POTENTIAL ENVIRONMENTAL IMPACTS OF TUNA CAGE FARMING IN THE AEGEAN SEA

The present study aimed to investigate the potential impacts of Atlantic Bluefin Tuna ( Thunnus thynnus ) farming in offshore cage systems in the Aegean Sea (Sigacik Bay-Izmir, Turkey), in respect to physico-chemical water quality parameters, nutrient loads, chlorophyll- a , total suspended solids, zooplankton groups, and TRIX index calculations for the potentially affected cage farm area and an unaffected reference site. Concentrations of physico-chemical variables (temperature, salinity, dissolved oxygen, pH) in the study carried out in May and August 2018, were within the acceptable limits for marine aquaculture in terms of water quality characteristics. The concentrations of PO 4 -P, NH 4 -N, and NO 2 -N showed no temporal or spatial changes, and were recorded below 0.01 mg/L (<0.01) for PO 4 -P and NH 4 -N, whereas lower than 0.005 mg/L (<0.005) for NO 2 -N values in both cage and reference stations in May and August 2018 periods. Results showed low levels of TSS (0.33-11.87 mg/L), both in the cage farm area and the reference site, remaining below the general quality criteria of 30 mg/L for marine environment. No eutrophication risk (TRIX index, T<4 ) was observed around the Tuna Cage Farm Site in Sigacik Bay, according to the legislations enacted for “Sensitive Areas of Enclosed Bays where fish farms are not allowed”. Based on these findings, demonstrating highly interactive trophic level variability, it can be concluded that the impacts of the Tuna Cage Farm were not significant, possibly due to the consistent movement of the water in currents in the study area.