Analysis of the factors affecting the discard fate for trawl fishery

In this study, a series of commercial and experimental studies were carried out on factors that predict and affect the discard mortality, an important issue of fisheries management. The effects of mortality rates and pressure treatment on survival rate were observed in commercial trawl operations. Virtual fishing experiments were carried out in laboratory using live fish from the nature under controlled conditions. In these two different studies, survival rate, acute mortality and delayed mortality were estimated after a fishing operation. The main factors affecting the survival rate, fish behavior, pressure changes, trawling speed and seawater temperature. These factors showed different effects on different species. The survival and mortality rates obtained as a result of experimental and marine studies were supported by biochemical blood parameters. The level of stress caused by factors affecting survival rate was determined by examining the amounts of cortisol, T3 and T4 hormones in the blood serum. In the study, when pressure treatment was applied, the survival rate of the species was higher. In the trawl simulation and flow channel experiments, different sea water temperatures and behavioral impairment according to trawling speed and survival rates for 24 hours were determined. In these experiments, E. costae, E. aeneus, E. marginatus did not float in the net or in the flow channel and thus they were found to be alive without fatigue. L. mormyrus and S. aurata showed high swimming performance and were able to survive to a considerable extent when released to the water. This thesis study showed that the discard survival rate is an important issue for sustainable fisheries and stock management. In addition, the survival of discarded fish released into the sea after fishing operations is an important issue for fisheries economic losses and responsible environmental approach.