OND99 Quarterly Rpt. sidebar
|
(Quarterly
Report for Oct-Nov-Dec 1999)
Alaska
Sablefish Assessment
The final sablefish
assessment was prepared by members of the Auke Bay
Laboratory (ABL) and Resource Ecology and Fisheries
Management (REFM) Division. The assessment
shows that sablefish abundance increased during the
mid-1960s due to strong year classes from the late
1950s and 1960s. Abundance subsequently
dropped during the 1970s due to heavy fishing;
catches peaked at 56,988 metric tons (t) in 1972.
The population recovered due to exceptional
year classes from the late 1970s; spawning abundance
peaked again in 1987. The population then decreased
as these exceptional year classes died off.
The longline survey abundance index increased 10% in
numbers and 5% in weight, and the commercial fishery
abundance index increased 11% in weight from 1998 to
1999. These increases follow decreases from
1997 to 1998, so that relative abundance in 1999 is
similar to 1997. Exploitable and spawning
biomass are projected to increase 3% and 1%,
respectively, from 1999 to 2000. Alaska
sablefish abundance now appears low and stable.
This is a change from previous assessments
where abundance appeared low and slowly decreasing.
Further years’ data are needed to confirm
that abundance has stabilized.
A simple Bayesian analysis was completed by
examining the effect of uncertainty in natural
mortality and survey catchability on parameter
estimation. A decision analysis was completed
using the posterior probability from the Bayesian
analysis to determine what catch levels likely will
decrease abundance. The decision analysis
indicates that a yield of about 17,000 t most
likely will keep spawning biomass the same and has
only a 20% probability of reducing the 2004 spawning
biomass to less than 90% of the 2000 spawning
biomass. The maximum permissible yield from an
adjusted F40% strategy is 17,300 t, which was the
2000 Acceptable Biological Catch (ABC) accepted by
the North Pacific Fishery Management Council (NPFMC)
for the combined stock, a 9% increase from the 1999
ABC of 15,900 t.
Stock assessment for major groundfish stocks in the
Bering Sea, Aleutian Islands, and Gulf of Alaska are
presented in this issue in the REFM Division’s
report in this section. Stock assessments of slope
and pelagic shelf rockfish in the Gulf of Alaska
follow.
By Michael Sigler.
Stock Assessment of Slope and Pelagic Shelf
Rockfish in Gulf of Alaska
Updated stock assessments of slope rockfish and
pelagic shelf rockfish in the Gulf of Alaska were
completed by ABL and REFM scientists. Results of the
1999 NMFS triennial trawl survey were included in
the updated stock assessments. The completed
assessment of Pacific ocean perch (POP), a
member of the slope rockfish assemblage, used an
age-structured model which showed that the stock is
increasing with an estimated exploitable biomass of
200,310 t. The assessment of most other
species of slope rockfish and pelagic shelf rockfish
in the Gulf of Alaska rely on biomass estimates
provided by trawl surveys, and abundance trends
based on these surveys are highly uncertain.
The most recently completed assessments
indicate the following stock levels (exploitable
biomass): shortraker and rougheye rockfish, 70,890
t; northern rockfish, 85,360 t; other slope
rockfish, 102,510 t; pelagic shelf rockfish, 66,440
t. Recommended ABC levels were Pacific ocean
perch,13,020 t; shortraker and rougheye rockfish,
1,730 t; northern rockfish, 5,120 t ; other slope
rockfish, 4,900 t; and pelagic shelf rockfish 5,980
t. These ABC values were all accepted by the
NPFMC.
A new age-structured assessment model for northern
rockfish was presented at the November NPFMC Gulf of
Alaska groundfish plan team meeting. The model
incorporates data from several disparate fisheries
and surveys and provides a quantitative framework
for evaluating the influence of different data
sources on the estimated population. The model
also provides a suggested rationale for determining
an appropriate level of confidence in apparently
inconsistent data components. Since an initial
review in September, the model was updated to
include 1999 survey biomass and length compositions,
1999 catch, and 1996 survey age compositions.
The model was also revised to include several
modifications suggested by the GOA plan team and by
the NPFMC Scientific and Statistical Committee.
A report describing the model was included as
an appendix in the 1999 stock assessment fishery
evaluation (SAFE) document. The model is expected to
be used for the determination of northern rockfish
stock status for the 2001 fishery.
By Dean Courtney and Jon Heifetz.
Eight Tagged Sablefish Recovered in 1999
ABL scientists began tagging sablefish in 1998 with
electronic tags that record depth and temperature.
(See feature article “New
Sablefish Research at the Auke Bay Laboratory”
in the July-September 1999 issue of the AFSC
Quarterly Report.) Recovery of the tags will yield
new insight into sablefish daily, seasonal, and
age-related depth movements and the marine
environmental conditions in which they live.
Knowledge of these movements will lead towards
better recommendations of sustainable harvests by
understanding what part of the population is
susceptible to the fishery and how this
susceptibility changes during the life of the fish.
During the 1998 NMFS longline survey of the Aleutian
Islands region and Gulf of Alaska (GOA), electronic
tags measuring 3/4 inches diameter by 2 1/4 inches
long were surgically implanted in the abdominal
cavity of 195 sablefish. The fish also were
externally marked with a flourescent pink and green
tag. More tagging is planned for the 2000
longline survey.
Nine electronic tags have been recovered so far, one
during 1998 and eight during 1999. One tagged
fish was at large 2 months, and the remainder about
1 year. Most fish were recovered near their
release location, except for one fish that traveled
from near Dutch Harbor to near Seward. Average
weekly depth for each recovered fish ranged from 200
to 500 m during summer and 400 to 700 m during
winter. Average weekly temperature ranged from
3.5o to 6.5oC, but no seasonal pattern was apparent.
Individual fish traveled a wide depth range,
sometimes during 1-2 days. For example, one
fish rose from about 1,100 m to 670 m in 1-1/2 days
and to 220 m in 9 days during October 1998.
By Michael Sigler.
Alaska Longline Survey Completed
On 5 September 1999, AFSC scientists completed
the twenty-first annual longline survey of the upper
continental slope of the Gulf of Alaska and a
portion of the slope of the eastern Bering Sea.
One hundred-fifty-two longline hauls (sets)
were completed. Sablefish was the most
frequently caught species, followed by giant
grenadiers, Pacific cod, arrowtooth flounder, and
Pacific halibut. A total of 88,949 sablefish,
with an estimated total round weight of 298,146 kg
(657,412 lb), was taken during the survey. The
highest total sablefish catch was observed at
station 105 in southern Southeast Alaska.
Station 98 in northern southeast Alaska had
the largest average length for sablefish.
A total of 4,633 sablefish, 603 shortspine
thornyhead, and 188 Greenland turbot were tagged and
released during the survey. Length-weight data
and otoliths were collected from 2,451 sablefish.
Thirty-six surface gillnet sets were completed to
assess the abundance of juvenile sablefish. A
very low number of sablefish (28 young-of-the
year-and 12 age-1) were caught in the gillnets
during the 1999 survey.
Killer whales preying on sablefish and Greenland
turbot caught on the gear were observed at seven
eastern Bering Sea stations.
By Thomas Rutecki.
Effects of Trawling on Soft-bottomed Marine
Habitat
An 11-day research cruise to study the effects
of bottom trawling on the seafloor near Kodiak
Island was completed on 24 August. The cruise
used the manned submersible Delta and the Alaska
Department of Fish and Game (ADF&G) vessel
Medeia and was the final cruise of a 2-year
study to make observations of the seafloor in areas
open to bottom trawling and adjacent areas that have
been closed to bottom trawling since 1986.
Processing of all sediment samples for
infaunal composition, grain size composition, and
organic carbon content were completed during the
quarter. Analysis of video footage taken from the
submersible, a labor intensive task, is continuing,
and fish and invertebrate counts for all sites
should be completed by October 2000, and project
analyses by the end of 2000. An expanded summary of
this project was provided in the July - September
1999 issue of the AFSC Quarterly Report.
Summaries of this and other AFSC studies on the
effects of fishing may be viewed at the following
Internet address: http://www.afsc.noaa.gov/abl/MarFish/pdfs/heifhabitatdec99.pdf.
By Robert Stone.
Alaska Chum Salmon Issues
A special meeting to discuss current chum salmon
(Oncorhynchus keta) production trends in
Alaska was hosted by Douglas Island Pink and
Chum Salmon, Inc. (DIPAC) at the Gastineau Hatchery
in Juneau, Alaska, on 5-6 January.
Attendees included representatives of the ADF&G,
University of Alaska School of Fisheries and Ocean
Sciences, Southern Southeast Regional Aquaculture
Association of Ketchikan, Northern Southeast
Regional Aquaculture Association of Sitka, Prince
William Sound Aquaculture Association of Cordova,
Trident Seafoods, Icicle Seafoods, Norquest Seafoods,
Taku Fisheries, Ward’s Cove Packing, and
scientists from the ABL.
An objective of the meeting was to review recent
returns of chum salmon throughout Alaska, with a
focus on hatchery returns, especially in Southeast
Alaska. The aquaculture associations and DIPAC
gave historical overviews of recent returns along
with analyses of their methodologies for forecasting
expected returns to their facilities in 2000.
Recent commercial harvests of chum salmon in
Alaska have approached or exceeded historical high
levels. The abundance of chum salmon, in turn,
has stretched the capabilities of traditional
processing and marketing methods for this species.
The statewide commercial harvest of chum
salmon in 1998 and 1999 exceeded 19.0 and 20.0
million fish, respectively, with about 75%
of the catch in the southeast region. A
majority of these fish were hatchery-produced.
Industry representatives indicated they were
pleased with the new quantities of chum salmon but
were interested in hearing from
aquaculture associations, scientists, and managers
about the prospects for continued large
returns. They emphasized a critical need for
long-range planning to develop adequate outlets for
various qualities of chum salmon product, including
bright- and dark-fleshed fish as well as different
grades of egg product. They pointed out that most
Alaska chum salmon eggs are processed as salmon
caviar for Japanese markets and that the eggs
are the source of Alaska chum salmon’s
commercial value. Developing products, markets, and
outlets for Alaska chum salmon, including dark and
maturing fish, takes concerted effort,
patience, and time in finding and developing
economically viable solutions to current production
levels.
The meeting also focused on recent age structure
patterns in chum salmon to determine if large
returns of age-3 fish are a precursor to large
returns of age-4 fish the following year.
Results of the review indicated that this
relationship was generally true, and aquaculture
associations are predicting returns to Southeast
Alaska hatcheries in 2000 of 14.0-16.0 million chum
salmon, similar to the last 2 years.
Jack Helle, from the ABL, reviewed age structure,
survival, and size-at-age patterns in wild stocks of
chum salmon based on a 25-year database of samples
throughout different parts of their North American
range. Until recent years, there has been a general
decline in size-at-age of chum salmon as abundance
of chum salmon has increased, which has been
interpreted as evidence of density-dependent
interactions and carrying capacity limitations in
ocean feeding areas. However, size-at-age has
increased dramatically for Southeast Alaska and
Pacific Northwest chum salmon in the past few years,
concurrent with historical record catches. Helle
also reviewed ABL’s Ocean Carrying Capacity
(OCC) Program current research on sampling juvenile
salmon during their first year at sea. He noted that
much new information on migration and distribution
of juvenile salmon is now possible due to the
otolith marking technology used by several
hatcheries in Alaska and elsewhere.
Discussions moved to variations in ocean survival
and size-at-age caused by regime shifts in climate
patterns and the large differences in survival
patterns and run strength in different regions
throughout the Pacific Rim. Examples included a
recent decline in chum salmon returns in Hokkaido
and Honshu compared to the many Alaska returns that
remain strong. A notable exception to the strong
upward trend for chum salmon in Alaska is the
extremely poor return in the Arctic-Yukon-Kuskokwim
(AYK) region. Reasons for the poor returns in
AYK are unknown and could relate to many factors
either in fresh water or at sea or both.
Southeast Alaska chum salmon have been
identified in salmon bycatch in the Bering Sea,
which has prompted some speculation that the high
abundance of chum salmon from Southeast Alaska and
other regions could be negatively influencing the
survival of western Alaska populations. These
by-catch recoveries have all been of immature (ocean
age 1-2) fish. However, juvenile salmon (ocean
age 0) captured in July and September 1999 during
OCC research cruises in Bristol Bay and the southern
Bering Sea were predominately sockeye salmon; no
juvenile chum salmon were captured. Previous
OCC cruises at this time of year in the Gulf of
Alaska have found juvenile chum salmon from
southeast Alaska distributed in a coastal band in
the Gulf of Alaska, from Cape Spencer to the Alaska
Peninsula. These observations suggest that
there is little mixing of the western AYK juveniles
with the southern stocks during their first ocean
year, the presumed critical period for
determining marine survival. Interactions of
older age groups are generally thought to influence
growth and size and age at maturity, but not
survival. Understanding where and how AYK chum
salmon spend their first year at sea could provide
important clues to some of the causes for poor
returns to that region. Although considerable
research has focused on Asian juvenile salmon that
enter the Bering Sea, unfortunately very little is
known about young salmon entering the Bering Sea
from the AYK Region.
By Bill Heard and Alex Wertheimer.
Origins of Sockeye and Chum Salmon Seized
From the Vessel Ying Fa
Samples of chum and sockeye (O. nerka) salmon
seized from the stateless fishing vessel Ying Fa
were analyzed to determine their region of origin
using genetic stock identification (GSI), otolith
marks, parasite analysis, and scale data.
Based on GSI, the chum salmon samples
originating in Russia were 86%; Japan,
2%; western Alaska, 2%; Alaska Peninsula and Kodiak,
8%; and British Columbia, 2%. Origins of the
sockeye salmon sample were not as clear because
there was some disagreement between the parasite
data and the GSI and scale data. Results of
parasite analysis suggested the sample was nearly
all of Alaskan origin, with at least 15% coming from
Bristol Bay. The GSI analysis indicated that
30% of the sockeye salmon originated in Russia and
70% in North America. The scale analysis
showed that 97% of the sockeye salmon sample were
ocean age 3, whereas the return to Bristol Bay in
1999 was approximately 70% ocean age 2 fish.
This report was submitted to the North Pacific
Anadromous Fish Commission (NPAFC) and is available
as a pdf file on the AFSC web site at http://www.afsc.noaa.gov/abl/StockID/pdfs/yingfa.pdf
By Richard Wilmot.
Comprehensive Allozyme Database Discriminates
Chinook Salmon Around Pacific Rim
The Chinook Salmon Genetics Working Group, which
is comprised of four west coast genetics
laboratories, met in Anchorage on 4-6 October 1999
to complete a coast-wide genetic database of 265
chinook salmon populations. Allozyme allele
frequencies from numerous studies have been
standardized and combined into a single
comprehensive database, which is managed by the
Northwest Fisheries Science Center (NWFSC). A report
was submitted to the NPAFC which documents the
collaborative database constructed at that meeting
and the results of simulations conducted to identify
genetic groups that can be accurately and precisely
identified in mixtures. Previous versions of
the allozyme database included nearly 200
populations ranging from the Sacramento River in
California to the Stikine River in British Columbia.
However, adequate coverage for Alaska and
Russia had been lacking, so no Alaskan, Russian, or
high-seas applications were possible. In
recent years, the ADF&G and the ABL have
initiated programs to update, enlarge, and
standardize allozyme data from northern and western
Alaska populations to develop a species-wide
database. Additional populations from British
Columbia as well as other Pacific Northwest
populations have also become available.
By Charles Guthrie.
Yukon River Radio-Tagging Project
The ABL’s radio-tagging study of Yukon River fall
chum salmon was completed in fall 1999 with over
1,000 fish radio-tagged and tracked to their final
destination. Fall aerial surveys were
conducted to locate fish in areas associated with
the Yukon River main stem.
Work continues on 1) planning for telemetry studies
on Yukon River chinook salmon and 2) completion of
the Proceedings of the 15th International Symposium
on Biotelemetry hosted by NMFS in Juneau
during May 1999.
By John Eiler.
Lipid Class and Fatty Acid Analysis of Forage
Fish Diets
Biologists at the ABL have been developing lipid
class and fatty acid analysis as a tool for
examining trophic relationships in forage fish
species. Surplus lipids acquired in a fish’s
diet are stored as triacylglycerides (TAG).
Consequently, the fatty acid (FA) composition
of a fish’s TAG should reflect that of its diet.
In addition, the amount of TAG in a fish relative to
the total lipid should provide a measure of its
energetic reserves because the FAs stored in TAG are
ultimately used to fuel metabolism. We have been
evaluating the use of these measures for detecting
dietary differences in forage fish collected in
Prince William Sound (PWS) and evaluating the
quality of the diets.
Our initial examination was to determine if there
was a spatial component to variation in FA
composition. We collected juvenile herring and sand
lance samples from several locations in PWS. All
collections were made within a 10-day period to
reduce any temporal variation. Initial analysis
revealed statistically significant differences in
the TAG content of herring and sand lance collected
at different locations. The highest TAG levels were
observed when both species co-occurred.
We compared the FA compositions of the TAG using a
supervised classification tool that devises a set of
rules for classifying samples into groups defined by
the user. Once the rules have been devised,
they are validated with samples whose types are
known, but were not used to devise the rules.
The classification tool provided a model for
classifying species by their FA compositions that
was accurate more than 95% of the time, and one that
correctly classified the sampling location more than
85% of the time. However, the spatial model failed
to make any distinction between species at a given
location. This suggests that there is an important
spatial component to the variation in FA
composition, and it is likely that this results from
similarities in the diets of the fish at a given
location regardless of species.
Work under way will compare the FA compositions of
the herring and sand lance to zooplankton sampled at
the same time, to determine if spatial differences
in FA composition are influenced by prey type. In a
related study we plan to examine the lipid class and
FA composition of sand lance sampled from a single
site every 2 weeks between May and September 1998.
By Ron Heintz.
Evidence and Consequences of Persistent Oil
in Pink Salmon Streams
Water of some Prince William Sound (PWS) salmon
spawning steams remains contaminated with Exxon
Valdez oil a decade after the spill (fall 1999).
Total aqueous polynuclear aromatic hydrocarbon
(PAH) concentrations were highest (300-400 ng/g) in
the lower intertidal area in two of six previously
oiled streams, supporting a hypothesis that oil
remaining in adjacent beaches can contaminate stream
water.
Persistent oil contamination may have inhibited
recovery of wild pink salmon stocks through the
mid-1990s. Reduced viability of pink salmon
embryos in oiled PWS streams through 1993 was
reported by Bue et al. (1998). This
observation, however, has been contested by others
(Brannon and Maki 1996). Thus, a decade after
the 1989 Exxon Valdez oil spill, the impact of the
spill on wild pink salmon populations remains
problematic and controversial. As a whole the
pink salmon population in PWS has been healthy for
some time, but there were reports of persistent oil
contamination in stream banks through 1995.
Central to the embryo viability controversy is
whether any salmon streams in PWS were ever oiled.
Flowing water did not allow oil to float
upstream in 1989, thus oil was stranded on stream
banks, deltas, and adjacent intertidal beaches, but
not on gravel in stream beds. However, a mixed
function oxidase enzyme, cytochrome P4501A, was
induced in alevins from oiled streams but not in
those from reference streams. Induction of
this biomarker enzyme signals exposure to PAH or
halogenated hydrocarbons, suggesting that
pre-emergent fish were exposed to oil.
Accumulating laboratory evidence demonstrates that
exposure of incubating pink salmon eggs to PAH
dissolved from oil reduces embryo survival, growth
rates, predator avoidance, and marine survival.
Exposure of developing pink salmon eggs to oil
was first verified as a plausible explanation for
reduced viability in 1992 by incubating pink salmon
eggs in gravel coated with known amounts of oil and
has been verified by repeated laboratory experiments
in Southeast Alaska.
Contamination of PWS stream water by PAH may explain
elevated pink salmon embryo mortality in oiled
streams from 1989 through 1993, but the mechanism
for oil transfer from surrounding gravel to stream
water was unknown. Coupled with the
observation that PAH dissolve from oiled rock into
water at concentrations sufficient to cause
toxicity, a hypothetical mechanism to explain toxic
levels of PAH in stream water was devised.
This hypothesis suggests that PAH from
oil on or in stream banks or adjacent intertidal
beaches will dissolve in interstitial water, and
that a portion of contaminated interstitial water,
driven by the dynamics of tidal fluctuations and
hydraulic gradients, will enter surface or
subsurface stream water. Lipophylic salmon
eggs buried in stream gravel could then be
contaminated by PAH even though gravel in stream
beds remains uncontaminated.
Current research is directed at verification of the
PAH-transfer hypothesis, and interpretation of
P4501A induction. The recent detection of PAH
in PWS stream water with lipophylic samplers is
evidence that oil in stream banks can contaminate
stream water. Further hydrographic research is
planned to further test the PAH-transfer hypothesis.
Graded oil-dose laboratory experiments with
pink salmon eggs are underway to link induction of
the P4501A biomarker to marine survival.
By Mark Carls.
NPAFC Annual Meeting and Symposium
The Auke Bay Laboratory cohosted the
Seventh Annual Meeting of the North Pacific
Anadromous Fish Commission (NPAFC) held on
24-29 October 1999 in Juneau, Alaska.
The NPAFC was established by the Convention
for the Conservation of Anadromous Stocks in the
North Pacific Ocean (the Convention) which entered
into force on 16 February 1993. The Convention
prohibits directed fishing for salmonids on the high
seas of the North Pacific Ocean and includes
provisions to minimize the number of salmonids taken
in other fisheries. The NPAFC promotes the
conservation of salmonids in the North Pacific and
its adjacent seas and serves as a venue for
cooperation in and coordination of enforcement
activities and scientific research. The commission
is made up of representatives of Canada, Japan,
Russia, and the United States.
Jack Helle of the ABL chaired the U.S. section of
the NPAFC Committee on Scientific Research and
Statistics which reviewed and discussed scientific
research on a broad range of issues concerning
Pacific salmonid stocks, including the relationship
between changes in abundance and in ocean and
atmospheric conditions and other biological and
ecological dynamics of salmonid production.
Following the annual meeting, salmon
scientists met on 1-2 November in Juneau for a 2-day
symposium entitled “Recent Changes in Ocean
Production of Pacific Salmon.” Keynote
speakers were Dr. Elbert (Joe) Friday from the
National Academy of Sciences and Dr. Bruce Finney
from the University of Alaska. Eight
presentations submitted by ABL staff were selected
for publication in the symposium proceedings.
Abstracts of the papers are given below.
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Back-Calculated Fish Lengths,
Scale Proportions, and Scale Increments for Two
Scale Methods Used in the Studies of Salmon
Growth-by Ellen Martinson, Michele Masuda, and
Jack Helle.
On chum salmon (Oncorhynchus
keta) scales, we compare the reference line
extending from the focus to the edge along an axis
drawn 75E from the transition zone (INPFC
(International North Pacific Fisheries Commission)
scale method) to the anterior-posterior line
(traditional scale method) by stock, brood year, and
age. Fish lengths calculated from the two
scale axes differed significantly (p = 0.004) for
all stocks, brood years, and ages except age-5 fish
from Fish Creek, Alaska, brood year 1981 (p = 0.27).
Mean calculated fish length at ocean age was greater
for the traditional scale method by 0%-4% (3-6 mm),
0%-4% (1-9 mm) at ocean age 2, 0%-2% (2-10 mm) at
ocean age 3, and 0%-2% (0-10mm) at ocean age 4.
Scale proportions for the two axes differed
significantly (p = 0.003) for all stocks, brood
years, and ages except age-5 fish from Fish Creek,
brood year 1981 (p = 0.28). Scale proportions
differed significantly between the two reference
lines; however, the absolute differences in
proportions were small. Scale measurements
were consistently greater for the INPFC scale method
in all years of marine growth: by 1%-9% in the first
year, 6%-13% in the second year, 0%-14% in the third
year, 0%-14% in the fourth year, and 7%-24% in the
last year. Scale measurements were
consistently different by brood year and age, but
varied by stock.
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Variation in Time of Annulus
Formation on Scales of Chum Salmon in the North
Pacific Ocean During El Niño and La Niña
Conditions-by Ellen Martinson and Jack Helle.
We examined
variation in time of annulus formation on scales (n
= 552) of chum salmon collected in the North Pacific
Ocean in April 1999 and May 1998 and 1999. May
samples were collected from approximately the same
location and same time, but during 2 years of very
different ocean conditions: 1998, a strong El Niño
year and 1999, a strong La Niña year. Annuli
occurred during April and May and were formed
earlier in 1999. Number of circuli beyond the
last annulus revealed an inverse relationship to
age-1, -2, -3, and -4 fish, but not for age-5 fish,
indicating that annulus formation takes place
earlier in younger fish. This was verified by
our findings. In most younger fish (age-1, -2, and
-3) the annulus was completed in April, and in older
fish (age-4 and -5) the annulus in many fish was not
completed by the end of May.
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Genetic Stock Identification,
Age, and Diet of Sockeye Salmon Captured in the
Bering Sea During April/May and Gulf of Alaska
During August 1998-by Chuck Guthrie, Ed Farley,
Noele Weemes, and Ellen Martinson.
Immature sockeye
salmon (Oncorhynchus nerka) were collected in
the coastal waters of the eastern Bering Sea (Cape
Cheerful; Unalaska Island) during April/May and in
the coastal waters of the Gulf of Alaska (Cape
Prominence; Unalaska Island) during August 1998.
Genetic stock identification techniques
(protein electrophoresis) indicated that Bristol Bay
stocks made up the largest percentage in the
samples. The majority of samples of immature
sockeye salmon collected during April/May (n = 430)
and August (n = 300) were age 1.1. Stomachs of
immature sockeye off Cape Cheerful contained mostly
fish, and off Cape Prominence mostly pteropods. The
substantial number of immature sockeye salmon
captured at Cape Cheerful during May 1998 was
unexpected based on current migration models of
western Alaska sockeye salmon. The large
percentage of immature sockeye salmon (98%) captured
at Cape Prominence during August 1998 was also
unexpected since immature chum salmon (O. keta)
constituted the largest percentage of the immature
salmon catch during August 1996 at the same location
(77%) (Carlson et al., 1996) and 1997 (66%) (Carlson
et al., 1997). These unexpected events may be
due to changes in distribution resulting from the
strong El Niño event during 1997-98.
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Spatial Variations in Early
Marine Growth and Condition of Thermally Marked
Juvenile Pink and Chum Salmon in the Coastal
Waters of the Gulf of Alaska–by Ed Farley and
Dick Carlson.
Spatial variations
in early marine growth and condition were examined
for hatchery-raised juvenile pink (Oncorhynchus
gorbuscha) and chum (O. keta) salmon
collected in the coastal waters of the Gulf of
Alaska (GOA) during 1996. Hatchery salmon
released in spring 1996 were recovered between 25
July and 9 August 1996. Most pink salmon from
Prince William Sound hatcheries were distributed
southwest along the continental shelf from Cape
Puget to Mitrofania Island along the Alaska
Peninsula. Chum salmon from southeastern
Alaska hatcheries were distributed northwest along
the continental shelf from Cape Spencer to Cape
Hinchinbrook. In general, mean lengths and
weights of juvenile pink salmon from Prince William
Sound hatcheries and juvenile chum salmon from
southeastern Alaska hatcheries increased as fish
migrated westward along the coast; the smallest
individuals were found near the exit corridors where
these salmon first entered the GOA.
Condition factor was lowest for salmon
caught nearest these exit corridors but increased as
fish migrated westward along the coast.
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The Use of Thermal Otolith Marks
to Determine Stock-Specific Ocean Distribution
and Migration Patterns of Pink and Chum Salmon
in the Gulf of Alaska, 1996-1999-by Dick
Carlson, Ed Farley, and Kate Myers.
We report the
results of broad-scale, shipboard surveys of ocean
distribution and migration patterns of Pacific
salmon (Oncorhynchus spp.) in coastal and offshore
waters of the North Pacific Ocean in spring and
summer 1996-99. A large, midwater rope trawl
was used to catch salmon and enhanced our ability to
sample broad oceanic areas in relatively short
periods of time, even under marginal weather and sea
conditions. Recoveries of hatchery salmon with
thermal otolith marks provided new stock-specific
data on the distribution of central and southeastern
Alaskan pink (O. gorbuscha) and chum (O.
keta) salmon in the Gulf of Alaska. In
general, the survey results corroborate the findings
of previous studies of ocean distribution and
migration patterns of salmon. New information
indicates that: 1) off-shore distribution of
juvenile (ocean age .0) pink and chum salmon varies
by geographic region, which may reflect differences
in the width of the continental shelf; 2) a
few juvenile southeastern Alaska hatchery chum
salmon were caught south of major exit corridors,
counter to the predominant northward migration
pattern; 3) the northern Shelikof Strait may be an
important summer migration corridor for juvenile
pink salmon, 4) the ocean range of central Alaska
pink salmon extends further to the southwest (to
42°N, 165°W) than shown by high-seas tag
experiments; and 5) some maturing chum salmon caught
in the coastal waters off Prince William Sound
in May are from an early southeastern Alaska
hatchery run (peak harvest in mid-July). We
conclude that sufficient numbers of thermally-marked
hatchery salmon can be recovered during coastal and
offshore salmon surveys to provide significant new
stock-specific information on ocean distribution and
migration patterns of salmon.
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Ocean Growth of Sockeye Salmon
from the Kvichak River, Bristol Bay, Based on
Scale Analysis – Alexey Isakov, Ole Mathisen,
Steve Ignell, and Terry Quinn.
Growth measurements
were taken from 9,414 legible scales of Kvichak,
Bristol Bay, sockeye salmon (Oncorhynchus nerka),
yielding a long time series (1914-97) of ocean
growth data. Growth rates in the first,
second, and third ocean years all declined prior to
the late 1950s and early 1960s after which they
began to steadily increase until 1970 when the three
growth patterns diverged: first year growth
continued to increase, but at a lower rate; second
year growth showed no further increase; and third
year growth began to steadily decrease. Growth
of sockeye salmon with the same ocean history (but
different broods) was highly correlated,
illustrating the importance of the environment in
affecting growth rates of sockeye salmon, not only
in the early marine environment but later in their
life history when the sockeye are more dispersed.
The importance of sea surface temperature
(SST), particularly during the growing season, was
noted in many of the regression models. SST
had its greatest influence on growth in the first
ocean year where sockeye are migrating out of
Bristol Bay and into the Aleutian Islands region.
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Food Habits of Juvenile Salmon
in the North Pacific Ocean, July-August 1996-by
Mary Auburn.
Four species of
juvenile salmon—pink (Oncorhynchus gorbuscha),
sockeye (O. nerka), chum (O. keta) and
coho (O. kisutch) salmon—were collected
during July and August 1996, using a midwater trawl
in near surface waters of the Gulf of Alaska from
Southeast Alaska to the Alaska Peninsula.
Stomach contents of these salmon were examined
to identify important prey items. Crustaceans—principally
hyperiid amphipods and euphausiids—and fish were
the primary prey, and decapod larvae, calanoid
copepods, and pteropods were also commonly found in
the juvenile salmon diets. The proportions of
prey type varied by habitat and regions for each of
the four salmon species examined. The large
variation in prey types and the small proportion,
3%, of empty stomachs suggest that the availability
of prey resources does not appear to be limiting
growth of juvenile salmon examined in this study.
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Early Marine Ecology, Habitat
Utilization, and Implications for Carrying
Capacity of Juvenile Pacific Salmon in
Southeastern Alaska-by Joe Orsi, Molly
Sturdevant, James Murphy, Don Mortensen, and
Bruce Wing.
The early marine
ecology of juvenile (age -.0) Pacific salmon (Oncorhynchus
spp.), their habitat utilization patterns, and
annual fluctuations in abundance were studied along
a seaward migration corridor in the northern region
of southeastern Alaska. From May to October in
1997, 1998, and 1999, up to 24 stations spanning 250
km were sampled at approximately monthly intervals
for biological and physical data in inshore, strait,
and coastal habitats extended 60 km offshore into
the Gulf of Alaska. Average surface (2-m)
temperatures and salinities ranged from 6.9o to
13.4oC and 16.7‰ to 31.8‰. A total
of 31,896 fish from 40 taxa was captured with 283
surface trawl hauls. All five species of
juvenile salmon were captured and comprised 61% of
the total catch; pink (O. gorbuscha)
and chum salmon (O. keta) were the
predominate species and comprised 29% and 24%
of the catch. Catch rates of juvenile
salmon were zero in May, highest in June and July,
and intermediate in August and October. The
highest catch rates of juvenile salmon occurred in
the strait habitats in June and July. A
maximum estimated aggregate density of juvenile pink
and chum salmon in strait habitats in June was less
than 1 fish per 1,000 m3, a density more than an
order of magnitude less than the neritic carrying
capacity previously reported for juvenile chum
salmon. Annual differences in the apparent
growth rates of juvenile pink and chum salmon
appeared to be more related to differences in
environmental conditions (temperature and
zooplankton) than to the densities of
juveniles. The seasonal decline in the
abundance of juvenile salmon in strait habitats
coincided with declining levels of zooplankton
biomass. Catch rates of juvenile salmon in
coastal habitats declined with distance offshore;
most juveniles were captured over the continental
shelf <25 km of shore. Juvenile salmon were
eaten by 4 of the 19 fish species examined for
predation, and were found in 33 (5%) of the 661 fish
examined. Information on origin from
marked juvenile salmon indicated stock-specific
spatial and temporal habitat utilization patterns,
including new documentation of Columbia River
Basin stocks of stream-type chinook off Alaska in
June, 3-4 months earlier that previously documented.
Origins of chum salmon in the strait
habitats suggest that hatchery stock groups comprise
over 50% of abundance in June and July, pulse
through the region coincident with the earlier
component of the wild stocks, and do not appear to
be impacting the carrying capacity of the region.
Our results indicate that juvenile salmon have
seasonal habitat utilization patterns synchronous
with factors that optimize growth, however,
long-term monitoring over varying environmental
conditions is needed to understand
relationships between early marine growth and
survival, and marine habitat utilization and
carrying capacity.
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