AFSC/ABL: Karluk sockeye salmon scale time series
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To better understand how density-dependent growth of ocean-dwelling Pacific salmon varied with climate and population dynamics, we examined the marine growth of sockeye salmon in relation to an index of sockeye salmon abundances among climate regimes, population abundances, and body sizes under varied life history stages, from 1925 to 1998 using ordinary least squares and multivariate adaptive regression spline threshold models. The annual marine growth and body size during the juvenile, immature, and maturing life stages were estimated from increments on the scales of adult age 2.2 sockeye salmon that returned to spawn at Karluk River and Lake on Kodiak Island, Alaska. Intra-specific density-dependent growth was inferred from inverse relationships between growth and sockeye salmon abundance based on commercial harvest. Density-dependent growth occurred in all marine life stages, during the cool regime, at lower abundance levels, and at smaller body sizes at the start of the juvenile life stage. The finding that density-dependence occurred during the cool regime and at low population abundances suggests that a shift to a cool regime or extreme warm regime at higher population abundances could further reduce the marine growth of salmon and increase competition for resources. Alaska salmon production fluctuates with climate and ocean conditions in the North Pacific Ocean. In this study, we evaluated the hypothesis that faster marine growth was related to higher survival as a consequence of more favorable ocean conditions for growth during the 1927-46 and 1977-2000 warm regimes, and slower growth was related to lower survival as a consequence of less favorable climatic and oceanic conditions for growth during the 1947-76 cool regime. We measured and compared the annual growth on scales collected from age 2.2 sockeye salmon that returned to Karluk Lake on Kodiak Island, Alaska from 1927 to 2000 to regime periods, climatic and oceanic indices, and survival. First and second marine-year scale growth fluctuated with the cool regime and recent warm regime. Survival estimated as the ratio of offspring to parental escapement was lower during the 1925-46 warm regime and 1947-76 cool regime. Survival was positively related to first and second marine year scale growth, eastern North Pacific atmospheric circulation, and reduced winter and spring coastal downwelling in the Gulf of Alaska. Winter and spring climatic and oceanic conditions influences on first and second year marine growth of Karluk Lake sockeye are a possible mechanisms linking Karluk Lake sockeye salmon survival to climate over the past half century.
AFSC/ABL: Stock composition, timing, and spawning distribution of Yukon River Chinook salmon
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Radio telemetry was used to determine the distribution, locate spawning sites, and evaluate the tagging response of wild Chinook salmon Oncorhynchus tshawytscha returning to a large, free-flowing river basin. A total of 2,860 fish were radio tagged in the lower Yukon River and tracked upriver. Fish traveled to spawning areas throughout the basin, ranging from several hundred to over 3,000 km from the tagging site. We found similar distribution patterns across years, suggesting that the major components of the return were identified. Most spawning fish were clustered in a number of principal tributaries, although small numbers of fish were located in other spatially-isolated areas. The cumulative contribution of these minor stocks was appreciable, making up 28-31% of the tagged sample. There was suggestive evidence of mainstem spawning in upper reaches of the basin. Large-scale elevation and physiographic data were useful in categorizing spawning areas, with most fish returning to relatively entrenched upland rivers. Fish were largely absent in lowland reaches characterized by meandering, low gradient, alluvial channels often associated with main river floodplains. The fish generally responded well to the capture, handling, and tagging procedures with most (2,790, 97.6%) resuming upriver movements, although the fish initially displayed a negative tagging response, with slower migration rates observed immediately after release. The duration of this response was relatively short (several days) and less severe as the fish moved upriver. The swimming speeds of radio-tagged fish after the initial delay were comparable to estimates for untagged fish, further suggesting that the capture, handling, and tagging methods used were relatively benign. Identifying the primary components of the run (including both major and minor stocks) and determining site-specific utilization patterns can fundamentally enhance salmon management in large river basins, and facilitate research and conservation efforts.
AFSC/ABL: Pink salmon data collected at Sashin Creek Weir 1934-2002
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A database describing a 67-year time series for Sashin Creek pink salmon (Oncorhynchus gorbuscha) data is presented. The database details the survival and other biological parameters of the pink salmon population living in Sashin Creek, a pristine environment in Little Port Walter, Baranof Island, Alaska. We assembled all the published and unpublished biological and environmental data pertaining to this population, which has been evaluated almost continually by researchers since 1934. We developed a database using Microsoft Access that includes annual estimates of the freshwater and saltwater survival for these fish. The database contains the daily counts of the number of emigrating fry and escaping adults during their annual migrations since 1934, and their lengths, weights, or fecundity. Environmental parameters in the database include stream temperature, stream discharge, daily minimum and maximum air temperatures, and precipitation where Sashin Creek enters seawater at Little Port Walter. All records have been evaluated and transformed to ensure comparability. References for all data are provided, including unpublished sources. The Sashin Creek Weir Database (SCWDATA) can be accessed through the Internet.
AFSC/ABL: Eastern Bering Sea (BASIS) Coastal Research on Juvenile Salmon
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Pacific salmon (Oncorhynchus spp.) runs in rivers that flow into the eastern Bering Sea have been inconsistent and at times very weak. Low returns of chinook (O. tshawytscha) and chum (O. keta) salmon to the Yukon River, Kuskokwim River, and Norton Sound areas of Alaska prompted the state of Alaska to restrict commercial and subsistence fisheries during 2000 and declare the region a fisheries disaster area. Weak salmon returns to these river systems follow several years of low sockeye (O. nerka) salmon returns to Bristol Bay, which was declared a fisheries disaster region during 1998 by both the State of Alaska and the U.S. Department of Commerce. Causes of the poor salmon returns to these river systems are not known however, the regional-scale decline of these stocks indicates that the marine environment may play a critical role. Ocean conditions, particularly in the first few months after the salmon leave fresh water, are known to significantly affect salmon survival (Holtby et al. 1990; Friedland et al. 1996; Beamish and Mahnken 2001). Mechanisms affecting marine survival of the eastern Bering Sea salmon stocks are unknown, principally due to the lack of marine life history information on western Alaska salmon. To improve understanding of the marine life-history stage of salmon in the Bering Sea, the North Pacific Anadromous Fish Commission (NPAFC) began an internationally coordinated research program on salmon in the Bering Sea called the Bering-Aleutian Salmon International Survey (BASIS) (NPAFC 2001). As part of BASIS, scientists from the National Marine Fisheries Service (NMFS), Ocean Carrying Capacity (OCC) program conducted a fall survey on the eastern Bering Sea shelf to provide key ecological data for eastern Bering Sea salmon stocks during their juvenile life-history stage. The goal of the OCC/BASIS salmon research cruise was to understand mechanisms underlying the effects of environment on distribution, migration, and growth of juvenile salmon on the eastern Bering Sea shelf. Primary objectives of BASIS include: 1) to determine the extent of offshore migrations of juvenile salmon from rivers draining into the eastern Bering Sea, 2) to describe the physical environment of the eastern and northeastern Bering Sea shelf occupied by juvenile salmon, and 3) to collect biological information on other ecologically important species. Summaries of previous Bering Sea juvenile salmon research cruises can be found in Farley et al. (1999, 2000, 2001, 2002, 2004, 2005).
AFSC/ABL: Longline Sablefish Survey
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Data is available from annual bottom longline surveys conducted cooperatively by Japan (1979-1994) and the U.S. National Marine Fisheries Service, Alaska Fisheries Science Center (1988-present). Starting in 1988, the U.S. started conducting the survey, creating overlap between the two countries between1988-1994. Since 1994, the U.S. has conducted the survey independently. Stations are spaced systematically (~20-30 km apart) along the slope from the eastern Gulf of Alaska west to the Aleutian Islands and north into the eastern Bering Sea. At each station, depths from ~150-1000 meters are sampled. Each year the captain attempts to set the gear along the same path. The same stations are sampled each year except in the Aleutian Islands and the Bering Sea, which are sampled every other year at the beginning of the survey (last week of May-early June). Since 1995, in odd years the Bering Sea stations are sampled and in even years the Aleutian Islands are sampled. The status of each hook is recorded. Lengths are taken from major species including, sablefish, giant grenadier, Pacific grenadier, Greenland turbot, arrowtooth flounder, Pacific cod, shortspine thornyhead, and all rockfish caught.