Interannual and interdecadal variability in juvenile coho salmon (Oncorhynchus kisutch) diets in relation to environmental changes in the northern California Current

Abstract

The feeding habits of juvenile coho salmon, Oncorhynchus kisutch, in the northern California Current were examined using samples from two different time periods (1980-85 and 1998-2003) of highly contrasting oceanographic conditions. The goal was to test the influence of interannual and interdecadal changes in taxonomic composition of prey, feeding intensity, and size spectra of teleost prey. Analyses were done for samples taken both early in the summer (June) shortly after the salmon enter the ocean, and also in late summer (September) following some ocean residency. Fish prey dominated coho salmon diets by weight during most years, but this trend was more pronounced during the 1980-85 sampling period. In terms of numerical composition, the diets were more variable on an interannual basis, but decapod larvae and euphausiids were important prey in most years. Pteropods and copepods were important prey during weak upwelling or El Niñ o years, whereas euphausiids were important during strong upwelling or otherwise highly productive years. Hyperiid amphipods comprised a substantial proportion of the diets only in 2000. Coho salmon showed highly significant differences in prey composition among years or between decades both in weight and numerical composition. The percentage of empty stomachs was highly variable by year in both June and September, but was significantly different only for September between decades. In contrast, an index of feeding intensity did not show many significant changes in either comparison. However, the relative size ratios for fish prey consumed were highly variable by year, and larger than average fish prey were consumed during 1998, leading to the highest feeding intensity observed.

Multivariate Models of Adult Pacific Salmon Returns

“…However, we know that many other ecological processes, such as predator and forage fish abundance [25], prey availability [22], [26], [27], and physiological condition and ontogeny [28], [29], are important to salmon growth and survival during their first ocean year, and should be useful in forecasting. These are not used in the Peterson et al [24] approach because the time series are not as long as the ones used in the qualitative forecasting (the 18 indicators used by Peterson et al [24] are compiled from 1998 through 2011, whereas many other indicators only go back to 2000).…”

Expanding the foraging history of juvenile Pacific salmon: combining stomach‐content and macroparasite‐ community analyses for studying marine diets

“…It was possible to identify common prey taxa (euphausiids, hyperiid amphipods and fishes) using either stomach contents or macroparasites. Unlike previous diet studies on juvenile salmonids caught off Washington, Oregon and California (Emmett et al , 1986; Brodeur & Pearcy, 1990; Schabetsberger et al , 2003; Brodeur et al , 2007), macroparasites extended Pacific salmon foraging history back several months before capture (Rohde, 1984).…”

Concerns in Marine Renewable Energy Projects

“…Dungeness crab was selected for the Humboldt wave energy project effects analysis because 1) it is abundant and is found in habitat directly comparable to the Humboldt wave energy project site (Pequegnat et al 1990); 2) evidence exists for inshore/offshore migrations that would at least partially traverse Humboldt wave energy project site depths ca 70m (Pequegnat et al 1990); 3) its importance to local commercial and recreational fisheries (Dewees et al 2004, Hankin andWarner 2001); and 4) its importance in the pelagic food chain, in particular the diet of salmon (Brodeur et al 2007, Hunt et al 1999). Dungeness crab juveniles and adults are found most commonly on sand or mud bottoms from the intertidal zone to 30-m depth Warner 2001, Pauley et al 1989).…”