Rise of oceanographic barriers in continuous populations of a cetacean: the genetic structure of harbour porpoises in Old World waters

<p>Abstract</p> <p>Background</p> <p>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.</p> <p>Results</p> <p>Analyses of 10 microsatellite loci for 752 individuals revealed that most of the sampled range in the eastern North Atlantic behaves as a 'continuous' population that widely extends over thousands of kilometres with significant isolation by distance (IBD). However, strong barriers to gene flow were detected in the south-eastern part of the range. These barriers coincided with profound changes in environmental characteristics and isolated, on a relatively small scale, porpoises from Iberian waters and on a larger scale porpoises from the Black Sea.</p> <p>Conclusion</p> <p>The presence of these barriers to gene flow that coincide with profound changes in oceanographic features, together with the spatial variation in IBD strength, provide for the first time strong evidence that physical processes have a major impact on the demographic and genetic structure of a cetacean. This genetic pattern further suggests habitat-related fragmentation of the porpoise range that is likely to intensify with predicted surface ocean warming.</p

Distribution, abundance and trends in abundance of fin and humpback whales in the North Atlantic

The North Atlantic Sightings Surveys (NASS) are a series of international cetacean line transect surveys, including participation from the Faroe Islands, Iceland, Norway and Spain, that have been conducted in 1987, 1989, 1995 and 2001. The NASS have covered a very large area of the central and eastern North Atlantic, from East Greenland east to coastal Norway, and from Svalbard south to the Iberian peninsula. The surveys used ships and aircraft as survey platforms. Target species were minke, fin and pilot whales, but all species encountered were registered. Here we present estimates of abundance for fin and humpback whales from the Northeast and Central portions of the survey area. The estimates are negatively biased because of whales diving during the passage of the survey platform and whales being missed by observers, but these and other potential biases are likely small for these species. Fin whales occurred in highest densities in Denmark Strait west of Iceland, while humpback whales were most abundant in shelf waters east and west of Iceland. The abundance of fin whales increased in the survey area over the period, with the greatest increase observed in the waters west of Iceland. There were 29,900 (cv 0.11) fin whales in the area in 2001. There has been a great increase in the abundance of humpback whales around Iceland, but not in other areas. Aerial surveys conducted in Icelandic coastal waters indicate an annual rate of increase of 15% in this area. There were 14,900 (cv 0.26) humpback whales in the entire survey area in 2001. The observed trends are consistent with increases in abundance following the cessation of whaling in this area, but the magnitudes of the observed increases, taken at face value, are greater than expected.. For humpback whales in particular, our recent estimates are substantially higher than some estimates of pre-whaling abundance. Other factors, including differential harvesting of sub-stocks, changes in carrying capacity, immigration from other areas, the near extirpation of some other cetacean species, and operational factors in the surveys themselves, may be involved

Inferring recent historic demographic events (bottlenecks) using genetic data, case study: North Atlantic blue whale (<i>Balaenoptera musculus musculus</i>)

Signals of past demographic changes can be found within the genetic diversity of a population long after an event has occurred. However, modern genetics is not always able to detect past demographic changes. Sometimes, signals of demographic changes are lost over time, overshadowed by other events or statistical power is insufficient to discriminate between different events. In this study we looked at the genetic diversity of the North Atlantic blue whale (Balaenoptera musculus musculus). Blue whales were intensively hunted during the early 1900’s, subjecting the entire species to a bottleneck. We attempted to estimate the timing of this demographic event based upon the current genetic diversity of the population. Additionally, we estimated effective population sizes before and after whaling. Standard bottleneck tests such as the M-ratio test and the heterozygosity-excess were used to see whether a signal of the bottleneck could be detected. MSVAR was used to estimate the timing and the abundances before and after the demographic event based upon genetic data. Finally, BEAST was implemented to look at demographic changes over a longer period of time. Preliminary results suggest other demographic changes distort the signal of the recent bottleneck, shifting the timing of the demographic even