Parasites in subyearling Chinook salmon (Oncorhynchus tshawytscha) suggest increased habitat use in wetlands compared to sandy beach habitats in the Columbia River estuary

Abstract

Many estuaries in the Pacific Northwest have been severely altered reducing wetlands habitat and resulting in an interest in their importance as rearing areas for juvenile salmon. To examine differences in habitat use during residency in the Columbia River estuary, we examined parasite communities acquired through food web interactions in subyearling Chinook salmon (Oncorhynchus tshawytscha) collected from four different habitat types in May and July of 2004 and 2005. Collections were made from two sandy bottom habitat types in the tidal freshwater and marine mixing areas of the estuary. These were compared to two wetlands types: one composed of scrub and shrub vegetation and another with emergent vegetation. Parasite assemblages differed among habitats suggesting differences in salmon feeding opportunities and rearing behaviors. In both years, the nematode, Hysterothylacium aduncum and the acanthocephalan, Echinorhynchus lageniformis, which use intermediate hosts found in the estuary, were more prevalent in lower wetlands suggesting increased feeding by salmon in these habitats. The differences in parasite assemblages among habitats suggests a variety of rearing and migration patterns through the Columbia River estuary and the increased prevalences of some parasites in the wetlands show that these habitats can be important feeding grounds for salmon.