No abstract

The existence of nearshore and o¡shore populations of the bottlenose dolphin has been documented throughout its range. In several cases the two regional forms have been shown to be morphologically distinct, although there is considerable overlap for most characters. The populations o¡ the eastern coast of North America have been the subject of a long-term programme of research on their distribution and movements. In this study, we compare mitochondrial and nuclear genetic markers between dolphins classi¢ed as either nearshore or o¡shore type. These putative populations were found to be distinct at both nuclear and mitochondrial genetic markers. Further, the level of variation among the nearshore dolphins was reduced compared with the o¡shore population. A broader geographical comparison suggests a shared lineage between o¡shore dolphins from the western North Atlantic and both o¡shore and nearshore dolphins from the eastern Atlantic. These results are consistent with local di¡erentiation based on habitat or resource specialization in the western North Atlantic, and suggest di¡erences in the character of the nearshore/o¡shore distinction in di¡erent parts of the world.

No abstract

The high variability in reproductive performance of North Atlantic right whales Eubalaena glacialis compared to southern right whales Eubalaena australis may reflect differences in lipid reserves. Amplitude-mode ultrasound was used to measure the thickness of right whale integument (epidermis and blubber, herein referred to as blubber thickness) in E. glacialis in the Bay of Fundy, Canada for 5 summer seasons and in E. australis off the South African coast for 2 austral winter seasons. E. glacialis had significantly thinner blubber layers (mean ±1 SD = 12.23 ± 2.16 cm, n = 172) than E. australis (16.13 ± 3.88 cm, n = 117), suggesting differing levels of nutrition between the 2 species. Blubber was thickest in females measured 3 to 6 mo prior to the start of pregnancy (E. glacialis), thinner during lactation (E. glacialis, E. australis) and then thicker with time after weaning (E. glacialis). These results suggest that lipids in blubber are used as energetic support for reproduction in female right whales. Blubber thickness increased in calves during suckling (E. glacialis, E. australis) but subsequently decreased after weaning (E. glacialis). Juvenile and adult male E. glacialis blubber thicknesses were compared between years of differing prey Calanus finmarchicus abundances (data from Pershing et al. 2005; ICES J Mar Sci 62:1511-1523; during a year of low prey abundance whales had significantly thinner blubber than during years of greater prey abundance. Taken together, these results suggest that blubber thickness is indicative of right whale energy balance and that the marked fluctuations in North Atlantic right whale reproduction have a nutritional component.

Although humpback whales are among the best-studied of the large whales, population boundaries in the Southern Hemisphere (SH) have remained largely untested. We assess population structure of SH humpback whales using 1,527 samples collected from whales at fourteen sampling sites within the Southwestern and Southeastern Atlantic, the Southwestern Indian Ocean, and Northern Indian Ocean (Breeding Stocks A, B, C and X, respectively). Evaluation of mtDNA population structure and migration rates was carried out under different statistical frameworks. Using all genetic evidence, the results suggest significant degrees of population structure between all ocean basins, with the Southwestern and Northern Indian Ocean most differentiated from each other. Effective migration rates were highest between the Southeastern Atlantic and the Southwestern Indian Ocean, followed by rates within the Southeastern Atlantic, and the lowest between the Southwestern and Northern Indian Ocean. At finer scales, very low gene flow was detected between the two neighbouring sub-regions in the Southeastern Atlantic, compared to high gene flow for whales within the Southwestern Indian Ocean. Our genetic results support the current management designations proposed by the International Whaling Commission of Breeding Stocks A, B, C, and X as four strongly structured populations. The population structure patterns found in this study are likely to have been influenced by a combination of long-term maternally directed fidelity of migratory destinations, along with other ecological and oceanographic features in the region.