Contrasting Early Marine Ecology of Chinook Salmon and Coho Salmon in Southeast Alaska: Insight into Factors Affecting Marine Survival

L. A. Weitkamp,J. A. Orsi,R. C. Francis,K. W. Myers

doi:10.1080/19425120.2011.588919

Abstract

AbstractTo identify processes potentially contributing to the differential marine survival rates of Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch originating from Southeast Alaska, we compared the early marine ecology of the two species during the critical first summer in marine waters. We predicted that the higher survival rates for coho salmon relative to Chinook salmon were related to the larger size, faster growth, or different habitat or species associations of coho salmon. Our size and growth expectations were largely substantiated: juvenile coho salmon were larger than juvenile Chinook salmon and had faster length‐based growth, although weight‐based growth rates were similar. The most obvious difference was in their distributions. Juvenile coho salmon overlapped spatially and temporally with abundant juvenile pink salmon O. gorbuscha and chum salmon O. keta, whereas juvenile Chinook salmon were geographically separated from other salmonids. This suggests that coho salmon benefited from a predation buffer that did not extend to Chinook salmon. Our results indicate that factors influencing marine survival of juvenile Chinook salmon and coho salmon in Southeast Alaska are attributable to species‐specific differences in their early marine distribution patterns and species interactions.

Highlights

To identify processes potentially contributing to the differential marine survival rates of Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch originating from Southeast Alaska, we compared the early marine ecology of the two species during the critical first summer in marine waters
Origins of Juvenile Salmon The coded wire tags (CWTs) recovered from juvenile Chinook salmon and coho salmon indicated that all fish originated from Southeast Alaska (Table 1)
69 CWTs (28 from Chinook salmon; 41 from coho salmon) were recovered from the 414 juvenile Chinook salmon and 1,107 juvenile coho salmon caught in strait and inshore habitats

Summary

Introduction

To identify processes potentially contributing to the differential marine survival rates of Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch originating from Southeast Alaska, we compared the early marine ecology of the two species during the critical first summer in marine waters. Marine mortality in anadromous Pacific salmon Oncorhynchus spp. is probably highest during the first few weeks or months of ocean residence, when juvenile salmon typically inhabit coastal waters (e.g., Pearcy 1992; Briscoe et al 2005; Pyper et al 2005). The relation between particular habitat conditions and salmon marine ecology (and survival) is largely unknown This limited understanding of processes controlling salmon recruitment hinders our ability to prudently manage these commercially and culturally important species. Several recent studies have shown that individual juvenile salmon that survive to adulthood are typically larger than average (Beamish et al 2004; Moss et al 2005; Cross et al 2009)

Methods

Results

Conclusion