Research Document - 2001/137

Assessment of Green Sea Urchin (Strongylocentrotus droebachiensis) stocks in British Columbia, 2001

By Perry, R.I., Waddell, B.J., Zhang, Z.Z.

Abstract

This paper (i) provides an analysis of the green sea urchin fishery in British Columbia by updating information from the fisheries in 1998, 1999, and 2000 fishing seasons; (ii) providing suggestions for limit and target reference points for the 2001-2002 and 2002-2003 fishing seasons; and (iii) presenting results from fishery-independent surveys of green sea urchins. Reference points were determined using biomass dynamic models applied to the core stocks in the South Coast - inside waters northern region (Queen Charlotte Strait; Pacific Fisheries Management Areas 11-13) and the South Coast - inside waters southern region (Gulf Islands; PFMA 17-20,28). Two methods were used to determine the parameters of these models: a linear approximation to the dynamic Schaefer model, and a time series fitting method. For both core stocks, both models produced similar (i.e. overlapping 95% confidence intervals) estimates of the maximum sustainable yields (MSY). The time series fitting method produced a lower MSY with narrower confidence intervals for the smaller stock (Gulf Islands region), and it is recommended as the more conservative method for calculating reference points. The calculated MSYs are recommended as limit reference points, with target reference points suggested in the range of 0.25 to 0.50 of MSY. The resulting target reference range for both core regions in the South Coast is therefore 96.3 to 192.5 t. Fishery-independent surveys have been conducted annually since 1995 at index sites in Area 12 (Queen Charlotte Strait) and indicate that the biomass of legal and sub-legal sized green urchins in this area in 1999 and 2000 were among the highest observed. Fishery-independent surveys in the Gulf Islands region have been conducted for two years. They show inconclusive trends in legal-sized biomass between the two key locations, but all locations appeared to have strong sub-legal sized biomass.

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