Didemnum vexillum is an aggressive, rapidly growing colonial ascidian and regarded as a global alien invasive species in temperate waters. It has recently become established in the western ...Mediterranean and the vectors of its introduction were assumed to be shipping or oyster trade. A dense settlement of it was encountered on nets of the bluefin tuna (Thunnus thynnus) cages placed at 60–65 m depths off the İzmir Peninsula (eastern Aegean Sea, eastern Mediterranean) in December 2022. It had considerably clogged net's eye openings, hindering water circulations inside cages. It had a vertical distributional pattern on 35 m long-nets, occurring solely on depths from surface down to 15 m, around where a summer thermocline develops. It has entirely replaced the native black mussel Mytilus galloprovincialis on nets. This colonial ascidian changed the routine cleaning procedure of nets in the farming. Three possible ways of its introduction to the eastern Mediterranean were proposed, but the most reasonable one is its secondary transfer via nets or ships from Malta. Mechanisms of its invasion biology and behaviour should be studied and monitored in the region.
Pterois miles (Bennett, 1828) is one of the worst aquatic invaders in history and its rapid dispersal in the Mediterranean Sea raise serious concerns for local communities. On August 2019, one ...specimen was caught by spear-fisher at depths of 15 m in Kokar Bay of Aegean Sea, Turkey. This occurrence represents the northernmost record of the species in the Aegean Sea.
Deployment of artificial wreck reefs (AWRs) near natural reefs can influence fish assemblages on both reefs. Here, we assessed fish attitudes (abundances, biomass and species richness) according to ...different level complexity areas of wrecks, feeding guilds of fish and body size of fish of two identical AWRs deployed at the same depth (36.6 m) and different distances from natural reefs. Scuba divers used visual census method to sample fish communities at wrecks for two years. An average of 2346 individuals per dive belonging to 52 species were observed on wrecks combined. Both mean fish abundance and mean biomass did not differ significantly between wrecks. Mean species richness was significantly greater at 9 Eylül than Alaybey. Planktivore was the most abundant feeding guild on wrecks, and its abundance statistically differed between AWRs. The comparisons of fish assemblages at the different level complexity areas of the wrecks show differences, the highest mean abundances were recorded at the areas of low complexity of the wrecks. The results of this study show that although deploying artificial wreck reefs near to natural rocky reefs catalyses fish colonization, it does not present an exact influence on the fish communities of AWRs. We have not known yet how creating an artificial wreck reef affects fish community of natural reefs. With giving extra importance to the choice of deployment area, AWR applications may transform to win-win projects for both the marine environment and recreational users, such as divers and anglers.
This study aims to reveal the by-catch rates for gillnet fishery, targeted Boops boops by small-scale fisheries around fish farms in Güllük Bay (Aegean Sea), and to determine the by-catch per unit ...effort (BPUE) rates. The study was carried out through deck sampling at Göltürkbükü, Gündoğan, Yalıkavak, and Torba fishing ports during two seasons between November and April (2017-2018 / 2018-2019). A total of 147 fishing operations from 13 boats were randomly monitored. In gillnet fishing for bogue, a total of 18163 kg of the catch was caught from 48 species belonging to 30 families, including invertebrates. The target Boops boops was the most common species with a rate of 91.9%, of which 8.1% was determined as a by-catch. The most caught by-catch species are Diplodus annularis (Linnaeus, 1758), Scomber colias (Gmelin, 1789), Trachurus trachurus (Linnaeus, 1758), Pagellus acarne (Risso, 1827), Scomber scombrus (Linnaeus, 1758). While the average BPUE was 4.77 ± 0.85 kg.1000 m-1 in 2018, it was 3.20 ± 0.58 kg.1000 m-1 in 2019. November gives the highest average in terms of BPUE values. The average BPUE ranged from 0 to 19.1 kg.1000 m-1 (mean: 7.97 ± 2.83 kg.1000 m-1). Statistically, there is a significant difference in BPUE values between the months (Kruskal-Wallis test, p < 0.05).
The food composition of whiting, Merlangius merlangus, caught around the sea-cage fish farms off the coast of Perşembe, was analysed and compared with the diet of whiting from a control site off the ...coast of Fatsa (Ordu Province, south-eastern Black Sea). A total of 815 stomach samples were collected during the study, and of these, 195 (23.9%) were empty. According to the percentage of relative importance index (IRI%), pellet food (47.8%) and Annelida (25%) were the main prey groups of whiting in the sea-cage fish farms area, while unidentified teleost (85.3%) and Engraulis encrasicolus (8.2%) were dominant in the control site. The other prey groups in both areas were Crustaceans (Mysidae, Amphipoda, Upogebia sp.), Sprattus sprattus and Gobius spp. Seasonally, pellet food was the most consumed food in all seasons, but Mysidae was the first preference of whiting around the sea-cage fish farms in spring. In the control site, unidentified teleost was the first preference in all seasons, except winter, where E. encrasicolus was the first choice, followed by crustaceans and S. sprattus in winter. Bray–Curtis analysis shows that seasonally, there is no significant difference in the sea-cage fish farms, while there is significant difference in the control site, and two-dimensional nMDS of IRI% revealed a clear separation between both sites. SIMPER analysis revealed that the most contributing factors to the differences between seasons were pellet food in the sea-cage fish farms, and E. encrasicolus in the control site.
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 (°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°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 Muğla 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).
•We used acoustic telemetry to observe Scorpionfish movements at an artificial reef.•Acoustic telemetry could use as an effective tool for the management of fisheries with artificial ...reefs.•Successful acoustic tagging of Scorpaena porcus and Scorpaena scrofa in artificial reefs.•The study has confirmed the role of artificial reefs for adults of S. porcus and S. scrofa in the Aegean Sea.
Artificial reefs (ARs) are defined as any structures that are placed on the seafloor to protect sensitive ecosystems, enhance biodiversity, and support small-scale fisheries or diving tourism. With the recent development of fine-scale acoustic tracking, ecologists and fishery managers have gained a powerful tool to explore how exploited species behave in newly created artificial habitats. Here, we report for the first time the space used by the black scorpionfish (Scorpaena porcus) and red scorpionfish (Scorpaena scrofa), two highly important exploited species in the Mediterranean Sea that are often managed with ARs. The Vemco VR2W positioning system (VPS) was used to examine the fine-scale movement patterns (home range) and residency time of these species. S. porcus (182–271 mm total length; n = 14) and S. scrofa (252–445 mm total length; n = 7) were tracked for up to 91 d in ARs located in Edremit Bay, northern Aegean Sea, Turkey. The results revealed high site fidelity during the tracking period and high variability (among individuals) in their home range areas, which ranged from 933 m2 to 28,674 m2 (Kernel Utilization Distribution 95%) for S. porcus and from 1895 m2 to 17,487 m2 for S. scrofa, with a mean and s.d. of 9591 ± 8998 m2 and 8104 ± 6113 m2, respectively. The variability in the home range areas was explained neither by the fish length nor diel phase (day vs. night), although residency indexes suggested stronger site fidelity in large S. scrofa. While the lack of size-dependent home range behavior could be explained by the limited size of the range (imposed by the telemetry system), the lack of diel differences in their home range sizes could be explained by the ambush predatory behavior of both species. Our findings suggested that ARs may facilitate the profitability of fisheries in both species by retaining adults and enhancing recruitment of newly settled fish, as suggested by the movement patterns and habitat utilization indexes considered in this study.
•The presence, frequency and occurrence of Atlantic Bluefin Tuna at Mediterranean fish farms have increased during last years.•This farm-attraction is generalized in the Mediterranean, which might ...have serious implications on the Mediterranean ABT populations.•These wild tuna aggregations might interact with farming and coastal fishing activities.•Knowledge on these issues is sparse and must be increased for better species conservation and management considerations.
In recent years, Atlantic Bluefin Tuna (Thunnus thynnus) is being observed to increasingly and more frequently aggregate around Mediterranean offshore fish farms. In the present work, potential interactions between aggregations of this important pelagic species and offshore fish farms and local fisheries were assessed through a questionnaire survey aimed at fish farmers, divers and stakeholders in the Mediterranean. Since the interactions may have implications for aquaculture and marine ecology, enhanced management strategies for the conservation of endangered Mediterranean stocks of Atlantic Bluefin tuna, as well as for sustainable development of aquaculture and fishery activities are discussed.
Sea-cage fish farms cause wild fish to aggregate nearby. Nevertheless, it is still not clear to what extent the attraction effect around sea-cage fish farms varies according to the type and size of ...the reared species. We examined this attraction effect in six sea-cage fish farms across the Aegean Sea using an integrated approach combining these variables with seasonal and spatial factors. Six 5-minute rapid visual counts were conducted on each farm complex for comparing the wild fish aggregations around the sea-cages concerning both cultivated species (seabass and seabream) and their sizes (adult and juvenile). We counted a total of 509,061 fishes, representing 36 species and 18 families. While 292,377 fish belonging to 34 species were counted in seabass cages, 216,684 fish belonging to 27 species were counted at seabream cages. In addition, 160,192 fish belonging to 28 species were counted around the juvenile cages, while 348,869 fish belonging to 34 species were counted at adult fish cages. The study shows that wild fish communities are formed around the sea-cages where seabass and seabream are reared in both adult and juvenile sizes in the Aegean Sea. According to our results, the fish species reared in the cages do not have a statistically significant effect on the wild fish community structure around the cages, whereas fish size, which was correlated with cage biomass and a longer history of feeding, had a strong effect. Other factors affecting the wild fish community structure around the cages are the season and the location of the cages.
Pterois miles (Bennett, 1828) is an aquatic invader and disruptive predator for marine ecosystems. A single lionfish was photographed and sampled in March 2021 during a scientific survey at 36 m ...depth in Karaburun/İzmir Bay. In this study presents an update on the lionfish's northward progression in the Aegean Sea.
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