Sexual segregation of spiny dogfish (Squalus acanthias) off the northeastern United States: Implications for a male-directed fishery

Abstract

Female spiny dogfish experienced high fishing pressure on the US east coast during the 1990’s. This led to a skewed population sex-ratio of 7 males per female which later declined to 4:1 as the stock was rebuilt. The current fishery still targets mature females, resulting in artificially high abundances of male spiny dogfish. Members of the fishing industry have proposed the creation of a male-directed fishery to sustainably harvest more of the available yield. To explore the potential for such a fishery, we investigated environmental factors associated with the spatiotemporal distribution of male spiny dogfish and male-skewed sex ratios. We analyzed data from 454,721 spiny dogfish caught in 2063 trawl samples during the Northeast Fisheries Science Center (NEFSC) annual spring and autumn bottom trawl surveys from 2009 to 2014. Consistent with previous research, there was clear spatial and temporal sexual segregation within the population. Male spiny dogfish could be harvested with little female bycatch along the continental shelf from Chesapeake Bay to Long Island at depths of 70–80m and 300–330m, approximately 90–150km or 240–270km from shore during spring. High proportions of male spiny dogfish in the catch were found in the western Gulf of Maine and on Georges Bank in the fall at depths 80–250m. Using boosted regression trees, we identified depth as the best environmental predictor of high (>75%) proportions of males in the catch, followed by distance from shore and temperature, for spring and fall season respectively. A new male-directed fishery appears to be feasible, and if responsibly managed, could potentially help return sex-ratios to natural levels (2:1), reduce fishing pressure on the female portion of the stock, and benefit local fishing communities that have struggled with restricted fishing opportunities in recent years.