Research Document - 2005/097

A review of longspine thornyhead Sebastolobus altivelis along the Pacific coast of Canada: biology, distribution, and abundance trends

By Haigh, R., Olsen, N., and Starr, P.

Abstract

This paper reviews the current data on the biology, distribution, and abundance trends for longspine thornyhead Sebastolobus altivelis. The information contained herein is primarily for use in a COSEWIC status report on this species. It is not meant to be a comprehensive stock assessment. This species has a mean weight of 114 g/fish. Allometric growth shows no difference between the sexes; information on size-at-age is sparse. The oldest fish aged was 71 years. With an estimated age-of-50%-maturity at 20 years, and an assumed natural mortality rate of 0.10, generation time is roughly 30 years. According to survey and commercial trawl records, longspine thornyhead occur at depths between 500 m and 1600 m. Using this interval, a bathymetric analysis estimates the potential extent of occurrence at 17,775 km² and the area of occupancy at 9,914 km². However, based on trawl observations alone, the area of occupancy could easily equal 11,700 km². Within its habitat, the two predominant concurrent species are shortspine thornyhead Sebastolobus alascanus and sablefish Anoplopoma fimbria. Total removal of longspine thornyhead from BC coastal waters by the commercial fleet from 1996 to 2005 equals approximately 57 million fish. The only available survey for indexing longspine thornyhead populations is that conducted off the WCVI in 2001 2003. The trend from this survey is flat. The commercial trawl CPUE indices show a declining trends in all areas of the coast: -8% y^-1 for the WCVI region from 1996 to 2004, -9% y^-1 for the Tidemarks region from 2000 to 2004, and -23% y^-1 for the Rennell region from 2000 to 2004.

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