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

PORCU, CRISTINA;BELLODI, ANDREA;CANNAS, RITA;MARONGIU, MARTINA FRANCESCA;MULAS, ANTONELLO;FOLLESA, MARIA CRISTINA

2015-01-01

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Abstract

In the present study the life history traits of Raja brachyura from Sardinian waters (central-western Mediterranean) were investigated and the results compared with previously published data. The age, growth and reproduction were studied using 1792 specimens. Females ranged from 13.1 to 105.5 cm in total length (TL) and males from 18 to 96.5 cm TL. This species was sexually dimorphic, with females attaining a larger size than males. Both females and males showed positive allometric growth, and significant differences in the relationship between length and weight among sexes were found. The von Bertalanffy growth function (3 parameters), which provided the following values: L∞=111.14 cm TL, k=0.10 and t0 =-1.3 for females, and L∞=108.81 cm TL, k=0.11 and t0 =-1.2 for males, was the best-fit age model. R. brachyura showed a relatively slow growth rate with males growing slightly more rapidly than females. Length and age at maturity were 87.2 cm (14 years) for females and 80.8 cm (10 years) for males corresponding to 83 and 83.7% of maximum observed length respectively, indicating that the blonde ray is particularly sensitive to fishing pressure. This ray exhibited a restricted reproductive cycle from late May to August, as confirmed by the GSI values. Ovarian fecundity reached a maximum of 44 yolked follicles. Given the relative abundance in Sardinian seas, it is hoped that these results will prove useful for the implementation of basic management measures in order to ensure the sustainability of catches of this species in the Mediterranean Sea.