Parasites of juvenile Pacific salmonids as Metrics of Diet and Habitat Use in the Nearshore Pacific Ocean

The life history of naturally produced juvenile Pacific Chinook salmon (Oncorhynchus tshawytscha) remains largely unknown. Analyzing the parasite communities in naturally produced and hatchery produced Chinook salmon allows us to gain information on diet, habitat use, and behavior, and helps determine if hatchery salmon can be used as a proxy for naturally produced salmon in freshwater, estuary, and nearshore ocean habitats. In better understanding the ecology of unmarked salmon, more informed decisions can be made to ensure that habitats and food sources crucial to juvenile salmon survival are conserved or restored. To achieve this, the digestive tracts (stomachs and intestines) of hatchery (n=25) and unmarked (n=25) yearling Chinook salmon caught off Washington state were examined for trophically transmitted parasites, acting as metrics for long-term diet. While the data for hatchery salmon are still being compiled, we expect to see smaller numbers of freshwater parasites in hatchery produced fish as they have less exposure to parasite-infected prey than naturally produced salmon. This may also help us identify naturally produced salmon, as not all hatchery salmon are marked. Parasites were identified, counted, and statistically analyzed. In total, 682 parasites of ten different taxa were recovered. Results show that 92% of naturally produced and 80% of hatchery produced Chinook salmon were infected with at least one parasite. The trematode Plagioporus shawi was the most common parasite, making up 42% of all parasites found. The highest prevalences, intensities, and species richness of freshwater parasites were in unmarked salmon. Marine taxa were recovered from both marked and unmarked salmon but potential differences in marine residence times makes direct comparisons difficult. Upon completion, this project should provide valuable information regarding unmarked salmonids’ behavior, diet, and habitat use as they migrate through freshwater into the ocean.