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    Influence of some physico-chemical variables on wild fish richness beneath sea-cage fish farms in the Aegean Sea, Turkey
    (Cambridge Univ Press, 2020) Akyol, Okan; Ozgul, Aytac; Ozan Duzbastilar, F.; Sen, Halil; Ortiz de Urbina, Jose M.; Ceyhan, Tevfik
    This study aims to determine the relationship between physico-chemical variables on a seasonal basis and wild fish assemblages beneath sea-cage fish farms. Assemblages of wild fish were counted monthly on two separate days at each of six fish farms between August 2015 and July 2017, by six rapid visual counts (RVC) in 5 minutes with scuba by two divers. Seawater samples were simultaneously taken by a Nansen bottle during the RVC from the fish farm barge. SST (degrees C), salinity (ppm), dissolved oxygen (mg l(-1)) and pH were measured by YSI multiparameter, while Secchi disk was also used for light transmittance. Wild fish species richness went up with increasing temperature and salinity in the Izmir region, however, this stopped at about 26 degrees C and about 39 ppm. Wild fish richness increased when the DO was at a level of 7 mg l(-1) and the pH at about 7.9 in Izmir. Between 10 and 20 m, light transmittance showed greater wild fish species richness in Izmir region. in contrast, the wild fish species richness of the Mugla region fluctuated more. in terms of wild fish species richness, these fluctuations increased with salinity and DO, while they decreased with SST, pH and light transmittance. However, the range of variation of the recorded physico-chemical variables is rather narrow. The results of the correlation matrix indicate that the relationship between wild fish species richness and pH and SST was statistically significant in Izmir region (P < 0.05).
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    Seasonal variations in wild fish aggregation near sea-cage fish farms in the Turkish Aegean Sea
    (Elsevier, 2020) Akyol, Okan; Ozgul, Aytac; Duzbastilar, F. Ozan; Sen, Halil; Ortiz de Urbina, Jose M.; Ceyhan, Tevfik
    This study sought to determine seasonal variations in wild fish assemblage events associated with fish farms with respect to fish biodiversity, abundance and biomass along the Turkish Aegean Sea. Assemblages of wild fish were determined bimonthly with six rapid visual counts (RVCs) at six fish farms in both the Izmir (Northern Aegean Sea, NAS) and Mugla (Southern Aegean Sea, SAS) regions. Data were pooled based on each season. Thirty-nine total fish species representing 21 families were identified, with three particularly abundant families: Sparidae (seven species), Carangidae (six species) and Mugilidae (four species). The greatest fish diversity was recorded in the summer, followed by spring, autumn and winter. Regionally, the greatest fish diversity was observed in the southern Aegean Sea. Significant differences across seasons and regions were observed. Boops boops was very abundant at all stations, except for the first station in the NAS. Approximately 80.5 % of farm-associated fish were B. boops, followed by Atherina boyeri (4.14 %), Scomber colias (2.82 %), Sardinella aurita (2.78 %) and Oblada melanura (2.73 %). A total of 105,041 individual fish and 3637 kg.11,250 m(-3) fish were identified in the NAS; 448,331 individual fish and 47,070 kg.11,250 m(-3) fish were identified in the SAS. These results indicate that the diversity of wild fish communities is relatively high, and vary between regions. Boops boops represents the predominant species, although the Sparids, Carangids, Mugilids, Scombrids, Clupeids and Pomatomids are also highly represented throughout the Mediterranean.