Early Marine Survival of Coho Salmon in the Strait of Georgia Declines to Very Low Levels (original) (raw)
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Evidence That Reduced Early Marine Growth is Associated with Lower Marine Survival of Coho Salmon
Transactions of The American Fisheries Society, 2004
Coho salmon Oncorhynchus kisutch from the Strait of Georgia were used to test the hypothesis that slower growing fish in their first ocean year had lower survival over the late fall and winter than faster growing fish. The Strait of Georgia provided a suitable area for this study because it is a semi-enclosed rearing area for juvenile Pacific salmon that is distinct from the open marine rearing areas off the west coast. Coho salmon that survived the winter had significantly larger spacing between circuli on scales, indicating that brood year strength is related to growth in the first marine year. Other studies have shown that smaller fish of a cohort are less able to survive periods of energy deficit than larger fish. Thus, size-related mortality in the first marine fall and winter may be an important determinant of brood year strength of some coho salmon stocks and stocks of other species of Pacific salmon.
North American Journal of Fisheries Management, 2003
The percentage of hatchery-reared coho salmon Oncorhynchus kisutch in the Strait of Georgia, British Columbia, increased from nearly 0% in the early 1970s to more than 70% by 2001. These estimates were derived from fin clip and coded wire tag data collected from commercial and sport fisheries, research surveys conducted in the summer and fall of 1997 to 2000, and examination of the microstructure of otoliths extracted from juvenile coho salmon collected during our marine surveys. The increasing trend may be related to the proportions of hatchery and wild smolts entering saltwater, fishing rates, and changes in the ecological processes regulating coho salmon production in the ocean. The consequence for management is that the abundance of wild spawning salmon (escapement) depends on hatchery as well as wild production. The consequence for policy makers is that future enhancement activities need to have clear policies for assessing the effects of hatchery fish on the population dynamics of wild fish as well as for producing hatchery fish.
Transactions of the American Fisheries Society, 2009
Correlation analyses, linear regression models, and multistock mixed effects models were used to examine the relationships between coho salmon Oncorhynchus kisutch marine survival and six biological and environmental covariates across 14 southeast Alaska (SEAK) stocks. A primary focus of the study was to investigate the influence of pink salmon O. gorbuscha and chum salmon O. keta fry abundances on coho salmon marine survival. The coho salmon stocks exhibited strong covariation; 88 of the 91 pairwise comparisons among the coho salmon stocks covaried positively and 54 of them were significant (P , 0.05). Only one of the covariates, the North Pacific index, which is a measure of the Aleutian low pressure zone, had consistent relationships (positive) across all 14 stocks. The other covariates, including freshwater discharge, the Pacific decadal oscillation, sea-surface temperature, and two indices of pink salmon and chum salmon fry abundances, all had inconsistent relationships with marine survival. The best-fit linear regression models varied greatly among the 14 stocks, as did the R 2 values, which ranged from 0.00 to 0.54. An index representing local hatchery pink salmon and chum salmon fry abundance was the most important variable in explaining the variation in marine survival, having a stronger estimated effect on survival than an index of local wild pink salmon fry abundance. The magnitude and sign of the hatchery pink salmon and chum salmon effect varied greatly among different localities. Our results suggest that (1) SEAK coho salmon stocks are not equally influenced by the same factors and (2) there are factors that appear to affect marine survival of SEAK coho salmon stocks at varying spatial scales. This study also provides evidence that coho salmon stocks throughout SEAK experience some degree of regional concordance in the marine environment but also that local stock-specific conditions are important in fully understanding variation in marine survival.
Fisheries Oceanography, 2002
Time series of adult recruitment for natural runs of coho salmon from the Oregon coastal region (1970± 94) and marine survival of hatchery-reared coho salmon from California to Washington (1960±94) are signi®cantly correlated with a suite of meteorological and oceanographic variables related to the biological productivity of the local coastal region. These variables include strong upwelling, cool sea surface temperature (SST), strong wind mixing, a deep and weakly strati®ed mixed layer, and low coastal sea level, indicating strong transport of the California Current. Principal component analysis indicates that these variables work in concert to de®ne the dominant modes of physical variability, which appear to regulate nutrient availability and biological productivity. Multiple regression analysis suggests that coho marine survival is signi®cantly and independently related to the dominant modes acting over this region in the periods when the coho ®rst enter the ocean and during the overwintering/spring period prior to their spawning migration. Linear relationships provided good ®ts to the data and were robust, capable of predicting randomly removed portions of the data set.
Deep Sea Research Part II: Topical Studies in Oceanography, 2009
Coho salmon (Oncorhynchus kisutch) are a vital component in the southeast Alaska marine ecosystem and are an important regional fishery resource; consequently, understanding mechanisms affecting their year-class strength is necessary from both scientific and management perspectives. We examined correlations among juvenile coho salmon indices, associated biophysical variables, and adult coho salmon harvest data from southeast Alaska over the years 1997-2006. We found no relationship between summer indices of juvenile coho salmon growth, condition, or abundance with subsequent harvest of adult coho salmon in the region. However, using stepwise regression, we found that variation in adult coho salmon harvest was largely explained by indices of juvenile pink salmon (Oncorhynchus gorbuscha) abundance (67%) and zooplankton abundance (24%). To determine if high juvenile pink salmon abundance indicates favorable ''bottom-up'' lower trophic level environmental conditions for juvenile coho salmon, we plotted abundance of juvenile pink salmon against growth and condition of juvenile coho salmon. No change in growth or condition of juvenile coho salmon was observed in relation to the abundance index for juvenile pink salmon. Therefore, we hypothesize that coho salmon year-class strength in southeast Alaska is influenced by a ''top-down'' predator control mechanism that results from more abundant juvenile pink salmon, which serve as a predator buffer during early marine residency.
Fishery Bulletin- National Oceanic and Atmospheric Administration
Fish stocks and fisheries in the Gulf of Alaska are strongly influenced by climatic and oceanic (C-O) conditions (Francis and Hare, 1994; Hare and Francis, 1995). In the past century C-O conditions in the North Pacific Ocean and Gulf of Alaska (GOA) have shifted from a warm regime and higher salmon (Oncorhynchus spp.) produc-tion (1927–46) to a cool regime and low salmon production (1947–76) and back to a warm regime and higher salmon production (1977–2000) (Francis and Hare, 1994; Hare and Francis, 1995). Changes in C-O conditions, either annually or over longer regime peri-ods, may affect salmon smolt-to-adult survival rates by affecting the growth rate of smolts after they enter the ocean. For example, higher survival rates of Alaska sockeye (O. nerka), pink (O. gorbuscha), and chum (O. keta) salmon have been associated with warmer coastal sea-surface tem-peratures (SST) during the first year that young salmon spend in the ocean (Mueter et al., 2002a). Relationships have been fou...
Fisheries Management and Ecology, 2012
Observations relevant to the North American stock complex of Atlantic salmon, Salmo salar L., suggest that marine mortality is influenced by variation in predation pressure affecting post-smolts during the first months at sea. This hypothesis was tested for Gulf of Maine (GOM) stocks by examining wind pseudostress and the distribution of piscivorous predator fields potentially affecting post-smolts. Marine survival has declined over recent decades with a change in the direction of spring winds, which is likely extending the migration of postsmolts by favouring routes using the western GOM. In addition to changes in spring wind patterns, higher spring sea surface temperatures have been associated with shifting distributions of a range of fish species. The abundance of several pelagic piscivores, which based on their feeding habits may predate on salmon post-smolts, has increased in the areas that serve as migration corridors for post-smolts. In particular, populations of silver hake, Merluccius bilinearis (Mitchell), red hake, Urophycis chuss (Walbaum), and spiny dogfish, Squalus acanthias L., increased in size in the portion of the GOM used by post-smolts. Climate variation and shifting predator distributions in the GOM are consistent with the predator hypothesis of recruitment control suggested for the stock complex. K E Y W O R D S : climate, migration, post-smolt survival, predation, recruitment, temperature.
Climate Indicators of Salmon Survival 12
1996
Using studies from the Columbia River, salmon survival and catch measures were correlated with several Pacific Northwest climate indices. Spring chinook survival rate and catch were varied with the Pacific Northwest climate index (PNI), which characterizes temperature and precipitation cycles in the Pacific Northwest. Cool/wet conditions were associated with higher survival and catch while warm/dry conditions were associated with lower stock measures. At a finer temporal scale, the survival of spring chinook from smolt to adult was correlated with the arrival time of smolts into the estuary and the spring transition date, which signals the beginning of spring and coastal upwelling. A match/mismatch hypothesis is suggested to explain how variation in spring transition and estuary entry dates can effect stock survival. The effects of hatchery production and hydrosystem passage on year class strength is also considered in terms of the match/mismatch mechanism.
Canadian Journal of Fisheries and Aquatic Sciences, 2011
We examined the effect of early marine entry timing and body size on the marine (smolt-to-adult) survival of Puget Sound Chinook salmon (Oncorhynchus tshawytscha). We used data from coded wire tag release groups of hatchery Chinook salmon to test whether hatchery release date, release size, and size in offshore waters in July and September influenced marine survival. Marine survival was most strongly related to the average body size in July, with larger sizes associated with higher survivals. This relationship was consistent over multiple years (1997)(1998)(1999)(2000)(2001)(2002), suggesting that mortality after July is strongly size-dependent. Release size and date only slightly improved this relationship, whereas size in September showed little relationship to marine survival. Specifically, fish that experienced the highest marine survivals were released before 25 May and were larger than 17 g (or 120 mm fork length) by July. Our findings highlight the importance of local conditions in Puget Sound (Washington, USA) during the spring and summer, and suggest that declines in marine survival since the 1980s may have been caused by reductions in the quality of feeding and growing conditions during early marine life.