Babine Lake sockeye salmon: Stock status and forecasts for 1998

Abstract

The Babine-Nilkitkwa lake system is the largest natural lake in British Columbia (500 km2). It also supports the largest sockeye salmon population in Canada, a total adult stock that has averaged over 4 million annually since 1990. This working paper provides a comprehensive assessment of sockeye production from the Babine-Nilkitkwa system in that it brings together, for the first time in many years, recently compiled information on trends in spawning escapements by run timing group, fry recruitment, smolt production, adult returns, harvest rate, and surplus production from Babine Lake Development Project (BLDP) facilities. Exploitation rate on Skeena River sockeye has increased over the last decade, averaging 68% since 1990, and exceeding 70% in 1996 and 1997. Recent escapements to enhanced sites in Babine Lake have exceeded spawning requirements such that over a third of the Babine fence count has been surplus produced by the BLDP. Enhanced fry now account for about 90% of fry recruitment to the main basin. As expected, increased fry and smolt production has increased adult returns although the relationship between adult returns and smolt abundance is non-linear. Available data indicate that further increases in adult returns could be expected by increasing smolt production, and that fry recruitment is still below levels required to yield maximum smolt biomass. However, prespawning mortality at the BLDP sites in 1994 and 1995 caused by parasitic infections has significantly reduced fry recruitment and smolt production. Near record low smolt production and jack returns from the 1993 brood, together with near record low smolt production and age 4 returns from the 1994 brood, provide clear signals that adult returns in 1998 and 1999 will be much lower than in recent years. The smolt forecast model indicates a 75% chance that adult returns to the Skeena River in 1998 will exceed 820, 000 sockeye, and a 50% chance that returns will exceed 1,420,000 sockeye.