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.
ABSTRACT1. As part of a project to identify marine protected areas (MPAs) in Spanish Mediterranean waters, habitat preference models were developed using 11 years of survey data to provide predictions of relative density for cetacean species occurring off southern Spain.2. Models for bottlenose, striped and common dolphin described, firstly, probability of occurrence (using GLMs) and, secondly, group size (using linear models) as predicted by habitat type defined by a range of physical and oceanographic covariates. Models for Risso's dolphin, long-finned pilot, sperm and beaked whales used only the first stage because of data limitations.3. Model results were used to define the boundaries of three proposed Special Areas of Conservation (SAC) (under the EU Habitats Directive) and one proposed Specially Protected Area of Mediterranean Importance (SPAMI) (under the Barcelona Convention).4. The study illustrates the value of habitat preference modelling as a tool to help identify potential MPAs. The analyses incorporate environmental data in a spatial prediction that is an improvement over simpler descriptions of animal occurrence. Contiguous areas covering a specified proportion of relative abundance can readily be defined. Areas with apparently good habitat but few observations can be identified for future research or monitoring programmes.5. Models can be refitted as new observations and additional environmental data become available, allowing changes in habitat preference to be investigated and monitoring how well MPAs are likely to be affording protection.6. The study represents an important contribution to the implementation of the Habitats Directive by the Spanish government by providing a robust scientific basis for the definition of SAC and providing results to inform conservation objectives and management plans for these areas. The results identified areas that are important for a number of cetacean species, thus illustrating the potential for MPAs to improve cetacean conservation generally in the Alboran Sea, a
The mechanisms that determine population structure in highly mobile marine species are poorly understood, but useful towards understanding the evolution of diversity, and essential for effective conservation and management. In this study, we compare putative sperm whale populations located in the Gulf of Mexico, western North Atlantic, Mediterranean Sea and North Sea using mtDNA control region sequence data and 16 polymorphic microsatellite loci. The Gulf of Mexico, western North Atlantic and North Sea populations each possessed similar low levels of haplotype and nucleotide diversity at the mtDNA locus, while the Mediterranean Sea population showed no detectable mtDNA diversity. Mitochondrial DNA results showed significant differentiation between all populations, while microsatellites showed significant differentiation only for comparisons with the Mediterranean Sea, and at a much lower level than seen for mtDNA. Samples from either side of the North Atlantic in coastal waters showed no differentiation for mtDNA, while North Atlantic samples from just outside the Gulf of Mexico (the western North Atlantic sample) were highly differentiated from samples within the Gulf at this locus. Our analyses indicate a previously unknown fidelity of females to coastal basins either side of the North Atlantic, and suggest the movement of males among these populations for breeding.
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.
The resolution of taxonomic classifications for delphinid cetaceans has been problematic, especially for species in the genera Delphinus, Tursiops and Stenella. The frequent lack of correspondence between morphological and genetic differentiation in these species raises questions about the mechanisms responsible for their evolution. In this study we focus on the genus Delphinus, and use molecular markers to address questions about speciation and the evolution of population structure. Delphinus species have a worldwide distribution and show a high degree of morphological variation. Two distinct morphotypes, long‐beaked and short‐beaked, have been considered different species named D. capensis and D. delphis, respectively. However, genetic differentiation between these two forms has only been demonstrated in the Pacific. We analysed samples from eight different geographical regions, including two morphologically defined long‐beaked form populations, and compared these with the eastern North Pacific populations. We found high differentiation among the populations described as long‐beaked instead of the expected monophyly, suggesting that these populations may have evolved from independent events converging on the same morphotype. We observed low genetic differentiation among the short‐beaked populations across a large geographical scale. We interpret these phylogeographical patterns in the context of life history and population structure in related species.
The design of ecological networks of marine protected areas (MPAs) is generally based on the identification of areas of high abundance for species of conservation concern or focal biodiversity targets. We discuss the applicability of this approach to marine top predators and contend that the design of comprehensive and effective MPA networks requires the following 7 principles: (1) the use of wildlife-habitat modelling and spatial mapping approaches to develop testable model predictions of species distribution and abundance; (2) the incorporation of life-history and behavioural data into the development of these predictive habitat models; (3) the explicit assessment of threats in the design and monitoring process for single-or multi-species MPAs; (4) the serious consideration of dynamic MPA designs to encompass species which use well-defined but spatially dynamic ocean features; (5) the integration of demographic assessment in MPA planning, allowing provision of advice to policy makers, ranging from no to full protection; (6) the clear articulation of management and monitoring plans allowing retrospective evaluation of MPA effectiveness; and (7) the adoption of an adaptive management approach, essential in the light of ongoing and anticipated ecosystem changes and species range shifts in response to climate change.
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