Testing for Density-Dependent Marine Survival in Pacific Salmonids

Abstract

Marine survival data for several different salmonid stocks were reviewed to determine whether there was significant density-dependent survival occurring in the ocean. Four classes of interaction were examined: (1) within-cohorts, (2) between-cohorts, (3) between stocks on the same or nearby rivers, and (4) between stocks of distant rivers. Results of statistical tests indicate that some stocks do not produce an increase in adult returns with increased smolt abundance, and that marine survival rate of other stocks is affected by abundance of other cohorts or stocks. Only a few stocks exhibit these density-dependent relations, but given present data, it is impossible to predict the frequency of occurrence of such limiting processes in future enhanced stocks. Salmonid enhancement planning is discussed in the context of this uncertainty and experimental enhancement projects are suggested that aim to obtain information about marine survival processes as well as additional catches. Key words: density dependent, marine survival, salmonids, experimental enhancement, stock interaction, adaptive