Spatiotemporal Density and Ecology of Batoids (Elasmobranchii) Along a Turkish Shelf-upper Slope of the Mediterranean Sea During Years 2009-2015

Spatiotemporal distribution of batoids was studied from the samples collected monthly using an Otter trawl during survey 2009-2011 and seasonally during survey 2014-2015 on the shelf and upper slope (shelf break) of the Gulf of Antalya. The study area had both a fishing zone and a non-fishing zone. Eleven batoid species were found. Seven species was found only on the shelf, one on the shelf break, and two in both zones. Recently, abundance and number of species have decreased by year. Distribution of the skates was contrasted to that of the rays along the bottom depth gradient. Raja clavata, Raja miraletus, and Dasyatis pastinaca were common and frequent species. Dasyatis centroura was an occasional visitor. The batoid abundance had two minimum periods, early summer and late autumn. Maximum values occurred in April and July. There were two types of the dispersal distribution of the batoids along the bottom depth gradient: the unimodally-distributed species peaked abundance at 75-100 m or at 300 m, and the bimodal distribution was composed of ubiquitous species of the batoids. This distribution was more pronounced in survey 2014-2015. The batoid assemblages were discriminated by a seafloor depth of 125 m, comprising the assemblages of the shallower and greater depth. The species-environment relation was correlated positively with bottom depths, near-bottom chl-a, and finest bioseston and negatively correlated with Secchi disk depth and water salinity. However, seasonal discrimination did not occur. The fishing effort, which was low in the present area, was not significantly correlated with any of the faunistic characters (abundance, biomass, and diversity indices). In relation of the batoids to the megafauna, the batoids were positively correlated with cephalopods, holoturids, and decapods but negatively correlated with stomatopods and bivalves.