Supplementing electronic tagging with conventional tagging to redesign fishery closed areas

Abstract

Fishery closed areas provide a resource management tool to protect predictable spawning aggregations of migratory fish species. Movement by individual fish however challenges the effectiveness of fishery closed areas. Recent developments in electronic tags and movement modelling offer new information to quantify fine-scale usages of fishery closed areas by free-ranging individuals. Conventional tagging data, on the other hand, inform on population broad-scale distribution patterns with respect to closed areas. Using the Atlantic cod (Gadus morhua) population from the northern Gulf of St. Lawrence as a case study, we demonstrate how electronic tagging experiments can be supplemented with conventional tagging experiments to evaluate and redesign fishery closed areas. A geolocation model was used to estimate time of arrival, time of departure, and proportion of time that individual cod equipped with data-storage tags spent within a fishery closed area. Two optimization algorithms were developed to seek out the spatial and temporal designs that maximized the proportion of time that the fish equipped with data-storage tags spent inside the closed area, relative to its size and duration. Bootstrap analyses quantified the effects of inter-individual variability in closed area usages. Conventional tagging data were used to estimate the proportion of the spawning population density function encompassed by the closed area. Results from the electronic and conventional tagging experiments suggested that the fishery closed area in the northern Gulf of St. Lawrence should be displaced south along the 200-m isobath and that the enforcement period be reduced. Electronic tagging data also suggested that alternative migratory behaviours within a population lead to disproportional levels of protection between migratory and non-migratory groups. A re-examination of past conventional tagging experiments in combination with recent electronic tagging experiments provides new information to evaluate the spatiotemporal design of fishery closed areas