Migration Timing and River Survival of Late‐Run Fraser River Sockeye Salmon Estimated Using Radiotelemetry Techniques

In recent years, large numbers of late‐run Fraser River sockeye salmon Oncorhynchus nerka have died in freshwater areas before they spawned. We used radiotelemetry techniques to determine river entry timing, migration rates, and survival for the summer and late runs of sockeye salmon in 2002 and 2003. Fishery removals and river detections accounted for 62% of the 873 fish tagged and released in marine areas in 2002. Some late‐run fish migrated from release sites to the Mission hydroacoustic site in 8–10 d and migrated upstream with the summer run. Most late‐run fish remained in the Strait of Georgia for 15–33 d and entered the river after the summer run. Tracking data indicated that individual sockeye salmon maintained essentially the same chronological order as they migrated up the Fraser and Thompson rivers. Summer‐run stocks traveled faster between Mission and the Thompson Junction (33–39 km/d) than late‐run fish (17–21 km/d). After accounting for fishery removals, the river survival rate for summer‐run fish was 92%, and differences between the three release timing groups were not significant. In contrast, the first migration group of late‐run fish that passed Mission had significantly lower survival (13%) than all other timing groups. The survival rate for the second and third river entry groups combined (74%) was significantly lower than that of the fourth group (92%). Period‐specific survival rates were used to define a relationship between river entry timing and survival and to identify additional factors influencing river entry timing for late‐run fish. These relationships may be useful in predicting river survival rates for late‐run stocks in future years.