The decline of short‐beaked common dolphin ( Delphinus delphis ) in the waters off the island of Ischia (Gulf of Naples, Italy) (original) (raw)
Related papers
Short-beaked common dolphins around the island of Ischia, Italy (southern Tyrrhenian Sea)
2002
The short-beaked common dolphin ( Delphinus delphis) -once one of the commonest cetacean species in the Mediterranean Sea -has faced a dramatic decrease in the last few decades. Between July-September 1997-2001, relatively large groups (mean group size = 65.48 SD=23.94, N=41, range 35-100) were consistently encountered off the island of Ischia, Italy. Observations, totalling 79 h 45 min, were carried out from a 18 m sailing vessel. Most of the survey effort was concentrated north of the island, within 11 km from the coast, during 256 daily surveys covering nearly 8,500 km. The animals were always sighted over the submarine canyon of Cuma, a highly productive marine area characterised by high pelagic biodiversity and multi-species associations. The area represents an important feeding site for other cetacean species, including Stenella coeruleoalba, Grampus griseus and Balaenoptera physalus. A total of 46 individuals could be opportunistically photo-identified based on natural marks on their dorsal fins. Of these, 19 individuals were re-sighted in different years, suggesting high levels of site fidelity. Breeding activities were often observed, and a high percentage of calves were always present in one or more of the group sub-units. Surface feeding was recorded frequently, and apparently focused on the skipper (Scomberesox saurus), a seasonal fish that is highly valued on local markets. Local fishermen claim that co-operative fishing may occur in the area, with fishermen taking advantage of fish aggregations that are actively schooled by short-beaked common dolphins near the surface. In the past, fish rewards were offered to the dolphins in reciprocation. Based on interviews conducted locally, the skipper fishery fleet has decreased by one order of magnitude due to declined fish stocks. The creation of a marine protected area has been proposed, which might provide research and conservation benefits in the future.
Journal of the Marine Biological Association of the United Kingdom, 2013
This paper represents the first quantitative assessment of the distribution and abundance of bottlenose dolphins (Tursiops truncatus) inhabiting the waters around Lampedusa Island, Italy. Eleven years of photo-identification data, collected from 1996 to 2006 by three different research groups, were brought together, reviewed and analysed to fulfil the following objectives: (i) to obtain baseline information on the abundance and residency of the local bottlenose dolphin putative population; (ii) to review the current Marine Protected Area (MPA) boundaries, especially those referred to waters around Lampedusa Island, with a view to establish a new Special Area of Conservation (SAC); and (iii) to explore the potential and limits of analysing heterogeneous datasets to improve future data collection methods. The most resident dolphins were regularly observed in six specific areas around Lampedusa Island. From a total of 148 photo-identified bottlenose dolphins, 102 were classified as wellmarked. The capture histories and the distribution of sightings clearly show a number of dolphins regularly use the study area. Best estimates for the first period within the 'core study area' were obtained for 1998 data. The 2005 estimate was significantly larger than the 1998 estimates (z ¼ 2.160; P , 0.05) compared to that of 1998. Implications of our results for the current MPA, for transboundary conservation initiative involving Italy, Malta and Tunisia and for directing future research within and outside the MPA are fully discussed.
The Mediterranean sub-population of short-beaked common dolphin is believed to have suffered a steep decline in the Mediterranean in recent years, and in 2003 it was listed as endangered in the IUCN Red List of Threatened Species. Effective conservation will depend critically on our understanding of the relationship between the species and its habitats. The Alborán Sea is believed to be the most important remaining Mediterranean habitat for this species, and thus constitutes a vital source of information for the development of conservation measures. We used spatial modelling to estimate the abundance and explore the habitat use of common dolphins in this area, examining regional, seasonal and interannual variations, as well as the influence of biological factors such as presence of calves, interspecific relationships and behaviour. From 1992 to 2004, 37 385 km of non-systematic line transects generated 738 sightings in a 19 189 km 2 study area. The point estimate of abundance was 19 428 (95% CI = 15 277 to 22 804) dolphins. Seasonal and geographical variations in abundance were detected, with higher average density in summer than in winter, and in the Western Alborán Sea than in the east Gulf of Vera, which has different physical/environmental characteristics. No overall trend in abundance was observed in the Alborán area. However, a decline was observed in the Gulf of Vera, with a summer density 3-fold lower in the period from 1996 to 2004 than in 1992 to 1995. A potential link of this decline with prey depletion due to the exponential growth of aquaculture in the area is discussed. Clear differences in habitat use were also found when examining the influence of biological factors. In particular, groups with calves and groups that were feeding preferred more coastal waters. This result could have important implications for the development of conservation measures for this species in the Mediterranean.
An understanding of the population dynamics and social organization of cetaceans is essential to manage the influence of anthropogenic activities. In this study, the population size, site fidelity and social interactions of bottlenose dolphins in the Strait of Sicily (Italy) were investigated to provide recommendations for their conservation. Mark-recapture analysis was based on the encounter histories of 103 marked dolphins from 2004 to 2015. The POPAN formulation of the Jolly–Seber model in MARK software was used to estimate the size of the super-population. Site fidelity and social organization were estimated for individuals re-sighted C3 times. The estimated population size was 140 (SE = 15.75; 95% CI = 106–164). Dolphins had low site fidelity, and both adults and sub-adults move outside the study area. Females with calves used the area longer than other individuals. Based on our results, dolphins' home range likely extended beyond the study area. The mean value of the Half-Weight Association Index was low and the preferred association was by casual acquaintance. However, we found a distinct aggregation of post-parturition females during the final 2 years of the study. Therefore, the pattern of association was apparently a response to an ecological requirement, which was the possibility to breed in high productivity waters. Whether these individuals are part of a larger pelagic population is unknown; however, we can conclude that the management of only coastal waters is insufficient for the conservation of dolphins in the Strait of Sicily.
Mammal Review, 2003
1. The recent decline in the Mediterranean population of short-beaked common dolphins Delphinus delphis has been the subject of scientific controversy and political indifference. Research on these animals has been very limited and there has been no large-scale, systematic effort to assess and monitor their abundance and distribution. The consequent lack of data has prevented a good understanding of historical and ongoing trends. 2. Nonetheless, literature and osteological collections confirm that common dolphins were widespread and abundant in much of the Mediterranean Sea until the late 1960s and that their decline occurred relatively quickly. Today, common dolphins remain relatively abundant only in the westernmost portion of the basin (Alboràn Sea), with sparse records off Algeria and Tunisia, concentrations around the Maltese islands and in parts of the Aegean Sea, and relict groups in the south-eastern Tyrrhenian and eastern Ionian Seas. Otherwise, these dolphins are rare in, or completely absent from, Mediterranean areas where information is available. 3. Circumstantial evidence and qualitative judgements by the authors suggest that the following factors may have contributed to the decline of common dolphins: reduced availability of prey caused by overfishing and habitat degradation; contamination by xenobiotic chemicals resulting in immunosuppression and reproductive impairment; environmental changes such as increased water temperatures affecting ecosystem dynamics; and incidental mortality in fishing gear, especially gillnets. The cumulative importance of these factors is poorly understood, and as a result, few conservation measures have been implemented. 4. This paper reviews current knowledge and suggests priorities for action aimed at identifying and mitigating the main threats to common dolphins in the Mediterranean, with the ultimate goal of restoring the species' favourable conservation status in the region.
Aquatic Conservation-marine and Freshwater Ecosystems, 2004
1.Nine cetacean species have been reliably reported to occur in the shallow northern Adriatic Sea since the 17th century. However, only two species were considered regular there until the 1970s: the short-beaked common dolphin (Delphinus delphis) and the common bottlenose dolphin (Tursiops truncatus).2.Short-beaked common dolphins have progressively disappeared from the northern Adriatic and are now rare in the region. The systematic culling campaigns and other takes that occurred between the second half of the 18th century and the 1960s, and habitat degradation in subsequent years are the most likely causes of their decline.3.Today, common bottlenose dolphins are the only regular component of the northern Adriatic cetacean fauna; however, they now occur at low densities, and their fragmented groups are facing significant anthropogenic threats.4.The future of northern Adriatic dolphins will depend on precautionary action to prevent further decline and on intensified research effort aimed at identifying the most effective mitigation strategies. Copyright © 2004 John Wiley & Sons, Ltd.Nine cetacean species have been reliably reported to occur in the shallow northern Adriatic Sea since the 17th century. However, only two species were considered regular there until the 1970s: the short-beaked common dolphin (Delphinus delphis) and the common bottlenose dolphin (Tursiops truncatus).Short-beaked common dolphins have progressively disappeared from the northern Adriatic and are now rare in the region. The systematic culling campaigns and other takes that occurred between the second half of the 18th century and the 1960s, and habitat degradation in subsequent years are the most likely causes of their decline.Today, common bottlenose dolphins are the only regular component of the northern Adriatic cetacean fauna; however, they now occur at low densities, and their fragmented groups are facing significant anthropogenic threats.The future of northern Adriatic dolphins will depend on precautionary action to prevent further decline and on intensified research effort aimed at identifying the most effective mitigation strategies.
INTRODUCTION Since 1996, a population study has been conducted in Lampedusa Island (Mediterranean Sea, Italy), whose objectives were: a) assess the eventual degree of recidency of bottlenose dolphins (Tursiops truncatus) in the island; b) estimate the population size; c) study habitat use and d) examine the dolphins' behaviour. METHODS Land and boat-based surveys, and photo-identification technique were used to derive the population estimate and to examine distribution and movements of individuals over a three-months summer period (July-September each year, from 1996 to 2000). Land-based observations lasting three hours were made from the two island's higher places (Albero Sole, NW and Capo Grecale, NE) at fixed times, both during the morning (07:00-10:00) and during the afternoon (17:00-20:00). Dolphins number, position, estimate behaviour and direction of movement were recorded onto data sheets. Using a 4,5 inflatable powered outboard, boat-based surveys were made, trying ...
Conservation management of common dolphins: Lessons learned from the North‐East Atlantic
Aquatic Conservation: Marine and Freshwater Ecosystems, 2019
1. The short-beaked common dolphin is one of the most numerous cetacean species in the NorthEast Atlantic and plays a key functional role within the ecosystem as a top predator. However, in 2013, its conservation status for the European Marine Atlantic, under Article 17 of the Habitats Directive, was assessed as 'Unfavourable-Inadequate'. Of key concern for this species is fishery bycatch, with pollution also being an issue. There are, however, major knowledge gaps concerning the extent of the effects of such pressures on the species. 2. Implementation of national observer bycatch programmes and bycatch mitigation measures under EC Regulation 812/2004 has been important. The responsibility for this is currently being transferred to the EU fisheries Data Collection Framework and Technical Measures Framework, the potential advantages and disadvantages of which are discussed. Collection of data and samples through national stranding schemes in some countries has enabled assessments of life-history parameters, dietary requirements, and the effects of stressors such as pollutants. 3. Nevertheless, in order to improve the conservation status of the NorthEast Atlantic population, a number of key actions are still required. These include the implementation of a species action plan, finalization of a management framework procedure for bycatch, and coordination between member states of monitoring programmes. It is important that there is monitoring of the state of the common dolphin population in the NorthEast Atlantic management unit through regular surveys spanning the range of the management unit, as well as continued assessment of the independent and interactive effects of multiple stressors. Above all, conservation status would be improved through application and enforcement of existing legislation in European waters. 4. This paper provides a summary of the current state of our knowledge of common dolphins in the NorthEast Atlantic along with recommendations for conservation management that may also be relevant to the species in the Mediterranean Sea.
Aquatic Conservation-marine and Freshwater Ecosystems, 2017
1. Abundance, density, daily variation in group size, activity and habitat use of the striped dolphin in the Gulf of Taranto (northern Ionian Sea, central Mediterranean Sea) were investigated using data from sightings collected between April 2009 and December 2016 during standardized vessel-based surveys. Density and abundance were estimated in the survey area by means of conventional distance sampling, resulting in 0.97 specimens/km 2 (CV = 5.77%; 95% CI = 0.86-1.08 specimens/km 2) and 615 specimens (CV = 5.77%; 95% CI = 549-689 specimens), respectively. 2. Group size data were analysed using multivariate methods. The changes in group size, depth and percentage occurrence of activity between daily periods were investigated with nonparametric tests. The spatio-temporal distribution of the striped dolphin in each predominant activity was investigated by means of the ordinary Kriging method. 3. Fifteen year-maps of spatial prediction were produced, allowing the identification of persistent areas. The results delineate a critical habitat of about 150 km 2 in the northernmost 'Taranto Valley' canyon system ranging between 140 and 910 m in depth. This critical habitat was persistently and regularly used by an important estimated population of striped dolphins for their day-today survival and maintenance in a healthy condition. 4. The intense human use occurring in the area highlights the need for local, national and EU management to set a comprehensive strategy. 5. The establishment of a SPAMI (Specially Protected Area of Mediterranean Importance) as an effective tool for the conservation of the species is suggested. The consequence of establishing a closed area could be reasonably accepted by local concurrent stakeholders. Indeed, limiting access through the establishment of this small closed area would result in the protection of a habitat acting as an ecological refuge for many other pelagic and demersal species of commercial interest, thus favouring their spill over.
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.