Assessments of the effects of fishing and of increases in the mesh size of trawls on the major commercial fisheries of the Newfoundland area (ICNAF subarea 3)

Hodder, Vincent MacKay (1962) Assessments of the effects of fishing and of increases in the mesh size of trawls on the major commercial fisheries of the Newfoundland area (ICNAF subarea 3). Masters thesis, Memorial University of Newfoundland.

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Abstract

A method, described by Gulland (1961), for estimating the effects on fisheries of changes in gear selectivity is reviewed and applied to data of the major commercial fisheries of the Newfoundland Area (ICNAF Subarea 3). Methods of estimating the essential parameters are also briefly- described. The changes in gear considered are in reality increases in the mesh size of trawls, the other gear components remaining unchanged. -- For assessment purposes the subarea has been divided into several regions, largely on the basis of a knowledge of the cod stocks, and the fisheries in them have been considered separately. Some evaluation of the effects of fishing on the cod and haddock stocks has been made, and for these fisheries both immediate and long-term assessments of increases in the mesh size of trawls have been computed. Also given are the effects of such mesh size changes on the landings by gears other than trawls. Because of the recent development of the redfish fisheries in most regions and of the scarcity of adequate data from the major redfish-producing countries, the assessments that can be made are restricted largely to the calculation of the immediate losses. -- The assessments indicate that the mesh sizes required to produce the optimum long-term yields vary greatly between regions for the different species. Since two or more species are often present on the same fishing grounds and caught by trawlers, for practical reasons a uniform mesh-size regulation must be considered for the subarea as a whole. A 41/2 inch mesh size in trawls is shown to be the optimum for the cod and haddock fisheries considered together. Despite the lack of long-term assessments for the redfish fisheries, the available information suggests that long- term benefits are unlikely from any increase in mesh size, although an increase to 4 inches would result in only slight immediate losses for most regions. No long-term assessments were made for the flounder fishery, but cursory examination of selection ogives and length composition data indicates that an increase in mesh size to 6 inches would not affect the commercial landings. Since it is not practical to have different mesh, sizes throughout the subarea, it is concluded that a minimum mesh size of 41/2 inches might be a fair choice for the regulation of the trawl fisheries on all species.

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