Expanding the foraging history of juvenile Pacific salmon: combining stomach-content and macroparasite- community analyses for studying marine diets
Stomach contents and macroparasites were examined from the same fishes collected off Oregon and California in June and August of 2000 and 2002 to provide a more comprehensive description of the diet of juvenile Chinook salmon Oncorhynchus tshawytscha and coho salmon Oncorhynchus kisutch during their first few months at sea. Temporal and spatial similarities of the two data sets were assessed using multivariate analyses. Both stomach contents and macroparasite communities indicated that fishes, euphausiids and hyperiid amphipods were consumed by both salmonid species, although their relative contribution to each species diet was highly variable. In June, the greater abundances of parasite species in Chinook salmon compared to coho salmon suggested that Chinook salmon consumed more infected intermediate hosts (crustaceans or larval fishes) shortly after ocean entry (April and May). Although the macroparasite analysis lacked the specificity of stomach analysis in identifying prey, macroparasites can provide a longer term history of feeding and diet information for fishes with empty stomachs.
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