Mitochondrial Control Region and microsatellite analyses on harbour porpoise (Phocoena phocoena) unravel population differentiation in the Baltic Sea and adjacent waters

Abstract

The population status of the harbour porpoise (Phocoena phocoena) in the Baltic area has been a continuous matter of debate. Here we present the by far most comprehensive genetic population structure assessment to date for this region, both with regard to geographic coverage and sample size: 497 porpoise samples from North Sea, Skagerrak, Kattegat, Belt Sea, and Inner Baltic Sea were sequenced at the mitochondrial Control Region and 305 of these specimens were typed at 15 polymorphic microsatellite loci. Samples were stratified according to sample type (stranding vs. by-caught), sex, and season (breeding vs. non-breeding season). Our data provide ample evidence for a population split between the Skagerrak and the Belt Sea, with a transition zone in the Kattegat area. Among other measures, this was particularly visible in significant frequency shifts of the most abundant mitochondrial haplotypes. A particular haplotype almost absent in the North Sea was the most abundant in Belt Sea and Inner Baltic Sea. Microsatellites yielded a similar pattern (i.e., turnover in occurrence of clusters identified by STRUCTURE). Moreover, a highly significant association between microsatellite assignment and unlinked mitochondrial haplotypes further indicates a split between North Sea and Baltic porpoises. For the Inner Baltic Sea, we consistently recovered a small, but significant separation from the Belt Sea population. Despite recent arguments that separation should exceed a predefined threshold before populations shall be managed separately, we argue in favour of precautionary acknowledging the Inner Baltic porpoises as a separate management unit, which should receive particular attention, as it is threatened by various factors, in particular local fishery measures. © Springer Science+Business Media B.V. 2009

The Future of Baltic Sea Populations: Local Extinction or Evolutionary Rescue?

“…For example, species with currently small and isolated Baltic populations like harbor seal and harbor porpoise (Härkönen et al 2005;Wiemann et al 2010) seem to do well at the moment despite very small population sizes (harbor seal N \ 50 during 1970s, and at present \400, Härkönen et al 2005; harbor porpoise N \ 100, Berggren et al 2004). Even if they have lost only minor proportions of their original genetic variation, which can be explained by long generation times and much larger population sizes earlier in history, genetic variation is expected to decrease during coming generations if low population sizes are maintained.…”

Baltic Sea harbour porpoise populations: status and conservation needs derived from recent survey results

“…Within the Baltic Sea (see Fig. 1), 2 populations or management units can be distinguished in the waters between Skagen (northernmost point of Denmark) in the west and the Gulf of Finland in the east (Tiedemann et al 1996, Berggren et al 1999, Huggenberger et al 2002, Wiemann et al 2010, Teilmann et al 2011. Using satellite tracking results, Teilmann et al (2011) determined the boundaries between the Skagerrak (i.e.…”

Correlation between the seasonal distribution of harbour porpoises and their prey in the Sound, Baltic Sea

“…Kattegat, Belt Seas, the Sound and the western Baltic are inhabited by a genetically distinct population of about 10,865 (CV = 0.32, 95% CI = 5,840-20,214) harbour porpoises Phocoena phocoena (SCANS-II 2008;Sveegaard 2011;Wiemann et al 2010) (Fig. 1).…”