engleski

Long-term changes in distribution and demographic composition of Thornback ray, Raja clavata, in the northern and central Adriatic Sea

Population structure and distribution of the Thornback ray, Raja clavata, L. 1758, in the northern and central Adriatic Sea were described based on data from bottom trawl surveys conducted in the area between 1996 and 2006 in the scope of the “ MEDITS” project. R. clavata was caught at depths between 23 and 270 m, and the highest abundance and density indices were recorded at depth stratum 50-100 m. The sex ratio was close to 1:1. Length at first sexual maturity for both sexes was calculated. Length-weight relationships were obtained for males, females and the whole sample. Calculated parameters of the length- weight ratio showed a positive allometry for both sexes. The recent state of the population was compared with existing data from 1948-49 (« ; Hvar» ; expedition). The comparison revealed that since « ; Hvar» ; expedition significant changes occurred in distribution and abundance of R. clavata in the Adriatic Sea. During « ; Hvar» ; expedition this species was distributed on the whole continental shelf, whereas during MEDITS it was found only in restricted areas and with much lower abundances. Besides, significant changes occurred in the demographic composition of the population. All described changes indicate an over-fishing of the Thornback ray in the Adriatic Sea, which is a result of the high fishing intensity to which the species has been exposed for the last 60 years.

Raja clavata ; population structure ; distribution ; Adriatic Sea

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