Journal of the Marine Biological Association of the United Kingdom

Research Article

The population biology of the thornback ray, Raja clavata in Caernarfon Bay, north Wales

J.M.  Whittamore a1p1c1 and I.D.  McCarthy a1
a1 School of Ocean Sciences, University of Wales—Bangor, Menai Bridge, Anglesey, LL59 5AB, UK

Article author query
whittamore jm   [Medline] [Google Scholar
mccarthy id   [Medline] [Google Scholar


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[infty infinity]=100.9 cm, k=0.18 y[minus sign]1 and t0=[minus sign]0.95 y for males; and L[infty infinity]=117.6 cm, k=0.16 y[minus sign]1 and t0=[minus sign]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[minus sign]1 which, in terms of replacement mortality (calculated as 0.7 y[minus sign]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.

(Received January 20 2005)
(Accepted August 3 2005)

c1 e-mail:
p1 School of Biosciences, Hatherly Laboratories, University of Exeter, Exeter, EX4 4PS, UK