Size selectivity of the scallop fishery in the southern Gulf of St. Lawrence: Effects of ring size and washer type

Abstract

In the southern Gulf of St. Lawrence (sGSL), there is a mostly supplementary fishery for sea scallops (Placopecten magellanicus) concentrated on three primary scallop beds in the Northumberland Strait. The fishery is not subject to an enforced minimum size limit and small scallops (<90 mm shell height) are often removed from this population before they have had time to adequately contribute to population recruitment, resulting in sub-optimal fishery yields and a partially size-suppressed population. This study aimed to provide stakeholders with information related to gear configuration changes that could potentially reduce catches of small scallops in the sGSL fishery by quantifying size-selectivity of different ring sizes (82.6 mm and 88.9 mm) and washer types (rubber and steel). We also compared the catches of small, fecund scallops (45–90 mm) across the different gear configurations. The gears with 82.6 mm rings had high retention of small scallops, with lengths of 50 % retention estimated to be 72.8 and 76.0 mm with rubber and steel washers, respectively. This increased to 87.9 mm and 95.5 mm, respectively, in the gears with 88.9 mm rings. It was estimated that with rubber washers, increasing ring size from 82.6 mm to 88.9 mm will reduce catch of small fecund scallops by 51 %, while reducing catch of large scallops by 27 %. Increasing ring size was more effective than changing washer type at increasing size selectivity of the gear. Previous research on scallop life history suggests that this reduction of large scallops will be temporary because the larger gear will ultimately shift the population size distribution towards larger scallops resulting in higher yield-per-recruit. These results will be useful to resource managers and stakeholders for stock assessments, and for future gear type decisions.