Atlantic Fisheries Research Document 1996/128

Scotian Shelf shrimp (Pandalus borealis) fishery in 1996

By P. Koeller

Abstract

The overall TAC for trawlers has been caught in each of the three years since the remaining individual SFA quotas were lifted in 1994. In 1996, the trawl fishery did not concentrate in the Big Hole as in the previous years; however, most catches were again taken during May and June. The industry trawl survey conducted in 1996 produced a valid biomass estimate of 28,808 mt, slightly higher than 1995, the previous record high. Expanded inshore coverage and stratification based on depth and bottom type indicates an inshore biomass of 5,000 mt. A comparative fishing experiment between 1996 and 1995 survey vessels indicated large, but consistent differences in fishing power between vessels despite similar vessel design, gears, fishing methods, and in sutu gear geometry. Differences in catch by length group are also evident and indicate that the present survey methodology is not workable in the long term due accumulation of errors in vessel conversion factors. Comparison of commercial catch rates shows less difference between the two vessels, and indicates that catch rates are negatively related to tow length. Trawl survey length frequencies corrected for the difference in selectivities between survey trawls show little difference in population composition between the 1995 and 1996 survey. Port sampling of the commercial catch are difficult to interpret because of sampling variability and the introduction of square mesh codends; however, there is no evidence that the population structure has changed in the exploited part of the population over the last three years. Comparison of survey length frequencies from unexploited and exploited parts of the offshore population indicate that fishing has changed population structure toward smaller animals. Recruitment appears unchanged in the last two years, in that the incoming year classes are of about similar strength; however, more years of data are needed before year class strength can be classified with confidence. The percentage of females carrying eggs during the ovigerous period remains high offshore, and does not appear to have decreased further inshore. The TAC has been held constant for three years after an increase in 1994. Since no detrimental effect has been detected from three years of the increased TAC, further increase may be sustainable. Both commercial CPUE indices show record high catch rates in 1996, despite a switch to square mesh codends by many vessels in 1996. The trap fishery began at the end of July 1996, shortly after shrimp returned to Chedebucto Bay. By mid-October all (9) licenses in LFAs 19, 30, and 31 A, were active and had caught about 100 tons of shrimp. An inshore fishery could take as much as 500 tons, based on the inshore biomass estimate, and an exploitation rate equal to the offshore.

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