Research Document - 2004/059

The British Columbia longspine thornyhead fishery: analysis of survey and commercial data (1996-2003).

By Schnute, J., Haigh, R., Krishka, B., Sinclair, A., Starr, P.

Abstract

This report presents an analysis of the biomass survey conducted annually in 2001 2003 on the deep water population of longspine thornyheads off the west coast of Vancouver Island (WCVI). We examine the survey data in the context of a coastwide longspine fishery that began in 1996 and extended northward from WCVI into two northern regions, Tidemarks and Rennell. Within WCVI, the survey appears to index longspine thornyhead biomass well, achieves coefficients of variation near 10%, and indicates no significant biomass change in 2001 2003. Because the survey has limited coverage in space and time, we compare that analysis with similar analyses of commercial catch per unit effort (CPUE) data in WCVI and the two northern regions, where no surveys exist. We present an integrated framework of three mathematical models for making these comparisons: (i) swept-area biomass estimates, (ii) standardized catch rates with fixed effects for various factors, and (iii) swept-area biomass estimates with standardized vessel effects. All commercial indices for the three regions show downward trends since the inception of the fishery, with the largest decline in the Rennell Sound area. The magnitude of decline depends on the model chosen for analysis. If these trends in the commercial data reflect real declines in population biomass, current removals of longspine thornyhead may not be sustainable. We conclude with recommendations for planning future surveys, integrating data from surveys and commercial fisheries, planning future reductions in the commercial fishery, and improving the basic biological information available for this species.

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