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Detection of Passive Integrated Transponder (PIT) Tags on Piscivorous Bird Colonies in the Columbia River Basin, 2001

Jolanta H. Glabek, Brad A. Ryan, Edmund P. Nunnallee, and John W. Ferguson

Report of research by

Fish Ecology Division

Northwest Fisheries Science Center

National Marine Fisheries Service

National Oceanic and Atmospheric Administration

2725 Montlake Boulevard East

Seattle, Washington 98112-2097

for

U.S. Army Corps of Engineers

Walla Walla District

201 North 3rd Street

Walla Walla, Washington 99362-1876

Delivery Order 2RL4SPTP00

September 2003

EXECUTIVE SUMMARY

            In 2001, the National Marine Fisheries Service detected the passive integrated transponder (PIT) tags of 45,065 juvenile salmonids on piscivorous bird colonies in the Columbia River Basin. These PIT tags accounted for 4.1% of the 1,099,291 PIT-tagged juvenile salmonids released into the Columbia River Basin to migrate during 2001. By species, they accounted for 8.7, 4.8, 3.4, and 2.6% of the PIT-tagged steelhead Oncorhynchus mykiss, coho O. kisutch, chinook O. tshawytscha, and sockeye salmon O. nerka respectively.

            Piscivorous bird colonies sampled were of Caspian terns (Sterna caspia), double-crested cormorants Phalacrocorax auritas, gulls Larus spp., American white pelicans Pelecanus erythrorhynchos, and three species of heron: Ardea alba, A. herodias, and Nycticorax nycticorax. The greatest number of tags was detected on East Sand Island in the Columbia River estuary.

            At Bonneville Dam (the first impoundment upstream from the Columbia River estuary), 47,246 PIT tagged juvenile salmonids were detected in the bypass systems in 2001, of which 12,847 originated in the Snake River Basin (SRB). Detections on bird colonies accounted for 24.2% of the SRB steelhead and 10.1% of the SRB spring/summer chinook salmon previously detected at Bonneville Dam. Of the remaining 34,399 non-SRB tags detected at Bonneville Dam, detections on the bird colonies accounted for 13.4, 10.3, 7.7, and 4.7% of the coho, steelhead, sockeye and chinook salmon, respectively.

            The second greatest number of tags was detected on Crescent Island in the McNary Dam reservoir. Upstream from Crescent Island at Lower Monumental Dam (the nearest upstream PIT tag detection facility), 48,779 juvenile spring/summer chinook and 15,486 steelhead tags from migration year 2001 were detected. Of these, 13.0% of the steelhead and 4.1% of the spring/summer chinook salmon were detected on the Crescent Island tern colony.

            Due to the low water flow and lack of spill in 2001, 168,734 PIT-tagged juvenile salmonids were barged around the Federal Columbia River Power System and released downstream from Bonneville Dam, which was a substantial increase compared to previous years. Of these we detected 6,405 tags, which accounted for 9.3, 7.5, 3.4, and 2.1% of the transported PIT-tagged coho, steelhead, chinook, and sockeye, respectively.

            In addition, we PIT tagged 8,754 juvenile salmonids during migration year 2001 and released them into rivers that discharge directly into the Columbia River estuary. From these releases, we detected 15.9, 8.4, and 3.7% of the fall chinook, steelhead and

spring chinook salmon, respectively. While detection percentages of steelhead and spring chinook salmon were not that different from those of upriver stocks, the percentage of fall chinook salmon detected was significantly higher than that of their upriver cohorts.

            Our PIT-tag detections in 2001 continue to provide minimum estimates of avian predation in the Columbia River Basin along with relative vulnerabilities of juvenile salmonids. In addition, these data were entered into the Columbia Basin PIT Tag Information System for use by other researchers and salmon managers.

CONTENTS

EXECUTIVE SUMMARY

INTRODUCTION

STUDY SITE

Columbia River Estuary

The Dalles Dam Reservoir—Lake Celilo

John Day Dam Reservoir—Lake Umatilla

McNary Dam Reservoir—Lake Wallula

Potholes Reservoir

METHODS

RESULTS

DISCUSSION

REFERENCES

APPENDIX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

INTRODUCTION

            Since 1991, the National Marine Fisheries Service (NMFS) has listed 12 evolutionarily significant units (ESUs) of Pacific salmon (Oncorhynchus spp.) in the Columbia River Basin as threatened or endangered under the U.S. Endangered Species Act (NMFS 2000). Under its mandate to identify and protect depressed or endangered salmonid populations, NMFS has undertaken research on several fronts, from evaluating criteria to define these genetically distinct populations (Waples 1991) to identifying causes of their decline at different life history stages (NMFS 2000).

            Recovery planning is at the forefront of this research, which includes a recent evaluation of the effects on chinook salmon (O. tshawytscha) demographics of potential reductions in mortality at different life stages (Kareiva et al. 2000). This evaluation found that reductions as low as 5% in early ocean and estuarine mortality could arrest population declines. Ironically, even as the habitats and life history stages central to recovery are beginning to be identified, growing populations of piscivorous birds present an additional risk to salmonid populations in these same habitats and life history stages (Collis et al. 2001a).

            Colonies of Caspian terns (Sterna caspia) along the north Pacific coast have expanded rapidly, from 3,500 breeding pairs in 1960 to 12,500 in 2001 (USACE 2001). Since the mid-1960s, Caspian tern colonies have shifted northward from California and by the 1980s began to concentrate on small islands in the Columbia River estuary (Gill

and Mewladt 1983). In 2001, 9,100 breeding pairs of Caspian terns were estimated near the mouth of the Columbia River on East Sand Island (Figure 1)(Collis et al. 2001b).

            Colonies of double-crested cormorants (Phalacrocorax auritas) also expanded rapidly in the Columbia River estuary, from initial sightings in the 1980s (Carter et al. 1995) to over 7,000 breeding pairs in 2001 (C. Anderson, Oregon State University, personal communication).

            In addition to terns and cormorants nesting in the Columbia River estuary, there are at least nine islands in the lower Columbia River Basin that host colonies of piscivorous birds. These birds include terns, cormorants, gulls (Larus spp.), American white pelicans (Pelecanus erythrorhynchos), and three species of herons (Ardea alba, A. herodias, and Nycticorax nycticorax).

Figure 1. Locations of avian nesting areas where PIT tags were detected in the Columbia River Basin, 2001.

            To evaluate the effects on juvenile salmonids of piscivorous birds nesting in the Columbia River Basin, we used juvenile salmonids tagged with passive integrated transponders (PIT). A PIT tag is a microchip bonded to an antenna coil and sealed in a glass cylinder, measuring 2.1 mm in diameter and 12 mm in length (Prentice et al. 1990a). When a PIT tag is within range of a magnetic field generated by a detection antenna it is energized and transmits its unique electronic code to the antenna (Prentice et al. 1990b). At the time of tagging, individual PIT-tag codes and information such as species and origin are recorded in the Columbia Basin PIT Tag Information System (PTAGIS), a regional database (PSMFC 1996). Codes in PTAGIS can be matched with records of subsequent detection and used to determine the migration history, and often the ultimate fate, of an individual fish.

            Since 1987, juvenile salmonids have been PIT tagged to evaluate measures implemented to improve their survival through the Federal Columbia River Power System (FCRPS). The total number of PIT-tagged juvenile salmonids released in the Columbia River Basin varies each year, but has increased from less than 50,000 in 1987 to over 1 million in 2001 (PSMFC 1996).

            In 1998, NMFS began detecting juvenile salmonid PIT-tags on piscivorous bird colonies in the Columbia River Basin (Ryan et al. 2001). These tag codes have been used to analyze bird feeding behavior, prey selectivity, and the relative vulnerability of various groups of juvenile salmonids to avian predators (Collis et al. 2001a; Ryan et al. 2003).

            Prior to 2001, PIT-tagged salmonids had been released throughout the Columbia River Basin; however, no PIT-tagged salmonids had been released from populations residing in streams and rivers that discharge directly into the Columbia River estuary. These stocks may be more vulnerable to avian predators nesting in the estuary if they rely more heavily on estuarine habitat than their upriver counterparts. For example, Reimers (1973) found a diverse number of estuary rearing periods and strategies for fall chinook salmon in the Sixes River, Oregon. To evaluate whether estuarine salmonids were more vulnerable to predation, we tagged a subset of these salmonids to compare with their upriver counterparts.

            Here we report the results of continuing PIT-tag detection efforts on piscivorous bird colonies in the Columbia River Basin in 2001 along with our estuary PIT-tagging effort. These data will be added to a growing database (PTAGIS) that will be used to evaluate the relative vulnerability of juvenile salmonids based on species, rear-type, and migration history.

STUDY SITE

            Our study site ranged from East Sand Island (RKm 8) near the mouth of the Columbia River to Solstice Island in the Potholes Reservoir (Figure 1), approximately 40 km east of the Wanapum Reservoir in the Columbia River (RKm 665). The sampling locations within our study site consisted of 15 bird colonies on 11 islands.

Columbia River Estuary

            East Sand Island (RKm 8) hosted a colony of Caspian terns and a separate colony of double-crested cormorants. The tern colony consisted of about 9,100 breeding pairs on 1.6 ha of open sand (Collis et al. 2001b). The cormorant colony consisted of about 7,000 breeding pairs (Collis et al. 2001b) on a 500 by 30-m colony situated on a jetty of large boulders. Rice Island (RKm 34) hosted a colony of about 200 breeding pairs of cormorants on 0.7 ha of open sand (C. Anderson, Oregon State University, personal communication).

The Dalles Dam Reservoir—Lake Celilo

            Little Memaloose Island (RKm 314) hosted a gull colony with a population index of about 300 on a small rock island (0.2 ha). Little Miller Island (RKm 331) hosted a gull colony, with a population index of about 1,700 on several small rock outcroppings (0.5 ha), and a small colony of terns with a population index of 20.

John Day Dam Reservoir—Lake Umatilla

            Three Mile Canyon Island (RKm 412) hosted tern and gull colonies. The tern colony had a population index of about 500 on 0.05 ha of open sand; however, the nest site was abandoned in early June due to predation by a mink (Mustela vision) (Collis et al. 2001b). The gull colony had a population index of about 10,000 on a combination of

0.5 ha of grassy field and sparsely vegetated rocky substrate.

McNary Dam Reservoir—Lake Wallula

            Crescent Island (RKm 509) hosted a tern colony of 720 breeding pairs on 0.1 ha of open sand (Collis et al. 2001b). Crescent Island also hosted a gull colony which has not had a population count, but we estimated at least several hundred breeding pairs. Badger Island (RKm 512) hosted an American white pelican colony with a population index of about 200 on 0.1 ha of shrubbery and sand. Foundation Island (RKm 519) hosted cormorant and heron colonies with population indices of about 400 and 200, respectively in 0.2 ha of deciduous trees. Due to the two colonies being intermixed within the trees, and our previous experience of detecting insignificant number of PIT tags from heron colonies (Ryan et al. 2002), all the tags from Foundation Island were identified as cormorant tags in 2001. Richland Island (RKm 545) and Island 18 (RKm 549) hosted gull colonies with population indices of about 19,000 and 12,000 on 1.0 and 0.5 ha of cobble, respectively.

Potholes Reservoir

            Solstice Island is a small sand island in Potholes Reservoir approximately 40 km from the Wanapum Reservoir in the Columbia River, which hosted a tern colony with a population index of about 400 on 0.05 ha of open sand (Collis et al. 2001b).

METHODS

            We sampled Caspian tern, double-crested cormorant, and gull colonies that had 50 or more nesting pairs, and that therefore had the potential to impact juvenile salmonid populations in the Columbia River Basin (Ryan et al. 2001). Smaller colonies of American white pelican and heron were sampled because logistics permitted sampling with minimal cost. During the spring nesting season (April-July), NMFS, Oregon State University, and Columbia River Inter-Tribal Fish Commission researchers established the boundaries of piscivorous bird colonies for each species by location and number of nesting birds.

            PIT tags were detected on bird colonies using two types of PIT-tag detectors. The first was a flat-plate detector, passed over the surface of abandoned colonies with a four-wheel-drive vehicle; the second was a pole-mounted detector, passed by hand over nest areas inaccessible to the vehicle (Ryan et al. 2001).

            Detection efficiency was evaluated by distributing PIT tags with known codes on colonies prior to the nesting season and then calculating the percentage of these tags detected at the end of the nesting season. Three hundred PIT tags were distributed on each of the following islands: East Sand, Little Miller, Foundation, Richland, and Island 18, while 150 PIT tags were distributed on Little Memaloose, Three Mile Canyon, and Crescent Islands. PIT tags were not distributed on Rice, Badger, or Solstice Islands due to the uncertainty of the nesting location prior to nesting season. Tag-reading depths for the flat plate antennas were evaluated on the East Sand Island tern colony at 0-, 2.5-, 5-, and 7.5-cm according to the protocol in Ryan et al. (2001).

            In addition, researchers from Biomark used manual sifting techniques to recover PIT tags from Crescent Island after we had completed our detection efforts (Dare et al. 2002). We used Biomark’s recovery efforts as an additional evaluation of our detection efficiency by calculating the percentage of tags they recovered that were missed during our detection effort.

            In the spring of 2001, we PIT tagged approximately 9,000 fall and spring chinook salmon and steelhead Oncorhynchus mykiss (about 3,000 of each type) and released them to rivers that discharge directly into the Columbia River estuary. Juveniles were tagged according to PIT-tagging protocols and standards outlined in the PIT Tag Marking Procedures Manual (CBFWA 1999), using mass marking and simple PIT-tag injectors. Following tagging, fish were held at the hatcheries for a minimum of 7 days to remove any tagging mortalities and rejected tags.

            Fall chinook salmon were tagged and released from Sea Resources hatchery on the Chinook River, 6 km upstream from where it enters the Columbia River. Spring chinook were released from net-pens in Deep River, 2 km upstream from where it enters the Columbia River at RKm 35. For tagging purposes, spring chinook were moved to Grays River hatchery where they were tagged and held in a raceway for a minimum of 7 days before being returned to the Deep River net-pens. Steelhead were tagged and released from the Elochoman hatchery, on the Elochoman River, 19 km upstream from its confluence with the Columbia River at RKm 58. A chi-square test of homogeneity of detection rates was used between estuarine salmonid stocks and their cohorts at Bonneville Dam.

RESULTS

            In 2001, we detected 49,283 juvenile salmonid PIT tags from piscivorous bird colonies in the Columbia River Basin. In addition, Biomark recovered 948 tags from Crescent Island, increasing the total to 50,231. Of these tags 45,065 were among the 1,099,291 salmonids PIT tagged and released into the Columbia River Basin for the 2001 migration year (4.1% of all salmonids). By species, tags detected on colonies accounted for 3.4% of the chinook salmon, 4.8% of the coho salmon O. kisutch, 8.7% of the steelhead, and 2.6% of the sockeye salmon O. nerka (Table 1). The majority of these tags were detected on colonies in the Columbia River estuary and McNary Dam Reservoir, where there are large colonies of terns and cormorants (Table 2).

            Of the PIT-tagged juvenile salmonids that migrated in-river and were detected at Bonneville Dam (the first impoundment upstream from the Columbia River estuary) in 2001, 12,847 originated from the Snake River Basin (SRB), while 34,384 came from other areas in the Columbia River Basin. Of the 12,487 SRB salmonids detected at Bonneville Dam, the percentages subsequently detected on piscivorous bird colonies in the Columbia River estuary ranged from 6.1% for fall chinook salmon to 24.2% for steelhead (Table 3). Of the 34,384 non-SRB salmonids detected at Bonneville Dam the percentages subsequently detected on piscivorous bird colonies in the Columbia River estuary ranged from 2.3 for fall chinook salmon to 13.4% for coho salmon.

            In addition to PIT-tagged salmonids that migrated in-river, 168,734 PIT-tagged salmonids were barged around the FCRPS and released approximately 10 km downstream from Bonneville Dam. Percentages of these salmonids that were subsequently detected on piscivorous bird colonies in the Columbia River estuary ranged from 2.0% for chinook salmon of unknown run-type to 9.3% for coho salmon (Table 4). The proportions detected on colonies were generally lower for barged fish than for in-river migrants detected at Bonneville Dam for both SRB and non-SRB salmonids.

Table 1. Total number of PIT tags released into the Columbia River Basin by migration year and percentages of these tags detected on piscivorous bird colonies. Land-based detection did not begin until 1998, and the lower percentages for detections from earlier years may be a result of tags being swept off the colonies during winter storms.

Table 2. Migration year 2001 salmonid PIT tags detected on piscivorous bird colonies in the Columbia River Basin.

Table 3. PIT-tagged Snake River Basin (SRB) and non-SRB salmonids detected at Bonneville Dam and the percentage of these tags detected on piscivorous bird colonies in the estuary, 2001.

* Species with less than 100 detections at Bonneville are not reported.

Table 4. PIT-tagged salmonids barged downstream from Bonneville Dam and the percentage of these tags detected on piscivorous bird colonies in the estuary, 2001.

            We also PIT-tagged and released an additional 8,754 salmonids for the 2001 migration year into rivers that discharge directly into the Columbia River estuary. From these releases, we detected tags on estuarine bird colonies in respective percentages of 15.9, 8.4, and 3.7% for fall chinook, steelhead, and spring chinook salmon (Table 5). Spring chinook salmon and steelhead released downstream from Bonneville Dam were detected at rates significantly lower than their cohorts detected at Bonneville Dam (c² = 34.4, P <0.001 for spring chinook; c² = 79.5, P <0.001 for steelhead; Table 6). However, detections of fall chinook released below the dam were significantly higher than those of their upriver counterparts (c² = 495.4, P <0.001).

            Outside of the Columbia River estuary, McNary Dam reservoir had the second highest number of PIT tags detected on piscivorous bird colonies (Table 2). There were 48,779 juvenile spring/summer chinook salmon and 15,486 steelhead from migration year 2001 detected at Lower Monumental Dam, the furthest downstream detection facility on the Snake River and the first detection facility upstream from McNary Dam. Of these salmonids, 13.0% of the steelhead and 4.1% of the spring chinook salmon were detected on the Crescent Island tern colony (hatchery and wild fish combined). Steelhead detection rates on Crescent Island were 6 to 10 times higher than in the previous three years, while chinook detection rates were 3 to 8 times higher (Table 7).

            Detection efficiencies based on our distributed tags ranged from 6 to 95% depending on colony and detection method (Table 8). Mean detection efficiencies for the flat-plate antennas and for the pole mounted antennas were 53.6 and 41.3%, respectively. While our tag detection efficiency on Crescent Island was low (44.7%), tag recovery efforts conducted by Biomark after our detection effort recovered 11,498 with 5.8% previously undetected. Tag-reading depth efficiencies for the flat-plate antennas were 100, 100, 97.3, and 91.2% at depths of 0-, 2.5-, 5-, and 7.5-cm, respectively.

Table 5. PIT tagged salmonids released into estuarine rivers downstream from Bonneville Dam and the percentage of these tags detected on piscivorous bird colonies in the estuary, 2001.

Table 6. PIT-tagged salmonids detected at Bonneville Dam and the percentage of these tags detected on piscivorous bird colonies in the estuary, 2001.

Table 7. PIT-tagged salmonids detected at Lower Monumental Dam and the percentage of these salmonids detected on the Crescent Island tern colony by migration year.

* Direct count of adult terns late in the nesting season, resulting in an estimate of breeding pairs.

Table 8. Detection efficiency of PIT tags distributed on colonies prior to the nesting season.

DISCUSSION

            The 50,231 juvenile salmonid PIT tags detected in 2001 resulted in a total of nearly 230,000 PIT tags detected on piscivorous bird colonies in the Columbia River Basin since 1998. While 230,000 PIT tags seems like a large number, these tags represent a minimum estimate of avian predation since our sampling effort only covers a portion of the area where tags can be deposited, and detection efficiency is less than 100%.

            Detections of PIT tags on the tern colonies of Crescent and East Sand Islands in 2001 indicated a large increase in the proportion of PIT tags from juvenile salmonids deposited on both islands compared with previous years. The greatest increase was in the proportion of PIT tags detected on Crescent Island, and was most likely due to the record low water flow and lack of spill.

            The low flow prompted fisheries managers to maximize the number of fish collected at Snake River Dams and transported around the FCRPS by reducing spill. This left fewer juvenile salmonids in the river to migrate past Crescent Island compared to previous years, and resulted in the terns consuming a higher proportion of the available salmonids. In addition, terns are surface predators (Cuthbert and Wires 1999), and the less turbid conditions created by low river flows may have benefitted foraging terns.

            The increase in proportion of PIT tags detected on East Sand Island may also be due to the low river flow which resulted in slower migration speeds below Bonneville Dam (R. Ledgerwood, NMFS, personal communication). Additional time spent migrating through the estuary may have increased the period during which salmonids were available for avian predation.

            The predation rate on SRB salmonids in the Columbia River estuary was surprisingly higher than the predation rate on non-SRB salmonids. While we do not have any substantial evidence as to why this is occurring, we intend to further investigate this increased vulnerability and monitor whether this pattern continues for future migration years. One area that we intend to investigate is the speculation that SRB juvenile salmonids, which migrate through more than one Snake River Dam bypass system, have lower smolt to adult return rates (Budy et al. 2002), and how this may relate to increased vulnerability to avian predation.

            We expanded our research to obtain additional data on salmonids released directly into the Columbia River estuary. These data provide preliminary evaluations of the vulnerability of salmonids to avian predation from three rivers that discharge directly into the estuary. We observed a high predation rate on fall chinook salmon, which may have resulted from having to pass through a small channel between Sand and East Sand Islands, where 7,000 nesting pairs of cormorants were concentrated. Had the fall chinook been released from a site to enter the estuary at a different location, detection rates may have been reduced. We plan to expand this effort in 2002 with additional release sites.

            PIT-tag data collected from piscivorous bird colonies throughout the Columbia River Basin continue to provide estimates of relative vulnerability to avian predation and data that can be used to evaluate relocation efforts in the Columbia River estuary (Collis et al. 2001a; Ryan et al. 2003). In addition, these data are stored on a central database allowing researchers to remove known mortalities from their data sets producing a more accurate set of data that can be used for many purposes, such as estimating survival past dams (Absolon et al. 2002).

            While we have not developed a method to evaluate the rate at which tags are deposited on the sampled sites, we have evaluated detection efficiency of tags known to be deposited on a colony. Evaluations of detection efficiency on the East Sand Island tern colony suggest over 90% of all the tags deposited on the colony in both 2000 and 2001 were detected. In contrast, our detection efficiency averaged around 40% for all colonies, and we would extrapolate our detection numbers based on this if these were the only data available.

             However, manual recovery of tags by researchers from Biomark on Crescent Island resulted in 11,498 in-river migrant tags of which only 5.8% were undetected by our detection efforts. This suggests that while our detection efficiency is probably greater than 40% it is still not 100%. Therefore, our sampling efforts continue to provide minimum estimates of predation.

REFERENCES

Absolon, R. F., E. M. Dawley, B. P. Sandford, J. W. Ferguson, and D. A. Brege. 2002. Relative survival of juvenile salmon passing through the spillway of The Dalles Dam, 1997-2000. Report of the National Marine Fisheries Service to the U.S. Army Corps of Engineers, Portland, Oregon.

Budy, P., P. G. Thiede, N. Bouwes, C. E. Petrosky, Schaller, H. 2002. Evidence linking delayed mortality of Snake River salmon to their earlier hydrosystem experience. North American Journal of Fisheries Management 22:35-51.

Carter, H. R., A. L. Sowls, M. S. Rodway, U. W. Wilson, R. W. Lowe, G. J. McChesney, F. Gress, and D. W. Anderson. 1995. Population size, trends and conservation problems of the double-crested cormorant on the Pacific Coast of North America. Pages 189-215 in D. N. Nettleship and D. C. Duffy, editors. The double-crested cormorant: biology, conservation and management. Colonial Waterbirds 18 (Special Publication1): 189-215.

Collis, K., D. D. Roby, D. P. Craig, B. A. Ryan, and R. D. Ledgerwood. 2001a. Colonial waterbird predation on PIT-tagged juvenile salmonids in the Columbia River Estuary: Vulnerability of different salmonid species, stocks, and rearing types. Transactions of the American Fisheries Society 130:385-396.

Collis, K., D.D. Roby, D.E.Lyons, and D.P. Craig. 2001b. Draft 2001 season summary:

Columbia Bird Research update. Available www.columbiabirdresearch.org (July 2001).

CBFWA (Columbia Basin Fish and Wildlife Authority PIT Tag Steering Committee). 1999. PIT Tag Marking Procedures Manual. Version 2.0.

Cuthbert, F., and L. Wires. 1999. Caspian tern (Sterna caspia). Pages 1-32 in A. Poole and F. Gill, editors. The Birds of North America, no.403. The Birds of North America, Inc., Philadelphia.

Dare, R. M., McCutcheon C. S., and Richmoond R.J. 2002. Manual PIT tag collection at the Caspian tern colony on Crescent Island, Washington. Biomark, Inc. Report to the U.S. Army Corps of Engineers, Walla Walla, Washington.

Gill, R. E. Jr., and L. R. Mewladt. 1983. Pacific coast Caspian terns: dynamics of an expanding population. The Auk 100:369-381.

Kareiva, P., M. Marvier, and M. McClure. 2000. Recovery and management options for spring/summer chinook salmon in the Columbia River Basin. Science 290:977-979.

NMFS (National Marine Fisheries Service). 2000. Biological opinion: reinitiation of consultation on the Federal Columbia River Power System, including the juvenile fish transportation system, and 19 Bureau of Reclamation projects in the Columbia Basin. (Available from NMFS Northwest Region, Hydro Program, 525 NE Oregon Street, Suite 500, Portland OR 97232.)

Prentice, E. F., T. A. Flagg, and C. S. McCutcheon. 1990a. Feasibility of using implantable passive integrated transponder (PIT) tags in salmonids. American Fisheries Society Symposium 7:317-322.

Prentice, E. F., T. A. Flagg, C. S. McCutcheon, and D. F. Brastow. 1990b. PIT-tag monitoring systems for hydroelectric dams and fish hatcheries. American Fisheries Society Symposium 7:323-334.

PSMFC (Pacific States Marine Fisheries Commission). 1996--. Columbia Basin PIT tag information system (PTAGIS). Pacific States Marine Fisheries Commission, Gladstone, Oregon. Online database. (Available through Internet, http://www.psmfc.org/pittag/ )

Reimers, P. E. 1973. The length of residence of juvenile fall chinook in Sixes River, Oregon. Fisheries Commission of Oregon Research Report 4(2):1-43.

Ryan, B. A., J. W. Ferguson, R. D. Ledgerwood, and E. P. Nunnallee. 2001. Detection of passive integrated transponder tags from juvenile salmonids on piscivorous bird colonies in the Columbia River Basin. North American Journal of Fisheries Management 21:149-153.

Ryan, B. A., J. H. Glabek, J. W. Ferguson, E. P. Nunnallee, and R. D. Ledgerwood. 2002. Detection of passive integrated transponder tags on piscivorous bird colonies in the Columbia River Basin, 2000. Report of the National Marine Fisheries Service to the U.S. Army Corps of Engineers, Walla Walla, Washington.

Ryan, B. A., S.G. Smith, J. M. Butzerin, and J. W. Ferguson. 2003. Relative vulnerability to avian predation of juvenile salmonids tagged with passive integrated transponders in the Columbia River Estuary, 1998-2000. Transactions of the American Fisheries Society 132:275-288.

USACE (U.S. Army Corps of Engineers). 2001. Environmental assessment: Caspian tern relocation FY 2001-2002 management plan and pile dike modification. U.S. Army Corps of Engineers, Portland, Oregon.

Waples, R. S. 1991. Pacific salmon, Oncorhynchus spp., and the definition of "species" under the Endangered Species Act. Marine Fisheries Review 53(3):11-22.

APPENDIX

Appendix Table A1. Migration year 2001 juvenile spring/summer chinook PIT tags released into the Columbia River Basin. Separated by hatchery, wild, and unknown rear types.

Appendix Table A1. Continued.

Appendix Table A1. Continued.

a. Release sites from the PIT Tag Information System specification document. 

b. Release site codes from the PIT Tag Information System specification document.

Appendix Table A2. Migration year 2001 juvenile fall chinook PIT tags released into the Columbia River Basin. Separated by hatchery, wild, and unknown rear types.

a. Release sites from the PIT Tag Information System specification document.

b. Release site codes from the PIT Tag Information System specification document.

Appendix Table A3. Migration year 2001 juvenile unknown chinook PIT tags released into the Columbia River Basin. Separated by hatchery, wild, and unknown rear types.

a. Release sites from the PIT Tag Information System specification document.

b. Release site codes from the PIT Tag Information System specification document.

Appendix Table A4. Migration year 2001 juvenile steelhead PIT tags released into the Columbia River Basin. Separated by hatchery, wild, and unknown rear types.