The Post-Release Survival of Two Skate Species Discarded by Bottom Trawl Fisheries in Antalya Bay, Eastern Mediterranean

Knowing post-release survival rates of fish escaping or being thrown back into the sea as discards is important for effective stock assessment. The aim of this study was to estimate the short-term discard survival rates of the two most abundant by-catch skate species (thornback skate: Raja clavata and brown skate: Raja miraletus) in the bottom trawl fisheries in Antalya Bay and to determine the factors affecting discard survival of skates. For the thornback skate the mean health score, the percentage with a health score [whitesquare]2 and percentage dead at time zero were 2.3, 91% and 2%, respectively. For brown skate, these values were 1.2, 43% and 26.5%, respectively. Considering the health score of these species, the fish length (P=0.001) and the tow duration (P=0.006) were significant parameters for the thornback skate, and the tow duration (P=0.046), the total length (P=0.044) and the catch amount (P=0.008) were found to be significant for brown skate. The mean survival time and the survival rate after 48 hours in tanks were 41 hours and 81% for thornback skate, and 15 hours and 21% for brown skate. The health condition of the individuals transferred to the tanks is an important reference point for their survival rates. Thornback and brown skates entering the tanks with a health score of 1 had a 44% and 9% chance of survival, respectively. On the other hand, skates entering the tanks with a health score of 2 or 3 had a 92% chance of survival for thornback skate and 49% for brown skate.