Once one of the most common cetaceans in the Mediterranean Sea, the short-beaked common dolphin has declined throughout the region since the 1960s and in 2003 this population was classified as Endangered in the International Union for Conservation of Nature (IUCN) Red List. Here, we document the species' precipitous decline in eastern Ionian Sea coastal waters across 13 yr. While 150 animals were present in the study area (1050 km 2) in 1996, only 15 were observed in 2007. A 12 mo assessment of fishing effort and catch, together with circumstantial evidence, suggests that the decline was caused largely by prey depletion resulting from overfishing. We analyzed the impacts of various fishing gear and estimated the degree of resource overlap between common dolphins and local fisheries. The total biomass removed annually by 308 fishing boats in the study area averaged 3571 t, while that consumed by common dolphins was 17 t. Resource overlap between common dolphins and fisheries-expressed as an average Pianka index of 0.5-differed according to fishing gear, being higher for purse seiners (0.7) and beach seiners (0.4) and lower for bottom trawlers (0.1), trammel boats (0.2) and longliners (0.0). Only about 10 active purse seiners (4% of the total active fishing fleet) were responsible for 33% of the biomass removal, and likely had the greatest impact on prey of common dolphins. This study indicates a high risk of local disappearance of common dolphins in the very near future, unless fishery management measures are implemented immediately. Purse seining should be the main management target.
Line-transect estimators were developed to assess abundance of coastal dolphins Tursiops truncatus and Stenella coeruleoalba encountered in low densities during aerial sighting surveys. The analysis improved on conventional approaches by objectively combining data from different species, survey areas and other covariates affecting dolphin detectability. Model selection and multimodel inference allowed robust estimates of precision in accounting for covariate selection uncertainty. These methods were used to estimate bottlenose dolphin abundance in NE Mediterranean waters that included a putative subpopulation in the Balearic Islands. . The results do not support an exclusively coastal Balearic Island subpopulation, but they strongly indicate that the islands contain critical habitats required for the conservation of the species. Given the observed decline of the species during the last few decades, conservation-oriented management should focus on reducing or eliminating adverse fishing interactions while key areas are protected from encroachment produced by human development.
ABSTRACT1. Dolphins are often claimed to compete with fisheries, including through removal of substantial biomass. To calculate the biomass removed by fisheries and the degree of resource overlap with dolphins in a coastal area of Greece, estimates of dolphin abundance based on photographic capture-recapture were combined with an assessment of fishing effort and catch.2. The estimated total biomass consumed annually by local dolphin populations -15 short-beaked common dolphins and 42 common bottlenose dolphins -was 15.5 and 89.8 tonnes, respectively. The total biomass removed by the local fishing fleet (307 fishing boats) was 3469.2 tonnes, i.e. about 33 times greater than that removed by dolphins.3. Dolphins removed 2.9% of the total biomass, fisheries 97.1%. Nine purse seiners (representing only 3% of the active fishing fleet) were responsible for 31.9% of biomass removal. Similarity of biomass composition between dolphins and fisheries was expressed by a Pianka index of 0.46 for common dolphins and 0.66 for bottlenose dolphins.4. Overlap differed according to fishing gear. Common dolphin overlap was higher with purse seiners (0.82), and lower with beach seiners (0.31), bottom trawlers (0.11) and trammel boats (0.06). There was virtually no overlap with longliners (0.02). Bottlenose dolphin overlap was higher with trammel boats (0.89) and bottom trawlers (0.75), and lower with longliners (0.38), purse seiners (0.24) and beach seiners (0.18). There was minimal overlap (0.12) between the two dolphin species.5. This study suggests that ecological interactions between dolphins and fisheries in this coastal area have minor effects on fisheries. Conversely, prey depletion resulting from overfishing can negatively affect dolphins. Fisheries management measures consistent with national and EU legislation are proposed to ensure sustainability and to protect marine biodiversity.
Despite their geographic proximity, the Gulf of Ambracia and the Inner Ionian Sea Archipelago are remarkably different in terms of environmental features, human activities, and dolphin species composition and densities. Interviews of small‐scale professional fishermen (n = 100) showed that younger generations do not see any future in fisheries and that the traditionally‐oriented fishing community is rapidly changing. Fish captures have reportedly decreased dramatically during the last 20 years. The main factors having an adverse impact on the sustainability of small‐scale fisheries differed significantly between areas. Net damage as a consequence of dolphin predation was almost unanimously reported. Hence, fishermen seemed genuinely interested in collaborating in future research initiatives to evaluate the damage caused by dolphins and to explore potential mitigation strategies. Dolphins were not the only animals held responsible for net damage, nor those reportedly causing the largest economic loss to small‐scale fisheries, which was attributed to either sea turtles or the critically endangered monk seal, depending on the area. The fishermen of the Gulf of Ambracia advocated the introduction of measures to curtail habitat degradation as the top priority, while their colleagues of the Inner Ionian Sea Archipelago identified fisheries management measures and effective law enforcement as the most urgently needed actions. Given the high dependency of local communities on fisheries, ensuring their sustainability is crucial to providing local fishers with sufficient income. The top management measures identified by local small‐scale fishermen perfectly match the priorities set out within the Natura 2000 network, achievable through an ecosystem‐based approach. Failure to take action in a timely manner may lead to irreversible environmental damage coupled with the need for harsher regulatory measures. Copyright © 2014 John Wiley & Sons, Ltd.
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