Early Ocean Life History of Harrison River Sockeye Salmon and their Contribution to the Biodiversity of Sockeye Salmon in the Fraser River, British Columbia, Canada

Abstract

AbstractDuring a study of the early marine survival of Chinook Salmon Oncorhynchus tshawytscha and Coho Salmon O. kisutch in the Strait of Georgia from 1998 to 2010, moderate abundances of juvenile Sockeye Salmon O. nerka were observed to remain in the strait much longer than previously thought. In 2008, DNA stock identification showed that these juveniles were from the Harrison River, a population with a sea‐type life history in which juveniles enter the ocean during the year of emergence from the gravel. Using information collected in 1998–2010, we describe the early ocean life and production of Harrison River sea‐type Sockeye Salmon. Juveniles entered the Strait of Georgia from the Fraser River over an extended period, with most entering after mid‐July—about 8 weeks later than lake‐type juveniles, which had virtually all left the strait by that time. The September diets of sea‐type juveniles were highly selective for hyperiid amphipods, which were not abundant in the zooplankton. Interaction with juvenile Pink Salmon O. gorbuscha during this early marine period was identified as potentially affecting the age structure of returning adults. Juvenile Sockeye Salmon remained in the strait until the fall and then moved offshore, where they remained until returning as age‐3 or age‐4 adults. There was a strong positive relationship between the September CPUE of juveniles in the Strait of Georgia and the total adult return of Harrison River Sockeye Salmon, indicating that total production in recent years was likely related to conditions in the strait. From 2005 to 2011, Harrison River Sockeye Salmon production exhibited a large increase in comparison with the total production of Sockeye Salmon in the Fraser River system. This recent increase in production of late‐ocean‐entering juveniles with a sea‐type life history identifies the importance of managing for biodiversity of Sockeye Salmon populations within the Fraser River drainage.Received April 28, 2015; accepted November 17, 2015