Data from the Northwest Atlantic suggests that the thorny skate began declining in the early 1980s and accelerated in the early 1990s (Burgess et al 2005). In US waters, dredging for scallops also poses a risk (Packer et al 2003). Additionally, a targeted fishery for the species emerged in Canada in order to meet a growing European demand for skate wings (Kulka et al 2009). Bycatch in Canadian waters occurs on the Scotian Shelf, though landings do not equal those of the targeted fishery (Kulka et al 2009). Thorny skates are less likely to be taken as bycatch in the Northeast Atlantic, as their distribution does not correspond with the main trawling areas and the animals are a smaller size at maturity in this region (Walker & Heessen 1996). In the North and Irish Seas, bycatch is problematic in demersal fisheries (Kulka et al 2009); in the Barents Sea, thorny skates make up an estimated 92% of skate bycatch by weight (ICES 2004). Because the species is long-lived, attains sexual maturity late in life, and bears relatively few young (Sulikowski et al 2005), it is difficult for the thorny skate to recover from population declines.
Overall skate landings in both the US and Canada have increased since 1981, but it is difficult to ascertain what percentage of the catch is composed of thorny skate, as in the US skate landing reports are not species-specific (Kulka et al 2009). Since the mid 1980s, thorny skate biomass has decreased (Kulka et al 2009), and in 1998-1999 abundance was estimated at 10-15% of peak abundance (NEFMC 2001). In 2009 and 2010, the skate discard rate for various types of fishing gear was over 70% (NEFSC 2011), with a 50% assumed mortality rate for those animals caught in trawls (SPDT 2011). Using this mortality rate, an estimated 1800 thorny skates have died as a result of incidental catch in otter trawls (Smith 2011). As of late 2008, the thorny skate has been considered overfished in the US (44th SAW 2007); commercial and recreational thorny skate fisheries are prohibited (NEFMC 2003). There is an active petition to list the thorny skate under the US Endangered Species Act (Smith 2011).
US thorny skate conservation recommendations include (1) species-specific skate landing reports, (2) cessation of or reduction in fishing activity in areas with large populations of thorny skates, and (3) reduction of mortality of discarded animals through gear modification and training in proper handling (Kulka et al 2009).
References
44th Northeast Regional Stock Assessment Workshop (44th SAW). 2007. 44th SAW assessment summary report. US Dep Commer, Northeast Fish Sci Cent Ref doc 07-03. 58 pp.
Burgess, GH, M Camhi, SV Fordham, JA Musick, R Bonfil, S Branstetter, A Chan, C Shint, LW Gonzales, & T Hoff. 2005. Regional Overview: Northwest Atlantic. In: SL Fowler, RD Cavanagh, M Camhi, GH Burgess, GM Cailliet, SV Fordham, CA Simpfendorfer & JA Musick (eds), Sharks, Rays and Chimaeras: The Status of the Condrichthyan Fishes: Status Survey. pp 95-112. IUCN SSC Shark Specialist Gropu, IUCN, Gland, Switzerland & Cambridge, UK.
International Council for the Exploration of the Sea (ICES). 2004. Report of the working group on fish ecology. ICES CM 2004/G:09 Ref. ACE, D, I. 257 pp.
Kulka, DW, J Sulikowski, J Gedamke, P Pasolini & M Endicott. 2009. Amblyraja radiata. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. www.iucnredlist.org. Accessed 29 November 2012.
New England Fishery Management Council (NEFMC). 2001. 2000 stock assessment and fishery evaluation (SAFE) report for the northeast skate complex. New England Fishery Management Council, Newburyport, MA.
New England Fishery Management Council (NEFMC). 2003. Skate Fisheries Management Plan. New England Fishery Management Council, Newburyport, MA.
Northeast Fisheries Science Center (NEFSC). 2011. Standardized bycatch reporting methodology 3-year review report - 2011 part 1. NEFSC Reference Document 11-09. 296 pp.
Packer, DB, CA Zetlin, JJ Vitaliano. 2003. Thorny skate, Amblyraja radiata, life history and habitat characteristics. NOAA Technical Memorandum NMFS-NE-178.
Skate Plan Development Team (SPDT) Report. 2011. 2012-2013 skate complex acceptable catch limits recommendations. 49 pp.
Smith, T. 2011. Petition to list the Northwest Atlantic distinct population segment (DPS) of the thorny skate (Amblyraja radiata) as an endangered or threatened species or, alternatively, to list the United States DPS of the thorny skate as an endangered species under the US Endangered Species Act. Animal Welfate Institute, Washington, DC. 20 pp.
Sulikowski, JA, J Kneebone, S Elzey, J Jurek, PD Danley, WH Howell & PCW Tsant. 2005. Age and growth estimates of the thorny skate (Amblyraja radiata) in the western Gulf of Maine. Journal of Fish Biology 69: 1449-1465.
Walker, PA & HJL Heessen. 1996. Long-term changes in ray populations in the North Sea. ICES Journal of Marine Science 53: 1085-1093.