Potential Environmental Impacts of Tuna Cage Farming in the Aegean Sea

Abstract

The present study aimed to investigate the potential impacts of Atlantic Bluefin Tuna (Thunnus thynnus) farming in offshore cage systems in the Aegean Sea (Sığacık 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 PO4-P, NH4-N, and NO2-N showed no temporal or spatial changes, and were recorded below 0.01 mg/L (<0.01) for PO4-P and NH4-N, whereas lower than 0.005 mg/L (<0.005) for NO2-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 Sığacık 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.

Physical carrying capacity of a potential aquaculture site in the Mediterranean: the case of Sigacik Bay, Turkey

“…However, the area allocated for cage farming would benefit from further experimentations with long-term monitoring of water conditions along with biological parameters, and bottom sediment analyses in the specific aquaculture-allocated zone as well as the entire bay area. In a long-term monitoring study, Gürses et al (2019) reported an "Eutrophication Risk Scala" less than four (T < 4) around an intensive Bluefin tuna cage farm deployed within the borders of the potential aquaculture site of Sigacik Bay, that is the same area investigated in the preset study. Even though Gürses et al (2019) concentrated on the specific area within the bay, namely a tuna cage farm, their findings in terms of biological evaluation in the potential aquaculture site PAS-9 support our findings for the physical carrying capacity indicating that the production capacity is still below limits of environmental tolerance.…”

“…In a long-term monitoring study, Gürses et al (2019) reported an "Eutrophication Risk Scala" less than four (T < 4) around an intensive Bluefin tuna cage farm deployed within the borders of the potential aquaculture site of Sigacik Bay, that is the same area investigated in the preset study. Even though Gürses et al (2019) concentrated on the specific area within the bay, namely a tuna cage farm, their findings in terms of biological evaluation in the potential aquaculture site PAS-9 support our findings for the physical carrying capacity indicating that the production capacity is still below limits of environmental tolerance. However, when necessary measures are to be taken in rather short time frame, practical and reliable tools may help to evaluate the potential culture area in terms of production capacity with reduced influences on the aquatic environment.…”

Influence of some physico-chemical variables on wild fish richness beneath sea-cage fish farms in the Aegean Sea, Turkey

“…There are some studies on seasonal changes in environmental variables (especially on nutrients and plankton) related to Mediterranean aquaculture (Pitta et al ., 1999; Karakassis et al ., 2001; La Rosa et al ., 2002; Aksu & Kocataş, 2007; Neofitou & Klaoudatos, 2008; Kaymakci Basaran et al ., 2010; Gürses et al ., 2019), but there is a lack of research on wild fish species richness. Thus, this study aims to determine the influence of some physico-chemical variables, i.e.…”