the population biology of the thornback ray, raja clavata in caernarfon bay, north wales

• Published in: Journal of the Marine Biological Association of the United Kingdom Vol. 85; no. 5; pp. 1089 - 1094
• Main Authors: whittamore, j.m., mccarthy, i.d.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.10.2005
• Subjects: 20th century; Females; Males; Marine; Mortality; Population; Population biology; Raja clavata; research article; United Kingdom > UK; Irish Sea; Wales; ANE, British Isles, Wales, Caernarfon Bay; ANE, British Isles, Wales
• ISSN: 0025-3154; 1469-7769
• DOI: 10.1017/S0025315405012130

amid concern about the status of skates and rays in welsh waters the present work set out to provide up-to-date information on the population biology of raja clavata in caernarfon bay. the von bertalanffy growth parameters were l∞=100.9 cm, k=0.18 y−1 and t0=−0.95 y for males; and l∞=117.6 cm, k=0.16 y−1 and t0=−0.7 y for females. male r. clavata reached 50% maturity at 58.8 cm and 3.9 y, which was smaller and younger than females (l50 and a50 were 70.5 cm and 5.3 y, respectively). although previously over-exploited, the present estimate of total mortality (z) was 0.48–0.49 y−1 which, in terms of replacement mortality (calculated as 0.7 y−1), suggests no immediate prospect of recruitment failure for r. clavata in caernarfon bay. the potential for the recovery of a depleted population is discussed in relation to the allee effect.