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Research Document - 2012/139

An assessment of Thorny Skate (Amblyraja radiata Donovan, 1808) in NAFO Subdivision 3Ps and Divisions 3LNO

By M.R. Simpson, C.M. Miri, and L.G.S. Mello

Abstract

Available information on the fishery, management, and biology of Thorny Skate in NAFO Subdivision 3Ps and Divisions 3LNO were reviewed to determine the status of this stock. Based on a continuous distribution and lack of physical barriers between Subdiv. 3Ps and Div. 3LNO, Thorny Skates in Div. 3LNOPs are considered to constitute a single stock. This stock is managed by Canada in Subdiv. 3Ps, and by the Northwest Atlantic Fisheries Organization in the NAFO Regulatory Area (outside Canada’s 200-mile limit) of Div. 3LNO. In Subdiv. 3Ps, with the commencement of a Canadian skate-directed fishery in 1994, NAFO-reported landings averaged 1 308 tons annually over 1994-2009; which decreased to a 808-t average in 2010-11. In 2005-11, reported landings from Div. 3LNO averaged 5 548 tons annually; down from an average of 13 064 t for all countries in 1997-2004. Commercially reported landings data do not include discards at sea, and skate landings are never reported by species; except by Canadian Fisheries Observers. At-sea sampling of Canadian commercial catches for skate lengths by Fisheries Observers was limited in 2010, and non-existent in 2011. An Index of Fishing Mortality for Subdiv. 3Ps remained below 8% since 1996, declined through the late 2000s, and reached its lowest value in 2010-11 (2%). Fishing Mortality in Div. 3LNO increased from the late 1980s to a peak of 29% in 1997; then averaged 17% during 1998-2004. In 2005, this Index reached its lowest value (4%), and subsequently remained below 8%. In Subdiv. 3Ps, Canadian Campelen spring research surveys suggest a gradually increasing trend in Thorny Skate biomass over 1996-2012; averaging 31 400 tons annually. The Subdiv. 3Ps spring survey abundance index was relatively stable in 1996-2012; fluctuating around 23 million skates. After a declining trend in Div. 3LNO over 1985-95 (Engel spring surveys), Campelen spring survey biomass indices followed a gradually increasing trend; averaging 85 500 tons annually. The Div. 3LNO spring abundance index was relatively stable in 1996-2012; fluctuating around 51 million skates. Thorny Skate distribution in Div. 3LNOPs has changed since the 1980s, from a widespread distribution over the Grand Banks in moderate to high concentrations, to a more limited distribution along the southwest edge of the bank in the late 1990s (Div. 3O); Thorny Skate distribution in 2007-12 continued to be concentrated on the southwest boundary of the bank in Div. 3O, in Subdiv. 3Ps, and along the shelf edge of the Grank Banks in Div. 3LN. Length distributions of Thorny Skate sampled in Canadian spring surveys of Subdiv. 3Ps and Div. 3LNO in 1998-2012 indicate that the highest percentage of young-of-the-year skates (5-20 cm TL) for this period was observed in 2009. The primary purpose of this paper is to provide an update on Thorny Skate stock status in Subdiv. 3Ps for use by fisheries managers in formulating conservation measures for this stock.

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