Development of indices for salmon and pollock survival in the rapidly changing environment of the eastern Bering Sea (original) (raw)
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Linkages between Alaskan sockeye salmon abundance, growth at sea, and climate, 1955–2002
Deep Sea Research Part II: Topical Studies in Oceanography, 2007
We tested the hypothesis that increased growth of salmon during early marine life contributed to greater survival and abundance of salmon following the 1976/1977 climate regime shift and that this, in turn, led to density-dependent reductions in growth during late marine stages. Annual measurements of Bristol Bay (Bering Sea) and Chignik (Gulf of Alaska) sockeye salmon scale growth from 1955 to 2002 were used as indices of body growth. During the first and second years at sea, growth of both stocks tended to be higher after the 1976-1977 climate shift, whereas growth during the third year and homeward migration was often below average. Multiple regression models indicated that return per spawner of Bristol Bay sockeye salmon and adult abundance of western and central Alaska sockeye salmon were positively correlated with growth during the first 2 years at sea and negatively correlated with growth during later life stages. After accounting for competition between Bristol Bay sockeye and Asian pink salmon, age-specific adult length of Bristol Bay salmon increased after the 1976-1977 regime shift, then decreased after the 1989 climate shift. Late marine growth and age-specific adult length of Bristol Bay salmon was exceptionally low after 1989, possibly reducing their reproductive potential. These findings support the hypothesis that greater marine growth during the first 2 years at sea contributed to greater salmon survival and abundance, which in turn led to density-dependent growth during later life stages when size-related mortality was likely lower. Our findings provide new evidence supporting the importance of bottom-up control in marine ecosystems and highlight the complex dynamics of species interactions that continually change as salmon grow and mature in the ocean. r
Transactions of the American Fisheries Society, 2008
Although early marine growth has repeatedly been correlated with overall survival in Pacific salmon Oncorhynchus spp., we currently lack a mechanistic understanding of smolt-to-adult survival. Smoltto-adult survival of pink salmon O. gorbuscha returning to Prince William Sound was lower than average for juveniles that entered marine waters in 2001 and 2003 (3% in both years), and high for those that entered the ocean in 2002 (9%) and 2004 (8%). We used circulus patterns from scales to determine how the early marine growth of juvenile pink salmon differed (1) seasonally during May-October, the period hypothesized to be critical for survival; between years of low and high survival; and (3) between hatchery and wild fish. Juvenile pink salmon exhibited larger average size, migrated onto the continental shelf and out of the sampling area more quickly, and survived better during 2002 and 2004 than during 2001 and 2003. Pink salmon were consistently larger throughout the summer and early fall during 2002 and 2004 than during 2001 and 2003
2005
Recent research demonstrated significantly lower growth and survival of Bristol Bay sockeye salmon (Oncorhynchus nerka) during odd-numbered years of their second or third years at sea (1975, 1977, etc.), a trend that was opposite that of Asian pink salmon (O. gorbuscha) abundance. Here we evaluated seasonal growth trends of Kvichak and Egegik river sockeye salmon (Bristol Bay stocks) during even- and odd-numbered years at sea by measuring scale circuli increments within each g rowth zone of each major salmon age group between 1955 and 2000. First year scale growth was not significantly different between odd- and even-numbered years, but peak growth of age-2 smolts was significantly higher than age-1. smolts. Total second and third year scale growth of salmon was significantly lower during odd- than during even-numbered years. However, reduced scale growth in odd-numbered years began after peak growth in spring and continued through summer and fall even though most pink salmon had le...
Transactions of the American Fisheries Society, 2005
We tested the hypothesis that survival rates from spawners to recruits in Pacific salmon Oncorhynchus spp. are primarily related to coastal ocean conditions during migration to the sea and soon after. We correlated measures of survival rate in units of log e (recruits/spawner) for 110 stocks of pink salmon O. gorbuscha, chum salmon O. keta, and sockeye salmon O. nerka with regional-scale indices of coastal sea surface temperature, sea surface salinity, and upwelling as well as with a large-scale index of ocean climate. We examined correlations by month and at multiple lags spanning the periods of spawning, freshwater residence, and early ocean residence of salmon. Survival rates of all three salmon species were related to ocean temperatures just prior to, during, and after out-migration, which are indicative of the early marine conditions experienced by juvenile salmon. This is consistent with the hypothesis that the early marine period is critical to the survival of juvenile salmon. However, survival rates of sockeye salmon were most strongly correlated with coastal sea surface temperature during freshwater residency (i.e., the winter and spring prior to out-migration). Survival rates of pink salmon were also related to sea surface salinity conditions prior to out-migration. There was no evidence for any relationship between the survival rates of salmon and coastal upwelling conditions. As in previous studies, we found that correlations between the survival rates of pink or sockeye salmon in Alaska and sea surface temperature have opposite signs from correlations for stocks in British Columbia and Washington at most lags and at both regional and large (basinwide) spatial scales. In general, however, the measures of coastal ocean conditions that we examined explain a relatively small proportion of the environmentally induced variability in salmon survival rates.
Marine and Coastal Fisheries, 2016
The productivity of Bristol Bay, Alaska, Sockeye Salmon Oncorhynchus nerka increased during the mid-1970s. This increase is believed to be partially due to an increase in early marine growth associated with the 1976-1977 cool-to-warm shift in summer sea surface temperature (SST). The body size of juvenile salmon during their first year at sea is believed to regulate their ability to survive over winter. The back-calculated smolt length, first-year ocean growth, and total juvenile length of Sockeye Salmon from five Bristol Bay river systems (Egegik, Kvichak, Naknek, Ugashik, and Wood) and two smolt ages were used to examine trends and factors influencing total juvenile length, compensatory growth, and size-selective mortality in the first year in the ocean from 1962 to 2007. Juvenile length increased in relation to summer sea temperature, the 1977-2001 and 2002-2007 warm temperature regimes, smolt length, and compensatory growth. Compensatory growth-an inverse relationship between first-year ocean growth and smolt size-increased over time as well as after the 1976-1977 climate regime shift, was more common in age-1.0 fish than in age-2.0 juveniles, and was important in determining the length of juvenile Sockeye Salmon from the Wood River (the shorter fish among rivers and smolt ages). The coefficient of variation in length did not change with SST, suggesting that size-selective mortality occurred prior to the end of the first year at sea for all 10 fish groups. The predictor variables that were significant in the models varied among river systems and smolt ages. This study demonstrated that the frequency of compensatory growth and the total lengths of juvenile Sockeye Salmon during their first year at sea increased with summer SST (range, 7.5-10.5°C) in the eastern Bering Sea, a possible mechanism for the increased productivity of Bristol Bay Sockeye Salmon associated with warmer sea temperatures.
2013
Global climate change is expected to change the distribution and growth of marine species. Therefore, understanding how climate, ocean productivity, and population abundance affect the dynamics of marine species will help predict how growth and recruitment of marine species will respond to future changes in climatic and oceanic conditions. Statistically significant intertemporal correlations have been observed between a variety of environmental factors and recruitment, growth, mortality, and abundance of fish populations. However, because these correlative relationships are not reflective of the actual biophysical processes, the relationships can break down, particularly when used for forecasting. Failure of these simple correlative relationships motivates the search for biological indicators that integrate ocean productivity across ecological dimensions and through time. Measured distances along Chum Salmon (Oncorhynchus keta) scale radii and associated body morphology were used to...
Eastern Bering Sea (BASIS) Coastal Research (August -October 2005) on Juvenile Salmon
An eastern Bering Sea research cruise was conducted by National Marine Fisheries Service scientists from the Auke Bay Laboratory, Ocean Carrying Capacity program during August -October 2005 to study early marine distribution, migration, and growth of juvenile salmon (Oncorhynchus spp.) salmon on the eastern Bering Sea shelf. A total of 16,615 salmon were captured including juvenile pink (O. gorbuscha; 9.2%), chum (O. keta; 14.9%), sockeye (O. nerka; 69.8%), coho (O. kisutch; 0.9%), and chinook (O. tshawytscha; 2.5%) salmon; less than 3% of the catch consisted of immature and mature chum, sockeye, and chinook salmon. Juvenile pink and chum salmon were generally distributed north of 58°N with large catches occurring near Nunivak Island. Juvenile sockeye salmon were widely distributed within Bristol Bay (159°W) to as far east as 170°W with the largest catches occurring within Bristol Bay and south of Nunivak Island. Juvenile coho and chinook salmon were distributed within nearshore waters less than 50m depth from Bristol Bay to Norton Sound with the largest catches occurring within Bristol Bay. Greater than 75% (percent body weight) of the prey items found in juvenile salmon stomachs consisted of larval and juvenile fish with the exception of juvenile pink and chum salmon (approximately 53% and 67% larval and juvenile fish respectively). Analyses of plankton, and of salmon age, size, growth data, and genetic stock identification, will be done to gain additional information on the early marine ecology of salmon along the eastern Bering Sea shelf. 13 Haul ID J M J I M J I M J M J I M 14 Haul ID J M J I M J I M J M J I M 2005035 Haul ID J M J I M J I M J M J I M Haul ID J M J I M J I M J M J I M