Age, Growth and Maturity of the Commercial Ray Species from the Irish Sea

Abstract

The age, growth and maturity of 1 554 individuals (268 Raja brachyura, 258 R. clavata, 468 R. montagui and 560 Leucoraja naevus) of the main commercial ray species from the Irish Sea were determined from samples taken from commercial and research trawls between 1997 and 1998. Sagittal sections of vertebral centra stained using crystal violet enhanced the underlying band patterns of each species, allowing the derivation of age and von Bertalanffy growth parameters. Age estimates were relatively low for each species, with a maximum age of 7 yr recorded for R. montagui and 8 yr for each other species. Growth rate parameters ranged between K = 0.093 (L = 139.500 and t 0 = -1.841) for female R. clavata and K = 0.304 (L = 72.400 and t 0 = -0.924) for male R. montagui, and were notably higher for both the smaller growing R. montagui and R. naevus. Morphological assessment of maturity, revealed that; male R. montagui matured at the smallest size (53.651cm) and earliest age (3.410 yrs), male and female R. clavata matured at the greatest age (6.130 yrs) and female R. brachyura matured at the largest size (83.560 cm). In each species, an abrupt increase in clasper size in males and nidamental gland width in females was closely associated with the onset of maturity. Age, growth and maturity are discussed for each species with respect to previous studies and observed trends in the fishery.