The Synchronous Failure of Juvenile Pacific Salmon and Herring Production in the Strait of Georgia in 2007 and the Poor Return of Sockeye Salmon to the Fraser River in 2009

R J Beamish,R Sweeting,K Lange,C Neville

doi:10.1080/19425120.2012.676607

Abstract

AbstractTrawl studies from 1998 to 2009 indicated that juvenile Pacific salmon Oncorhynchus spp. and Pacific herring Clupea pallasii represented 98% of the fish in the surface waters of the Strait of Georgia during the day in the spring and early summer. Standardized catches of all juvenile Pacific salmon in the trawl surveys were lowest in 2007. Catches of young‐of‐the‐year Pacific herring were also extremely low in 2007. Three years later, the 2007 year‐class had the lowest recruitment to the fishery in recorded history. In 2007, juvenile coho salmon O. kisutch and Chinook salmon O. tshawytscha were small and had the lowest condition of the fish in all surveys as well as a high percentage of empty stomachs. The early marine survival of coho salmon in 2007 and the total survival in 2008 were exceptionally poor. Trawl catches of juvenile chum salmon O. keta in 2007 were the lowest of all surveys. Adult chum salmon from these juveniles that returned in 2010 had extremely poor survival. Juvenile sockeye salmon O. nerka that entered the Strait of Georgia in the spring of 2007 and returned to the Fraser River as adults in 2009 also had such exceptionally poor marine survival that a judicial inquiry was conducted to determine the causes. The synchronous poor growth, survival, or both of all of the major species in the surface waters of the Strait of Georgia in the spring of 2007 indicated that there was a common cause which we propose as poor food production. The causes of the high mortality likely represented a unique extreme in the variability of the factors that normally affect the survival of juvenile Pacific salmon and Pacific herring in the early marine period in the Strait of Georgia.Received September 27, 2011; accepted March 8, 2012

Highlights

The Strait of Georgia is the most important rearing area for juvenile Pacific salmon Oncorhynchus spp. on Canada’s West Coast
The causes of the high mortality likely represented a unique extreme in the variability of the factors that normally affect the survival of juvenile Pacific salmon and Pacific herring in the early marine period in the Strait of Georgia
It is likely that the conditions causing the poor production in the Strait of Georgia were a major cause of the poor returns of the adult sockeye salmon to the Fraser River in 2009

Summary

Introduction

The Strait of Georgia is the most important rearing area for juvenile Pacific salmon Oncorhynchus spp. on Canada’s West Coast. The juvenile sockeye salmon O. nerka that entered the Strait of Georgia from the Fraser River in 2007 would return as adults in 2009. It is likely that the conditions causing the poor production in the Strait of Georgia were a major cause of the poor returns of the adult sockeye salmon to the Fraser River in 2009. There would not be spawning pink salmon in 2006 and virtually no juvenile pink salmon from the Fraser River in the Strait of Georgia in 2007. For this reason our analysis excluded this particular species

Methods

Results

Conclusion