Presentation on theme: " Thorny skate (Raja radiata )… Can be identified by the row of thorns. 2 or 3 large thorns on each shoulder. The bases of the thorns on the pectorals."— Presentation transcript:
Thorny skate (Raja radiata )… Can be identified by the row of thorns. 2 or 3 large thorns on each shoulder. The bases of the thorns on the pectorals are star-shaped, a very distinctive character. Adult males have 2 rows of hooked, erectile thorns near the outer corners of the pectorals. The snout is blunt. There are 36 to 46 series of teeth in each jaw.
Brown on the dorsal side,either uniform or slightly clouded. Sometimes there is a white spot beside each eye, and another on each side on the rear part of the disc. The ventral side is white, may have slight brown blotches. The thorny skate is about 4 inches (100 mm.) long from snout to first dorsal fin at hatching, may grow up to 100cm in length(40 inches).
Is widely distributed throughout the North Atlantic region from Hudson Bay to South Carolina Also occurs in areas such as: USA, Greenland, Iceland, Spitzbergen in the north, and from Norway to the southern North sea.
1) Sampling: Thorny skates is captured using an otter trawl. Skates are kept alive on board the vessel Total length was measured as a straight line distance from the tip of the rostrum to the end of the tail, and disc width as a straight line distance between the tips of the widest portion of pectoral fins. Total wet weight (kg) was also recorded.
Vertebral samples is taken from above the abdominal cavity, labelled and stored frozen. After having been thawed, three centra from each specimen is removed from the vertebral column, stripped of excess tissue and air dried. Large centra is cut sagittally using a mini-saw attachment. Processed vertebrae is mounted horizontally on glass microscope slides and ground on both sides with successively finer-grit wet-dry sandpaper to produce a thin hourglass section. Vertebral sections is digitally photographed. The age can now be determined.
1. Bigelow and Schroeder. Thorny Skate[ internet].Thorny Skate(Raja radiata) Donovan 1807[28 July 2009] Available from: http://www.gma.org/fogm/Dasyatidae.htm. http://www.gma.org/fogm/Dasyatidae.htm 2. Bergstad O.A, Skjaeraasen J.E. Distribution and feeding ecology of Raja radiata in the northeastern North sea and Skaerrak(Norwegian Deep)[internet]. 2000 June 5[cited 2009 July 28]; 57(1) : (12 pages). Available from: http: www.idealibrary.comwww.idealibrary.com 3. Chevolot M, Olsen J.L, Rijnsdorp A.D, Stam W.T, Wolfs P.H.J. Population Structure and historical demography of the Thorny Skate( Amblyraja radiata, Rajidae) in the North Atlantic. Marine biology[internet] 2006 Dec 19[cited 2009 August 1] ; 151(10) : (12 pages). Available from: http://www.biomedcentral.com/1275- 1286/151/10.http://www.biomedcentral.com/1275- 1286/151/10 4. Danley P.D, Elzey S, Howell W.H, Jurek J, Kneebone J, Tsang P.C.W. Age and growth estimate of the thorny states (Amblyraja radiata) in the Western Gulf of Maine. Fish Bulletin [internet] 2003 August 21 [cited 2009 August 4] 103(1): (9 pages) Available from: http://www.google.com http://www.google.com