Population dynamics of demersal shark species (Galeus melastomus, Squalus blainvillei, Etmopterus spinax and Centrophorus granulosus) in the gulf of Antalya

The present thesis study focused on the fisheries, life history traits, spatial and temporal distribution patterns, reproductive biology, age-growth and population dynamics of the four shark species distributed in Antalya Bay. Data were collected by monthly deep-water trawling hauls in 2016 and in 2019. The results of the study shows that the species are distributed in the entire Antalya Bay in the range of 300 m to 1000 m. A total of 1821 individuals from G. melastomus, 236 individuals from S. blainvilliei, 995 individuals from E. spinax and 74 individuals from C. granulosus were sampled. There was no difference between the length frequency distributions in all four species. Only in E. spinax species, a difference was found between the sexes and the mean lengths. It has been determined that mature individuals in G. melastomus and E. spinax species are especially found at depths of more than 500 m whereas S. blainvillei were not found deeper than 600 m stratum. It was determined the total length (TU) of the species increases as the depth increase. Only G. melastomus has mature individuals throughout the year. In addition, strategies such as a long maturity period, slow growth, early maturation of males compared to females were observed. Age examination of the dorsal spines of S. blainvillei revealed that it has a long life cycle (~26 years) and females can reach greater overall lengths (~73 cm) and are very sensitive to fishing activities with a late maturity cycle. Among these species, only the individuals of G. melastomus species showed negative allometric development. It was determined that the least sampled C. granulosus species were distributed in the West - East areas of the bay and in the stratums of 400 - 900 m. The smallest mature individual (~ 75 cm) was determined, and due to late maturity, slow growth (K ~ 0.1) not enough mature individuals could be sampled. In the stomach content examinations, it was determined that C. granulosus fed on bony fish (36.2%IRI) at the highest rate, while the other three species fed mostly on cephalapoda. Among the fishing regulations applied in the region, the limitation of the fishing season and the legal fishing zone (3 miles away from the shore) seem to be in favor of deep water shark species, but they have a long lifespan and low reproductive abilities and even if the legal fishing zone is applied, it is not effective because the fishing gear - species interaction occurs uninterruptedly.