Bottlenose dolphins (Tursiops truncatus) are widely distributed and a high degree of morphometric and genetic differentiation has been found among both allopatric and parapatric populations. We analysed 145 samples along a contiguous distributional range from the Black Sea to the eastern North Atlantic for mitochondrial and nuclear genetic diversity, and found population structure with boundaries that coincided with transitions between habitat regions. These regions can be characterized by ocean floor topography, and oceanographic features such as surface salinity, productivity and temperature. At the extremes of this range there was evidence for the directional emigration of females. Bi-parentally inherited markers did not show this directional bias in migration, suggesting a different dispersal strategy for males and females at range margins. However, comparative assessment based on mitochondrial DNA and nuclear markers indicated that neither sex showed a strong bias for greater dispersal on average. These data imply a mechanism for the evolutionary structuring of populations based on local habitat dependence for both males and females.

We describe the diet of bottlenose dolphins Tursiops truncatus in Galician waters, north-western Spain, based on 82 non-empty stomachs recovered and analysed from stranded animals between 1990 and 2005, quantifying interannual and seasonal variation in the diet, as well as dietary variation related to sex and size. The most important prey species (in terms of numerical importance and biomass) were blue whiting (Micromesistius poutassou) and hake (Merluccius merluccius), both of high commercial importance in Galician waters. Most blue whiting eaten by dolphins were mature fish but the estimated total consumption was relatively low (around 10%) compared to Spanish fishery landings of this species. In contrast, most hake eaten by dolphins were probably immature but the estimated total consumption is more than 20% of current annual fishery landings. The diet of by-caught animals, which made up around one third of the sample, was very similar to that in the overall sample. Although bottlenose dolphins are often seen close inshore, evidence from the diet suggests that they feed at the shelf edge. Evidence was found of ontogenetic dietary shifts and differences between diets of male and female dolphins. There were also clear changes in average diet over the 16-year study period, although there was no evidence that they were in response to changes in fish abundance. The amount of hake in the diet remained stable against a background of falling local abundance while the amount of blue whiting declined despite an increase in spawning stock size.