Sulfur isotopes in otoliths allow discrimination of anadromous and non-anadromous ecotypes of sockeye salmon (Oncorhynchus nerka)

Oncorhynchus nerka occur both as anadromous sockeye salmon that spend most of their life in the ocean, and as non-anadromous kokanee salmon that remain in fresh water their entire lives. We assessed whether stable isotopes of sulfur (δ34S) in otoliths could be used to distinguish sockeye salmon and kokanee ecotypes that are otherwise difficult to identify when they share a common freshwater rearing environment. We also investigated the chemical link between salmon and their diet by measuring δ34S in various fish tissues (eggs, muscle, scales) and zooplankton. δ34S (mean±SE) in sockeye salmon eggs (18.7 ± 0.4‰) and marine zooplankton (20.5 ± 0.1‰) were enriched by 10–14‰ compared with kokanee eggs and freshwater zooplankton. δ34S in the otolith cores of sockeye salmon (19.2 ± 0.7‰) and kokanee salmon (5.3 ± 1.1‰) were similar to δ34S in marine and freshwater zooplankton, respectively, indicating that the core is derived from maternal yolk tissue and reflects the maternal diet. δ34S in the freshwater growth zone of otoliths did not differ significantly between sockeye (5.9 ± 1.1‰) and kokanee salmon (4.4 ± 1.2‰), and was similar to freshwater zooplankton. The mean difference between δ34S in the otolith core and first year of growth was 13.3 ± 1.4‰ for sockeye and 0.65 ± 1.3‰ for kokanee salmon. A quadratic discriminant function developed from measurements of δ34S in otoliths of known maternal origin provided perfect classification rates in cross-validation tests. Thus, sulfur isotope ratios in otoliths are effective in discriminating between anadromous and non-anadromous ecotypes of O. nerka

Empirical models predicting catch of brook trout (Salvelinus fontinalis) in Québec sport fishery lakes

The aim of this thesis is to develop empirical models of the stable catch of brook trout in the Laurentian lakes of Quebec. Current estimators of fish yield are biased and predict poorly.A model resulting from this study shows that catch increases with fishing effort, but that the rate of increase is smaller at higher effort. For a given effort, the catch-per-unit of effort (CPUE) is greater in larger lakes. Catch is also greater in phosphorus rich lakes and smaller in acid lakes. Catch of bigger fish is associated with a lower CPUE.No dome-shaped relationship between catch and effort, standardized for the effects of lakes characteristics, could be established. Thus the maximum sustainable yield (MSY) concept provides no guidelines for management of the fishery. However, an early warning of overexploitation is an exceptionally high rate of fishing success. In addition logistic regression based on easily obtained variables can predict the likelihood of stability of the fisheries

Disentangling individual- and population-scale processes within a latitudinal size-gradient in Sockeye Salmon

We examined how individual processes contribute to a latitudinal gradient in body size within populations of migrating juvenile Sockeye Salmon (Oncorhynchus nerka) while simultaneously testing for size-selective mortality, a potentially confounding population scale process. Using otolith microstructure techniques and structural equation modeling, we determined that ocean entry size and phenology had strong, direct effects on size at capture. Population identity and freshwater age also had strong indirect effects, moderated by size at entry. Conversely, marine growth rates immediately after entry or before capture were relatively weak predictors of size during migration. We next tested for shifts in size distribution indicative of selective mortality, but detected no evidence of smaller individuals experiencing lower survival during early marine migrations. These results indicate that the migratory distributions of juvenile Sockeye Salmon are influenced by body size and that this variation is predominantly driven by traits present prior to freshwater outmigration, rather than marine growth or differential survival. We suggest integrating individual variation in migratory characteristics with the effects of environmental conditions experienced en route to provide an improved understanding of migratory species.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Divergent migratory behaviours associated with body size and ocean entry phenology in juvenile sockeye salmon

Survival during early marine life stages is hypothesized to contribute disproportionately to variation in salmonid recruitment, yet estimates of cumulative mortality are constrained by knowledge of how long juveniles reside in specific regions. We used otolith microstructure techniques to examine the relationship between migratory rate and ocean entry characteristics of juvenile sockeye salmon. We observed differences in migratory rate between catch locations that are consistent with divergent migratory behaviours. Individuals captured in northern regions were typically older, larger at ocean entry, and migrated more rapidly. Migratory rate was also correlated with entry size, phenology, population group, and year. Next, we compared â lingeringâ individuals captured nearshore during fall surveys to juveniles from the same populations captured during the peak, summer migratory period. We determined that individuals that entered after May 24 and at smaller sizes (The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Relationship between early marine growth and returning adults of Fraser sockeye salmon

Smolt-to-adult survival of sockeye salmon returning to Chilko Lake was lower than average for the 77.1 million smolts that entered marine waters in 2007 ([lesser than] 0.25%), and high for the 71.9 million that entered the ocean in 2008 (6.7%). As recruitment dynamics of Pacific salmon is generally expected to be determined by growth during their early marine life, we tested the hypothesis that early marine growth of Chilko Lake sockeye salmon was higher in 2007 than in 2008. We used daily growth increment from otoliths to determine how the early marine growth rate of juvenile Chilko Lake sockeye salmon differed between years of low and high survival after 30-60 days at sea, the period hypothesized to be critical for survival. Juveniles that entered the ocean in 2008 grew at a significantly faster rate than those in 2007. The 2008 juveniles spent on average the same number of days at sea as the 2007 juveniles, but were significantly larger than those caught in 2007, despite the fact that they entered the ocean at a smaller size. Somatic growth rates of the smolts that entered the ocean in 2008 were on average 20% faster than the smolts that entered the ocean in 2007, suggesting that the higher survival observed in 2008 may be related to ocean conditions that were favorable to growth. To test this hypothesis further, we examined the relationship between adults return and early marine growth rate during the first 30-60 days at sea and other variables using 10 years of data (2004-2013). We found that somatic growth rate explained the greatest proportion of the variation in adult returns, after taking considering the number of out-migrating smolts