Overwinter shifts in the feeding ecology of juvenile Chinook salmon

Abstract

Winter is thought to be a critical period for many fish in the ocean, but their ecology during this time tends to be poorly understood. We quantified the feeding ecology of juvenile Chinook salmon (Oncorhynchus tshawytscha) off the west coast of Vancouver Island in British Columbia, Canada, in autumn and winter to determine how seasonality could affect diet. Using stomach contents and stable isotopes, we tested the hypothesis that the winter diet of juvenile Chinook salmon differs from that of the autumn diet. Stomach-content data showed a shift from a primary reliance on amphipods in autumn to euphausiids in winter. This finding was generally corroborated by the stable isotope analysis, although mixing models suggested a greater contribution of fish prey to the diet in both autumn and winter. Understanding the diet of fish during winter may provide useful information for management as a first step in understanding the factors influencing mortality across life stages.

Analyzing mixing systems using a new generation of Bayesian tracer mixing models

“…Once an informative prior for the proportional contribution of sources is established, MixSIAR can accept the prior as an input during the model specification process (for details and examples, see Stock & Semmens, 2016a ). For diet studies, these other information sources are often fecal or stomach contents ( Moore & Semmens, 2008 ; Franco-Trecu et al, 2013 ; Hertz et al, 2017 ), but can also include prey abundance or expert knowledge ( deVries et al, 2016 ). As a simplified example from Moore & Semmens (2008) , suppose we wish to construct an informative prior for a 3-source mixing model of 10 rainbow trout diet using sampled stomach contents (30 eggs, 8 fish, 25 invertebrates).…”

Offshore wind farms and the attraction–production hypothesis: insights from a combination of stomach content and stable isotope analyses

“…This follows from the contradicting dietary results between the SCA (diet mainly based on fouling amphipods) and the SIA, as revealed by its isotopic niche (diet mainly composed of pelagic prey items-since the overlap of the isotopic niches of horse mackerel and mackerel was large). This was the only species for which SCA and SIA did not reveal similar results, confirming that both methods can yield complementary information on dietary compositions (Kadye & Booth, 2012;Hertz et al, 2017). Discrepancy between SIA and SCA can be a result of the differences in assimilation efficiencies among the prey items (Hertz et al, 2017).…”

“…This was the only species for which SCA and SIA did not reveal similar results, confirming that both methods can yield complementary information on dietary compositions (Kadye & Booth, 2012;Hertz et al, 2017). Discrepancy between SIA and SCA can be a result of the differences in assimilation efficiencies among the prey items (Hertz et al, 2017). This discrepancy could also derive from the similarities in the stable isotope ratios of zooplankton and Jassa herdmani (Mavraki et al, 2020a) resulting in a less reliable resolution of the SIA for these two main food resources and leading to the a posteriori combination of these two prey items in the mixing model.…”

Effectiveness of nutrient enhancement as a remediation or compensation strategy of salmonid fisheries in culturally oligotrophic lakes and streams in temperate climates

“…One technique that could offer insight into the transfer of nutrients throughout the food web is stable isotope analysis (Quinn & Hamilton ; Moore et al ; Hertz et al ). If nutrient enhancement stimulates primary producer or invertebrate communities in such a way as to increase fisheries production, primary producer isotope signatures should increase in fish consumers.…”