JUVENILE PACIFIC SALMON IN ESTUARIES: THE LIFE SUPPORT SYSTEM

Abstract

This report summarizes information on the abundance, food requirements and production of five species of Pacific salmon (genus Oncorhynchus) in two estuaries in southern British Columbia and compares some of these features among seven other estuaries. Chum salmon are abundant in estuaries for 2 months in early spring, coho for 2 months in late spring, and chinook throughout the spring, summer and autumn. Pink and sockeye spend little time in estuaries. Habitats occupied by each species vary with fish size, tidal stage, and time of year. Tidal creeks through marshes, the junction of major and minor distributaries in the intertidal zone, and the delta front are favoured habitats. Many taxa contribute to the diet of juvenile salmon in different estuaries but relatively few taxa generally constitute the bulk of the diet. Food requirements of juvenile salmon are generally a small percentage of the total standing crop and annual production of prey, but a high proportion of the production of preferred prey is sometimes taken. Major prey tend to be detritus feeders, indicating that the food web supporting juvenile salmon is detritus based. The value of an estuary as rearing habitat for juvenile salmon appears to be influenced by delta configuration, and by the efficiency with which allochthonous organic carbon is trapped.