Research Document - 2000/160

Status in 1999 of Coho Stocks on the West Coast of Vancouver Island.

By D. Dobson, K. Simpson, J. Till, S. Lehman, R. Ferguson, P. Tschaplinski, and S. Baillie

Abstract

The assessment of West Coast Vancouver Island (WCVI) coho stocks indicates a general trend of improving escapement and juvenile density since the period of extremely low marine survival rates resulting from the El Nino event of the early 1990s. This improvement is attributable mostly to dramatically reduced exploitation rates. Prior to the severe restrictions implemented for conservation in 1997 and 1998, exploitation rate of WCVI coho averaged approximately 62%. Since then, estimated exploitation rates have ranged between 5 to 10%. In recent years marine survival rates have been higher than the critically low level experienced in 1994, but 1996 brood survival still remained below long-term averages and decreased from the previous year.

In the absence of significant exploitation, escapement has improved to the point that 1999 levels exceeded 1996 brood year escapement for most WCVI streams having reliable escapement data. An important exception to this trend was the Carnation Creek wild indicator stock. The 1996 brood year experienced extremely low marine survival rate (1.1%) compared to the long-term average (9.0%) and consequently escapement was below brood replacement levels. The Robertson Creek Hatchery 1996 brood also had a low survival rate of 1.8%, but this rate deviates less from the 4.5% long-term average survival experienced by this stock.

Patterns of juvenile abundance are consistent with escapement trends. In the summer of 1999, the highest juvenile densities were observed since the survey began in 1995. These levels likely resulted from high 1998 brood escapement and suggest there may have been a relatively strong 2000 smolt run on the WCVI. Correspondingly, smolt counts from wild indicator streams were high. Preliminary data from 2000 returns indicates escapement will meet or exceed 1999 levels.

Complete document (PDF, 977 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.