Changes in Spiny Dogfish Sex Ratio in Longline Commercial Fishery in the Cape Cod Area: Fishery Management Aspects

Observation by New England longline fishers, and results from past and ongoing research studies conducted by East Carolina University (Rulifson), provide support for daily sexual differences in habitat use between male and female spiny dogfish in the Cape Cod area and surrounding waters. We have observed this using commercial longlines in fall 2008 near Green Harbor, and again by longlines in fall 2010 near Chatham and off Stellwagon Banks. Gillnets have not shown this pattern. We present here result from a longline survey conducted off the coast of Chatham, southeast of Cape Cod. This survey is part of an ongoing project which was designed to assess migration patterns of spiny dogfish along the Northwest Atlantic coast. One of the study objectives is to test an hypothesis suggested by New England commercial longline fishers, that the male:female ratio in catches changes to mostly females as the day progresses. Our preliminary results for 11 October, 2010, show that this ratio changes occurs, with an higher number of males in early morning, while an increasing number of adult females in later morning. Also, the average length of females increased as the day progresses, while male average length didn’t significantly changed. If changes in the male:female ratio is consistent through day and season in specific locations, the possibility for a male-only directed longline fishery on a specific time and space scale framework could be considered for the implementation of spiny dogfish fishery regulation management in the study area. Avoiding fishing adult females, which are used as reference points for the determination of the spawning stock biomass (SSB), can provide direct benefits to the sustainability of the fishery targeting this species, which it is cause of concerns overseas in term of conservation and trade.