A Changing Gulf of Maine: Investigating the Role of Benthic Water Temperature in Determining the Timing of Spiny Dogfish (Squalus acanthias) Arrival and Departure in the Gulf of Maine

Abstract

Spiny Dogfish (Squalus acanthias) is a highly migratory elasmobranch that undergoes annual migrations along the East Coast of the United States. Spiny dogfish have been studied extensively on the West Coast, but little information currently exists on the life history of this species in the Gulf of Maine (GOM). In the last few years, commercial gillnet fishermen in the GOM have been reporting unusual catch patterns while fishing offshore, perhaps indicating an increased abundance in dogfish and an extension of the length of time that dogfish occupy the GOM in a given year. Concurrent with these changes, rising average global temperatures have led to increased ocean temperatures in the GOM, a variable that could be altering the historical movement patterns of GOM fish. These changes are likely to have important ecological impacts and implications for commercial fisheries. This project sought to investigate the relationship between benthic water temperature and the presence or absence of spiny dogfish off the coast of New Hampshire. A greater understanding of the relationship between benthic water temperature and dogfish presence could increase the efficiency of commercial gillnet fishermen targeting spiny dogfish (e.g. targeting specific areas of a certain water temperature), increase our capacity to successfully manage the dogfish fishery, and suggest ecological impacts for these changes. Utilizing vessels in the NH Gillnet fishing fleet, dogfish catch and benthic water temperature were tracked seasonally from 2014-2016 over the course of three separate phases (Phase I – 2014, Phase II – 2015, Phase IIIA/IIIB – 2016). Limited data was also collected by recreational fishermen during 2016. Results indicated a threshold of approximately 5.0˚C benthic water temperature before dogfish arrival in 2014 in late June. In 2015 and 2016, dogfish time of departure was calculated on 8/17/2015 and 8/08/2016 when benthic water temperature was 6.16˚C and 7.42˚C respectively. The similarity in date but difference in water temperature indicate potentially a potential photoperiod correlation associated with the timing of dogfish departure. Initial observations were also made concerning patterns of sex ratio associated with spiny dogfish at Jeffrey’s Ledge, perhaps indicating separate movement patterns associated with differences in age/sex. Additional data is needed to improve the foundational work presented in this pilot study