Age, growth, mortality, reproduction, and exploitation rates for fishery management of grey mullet species in the Köyceğiz Lagoon–Estuary (Mediterranean coast)

Background. The Mugilidae is a widely distributed family in the tropical, subtropical, and temperate waters. These fish species have a global economic value because of the high quality of their flesh and caviar. This study provides new data on the age, growth, and reproduction parameters of commercially exploited grey mullets from the Köyceğiz Lagoon, Turkey, namely golden grey mullet, Chelon auratus (Risso, 1810), leaping mullet, Chelon saliens (Risso, 1810), thicklip grey mullet, Chelon labrosus (Risso, 1827), and flathead grey mullet, and Mugil cephalus Linnaeus, 1758. The obtained results are intended for fisheries management of golden mullets in the area. Materials and methods. A total of 1195 fish specimens were collected from the Köyceğiz Lagoon (south-western Anatolia). The mullets were caught monthly, between January 2017 and December 2017, using fish barrier, trammel net, beach seine, and cast-net. The fish age was determined from sagittal otoliths. Growth parameters were determined by applying the von Bertalanffy growth function. Reproduction period, mortality and exploitation, relative yield per recruit (Y'/R), and biomass per recruit (B'/R) were determined. Results. The most frequent mullet age groups were 3+ and 4+ (for M. cephalus and C. labrosus) and 4+ (for C. auratus and C. saliens). The following von Bertalanffys growth models were calculated: Lt = 58.78(1 - e-0.163(t + 0.0195)) for C. auratus, Lt = 59.99(11 - e-0.169(t + 0.0132)) for M. cephalus, Lt = 49.77(111 - e-0.193(t + 0.0293)) for C. labrosus, and Lt = 46.41(111 - e-0.232(t + 0.0283)) for C. saliens. The growth performance index (Ø') for C. auratus, M. cephalus, C. labrosus, and C. saliens was calculated as 2.750, 2.772, 2.679, and 2.698, respectively. The reproduction periods of C. auratus, M. cephalus, C. labrosus, and C. saliens were found as October-January, June-September, December-March, and April-July, respectively. The exploitation rate E was determined for C. auratus, M. cephalus, C. labrosus, and C. saliens as 0.68, 0.80, 0.66, and 0.62 year-1, respectively. Conclusions. Fisheries management policies need to be established and implemented immediately in the Köyceğiz Lagoon considering the intense fishing pressure, environmental pollution, and tourism.