Jan 2018 Elasmobranch of the Month: Thornback Ray
Image credit: Andy Murch
Key Features Characterized by the many thorns often present on their dorsal side, thornback rays have “30-50 thorns along the midline” (Shark Trust, 2009) which continues along the tail. The number of thorns vary between individuals and can be present on both the dorsal and ventral sides (SSACN, 2015), with buckler thorns (Shark Trust, 2009) often being found on mature fish. This species varies in coloration from dark brown/sandy brown-grey on the dorsal side and white on the ventral side, where spots and patches can be black, purple and yellow. Thornback rays also have distinctive and alternating dark-light bands along the tail (SSACN, 2015). Habitat Distributed throughout the northeast Atlantic and into western Africa, this species can be found across a wide variety of seafloor habitats, including: soft sand, mud, gravel (SSACN, 2015), as well as covering an extensive depth range (10-300m; Ellis, 2006; Shark Trust, 2009). Mature thornback rays are considered to have seasonal migrations, where individuals spend the winter offshore in deeper waters before returning to shallow waters in summer for breeding (Hunter et al., 2005; Shark Trust, 2009; SSACN, 2015). Food Source Thornback rays diet mostly consists of crustaceans such as crabs and shrimp as well as bony fish. Status Unfortunately, thornback rays are listed as “Near Threatened” on IUCN Red list of Threatened Species. Threats Threats of this species include both target fisheries and as bycatch in mixed trawl and gillnet fisheries (Shark Trust, 2009; SSACN, 2015; Ellis, 2016).
Image credit: Andy Murch
References Ellis J. 2016. Raja clavata. The IUCN red List of Threatened Species 2016: e.T39399A103110667. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T39399A103110667.en. (Accessed 5th October 2017). Hunter E, Buckley AA, Stewart C and Metalfe JD. 2005. Migratory behaviour of the Thornback Ray, Raja clavata, in the Southern North Sea. Journal of the Marine Biological Association of the United Kingdom, 85: 1095-1105. Scottish Sea Angling Conservation Network. 2015. Fish Factoids. Available at: https://www.ssacn.org/wp-content/flipread/SSACN%20Factoids%202015/files/assets/basic-html/page-44.html . (Accessed 5th October 2017). Shark Trust. 2009. An Illustrated Compendium of Sharks, Skates, Rays and Chimaera. Chapter 1: The British Isles. Part 1: Skates and Rays.