Science Advisory Report  2014/055

Assessment of Spiny Dogfish in the Northwest Atlantic

Summary

• Canadian landings averaged about 2500 mt annually between 2000 and 2008.  The quota for Spiny Dogfish has been set at 2500 mt since 2004.  Landings since 2008 have been markedly lower, dropping to only 5 mt in 2010 and have remained at very low levels since.  There are no restrictions on discarding and bycatch in other fisheries.
• Population estimates indicate a dramatic increase in Spiny Dogfish abundance during the 1980s, peaking about 1992, and then declining.  The updated model demonstrates increased abundance since 2009, especially of juveniles, with a total population abundance of 789.2 million Spiny Dogfish for 2013.  Adult females have remained at relatively high abundance since 2006.
• Spiny Dogfish migrate seasonally, their distribution shifting between USA and Canadian waters as many migrate south in winter and north in summer, with the Gulf of Maine roughly corresponding to their centre of distribution in the Northwest Atlantic.
• Approximately half the population (53-56%, varying by sex and maturity stage) is estimated to be resident in Canadian waters during the summer.  This varies considerably from year to year, with annual estimates ranging from 9% to 95%.
• Projections to evaluate the consequences of various catch levels suggest that a total catch (USA and Canada, landings and dead discards) of Spiny Dogfish in the vicinity of 47,350 mt (varies with assumed proportions of catch by region) would result in a 50% risk of decline in adult female biomass after 40 years.
• Abundance of adult females (SSN) and fishing mortality on adult females (Fssn) are used to evaluate stock status.  Given the low productivity and associated recovery time of Spiny Dogfish, SSN_msy (32.8 million) is proposed as the USR and 65% of SSN_MSY (21.3 million) is proposed as a Lower Reference Point (LRP). Fssn_msy is 0.072. Spiny Dogfish is currently above the USR, i.e., is in the healthy zone.
• Loss of trophic level competitors due to population declines of other fish species may have produced a non-equilibrium ecosystem in which Spiny Dogfish responded very positively, possibly exaggerating the estimate of carrying capacity as a long-term expectation.
• The current population model provides a reasonable basis for defining reference points and precautionary catch levels but cannot be rigorously updated without USA data.

This Science Advisory Report is from the January 20-21 and May 29, 2014, Northwest Atlantic Spiny Dogfish Framework and Assessment meetings. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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