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.

1. The ecology and status of fin whales Balaenoptera physalus in the Mediterranean Sea is reviewed. The species’ presence, morphology, distribution, movements, population structure, ecology and behaviour in this semi‐enclosed marine region are summarized, and the review is complemented with original, previously unpublished data. 2. Although the total size of the fin whale population in the Mediterranean is unknown, an estimate for a portion of the western basin, where most of the whales are known to live, was approximately 3500 individuals. High whale densities, comparable to those found in rich oceanic habitats, were found in well‐defined areas of high productivity. Most whales concentrate in the Ligurian‐Corsican‐Provençal Basin, where their presence is particularly noticeable during summer; however, neither their movement patterns throughout the region nor their seasonal cycle are clear. 3. Based on genetic studies, fin whales from the Mediterranean Sea are distinct from North Atlantic conspecifics, and may constitute a resident population, separate from those of the North Atlantic, despite the species’ historical presence in the Strait of Gibraltar. Fin whales are known to calve in the Mediterranean, with births peaking in November but occurring at lower rates throughout the year. They feed primarily on krill Meganyctiphanes norvegica which they capture by diving to depths in excess of 470 m. It is suggested that the extensive vertical migratory behaviour of its main prey may have influenced the social ecology of this population. 4. Known causes of mortality and threats, including collisions with vessels, entanglement in fishing gear, deliberate killing, disturbance, pollution and disease, are listed and discussed in view of the implementation of appropriate conservation measures to ensure the species’ survival in the region.

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ABSTRACT1. The Pelagos Sanctuary is the largest marine protected area of the Mediterranean Sea (87 500 km 2 ), and is located in the north-west part of the basin. The presence of the bottlenose dolphin in this area is well documented but its distribution and abundance are not well known.2. The present study collected and analysed data from 10 different research groups operating in the Pelagos Sanctuary from 1994 to 2007. Photo-identification data were used to analyse the displacement behaviour of the dolphins and to estimate their abundance through mark-recapture modelling.3. Results show that the distribution of bottlenose dolphin is confined to the continental shelf within the 200 m isobath, with a preference for shallow waters of less than 100 m depth.4. Bottlenose dolphins seem to be more densely present in the eastern part of the sanctuary and along the north-west coast of Corsica.5. Bottlenose dolphins show a residential attitude with excursions usually within a distance of 80 km (50 km on average). A few dolphins exhibit more wide-ranging journeys, travelling up to 427 km between sub-areas.6. The displacement analysis identified two (sub)populations of bottlenose dolphins, one centred on the eastern part of the sanctuary and the other one around the west coast of Corsica.7. In 2006, the eastern (sub)population was estimated to comprise 510-552 individuals, while 368-429 individuals were estimated in the Corsican (sub)population. It was estimated that in total, 884 -1023 bottlenose dolphins were living in the Pelagos Sanctuary MPA in the same year.8. The designation of a number of Special Areas of Conservation (SACs) under the Habitats Directive is discussed as a possible tool to protect the bottlenose dolphin in the Pelagos Sanctuary and in the whole of the Mediterranean Sea.