a large and diverse flora and fauna.

The St. Clair system is heavily used by recreational boaters, waterfowl hunters, and anglers. Fishing through the ice is a popular winter activity in some parts of the system. The waters of the St. Clair system are also used for navigation and for the disposal of municipal and industrial wastes, while the shorelines support industrial and residential development and agriculture. Recognition of potentially severe use conflicts has focused concern on preparation by Michigan and Ontario of Remedial Action Plans designed to control pollution by toxic substances and restore all beneficial uses to each affected area, consistent with a continued, multiple-use philosophy for the system.

This profile is a synthesis of available information on this waterway, especially information pertinent to managing the biological resources of the river and lake. Information gaps are identified and accommodated by reference to research done elsewhere or to management plans for other similar rivers and lakes. Wherever possible, the river and lake are described from a systems viewpoint as an intact, integrated unit of the Great Lakes ecosystem.

Undated

Distribution and Characterization of E. coli within the Dunes Creek Watershed, Indiana Dunes State Park (PDF file - 3.12 MB)

This study documents elevated E. coli counts throughout the Dunes Creek, Indiana Dunes State Park, watershed and shows that stream contamination originates from bank sediments, adjacent forest soils, and perhaps an undefined quantity from resident wildlife; similar problems were found in other coastal watersheds. There is little evidence of direct contamination, but the anthropogenic impact of heavy ditching and wetland draining has increased transport of E. coli from the Dunes Creek watershed to the state park beach, resulting in a high rate of beach closures.

Status, Trends, and Potential of Biological Communities of the Grand Calumet River Basin (PDF file - 1.18 MB)

This report provides an examination of the biological communities in the Grand Calumet River basin. The report highlights plants, aquatic macroinvertebrates, fishes, amphibians and reptiles, birds, and mammals that have been documented in the area from historical documents and current surveys. The comprehensive work was written as a supplement to planning documents for the restoration of the heavily degraded Grand Calumet River.

The Effects of Shooting Range Lead Shot on the Sand-dwelling Animals in the Near Shore Waters of Lake Michigan (PDF file - 415 KB)

In an attempt to determine the effects of lead shot on sand dwelling animals, Lake Michigan sands were surveyed in areas impacted by the Lincoln Park Gun Club and a control area. Lead shot accumulated over years of gun club activity in the Lincoln Park area of Chicago has been buried in the Lake Michigan sands at the clay sand interface. The effects of the presence of this lead shot on benthic meiofauna were studied by collecting surface grab sand. Community composition was determined statistically, and no significant differences were found in either total counts or composition between the two locations. Based on data from the surface sands, we failed to show that buried lead shot is having an effect on the sand-dwelling animals.

The Nearshore Benthic Invertebrate Community of Southern Lake Michigan and its Response to Beach Nourishment (PDF file - 379 KB)

The nearshore benthic environment of Lake Michigan represents a dynamic and little studied habitat. To explore the biology and response of this community to beach nourishment, Ponar samples were taken at 1.5, 3, and 6 m depths at 10 transects along the southern shore of Lake Michigan. Forty taxa were identified, and two of these, Chaetogaster diastrophus and Nematoda, made up over 81% of all organisms collected. Shallow sites (< 3 m) were generally dominated by C. diastrophus and Nematoda, and these sites represent communities adapted to constant wave induced sediment disturbance. Deep (6 m) sites were generally dominated by Nematoda, but fair numbers of C. diastrophus, Amphichaeta leydigi, Paracladopelma spp., and other less abundant taxa were identified. Greater diversity at deeper sites may be related to the stability resulting from reduced wave disturbance. A notable decrease in mean invertebrate density (P < 0.01) from 2001 to 2002 downdrift from the site of beach nourishment suggests that sand placement affected invertebrate populations, although a more thorough understanding of this community’s response to environmental variables is required to further support this conclusion.