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Coastal Fish Farms as Fish Aggregation Devices (FADs)
... Marine finfish species rearing in sea-cages has firstly been capacity to attract pelagic fishes ( Hunter and Mitchell 1967 ;Deudero 2001 ). Sea-cages fish farms may be analogous to large FADs and the floating cages provide structure in the pelagic environment, although the unused portion of feed that falls through the cages probably enhances the attraction effect ( Bjordal and Skar 1992 ;Dempster et al. 2002 ;Sanchez-Jerez et al. 2011 ). The phenomenon is widespread, and the large aggregations of wild fish have been well-known around the sea-cage fish farms throughout the Mediterranean, including Spain ( Dempster et al. 20 02 , 20 04 , 20 05 ;Valle et al. 2007 ;Fernandez-Jover et al. 2008 ;Arechavala-Lopez et al. 2011 ;Bacher et al. 2012 ), Greece ( Machias et al.,20 04 ;20 05 ), Adriatic ( Segvic Bubic et al. 2011 ) and Turkey ( Akyol and Ertosluk 2010 ;Akyol et al. 2020a , b) as well as the Canaries ( Boyra et al. 2004 ;Tuya et al. 2005 ). ...
... Pelagic A. boyeri, the typical FADassociated fish, have smaller sizes than carangids and clupeids. Sea-cages can act as conventional FADs by attracting wild fish, and FAD-associated fish are usually smaller ( < 15 cm) in the Mediterranean ( Dempster et al. 2002 ;Sanchez-Jerez et al. 2011 ). As mentioned above that the farm-aggregated wild fish consume large quantities of pellets lost from cages ( Dempster et al. 2002 ;Fernandez-Jover et al. 2008 ). ...
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.
... The performance of cage fish farms as fish aggregation devices (FAD) is well known in the marine environment (Dempster et al., 2002;Sanchez-Jerez et al., 2011) and is mainly related to the availability of excess feed (Tuya et al., 2006). This same attractive effect of fish farms is reported in several studies in freshwater (Boyra et al., 2004;Brandão et al., 2012;Demétrio et al., 2012;Díaz López, 2017;Nobile et al., 2018), indicating that cage fish farms in inland waters can also act as a FAD. ...
Cage fish farming in hydroelectric reservoirs has been reported to promote variations in environmental conditions, which directly interfere with the foraging behavior of wild fish. We have hypothesized that the abundance of foods derived from fish farming activities alters the interspecific relationships of wild fish. To test this, we evaluated the diet composition, trophic niche breadth, and trophic niche overlap of the wild fish fauna sampled in two areas (cage farm and control area). Changes in diet composition between areas were observed, resulting in contraction of the trophic niche, and partitioning of food resources in the cage farm area. These results indicate the complexity of the influence of cage fish farms and demonstrate the importance of studies on the wild fish fauna under the influence of these systems. Furthermore, the species evaluated here have economic potential for local fishing, and our results suggest the maintenance of fish stocks in the short term due to the energy supply of the cages.
... For example, a population dynamics and genetics model developed to support the hatchery reform process in the Pacific Northwest of the USA (Mobrand et al. 2005, Mobrand, Jones, andStokes 2006) has been modified to serve as a tool for genetic risk assessment of escapes from offshore aquaculture (Volk et al. 2015). Likewise, artificial reef science has provided a framework for understanding and managing the ecological and fisheries impacts of attraction of wild fish to offshore cages (Sanchez-Jerez et al. 2011). To facilitate such cross-fertilization and cross-discovery of knowledge, we draw attention to the many different terminologies and communities of practice involved in fisheries enhancement and related research. ...
Fisheries enhancements are management approaches involving the use of aquaculture and habitat technologies (in the broadest sense) to enhance or restore fisheries. The technologies most commonly used include hatchery rearing and release of aquatic animals and provision of artificial structures such as artificial reefs. Both are associated with distinct fields of knowledge and communities of practice. Recent calls to expand and broaden the role of aquaculture and habitat enhancements in marine conservation and an increasingly integrated view of living marine resource management have led to an aspirational broadening of concepts in this area. The 10th William R and Lenore Mote Symposium and 6th International Symposium on Stock Enhancement and Sea Ranching aimed to advance and integrate knowledge across enhancement technologies and practices. Substantial progress was noted in multiple technical areas such as understanding the potential and limitations for rearing organisms fit for release into the wild, and the design of artificial reefs to enhance local fish abundance. Crucial higher-level goals such as effectively enhancing or restoring fish abundance and fisheries at the stock level continue to receive insufficient attention across the enhancement sciences. Integration of enhancement strategies provides opportunities and challenges including a need to recognize, cross-discover, and engage other distinct areas of knowledge and communities of practice. A quick reference guide is provided to facilitate this process.
... Aquaculture is a growing industry throughout many areas of the world (Duarte et al., 2009), with a reported 54.1 million tonnes (t) of finfish farmed in marine and coastal waters in 2016 . The benefits of providing added food security through fish proteins also assists to reduce the pressure of over-harvesting wild fisheries (Tidwell and Allan, 2001), however, these correspond with increasing fish aggregations in the local vicinity from the artificial structure and artificial pellets wastage from unconsumed food (Sanchez-Jerez et al., 2011). In Israel, 100 km 2 of marine space has been allocated for potential offshore development (Ayalon et al., 2015). ...
The Gippsland Basin is the location of Australia’s oldest offshore oil and gas (O&G) structures, with hydrocarbon production beginning in the 1960s. The Bass Strait flows over this area with fisheries providing seafood for the major population centers of Melbourne, Sydney and beyond. Since Australia’s maritime legislation restricts activities to outside of 500 meters from O&G structures as a security exclusion zone, these O&G structures may serve as de facto marine protected areas that may have spillover effects to local fisheries. Therefore, it is critical to understand the habitat value of O&G infrastructure to marine life in the Bass Strait and whether decommissioning of these structures affect local marine ecosystems and fisheries. We analyzed industry-collected remotely operated vehicle (ROV) imagery from 2008-2018 and compared this data with reported catch data from fishing vessels operating in this region collected by the Australian Fisheries Management Authority (AFMA) from 2008-2018. We assessed species richness and relative abundance on two platforms and two pipelines and compared the species composition with retained catch reported by commercial fishers operating in Commonwealth fisheries. We found diverse communities of fishes and invertebrates around O&G structures, with a different subset of species inhabiting pipelines than platforms. We found little overlap between the species that were targeted by commercial fishers and those found around O&G structures (10% overlap), however, species composition data from fisheries often groups species making the data coarse and under-representative of true species diversity. Fishery-independent data from ROV imagery or other methods greatly augments our understanding of deepwater marine communities, including those around O&G structures. Combining data sources provides a holistic look at these novel ecosystems and provides better insight into future decommissioning scenarios.
Wild fish aggregate at aquaculture net pens, but the underlying mechanisms are not fully understood. This study examines how salmon farms attract coastal Atlantic cod Gadus morhua from their inshore spawning grounds. Acoustic receivers were deployed at 5 known cod spawning grounds and at 6 salmon Salmo salar farms located at varying distances from these grounds in a mid-Norway study site. Cod were caught at each ground annually from 2017 to 2019, fitted with acoustic transmitters, and released (n = 535). A total of 289 tagged cod (54%) were detected at the salmon farms, with more cod detected at the farms closest to the focal spawning grounds and at operational farms. The latter result is likely linked to the availability of feeding opportunities at farm locations. If detected, cod spent less time at farms farther from their release locations. For the farm-associated cod, 70% were detected for <1 wk at the farms. However, 48 cod spent >1 mo close to the farms, with 1 individual staying 720 d underneath the farm. It is likely that some cod utilizing these local spawning grounds have considerable dietary input from salmon feed. A total of 135 cod visited two or more farms, with farms in proximity more connected in terms of inter-farm movement.
Sea cage aquaculture can alter the spatial distribution of wild fish populations, however little is known about the dietary habits of wild fish frequenting sea cages. We used wild juvenile cod (Gadus morhua) reared in the laboratory and fed either an aquafeed pellet or marine-based diet to determine trophic discrimination factors (TDFs) of stable carbon (𝛿13C) and nitrogen (𝛿15N) isotope values in white muscle tissue and baseline liver proportions of vegetable-oil based (VOB) fatty acids. We then used 𝛿13C and 𝛿15N and proportions of VOB fatty acids to investigate the dietary habits of wild cage-associated juvenile and adult Atlantic cod and adult Atlantic redfish (Sebastes fasciatus). Cod and redfish were collected in the immediate area of sea cages and reference areas of no aquaculture production. Juvenile cod captured around sea cages had both elevated 𝛿13C and 𝛿15N values and proportions of VOB fatty acids, and isotopic fractionation comparable to laboratory cod fed an aquafeed diet. However, differences in 𝛿13C and 𝛿15N and proportions of VOB fatty acids between cage-associated and reference site adult cod and redfish were predominately absent. Results suggest that sea cages may provide an energetic subsidy to juvenile cod but perhaps not at the level to sustain adult cod or redfish. Therefore, the lack of differences suggests that both adult groups may be using cage sites opportunistically and only for short duration, as isotopic values and fatty acid proportions were not consistent with waste feed consumption despite individuals being collected in close proximity to sea cages.
Fish farms, as artificial marine structures with a constant food supply, have a high capacity to attract surrounding wild fish. Different phenotypes of abundant gilthead seabream have been recorded in natural and aquaculture pressured environments in the eastern Adriatic Sea, where the influence of tuna farming on plastic traits associated with habitat use and foraging behaviour remains largely unknown. Several traits, such as body and otolith shape, external colouration, diet preference, and proximate tissue content, were analysed to examine habitat selection of the tuna farm-associated phenotype in comparison to wild and farmed phenotypes. Foraging behavioural shifts in prey selectivity, from hard-shelled bivalves towards soft textured baitfish feed, and local hydrodynamic conditions have initiated plastic responses in farm-associated seabream. Consequently, morphological traits connected with feeding and swimming performance and paler vs. vivid body colouration patterns differed between wild and farm-associated fish, highlighting the existence of resource polymorphism in gilthead seabream. While otolith shape proved to be a reliable phenotypic tracer in distinguishing farmed from wild and farm-associated fish, reduced sensitivity was found between individuals residing in the vicinity of tuna farms and wild ones. To fully understand the impact of fish farms on associated gilthead seabream and its plastic response with a distinctive morph outcome, the underlying molecular mechanisms involved in the regulation of alternative phenotypes needs to be investigated.
There is a growing interest in cod farming, this time with a domesticated farmed cod that will have characteristics that differ from wild cod. There is a need for an updated knowledge base on the risk of impact on wild cod, especially genetic and ecological interactions and localization in relation to spawning and on-growing areas. This report, which has been commissioned by the Norwegian Directorate of Fisheries, updates the knowledge status in the area with associated recommendations:
a) Research shows that coastal cod stocks are threatened, and a re-building plan has been proposed in the north. We recommend that the environmental impacts of cod farming are included in this work. We further recommend closing knowledge gaps related to ecology and life history of coastal cod in the north. Local spawning grounds along the entire coast, especially vulnerable fjord populations, should be protected against cod farming. Restrictions on the movement and live storage of cod near spawning grounds should also be considered.
b) Until better knowledge is available, we recommend that feeding and rearing grounds in the vicinity of spawning grounds in the inner fjord area with a high degree of eggs and larvae retention and vulnerable populations, should be given protection.
c) Knowledge about the effects of genetic interactions between domesticated and wild cod is largely lacking. However, we know a lot about the negative effects of escaped farmed salmon. The risk profile for cod is assumed to be higher, especially for weak stocks of coastal cod, and will depend on the level of pressure from the farmed population in relation to the size of local stocks, as well as the degree of domestication and genetic distance to wild cod. In addition, farmed cod may escape and/or spawn in the net pens, and there are no barriers between generations in marine species such as cod. By using sterile cod in farming, the risk of genetic interactions is eliminated, and we recommend that the use of sterile cod should be considered.
Aquaculture is one of the fastest growing food production sectors and has great potential for food security and livelihoods. However, it generates concerning consequences for the environment, including chemical and biological pollution, disease outbreaks, unsustainable feeds and competition for coastal space. Recent investigations are focusing on sustainable techniques (e.g., polyculture, offshore facilities) to improve the relationship between the industry, environment and society. This review provides an overview of the main factors of ecological concern within marine finfish aquaculture, their interactions with the environment, and highlights sustainable alternatives that are currently in use or development. Adequate environmental monitoring and location of farms, the reduction and exploitation of wastes and chemicals being used is crucial to ensure the growth and continuity of aquaculture production.
There is widespread use of fish attraction devices (FADs) in commercial fisheries and research. Investigations on the utility of FADs to catch fishes, and factors influencing fishes associated with FADs, require careful consideration of experimental designs. The development of appropriate models, from observations and the literature, should be developed before hypotheses can be tested with robust sampling designs. Robust sampling designs may only be possible if investigators have some role in the planning stage of deploying FADs. If the objective of the study is to determine the influence of FADs on assemblages of fishes, then experimenters need to consider that a 'FAD-effect' (=impact) cannot be demonstrated without controls. Some preliminary studies may be required to determine the spatial extent of a FAD-effect before suitable sites can be chosen for controls. Other controls may also be necessary, depending on the method used to estimate numbers of fishes (e.g. controls for disturbance). Recent advances in sampling designs that are applicable to impact studies are discussed. Beyond-BACI (Before After Control Impact) and MBACI (Multiple BACI) designs are recommended because they cater for temporal and spatial variation in the abundance of organisms, which is generally great for pelagic fishes. The utility of orthogonal sampling designs is emphasised as a means of elucidating the influence of multiple factors and, importantly, interactions between them. Further, nested analyses are suggested to deal with multiple temporal and/or spatial time scales in sampling designs. The independence of replicate FADs should also be considered. Problems of independence include: FADs that are connected, thus providing potential routes of movement of associated fishes; temporal dependence where the number of fish at a time influences the number at the next time due to fish becoming residents; and the fact that the proximity of other FADs may influence numbers of fishes. Solutions to these problems are suggested. The recommendations in this paper are relevant to investigations on pelagic fish of all sizes, with and without FADs.
In the Mediterranean Sea, common bottlenose dolphins (Tursiops truncatus) adversely interact with the fisheries, particularly when trammel nets are used. This results in an economic loss to fishermen and incidental catches of dolphins. The first stage to solve the conflict is the evaluation of its nature to describe in which way the presence of trammel nets can influence a bottlenose dolphin population.
This is the objective of the project initiated in October 1999 on the North-eastern coast of Sardinia (Italy). Observations were made by experienced researchers in presence and absence of trammel nets. For each group we recorded on an audio tape: date, start and end time, number of bottlenose dolphin adults and calves, water depth and description of behaviours (focal-group sampling method). Observations were made during daylight hours and during the night with night-vision binoculars. Opportunistic video recordings were also made to document and verify behavioural interaction.
A total of 496 sightings were carried out in over 1420 hours of research of dolphins during 478 days at sea. In presence of trammel nets: 218 sightings were recorded in 161 days at sea, in absence of trammel nets: 278 sightings were realized in 317 days of research. The presence of bottlenose dolphins in the study area has changed with the presence of trammels nets. School size doesn’t show any variations with the presence of fisheries. The possible competition between fisheries and bottlenose dolphins on the north-eastern coast of Sardinia may produce when target prey for cetaceans and fishermen overlap close to a FAD (Fish Attraction Device).
Purse-seining for tropical tuna is one of the most technologically advanced fisheries in the world. The purpose of this study was to apply local ecological knowledge (LEK) to assist in the planning of future in situ studies of fish behaviour around drifting fish aggregating devices (DFADs) by prioritizing research topics, thereby reducing the number of potential hypotheses to explore. Interviews of fishing masters of the purse-seine fleets working in the western Indian Ocean provided an alternate, independent, and previously unexplored source of behavioural information, specifically on the attraction, retention, and departure behaviours of tuna schools in relation to DFADs. Most fishing masters agreed that the maximum attraction distance of a DFAD is approximately 10 km and generally agreed to the following statements. Tuna form distinct schools under FADs, commonly segregated by species and size. The main reasons for the departure of tuna aggregations from FADs are changes in currents or FAD movements and location in relation to physical or oceanographic features. The number of actively monitored DFADs at sea in the western Indian Ocean was estimated at approximately 2100. Incorporating fishers into the planning and design stages of future research projects will facilitate collaborative and integrated approaches.
The damselfish Pomacentrus amboinensis (Pomacentridae) was examined on natural patch reefs of c8m2 in the lagoon of One Tree Reef, S Great Barrier Reef. Natural variation in recruitment success affects the importance of post-recruitment processes. In good recruitment years, adult densities on a substantial number of reefs may be limited by density-dependent processes, which may affect the majority of individuals in a region. Density-dependent juvenile growth may buffer adult populations on these reefs against the effects of poor recruitment years, since input may come from a number of immature age classes. Where recruitment success is always below a certain level, the dynamics of adult populations will reflect variation in recruitment success. -Author
Parasitology of cultivated salmonids from southern Chile is currently focussed on the agents causing diseases, whereas little attention has been placed on the vector potential of native fish stocks surrounding aquaculture areas. This study describes the variation of both population and community descriptors for metazoan parasite fauna in seven species of wild native fish and in the farmed Atlantic salmon (Salmo salar) obtained from aquaculture sites in southern Chile. Fish were collected by standard methods, identified, measured and gutted for stomach content determination. Each parasite species was rated for prevalence and abundance, and parasite community richness was determined at the infracommunity and component level. Nine species of ectoparasites and 21 species of endoparasites were found in native fish. Although the diet of S. salar overlapped with that, of some native fish, they only harboured two parasite species. Richness of the component parasite community was higher than in other parts of Chile, and was generally related to host body size and diversity of habitat use. Results suggested that salmon farming affects distribution, feeding habits and ingested food items of native species, and may explain the higher species richness of the component community of native fish inhabiting areas surrounding salmon farms when compared to those of north and central Chile where salmon is absent. Native fish species may infect farmed salmonids with two ectoparasites and one endoparasite. However, the natural patterns of migration of some native fish species may enhance the increase of this number, or may cause outbreaks of parasitic species currently under control.
Global production of farmed fish and shellfish has more than doubled in
the past 15 years. Many people believe that such growth relieves pressure
on ocean fisheries, but the opposite is true for some types of aquaculture.
Farming carnivorous species requires large inputs of wild fish for feed. Some
aquaculture systems also reduce wild fish supplies through habitat modification,
wild seedstock collection and other ecological impacts. On balance, global
aquaculture production still adds to world fish supplies; however, if the
growing aquaculture industry is to sustain its contribution to world fish
supplies, it must reduce wild fish inputs in feed and adopt more ecologically
sound management practices.
Small fish associated with drift algae, and in open water adjacent to algae, were sampled off the northeastern coast of New Zealand (1981 to 1984). Estimates of the abundance of drift algae and rates of colonisation of fish to drift algae were also obtained. A number of species of fish were more abundant around drift algae than in open water (e.g. representatives of Monacanthidae, Arripidae, Emmelichthyidae, Syngndthidae, Clinidae, Tripterygiidae). Although some fish associated with algae were preflexion forms, most were postflexion or juvenile forms. Relationships between weight of drift algae and numbers of fish varied among times. Some small fish were abundant in surface waters and showed no association with drift algae (e.g. representatives of Tripterygiidae, Clupeidae, Engraulididae, Pleuronectidae, Bothidae). Abundance of total drift algae at nearshore and offshore stations over a period of 2.5 yr was highly variable. Seasonal peaks in abundance of Sargassum sinclairii were found from November to January and appeared to relate to the demography of this species. Most clumps of drift algae were < 100 g. A detailed examination of the abundance of algae nearshore showed that the input of drift algae to reef environments is extremely variable among times and may relate to detachment of algae from reefs and conditions that facilitate onshore movements of drift from coastal waters. Fish were quickly attracted to algae left to drift in coastal waters for under 8 h. Colonisation relationships and developmental forms of fish attracted to algae varied among species. Drifting algae is periodically abundant in coastal waters and has an important influence on the distribution, and potentially the movements, of some presettlement fish.
During heavy storms in 1994–1995, salmon farms in southern Chile lost several million fish from the most commonly farmed species, rainbow trout (Oncorhynchus mykiss), coho salmon (Oncorhynchus kisutch), and Atlantic salmon (Salmo salar). To determine the abundance and distribution of such exotic salmon populations in the wild and their effect on native organisms, we conducted experimental fishing, in six locations in the salmon farming regions (41°–46° S) in the inner seas of Chiloé (X Region) and Aysen (XI Region), between November 1995 and December 1996. At the same time, we collected information from salmon farms and insurance companies about escaped individuals. During the experimental fishing we captured 2602 coho salmon, 984 trout, and 271 Atlantic salmon. Captures of the three species declined through the duration of the study; thus in November 1996 we captured <10% of initial catches. Population projections based on three possible mortality rates (0.4, 0.8, and 1.2) predicted the disappearance of salmon by year 2000, and the highest mortality rate was the best predictor of the observed available biomass in 1996. Thus, artisanal fishing may control escaped salmon. Of the three species, coho salmon had the best chances of becoming established in the remote XI Region where the artisanal fishing pressure was less intense.
Net deformations of sea-cages in two full-scale commercial Atlantic salmon (Salmo salar) farms (Varaldsøy, Norway, Hestur, Faroe Islands) were determined in relation to incoming currents of varying velocities. Ambient currents were measured with acoustic current meters, and net deformation behaviour and cage volume reductions were found by using depth sensors (pressure sensors) placed on strategic locations at the net cage. Cages deformed in current flow largely through lifting of the bottom netting and deformation of the front and back walls. Currents and therefore net volume reductions differed between the two farms: at Varaldsøy, the most critical current/deformation combination was 0.13 m s−1 and an estimated 20% cage volume reduction, while at Hestur, current speeds of 0.35 m s−1 caused a corresponding 40% cage volume reduction. Substantial net deformation and cage volume reductions may have significant implications for both fish production and welfare. Development of a real time net volume indicator could assist farmers in maintaining adequate cage volumes for optimal production and serve as an indicator of the optimal timing for net replacement if biofouling levels contribute significantly to deformation.
Thesis (M.S.)--University of North Carolina at Chapel Hill, 2005. Includes bibliographical references (leaves 43-47).