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Canadian Stock Assessment Secretariat
Research Document - 1999/26
Catch composition of British Columbia shrimp trawls and preliminary estimates of bycatch - with emphasis on eulachons.
By D.E. Hay, R. Harbo, K. Southy, J.R. Clarke, G. Parker and P.B. McCarter
Abstract
An observer program was started in 1997 to determine the composition of catches in shrimp trawls in British Columbia. The project was intended to sample catches approximately according to the fishing effort, season, area and type of gear. A total of 530 catches were examined: 356 from otter trawlers and 174 from beam trawlers. A specific concern about bycatch in shrimp trawl catches is the catch of eulachons (Thaleichthys pacificus). There are relatively few eulachon populations and many have declined sharply in recent years. This paper provides a brief analysis of the relative bycatch in shrimp trawls for all species and provides a preliminary estimate of total bycatch of eulachons (tonnes) in different areas of the coast. The estimates are preliminary because data on fishing effort (duration of fishing time and total tows made) are not yet available. As an alternative to data on effort, we relate the catch of eulachons to the catch of shrimp (bootstrap estimates of the mean and 95% confidence limits) from the hailed data on area-specific catches. The hailed data are known to be approximations for some areas and may slightly under- or over-estimate total shrimp catches (and therefore eulachon bycatch). We also use the ratio of kg of eulachons to kg shrimp estimated from data collected from the observer program. We used the hailed catches of shrimp from the commercial fishery (estimated in kg for all main Statistical Areas) to estimate the total eulachon catches. The highest bycatch was from otter trawlers in the central coast where the ratio of eulachons to shrimp was 0.210. Therefore, for every 1000 kg of shrimp, 210 kg (95% CL = 173 to 251) of eulachons were caught. When adjusted by total (hailed) catch, an estimated 90 tonnes of eulachons were taken in the central coastal areas. Eulachon bycatch also was high in otter trawls off the west coast of Vancouver Island, where an estimated 52 tonnes were taken. In general, eulachon bycatch estimates were lower in other areas and negligible in the Strait of Georgia. Also, beam trawls had lower eulachon catches, although they took an estimated 22 tonnes of eulachons on the West Coast of Vancouver Island. We conclude with a brief discussion of the biological implications of these catch rates.
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