Distribution and Food Habits of Juvenile Salmonids in the Duwamish Estuary, Washington, 1980
Rept. for Apr-Jul 1980
FISH AND WILDLIFE SERVICE OLYMPIA WA FISHERIES ASSISTANCE OFFICE
Pagination or Media Count:
Juvenile salmonid and plankton samples were collected from several stations in the Duwamish River estuary, Washington, from April to July, 1980 in a study to examine food habits and distribution of juvenile salmonids, and prey distribution. Chinook Oncorhyunchus tshawytscha, chum O. keta and coho salmon O. kisutch and steelhead Salmo gairdneri and cutthroat trout S. clarki are the salmonid species which we found present in the Duwamish estuary. Juvenile salmonids occurred in greatest numbers from mid-April to early June. Chum were oriented toward shoreline areas while other species utilized near and offshore areas. Chinook tended to move inshore at night, although they intended to move offshore with increasing size. Few cutthroat were encountered. Much of the salmon diets were composed of dipteran insects particularyly Chironomidae and gammarid amphipods particularly Corophium salmonis, C. spinicorne and Eogammarus confervicolus. Corophium and harpacticoid copepods were important to some salmon. Steelhead trout diets consisted largely of the mysid Neomysis mercedis. In general, epibenthic crustaceans were consumed more at nighttime in the nearshore estuary zone by smaller sized predators in the earlier months of the study. Pelagic crustaceans and insects were consumed more during the daytime, offshore by larger predators in later months. Predation of juvenile fish occurred primarily during the day, near shore by larger sized predators.