Research Document - 2004/036

Petrale Sole Stock Assessment for 2003 and Recommendations for Management in 2004

By Starr, P.J., Fargo, J.

Abstract

We summarise results of analysis of biological data, research survey data and fishery observer data for Petrale sole (Eopsetta jordani). Size composition summaries suggest that the proportion of smaller fish entering the fishery has increased over the 1998-2002 period. The estimated instantaneous total mortality rate from survey data in 2000 was only slightly larger than the best estimate of the natural mortality rate. We conclude that the current fishing mortality rate for Petrale sole stocks off the West Coast of Canada is at or below the sustainable level. We present time series of previously unsummarised results for petrale sole from three sets of trawl surveys from the west coast of Canada, all of which show a generally increasing trend of biomass indices since the mid- to late-1990s, although the trend from the NFMS triennial survey is probably not significant.

We present a series of general linear models for three areas of the coast: west coast Vancouver Island, Queen Charlotte Sound and Hecate Strait. The models presented explore the non-zero landings, the change in the proportion of zero landings and a model combining the two sets of indices over a period 1996/97 to 2002/03. The non-zero models for WCVI and Queen Charlotte Sound do not show much change over this period, except for an increase in the most recent one or two fishing years, while the Hecate Strait non-zero model shows an increasing trend beginning in 1998/99. The binomial models are not greatly different from the lognormal models from the same area over the seven years modelled and the combined models indicate an increasing trend in CPUE in all three areas for the most recent three to four fishing years.

A delay-difference model was developed which uses the biological parameters for growth and the length/weight functional relationship along with six sets of data representing respectively the mean annual weight of petrale sole, the time series of catch and CPUE, and three sets of trawl survey indices. A model which combines all the available data sets estimates a large standing stock, low fishing mortality rates and a stock status above B_msy. One year catch projections based on this model predict that the stock size will remain above F_msy with catch levels up to about 2000 t. The only model which is somewhat pessimistic is the model which omits the weight data. This model also estimates that the current stock status exceeds B_msy, but predicts that the stock would fall below this level at a catch in 2004/05 of 400 t and the F in 2004/05 would drop below F_msy at 650 t.

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