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.

New biological data onRaja brachyura(Chondrichthyes, Rajidae) from around Asinara Island (NW Sardinia, Western Mediterranean)

“…This characteristic is a common feature in elasmobranchs where females reach a greater size and weight than males (Braccini & Chiaramonte 2002) as found in Leucoraja wallacei and Dipturus pullopunctatus (Walmsley-Hart et al 1999) where females grow larger but more slowly than males. A similar feature was described also by Gallagher et al (2004) for several rajid species in the Irish Sea, including the blonde ray where the growth rates found in males were higher than that found in females (male: K50.145; female: K50.129). The larger size and age at maturity reached by female rajids is probably related to different reproductive strategies between sexes (Walmsley-Hart et al 1999).…”

“…The high age at maturity reported for the blonde ray (Tm year59, f540; Frisk et al 2001) was generally confirmed by the large size at maturity for males (Gallagher et al 2004). This aspect, with low fecundity values and low growth rates, reflects the high vulnerability of R. brachyura to fishing activities and it needs to be considered in management and conservation strategies (Holden 1973(Holden , 1974Compagno 1990;Hoenig & Gruber 1990).…”

“…For blonde ray of Irish Sea, Gallagher et al (2004) found that the length at 50% maturity was 83.56 cm and 81.92 cm TL for females and males, respectively. In our samples, most of the animals were well below these values except a few males.…”

“…Despite the low number of specimens recorded from the Italian waters, Fischer et al (1987) stated the regular presence of this ray in the Tyrrhenian fish markets. The knowledge on the biology and ecology of the blonde ray is very scarce and only related to specimens from Atlantic sectors (Dorel 1986;Ellis et al 1996;Frisk et al 2001;Gallagher et al 2004).…”

Life-history traits of a commercial ray, Raja brachyura from the central western Mediterranean Sea

“…Studies on the biology of this species have been carried out mainly in the north-eastern Atlantic Ocean. They have focused on growth rates and ageing (Holden, 1972;Fahy, 1991;Gallagher et al, 2005;Serra-Pereira et al, 2005a), conversion factors (Dorel, 1986;Serra-Pereira et al, 2010;McCully et al, 2012), some reproductive aspects (Clark, 1922;Holden et al, 1971;Gallagher et al, 2005;McCully et al, 2012) and diet (Holden & Tucker, 1974;Quiniou & Rabarison Andriamirado, 1979;Ajayi, 1982;Ellis et al, 1996;. However, information on its general biology in the Mediterranean is very limited.…”