Bottlenose dolphin (Tursiops truncatus) presence and incidental capture in a marine fish farm on the north-eastern coast of Sardinia (Italy (original) (raw)
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THE IMPACT OF A FISH FARM ON A BOTTLENOSE DOLPHIN POPULATION IN THE MEDITERRANEAN SEA
The increasing presence of aquaculture in coastal waters calls for a better understanding of its environmental effects. Despite a number of studies focusing on the impact of aquaculture on marine mammals, the interaction between common bottlenose dolphins (Tursiops truncatus) with fish farms has been the subject of few investigations (Watson-Capps and Mann, 2005). In this paper we report the results of our research on the interaction between bottlenose dolphins with a fish farm on the Sardinian coast (Italy) from 1991 to 2004. We divided the study area latitudinally into two sections: southern (Gulf of Olbia) and northern (Gulf of Congianus). In the southern section in November 1995 the plant of a small fish farm was completely increased and transformed. Data were pooled into two periods (1991 to 1994 and 1999 to 2004). All years but 2003 were sampled. During the first and second research periods the same land-based searches were conducted under fair to excellent weather conditions. A total of 255 sightings were carried out in over 1320 hours of research of dolphins: in the first period 52 sightings were recorded in 517 hours of research, in the second period 203 sightings were realized in 803 hours of research. The presence of bottlenose dolphins changed dramatically between the two research periods. Observations of dolphins indicate that are mainly present in the southern area during the second period. The preference for the southern section seemed to be consistent after the transformation of the fish farm, since 1995.
ICES Journal of …, 2009
There is increasing evidence from previous studies, and from fishers' observations, that coastal dolphins use fishing nets as an easily accessible feeding source, damaging or depredating fish caught in the nets. This study investigates the impact of dolphin depredation on artisanal trammelnets by analysing the catch composition of 614 artisanal fishing operations in the Bonifacio Strait Natural Reserve (France). Common bottlenose dolphins (Tursiops truncatus) attacked, on average, 12.4% of the nets and damaged 8.3% of the catch. However, attacked nets were characterized by statistically significantly higher catch per unit effort than unattacked ones. Catch composition also differed significantly after dolphin attacks; bentho-pelagic fish were more represented and reef-associated fish less represented. Our results suggest that (i) dolphins are attracted by high fish densities in the fishing area and/or nets, and (ii) their attacks induce specific fish-avoidance behaviour, according to the fish position in the water column. Although dolphins depredate a small part of the catch, damage to nets, not yet assessed in this area, could weaken the benefits that reserves can provide to artisanal fisheries.
In 1999, the Italian Central Institute for Applied Marine Research (ICRAM), in response to reports made by local fisheries, began a study into the interactions between common bottlenose dolphins (Tursiops truncatus) and the artisanal fishery in the Asinara Island National Park (Sardinia). Using onboard observers, fishing boat surveys were carried out to determine the frequency of interactions, variations in the catch of target species and damage to two different types of trammel net caused by dolphins. Interactions occurred primarily with trammel nets targetting striped red mullet (Mullus surmuletus; the less valuable peacock wrasse, Simphodus tinca, was also caught). Interactions also occurred with trammel nets set for lobster (Palinurus elephas), cuttlefish (Sepia spp.) and scorpionfish (Scorpaena spp.), but these were considered negligible. The target species, catch and damage inflicted on the catch was recorded, both in the presence and absence of dolphins, in an effort to ascertain associated damage and economic cost. Loss of catch was found to be significant only in the case of nets deployed during the red striped mullet fishing season. Although the level of interaction was high relative to the narrow red striped mullet fishery season, the overall economic impact on the fishing community was found to be modest. The presence and regulations of the national park area may provide an opportunity for investigating mitigation activities compatible with both cetacean conservation and the maintenance of the traditional fisheries.
Ethics in Science and Environmental Politics, 2018
Anecdotal information provided by local fishers is an invaluable tool in the study of marine mammal−fisheries interactions. This paper summarizes empirical and anecdotal information voluntarily provided by fishers during a survey monitoring the damage to coastal fisheries caused by dolphins. We visited 23 fishing harbours along the northern Aegean Sea coastline and monitored the fishing gear of 113 coastal fishers in order to identify the damage caused by dolphins. While we were monitoring the damage, the fishers voluntarily shared their general views on marine mammals and fisheries interactions, which were recorded and are presented here. The majority of fishers indicated that fishing gear, mesh size, depth and target species were important factors that determine depredation frequency and gear damage, whereas soaking time, time of day and season were not considered crucial. These findings provide useful insight in the study of dolphin−fishery interactions, especially for data-poor areas such as the northeastern Mediterranean Sea. The empirical knowledge of the fishers and their views is also important from an ethical perspective because, historically, dolphins in the Mediterranean had been culled and hunted for bounties for many years; even today, occasional deliberate dolphin killings are still recorded. Such information is required in the design of any management strategy that aims to minimize the conflicts with dolphins, thus preserving the fishers' livelihood.
Bottlenose dolphin distribution in a Mediterranean area exposed to intensive trawling
Marine Environmental Research
The Adriatic Sea is one of the areas most exposed to trawling, worldwide. We used four years (2018-2021) and 19,887 km of survey data to investigate factors influencing daylight dolphin distribution in its northwestern sector, where common bottlenose dolphins Tursiops truncatus routinely follow fishing trawlers. We validated Automatic Identification System information on the position, type and activity of three types of trawlers based on observations from boats, and incorporated this information in a GAM-GEE modelling framework, together with physiographic, biological and anthropogenic variables. Along with bottom depth, trawlers (particularly otter and midwater trawlers) appeared to be important drivers of dolphin distribution, with dolphins foraging and scavenging behind trawlers during 39.3% of total observation time in trawling days. The spatial dimension of dolphin adaptations to intensive trawling, including distribution shifts between days with and without trawling, sheds light on the magnitude of ecological change driven by the trawl fishery.
2003
Interactions between various cetacean species and fisheries in the Mediterranean Sea are reported in some geographic areas, although most data are sparse and difficult to evaluate. Since 1996, a population study on bottlenose dolphin (Tursiops truncatus) has been conducted in Lampedusa Island (Italy). One of the primary focus of the research trips in the 1997-1999 period was to monitor the interactions between a) dolphins and trawls, and b) dolphins and aquaculture facilities, in order to assess degree and nature of these relationships and eventual threats for the animals.
Ecology and conservation of common bottlenose dolphins Tursiops truncatus in the Mediterranean Sea
Mammal Review, 2009
1Bottlenose dolphins Tursiops truncatus are amongst the best-known cetaceans. In the Mediterranean Sea, however, modern field studies of cetaceans did not start until the late 1980s. Bottlenose dolphins have been studied only in relatively small portions of the basin, and wide areas remain largely unexplored.2This paper reviews the ecology, behaviour, interactions with fisheries and conservation status of Mediterranean bottlenose dolphins, and identifies threats likely to have affected them in historical and recent times.3Whilst intentional killing was probably the most important cause of mortality until the 1960s, important ongoing threats include incidental mortality in fishing gear and the reduced availability of key prey caused by overfishing and environmental degradation throughout the region. Additional potential or likely threats include the toxic effects of xenobiotic chemicals, epizootic outbreaks, direct disturbance from boating and shipping, noise, and the consequences of climate change.4The flexible social organization and opportunistic diet and behaviour of bottlenose dolphins may allow them to withstand at least some of the effects of overfishing and habitat degradation. However, dolphin abundance is thought to have declined considerably in the region and management measures are needed to prevent further decline.5Management strategies that could benefit bottlenose dolphins, such as sustainable fishing, curbing marine pollution and protecting biodiversity, are already embedded in legislation and treaties. Compliance with those existing commitments and obligations should be given high priority.Bottlenose dolphins Tursiops truncatus are amongst the best-known cetaceans. In the Mediterranean Sea, however, modern field studies of cetaceans did not start until the late 1980s. Bottlenose dolphins have been studied only in relatively small portions of the basin, and wide areas remain largely unexplored.This paper reviews the ecology, behaviour, interactions with fisheries and conservation status of Mediterranean bottlenose dolphins, and identifies threats likely to have affected them in historical and recent times.Whilst intentional killing was probably the most important cause of mortality until the 1960s, important ongoing threats include incidental mortality in fishing gear and the reduced availability of key prey caused by overfishing and environmental degradation throughout the region. Additional potential or likely threats include the toxic effects of xenobiotic chemicals, epizootic outbreaks, direct disturbance from boating and shipping, noise, and the consequences of climate change.The flexible social organization and opportunistic diet and behaviour of bottlenose dolphins may allow them to withstand at least some of the effects of overfishing and habitat degradation. However, dolphin abundance is thought to have declined considerably in the region and management measures are needed to prevent further decline.Management strategies that could benefit bottlenose dolphins, such as sustainable fishing, curbing marine pollution and protecting biodiversity, are already embedded in legislation and treaties. Compliance with those existing commitments and obligations should be given high priority.
Consumption rates and interaction with fisheries of Mediterranean common dolphins in the Alboran Sea
Regional Studies in Marine Science
Common dolphins (Delphinus delphis) are top predators, feeding on a wide variety of prey species, several of which are also targeted by fisheries. The last remaining healthy group of the endangered Mediterranean common dolphin subpopulation is located in the Alboran Sea. Their feeding grounds overlap with the fishing grounds of trawlers targeting European hake (Merluccius merluccius) and blue whiting (Micromessistius poutassou) as well as purse seiners targeting small pelagic species such as European sardine (Sardina pilchardus), European anchovy (Engraulis encrasicolus), horse mackerel (Trachurus spp.) and mackerel (Scomber spp.). In the present study, we estimated that individual common dolphins in the Alboran Sea have a food consumption of 3.35 ± 0.67 kg/day, based on scaling equations applied to stranded animals. This figure is similar to the ones reported for other European populations. Although common dolphins mainly feed on mesopelagic species of none or little commercial interest, they also feed on commercial species, which could lead to a potential conflict with fisheries in the area. We estimated common dolphins in the Alboran Sea could consume more than 16,000 tonnes of fish annually, including ca 7,365 (95% CI: 3,838-11,639) tonnes of Madeira lanternfish (Ceratoscopelus maderensis), 2,888 (1,123-5,223) tonnes of bogue (Boops boops), 2,770 (879-5,270) tonnes of European sardine, 1,850 (170-4,116) tonnes of gobies (Gobiidae), and 1,497 (65-3,352) tonnes of European hake (reference period 2006-2011). Estimated sardine, anchovy and blue whiting consumption was low when compared to the landings in the area, however estimated hake consumption was above the reported hake landings in recent years (393.4 ± 146 tonnes landed annually between 2006-2011). Additionally, direct interactions between common dolphins and main fisheries were evaluated in a total of 111 observed fishing trips (70 in trawlers and 41 in purse seiners) in the area. Although no bycatch of common dolphin was recorded, non-lethal interactions between dolphins and the fishing activity were detected from observations of this on-board observer program. These interactions, together with the high prevalence of stranding with signs of fishing interactions from the study area, may imply an additional threat to this endangered cetacean subpopulation.