Background: Understanding the role of seascape in shaping genetic and demographic population structure is highly challenging for marine pelagic species such as cetaceans for which there is generally little evidence of what could effectively restrict their dispersal. In the present work, we applied a combination of recent individual-based landscape genetic approaches to investigate the population genetic structure of a highly mobile extensive range cetacean, the harbour porpoise in the eastern North Atlantic, with regards to oceanographic characteristics that could constrain its dispersal.

We present the findings of a 2-yr study of habitat use by bottlenose dolphins in the outer Shannon estuary on the west coast of Ireland. Data were collected during repeated, standardised, boat-based surveys of dolphins in a predefined 150 km 2 area of the outer estuary. Areas found to exceed a uniform-use pattern were termed 'critical areas' and delimited using the 50% contour derived from harmonic mean transformation of sighting locations. Dolphins exhibited preferential use of areas of the estuary with the greatest benthic slope and depth, highlighting the influence of environmental heterogeneity on habitat use by this species. Additionally, photo-identification was used to catalogue sightings of uniquely marked dolphins which provided distribution data at an individual level. Although the ranges of frequently sighted dolphins overlapped, a degree of partitioning was found in the use of up-river parts of the study area. The methods presented here could be applied at a range of spatial scales and we suggest that the identification of critical areas within a population's range is a priority when planning any conservation management strategy for marine mammals. KEY WORDS: Bottlenose dolphins · Habitat use · Critical areas · ConservationResale or republication not permitted without written consent of the publisher

Population genetic structure of North Atlantic killer whale samples was resolved from differences in allele frequencies of 17 microsatellite loci, mtDNA control region haplotype frequencies and for a subset of samples, using complete mitogenome sequences. Three significantly differentiated populations were identified. Differentiation based on microsatellite allele frequencies was greater between the two allopatric populations than between the two pairs of partially sympatric populations. Spatial clustering of individuals within each of these populations overlaps with the distribution of particular prey resources: herring, mackerel and tuna, which each population has been seen predating. Phylogenetic analyses using complete mitogenomes suggested two populations could have resulted from single founding events and subsequent matrilineal expansion. The third population, which was sampled at lower latitudes and lower density, consisted of maternal lineages from three highly divergent clades. Pairwise population differentiation was greater for estimates based on mtDNA control region haplotype frequencies than for estimates based on microsatellite allele frequencies, and there were no mitogenome haplotypes shared among populations. This suggests low or no female migration and that gene flow was primarily male mediated when populations spatially and temporally overlap. These results demonstrate that genetic differentiation can arise through resource specialization in the absence of physical barriers to gene flow.

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Short-beaked common dolphins Delphinus delphis in the eastern North Atlantic (ENA) are subject to mortality due to entanglement in various types of fishing gear. However, for this region, there is no population-level information available on trends in abundance, (incidental) mortality rates or even the actual distributional range. Working under the assumption that only 1 population exists in ENA waters, the current study presents basic life history data and investigates whether biological information obtained from postmortem data is, in itself, useful for managing this population. Life history parameters were estimated by analysing postmortem data obtained over a 16 yr period by UK, Irish, French, Galician (northwest Spain) and Portuguese stranding and bycatch observer programmes. An annual pregnancy rate of 26%, a calving interval of 3.79 yr, an average age attained at sexual maturity of 8.22 yr and an average length at sexual maturity of 188 cm were determined. With respect to the findings based solely on mortality data, significance testing failed to detect differences that could be construed as evidence of the population exhibiting what might be density-dependent compensatory responses. The low annual pregnancy rate reported throughout the sampling period may suggest either that the level of anthropogenic mortality did not cause a substantial population level decline, or a prey base declining at approximately the same rate as the dolphin population. However, this approach alone does not facilitate an assessment of the current state of the D. delphis population in the ENA. Population abundance estimates, trends in abundance and knowledge of factors that affect the dynamics of the population, such as annual mortality rates in fisheries, temporal variations in prey abundance and effects of contaminants on reproductive activity, are required not only to set management objectives, but also to give context to cross-sectional life history information.