Sexual Segregation of Spiny Dogfish in Fishery-Dependent Surveys in Cape Cod, Massachusetts: Potential Management Benefits

Abstract

Commercial gill-net and longline surveys were conducted in the Cape Cod, Massachusetts, area to assess whether the proportion of male Spiny Dogfish Squalus acanthias in the catch changes throughout a normal fishing day (an event frequently observed by local commercial longliners) and to identify the associated potential benefits for fishery management in the study area. Sex ratio changes were examined with respect to location (north and south of 42°N), environment (depth, surface and bottom temperatures, and salinity) and fishing (type of gear and time of activity). Spiny Dogfish showed differences in sex ratios (the proportion of males in the catch [PM]) that were related to location and type of fishing gear as well as to depth and time. Higher numbers of fish were caught with longlines, and higher numbers of males were caught in the southern area in inshore shallower waters early in the day. In the northern area, the sex distribution found within sets indicated a higher presence of females and a lower presence of males in shallower inshore waters. Changes in environmental parameters (depth and bottom temperature) were correlated with PM only in the south. A consistent seasonal (summer and early fall) diurnal shift in the sex ratio was found within 10 mi (16.1 km) of the east coast of the Cape Cod peninsula. This shift suggests that the implementation of a seasonal, male-only directed longline fishery be considered for this location. Such a fishery would enhance the sustainability of the U.S. Atlantic Spiny Dogfish stock by reducing fishing pressure on adult females. The sex ratios observed suggest that sexual segregation in Spiny Dogfish in the Cape Cod area corresponds to female avoidance of males coupled with specific mating and/or feeding behavior by males.

Received March 19, 2013; accepted November 20, 2013

ACKNOWLEDGMENTS

This study was supported by the Commercial Fisheries Research Foundation (NOAA Prime NA09NMF4720414). The Institute for Coastal Science and Policy at East Carolina University provided additional equipment as well as logistical and personnel support. We are particularly thankful to local commercial fishers Mike Pratt, Tom Bell, and Ian Parente for taking us out to sea and for providing inestimable local ecological knowledge of Spiny Dogfish behavior and distribution in the Cape Cod area. We are grateful to Lyndell Bade, Evan Knight, Chuck Bangley, and Gary Weaver for helping in field data collections and with tagging and release. We thank Mahealani Kaneshiro-Pineiro and four anonymous reviewers for providing comments on an earlier version of the manuscript. We also thank Thomas Allen for providing help in developing a bathymetric map of the study area.