Sea-cage Fish Farms Research Articles

İskenderun Körfezi'nde (Türkiye, Kuzey-Doğu Akdeniz) Balık Çiftliği Etrafında Aetomylaeus bovinus (Myliobatidae) Sürüsünün Varlığı

In this study, a shoal of bull rays, Aetomylaeus bovinus (E. Geoffroy Saint-Hilaire, 1817), around a sea-cage fish farm in Iskenderun Bay, Turkey is reported. Such an aggregation is probably due to ontogenetic shift but may also be a factor of reproductive process as some pregnant females were observed. The number of individuals recorded, in all more than 25, shows that the species is still present in the area but needs a conservation plan due to its k-selected life-histories and potential for extinction.

Wild fish aggregations near sea-cages rearing adult and juvenile fish in the Aegean Sea

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.

A Substrate-Independent Benthic Sampler (SIBS) for Hard and Mixed-Bottom Marine Habitats: A Proof-of-Concept Study

Sea cage fish farms are increasingly situated over hard and mixed substrate habitats for production and waste-dispersion reasons; yet in many cases, these installations are not being effectively managed with respect to benthic impacts due to the lack of a practical sampling method. This study presents the first set of results from a newly developed Substrate Independent Benthic Sampler (SIBS) device that captures the unconsolidated organic and inorganic matter that overlies almost all substrates. The contents of the samples were analyzed using extracted environmental DNA (eDNA) followed by metabarcoding of the bacterial 16S rRNA gene. SIBS microbial assemblages reliably changed with proximity to farm and concurred with visual assessments of impact. Moreover, the approach appeared to be very sensitive with respect to the enrichment gradient, being able to discern influences at distances of 500–1500 m from the impact source. Other spatial differences, due to region and farm, were small in comparison, and the effect of the underlying substrate type was minor. The samples contained sufficient previously described bacterial bioindicator taxa from enriched sediments, such that a meaningful biotic index could be calculated, thereby placing them on a well-established benthic enrichment spectrum with established environmental thresholds. SIBS-derived bacterial data provide a powerful new approach for mapping spatial boundaries of farm effects irrespective of substrate type and topography. More importantly, the tool should also permit quantitative assessment of benthic enrichment levels irrespective of substrate type from depths of at least 100 m. It therefore has the potential to solve the hard-bottom problem that has until now prohibited effective environmental monitoring at mixed and hard-bottom locations.

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

AbstractThis 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).

Seasonal variations in wild fish aggregation near sea-cage fish farms in the Turkish Aegean Sea

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.

Ege Denizi’nde kıyı balıkçılığı ve deniz kuşları arasındaki bazı etkileşimler

In this study, it is aimed to determine the some interactions between various fishery types and seabirds, results of this interaction and sea bird species that have been interacting due to secondary attraction factors. A total of 80 fishermen, working in fish farms, small scale fishery (SSF) and lagoons located in Izmir, Aydın and Muğla were face-to-face interviewed between September 2016 and December 2018. The great cormorant (Phalacrocorax carbo), yellow-legged gull (Larus michahellis), great white egret (Ardea alba), some yelkouan shearwater (Puffinus yelkouan) and great white pelican (Pelecanus onocrotalus) are the bird species that have an interaction with coastal fishermen and sea-cage fish farms. 82% of employees in sea-cage fish farms mentioned that they have an interaction with sea birds in winter, besides %50 of SSF have an interaction with sea birds in summer. The difference between interaction rate according to seasons has been found as statistically significant (p<0.05). 33% of employees in fish farms expressed that they see sea birds during the day. This ratio is 21.7% and 15% for SSF and fishermen in lagoon, respectively. Furthermore, 8.3% of fishermen in lagoon, 11% of employees in fish farms and SSF mentioned that they have an interaction with seabirds especially in the morning time.

Determining potential conflicts between small-scale fisheries and sea-cage fish farms in the Aegean Sea

Background. Fish farms attract both juvenile and adult wild fishes in great numbers and diversity. These wild fishes also become an easy target stock for local fishers, both professional and recreational. There are three groups of interest in this study, the fish farmers, small-scale fishermen (professional), and recreational fishers (mostly anglers but also spear fishers). This study was intended to determine conflicts derived from the adverse social and bioecological interactions from the perspective of both local fishermen and fish farmers and to determine the observed incidence of predators. Materials and methods. In this study, 48 randomly selected fish farms, 28 fishery cooperatives, and 33 fishing ports located close to aquaculture areas were visited for face-to-face interviews with the fishermen of small-scale fisheries (SSF) between July 2015 and July 2017. The main purpose of the survey questionnaire was to ask SSF fishermen for their opinion about offshore aquaculture and vice versa—ask the fish farmers about SSF, emphasizing issues potentially creating problems. Data were collected mainly on sociodemographic profiles, current problems, reciprocal conflict issues, the impact of offshore fish farming on SSF activities, and on bioecological interactions such as predator attacks and problems with farm fish escapes. Results. Approximately 77% of fishermen in Izmir and 71% of fishermen in Muğla declared that they had problems with the sea-cage fish farms. On the other hand, 40% of fish farmers in Izmir and 54% of fish farmers in Muğla reported problems with local SSF. The fishermen believe that in recent years, Mediterranean monk seal (Monachus monachus), sea turtle (Caretta caretta), and invasive fish (pufferfish, etc.) populations have been increasing in Muğla. Additionally, 46% of Muğla fish farmers and 60% of Izmir fish farmers acknowledged cases of fishes escaping from sea-cages. In terms of the predators, 84% of Muğla and 75% of Izmir’s fishermen expressed their concerns regarding predator attacks on the sea-cage farms. Conclusion. Further studies, based on socioeconomic issues, are needed for better understanding the dimensions of incomes and economic losses of SSF and cooperation issues in the area where the interaction is high. We suggest that all stakeholders, small-scale fishermen, in particular, must be integrated with a management plan, and the cooperation among both fishing groups should be encouraged.

Ege Denizi‘nde Balık Çiftliklerinden Balık Kaçışlarının Nedenleri Üzerine

Temmuz 2015 ve Temmuz 2017 arasında, Ege Denizi‘nde İzmir ve Muğla kıyılarından rastgele seçilmiş 48 balık çiftliği ziyaret edilmiş, ayrıca balık çiftlikleri etrafında av yapan toplam 329 kıyı balıkçısıyla yüz yüze anketler yapılmıştır. Anketlerde balık çiftliklerinden balık kaçış nedenleri sorulmuştur. Verilen yanıtlar predatör saldırıları, fırtınalar, kafes ağlarının yetiştirilen balıklar ve deniz kuşları tarafından ısırılması, ağ yırtıkları, balıkların aktarılması esnasındaki düşmeler olarak katılımcılar tarafından sınıflandırılmıştır.

Ege Denizi’nde balık çiftlikleri etrafındaki doğal balık tür çeşitliliği

Structures, floating on the surface of the ocean attract both juvenile and adult fishes in great numbers and diversity. Natural and artificial Fish Aggregation Devices (FADs) in open seas are widely recognised for their capacity to attract pelagic fishes. It can be assumed that floating sea-cages act as a kind of FAD. Even, fish aggregations beneath the sea-cages increase much more by the influence of feeding. In this study, aggregations of wild fish were counted around six sea-cage fish farms in both northern and southern Aegean Sea. Each fish farm cultivated Sparus aurata and Dicentrarchus labrax and the farms deployed between 720 m and 3 km far from the coast. Between July 2015 and July 2017, assemblages of wild fish were counted bimonthly on two separate days at each of these farms. The Rapid Visual Counts (RVC) in five minutes with SCUBA and covering 11250 m3 were performed for six times within each farm. A total of 40 species, belonging to 22 families were recorded at fish farms, with 3 families, Sparidae (7 species), Carangidae (6 species) and Mugilidae (4 species) being particularly abundant. The results of the study and other studies conducted in other parts of the Mediterranean were merged; it was found that a total of 99 fish species were listed around sea-cage fish farms in the Mediterranean Sea.

Food composition of whiting Merlangius merlangus, captured around the sea-cage fish farms in Ordu, south-eastern Black Sea

AbstractThe 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.

The short-term effects of farmed fish food consumed by wild fish congregating outside the farms

We simulated in the laboratory the possible effects on fatty acids and immune status of wild fish arriving for the first time in the vicinity of a sea-cage fish farm, shifting their natural diet to commercial feed consumption, rich in fatty acids of vegetable origin. The flesh fatty acid profile of golden mullet specimens was altered after 2weeks of commercial feed consumption, showing an increase in fatty acids of vegetable origin. The serum peroxidase and bactericidal activities, and head-kidney leucocyte phagocytic capacity, increased after eight weeks of the new diet, while the respiratory burst activity decreased. The extent of these changes cannot be considered large enough to regard them as compromising the health status of fish. More research is needed in order to elucidate whether the rapid assimilation of the dietary fatty acids could harm the immune status of fish when feeding for longer periods than two months.

Monitoring a Massive Escape of European Sea Bass (Dicentrarchus Labrax) at an Oceanic Island: Potential Species Establishment

The post-escape behavior of aquaculture escapees is a growing topic of research. We monitored a massive escape event of the European sea bass, Dicentrarchus labrax, which occurred at a sea-cage fish farm off the oceanic island of La Palma, Canary Islands, eastern Atlantic. Stomach contents and gonadal development of escapees were analyzed from two islands (Gran Canaria and La Palma) in order to assess the degree of postescape establishment,. We also tested (at both islands), the suitability of fatty acid profiles as biomarkers of aquaculture escapes, processing recaptured escaped fish at a range of distances away from aquaculture facilities. Escaped European sea bass concentrated within breakwaters and decreased in abundance through time after the massive escape at La Palma. Decapod crustaceans (particularly Percnon gibbesi and Rhynchocinetes sp) were the main diet constituents of escapees, followed by fishes (mainly the parrotfish, Sparisoma cretense). Only one spawner male was found. Crude lipid, oleic acid, linoleic acid, linolenic acid, eicosapentaenoic acid, Σn-9 fatty acids and Σmonounsatured fatty acids showed higher values in cultured or escaped individuals near cages relative to fish far away from farms. Arachidonic acid, docosahexaenoic acid, Σn-3, satured fatty acids, Σn-3/Σn-6 ratio and Palmitic acid showed the opposite pattern. Our data showed that escaped European sea bass is able to exploit natural recourses, altering their fatty acid profiles relative to farmed conspecifics. The usefulness of fatty acids as biomarkers is, however, limited to a short period of time after escape events.

Description and sensitivity analysis for the LESV model: Water quality variables and the balance of organisms in a fjordic region of restricted exchange

In this paper we describe a new ecological model for Regions of Restricted Exchange (RRE), such as fjords, estuaries, rias and lagoons. The model is intended to simulate the impact of external nutrient input on microplankton (phytoplankton plus pelagic microheterotrophs) in RREs. We have implemented the model with the practical purpose of finding a safe limit to the capacities of RRE to assimilate fish-farm waste. Sea-cage farming of fish is increasing in fjords in northern and southern hemispheres, and its external nutrient input can lead to environmental problems such as eutrophication and deoxygenation. The model includes a physical system of three layers with exchanges driven by tidal movement, freshwater input, wind stirring. The biological part includes two microplankton compartments, each parameterizing a microbial loop and each containing chlorophyll. The first compartment represents diatoms and associated heterotrophs, and the second compartment represents flagellates and associated heterotrophs. As well as the balance of these organisms, the model simulates concentrations of nutrient N, P, and Si, dissolved oxygen, and water transparency. Chlorophyll and nutrient change are linked by yields ( q). Losses of microplankton to grazing by mesozooplankton or benthos are simulated by a temperature-dependent grazing pressure acting on a mean loss ( L 0 ) . The model also includes the ability to simulate point source inputs of nutrients or organic matter and a generic tracer with first order decay. Sea-cage fish-farms exemplify such point sources. In order to explore model behaviour, we included inputs from a 1500 tonnes salmon farm multiplied by a factor ( γ ) . We carried out sensitivity analysis to identify the most influential model parameters and forcing variables in the case of the shallow Scottish fjord, Loch Creran, in 1975 before the introduction of salmon farming. We tested the model fit to this pristine state ( γ = 0 ) , using Major Axis Regression of simulated variables on observed variables. The model successfully follows the seasonal cycles of chlorophyll (summer over both microplanktons) and the limiting nutrients (P, N). The sensitivity analysis identified three sets of key parameters: ( γ ) and other fish-farm coefficients, which control farm waste effects on an RRE; ( L 0 ) parameters for each microplankton, which link these to the rest of the ecosystem and which have implications for future inclusion of shellfish farming in the model and, chlorophyll yields from nutrients ( q), which are crucial for the predication of eutrophication and the ecological understanding of the model.

Coastal fish farms are settlement sites for juvenile fish

Two south-west Mediterranean fish farms were monitored over a period of 22 months to test if sea-cage fish farms act as settlement habitats for juvenile fish. Twenty juvenile fish species were found to settle at farms throughout the year. Fish assemblage composition varied markedly over time and was dependent on the spawning period for each species. The most abundant species were Oblada melanura, Atherina sp., Diplodus sargus, Boops boops and Liza aurata. Up to 3783 ± 1730 individuals/cage were found closely associated with the cages. Highest densities were observed during the warmer summer and autumn months. Zooplankton sampling and stomach content analyses of the most abundant species were done to assess prey availability, selectivity and diet overlap among species. Copepods were the main prey item for all juvenile fish species, irrespective of fish size. Ivlev’s Index indicated that food was not a limiting factor for juvenile fish at farms. Furthermore, food pellets from the farm affected the food chain by modifying the fatty acid profiles of farm-associated zooplankton and juveniles of L. aurata and O. melanura. These results show that aquaculture can directly influence the body composition of juvenile fish that recruit to sea-cage fish farms.

Temporal variability of wild fish assemblages associated with a sea-cage fish farm in the south-western Mediterranean Sea

The abundance and size structure of wild fish aggregated around a floating sea-cage fish farm were assessed and compared with control sites over a period of 1 yr. The farm was located 3.1 km offshore from El Campello (Alicante, SE Spain) and cultivated Sparus aurata and Dicentrarchus labrax in 14 sea-cages. Fish assemblages were evaluated by visual census using SCUBA on three separate days in each season. On each sampling day, six 5-min visual counts were made around the cages and six counts were made at control sites, 200 m distant from the farm. Assemblages of wild fish differed greatly between the control sites and the farm, with 12 species observed in farm counts and only 4 in the control counts. Abundance, biomass and diversity were greater in the farm-associated fish assemblage. In most controls, fish were not observed. The most abundant families were Sparidae and Carangidae (>98% of aggregated fish). Assemblages at farms differed among seasons, with Trachurus mediterraneus dominant during spring, Oblada melanura in summer and Boops boops in autumn and winter. The results indicate great temporal variability in the farm-associated fish assemblage, which may be related to recruitment periods for juveniles (e.g. O. melanura in summer) and specific preferences by other species for warm (e.g. T. mediterraneus) or cold (e.g. B. boops) water periods.

Changes in body condition and fatty acid composition of wild Mediterranean horse mackerel (Trachurus mediterraneus, Steindachner, 1868) associated to sea cage fish farms

Net-cage fish farms attract a great number of wild fishes, altering their behaviour and possibly their physiology. Wild Mediterranean horse mackerel (Trachurus mediterraneus), sampled from populations aggregated around two Mediterranean fish farms and from two natural control populations, were analyzed for differences in body condition, stomach content and fatty acid composition. Pellets used to feed caged fish in both farms were also analyzed to identify their relationship with the fatty acid composition of tissue of wild fish. T. mediterraneus aggregated around the farms throughout the year although large seasonal changes in abundance and biomass occurred. Wild fish aggregated at farms mainly ate food pellets while control fish fed principally on juvenile fish and cephalopods. Wild fish that fed around the cages had a significantly higher body fat content than the control fish (7.30+/-1.8% and 2.36+/-0.7%, respectively). The fatty acid composition also differed between farm-associated and control fish, principally because of the significantly increased levels of linoleic (C18:2omega6) and oleic (C18:1omega9) acids and decreased docosahexaenoic acid (C22:6omega3) in farm-associated fish. The increased condition of wild fish associated with farms could increase the spawning ability of coastal fish populations, if wild fish are protected from fishing while they are present at farms. The fatty acids compositions could also serve as biomarkers to infer the influence of a fish farm on the local fish community, helping to better describe the environmental impact of fish farming.

Multivariate analysis of the bentho-demersal ichthyofauna along soft bottoms of the Eastern Atlantic: comparison between unvegetated substrates, seagrass meadows and sandy bottoms beneath sea-cage fish farms

By means of multivariate techniques, we studied: (1) the differences in the structure of bentho-demersal, non-cryptic, fish assemblages associated with unvegetated sandy substrates, vegetated meadows constituted by the seagrass Cymodocea nodosa and the bottoms under the influence of sea-cage fish farms; as well as (2) the persistence of these patterns with regard to different scales of spatial variability, across three islands of the Canarian Archipelago (Central East Atlantic). Our sampling strategy (involving three islands, with five locations per island, and two sites within each location) detected significant changes in the composition and structure of the fish assemblages between the three habitats. Fish assemblages associated with the unvegetated and vegetated bottoms were similar among the surveyed islands. In contrast, we observed a significant inter-island variability in the fish populations associated with the sea-cage fish farms. The presence of the sea-cage fish farms increased the overall fish abundance (184.8±49.8 ind 100 m−2) as compared to both the vegetated (38.8±9.7 ind 100 m−2) and unvegetated habitats (1.1±0.4 ind 100 m−2). Differences within and between the habitats were found to be associated with the relative abundance of a few fish species. The most abundant species were Xyrichthys novacula in the unvegetated bottoms and Diplodus annularis, Spondyliosoma cantharus and Mullus surmuletus on the seagrass meadows. Finally, we recorded an increase in the abundance of Heteroconger longissimus, Trachinus draco and Pagellus acarne in the bottoms beneath the sea-cage fish farms. These species, in addition to a group of large benthic chondrichthyes, were responsible for the differences between islands in the composition and structure of the demersal ichthyofauna beneath the sea-cage fish farms.

Vertical variability of wild fish assemblages around sea-cage fish farms: implications for management

Wild fish were counted in 4 depth-related strata (bottom, midwater, cage and surface) around 3 floating sea-cage fish farms (Altea, Campello, Guardamar) along the Spanish coastline and 2 farms (Los Cristianos, San Andres) in the Canary Islands. Almost 200000 wild fish belonging to 53 species were seen; representatives of Sparidae (8 species), Carangidae (6 species), Mugilidae (5 species) and Chondrichthyid rays (7 species) were commonly observed. At all 5 farms, 1 to 3 taxa accounted for >74% of the abundance and >94% of the biomass of aggregated wild fish. Abun- dances (5.7 to 162 times) and biomasses (42 to 1728 times) of wild fish were higher in the cage stratum at the 3 Mediterranean farms than at the bottom. In contrast, abundances and biomasses of wild fish at the Canary Island farms were highest at the bottom at San Andres and highest at the sur- face at Los Cristianos. Large differences in the sizes of associated fish existed among farms, with low percentages of fish >20 cm total length at Guardamar, Los Cristianos and San Andres (11 to 25%) compared to Altea and Campello (81 to 95%). However, the greatest proportions of large fish were present in the cage stratum at each of the 5 farms. This variability suggests that assemblage structure and aggregated biomass of wild fish at farms cannot be predicted prior to their installation, causing uncertainty in modelling of nutrient dispersal. Further, the sedimentation 'footprint' of temperate sea- cage fish farms may vary depending on (1) the species and biomass of associated wild fish, and (2) where these fish are distributed in the water column. As wild fish consume lost feed and assimi- late nutrients, we suggest that coastal managers prohibit fishing of large planktivorous species at farms to fully harness their ability to ameliorate benthic impacts.

Extensive Aggregations of Wild Fish at Coastal Sea-Cage Fish Farms

We present evidence of a largely undocumented environmental effect of coastal sea-cage fish farms on wild fish. We estimated the total abundance and biomass of wild fish aggregated in the immediate vicinity of nine fish farms in the Mediterranean Sea and one farm off the east coast of Australia. Estimates of wild fish aggregations ranged from 2000 to 86000 individuals and from 100 kg to 38.5 tons of fish per farm and were always greater than control locations. Particularly large aggregations (>30000 fish, > 12 tons) occurred at half of the farms. Aggregations were temporally stable for weeks to months and most wild fish associated with farms (88%) were of adult size. Potential effects of such large aggregations of wild fish in the immediate vicinity of fish farms include increased vulnerability to fishing and pathogen transfer between caged and wild fish. We suggest specific legislation should be enacted wherever large aggregations of wild fish occur around fish farms to enhance the positive and reduce the negative effects of association.

Attraction of Wild Coastal Fishes to an Atlantic Subtropical Cage Fish Farms, Gran Canaria, Canary Islands

We assessed the influence of two commercial fish farms on the local aggregation of coastal wild fishes through a 'post-impact' sampling design at Gran Canaria Island (Canary Islands). At each farm, we established two controls and one impact location and estimated fish abundance bimonthly by means of SCUBA diving. Results provide evidence of local aggregation in the associated fish assemblages around sea-cage fish farms. Dissimilarities between control and impact locations for both fish farms were due to differences on the abundance of a few species. However, we detected significant differences by means of some assemblages between controls in one fish farm, as a consequence of the removal and re-location of cages. Moreover, we also detected significant within location small-scale variability for several fish assemblages around both sea-cages farms. Otherwise, we did not observe any effect of sampling times.