Research Document 1997/142

Offshore herring distribution and 1998 recruitment forecast for the West Coast of Vancouver Island stock assessment region

By D. Ware and R. Tanasichuk

Abstract

A multispecies mid-water trawl survey off the southwest coast of Vancouver Island (WCVI) was conducted between August 3 - 9, 1997. Twenty-five tows were made to assess the species composition, catch-per-unit of effort, diet, condition factor, size and age compositions of the dominant pelagic fish species in the WCVI stock assessment region. The offshore distribution of herring in this area returned to a more normal state this year after the unusual 1996 summer. The apparent abundance of herring sounded this summer was much higher than last year, and the schools were found in their usual concentration centers on 40-mile and Swiftsure Banks. There was also a good showing of herring along the outer edge of the continental shelf. Seven tows targeted on herring. Analysis of the length compositions suggests that the west coast of Vancouver Island herring spawning stock will contain 33 % age 2+ recruits in March 1998. Based on stock assessment model projections of the biomass of surviving repeat spawners, we estimate that the strength of the recruiting 1995 year-class will be midway between the "poor" and "average" categories (about 8,000 t). Our long-term research program on the west coast of Vancouver indicates that herring recruitment tends to improve when ocean temperatures are cool, and the summer biomass of migratory predators (like hake and mackerel) in the region is low.

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