No abstract

Southern Hemisphere humpback whales Megaptera novaeangliae migrate from wintering grounds in tropical latitudes to feeding areas in the Antarctic Ocean. It has been hypothesized that the population wintering off eastern South America migrates to feeding grounds near the Antarctic Peninsula (ca. 65°S, 60°W) and/or South Georgia (54°20' S, 36°40' W), but direct evidence to support this has never been presented. Between 19 and 28 October 2003, 11 humpback whales (7 females and 4 males) were instrumented with satellite transmitters off Brazil (ca. 18°30' S, 39°30' W) to investigate their movements and migratory destinations. Mean tracking time for the whales was 39.6 d (range = 5 to 205 d) and mean distance travelled was 1673 km per whale (range = 60 to 7258 km). Movements on the wintering ground showed marked individual variation. Departure dates from the Brazilian coast ranged from late October to late December. Whales migrated south through oceanic waters at an average heading of 170°and travelled a relatively direct, linear path from wintering to feeding grounds. Two whales were tracked to feeding grounds in offshore areas near South Georgia and in the South Sandwich Islands (58°S, 26°W) after a 40 to 60 d long migration. Historical catches and current sighting information support these migratory routes and destinations. This study is the first to describe the movements of humpback whales in the western South Atlantic Ocean.

The distribution of dolphins of the genus Stenella is poorly known in the southwest Atlantic Ocean. A complete review of records (n = 311) of these dolphin species was performed to describe distribution and habitat. Atlantic spotted dolphins S. frontalis occur in both southern (21 to 33°S) and northern Brazil (north of 06°S), with a hiatus in its distribution off eastern South America. This species presents the highest preference for nearshore habitats, restricted to waters within the 1000 m isobath. Pantropical spotted dolphins S. attenuata are found in tropical waters as far south as 22°S and are mainly observed off northeastern South America. They occur beyond the continental shelf break in depths > 850 m. Clymene dolphins S. clymene are distributed in deep waters (1390 to 4500 m) as far south as 30°S. Strandings are more common where the continental shelf is narrower. Spinner dolphins S. longirostris are found in oceanic waters as far south as 30°S. They inhabit tropical waters over the shelf and slope (depths ranging from 170 to 2700 m). The striped dolphin S. coeruleoalba is the least known species of the genus in the western South Atlantic. Most records are from temperate waters in southern Brazil and Argentina. The distributions of S. attenuata, S. clymene and S. longirostris overlap to a great extent and are predominantly oceanic and associated with warm ocean currents. S. frontalis seems to prefer a different, coastal habitat, influenced both by warm currents and upwelling areas. The discontinuous distribution of this species suggests that an isolated population inhabits the southern coast of Brazil.

How do populations of highly mobile species inhabiting open environments become reproductively isolated and evolve into new species? We test the hypothesis that elevated ocean-surface temperatures can facilitate allopatry among pelagic populations and thus promote speciation. Oceanographic modelling has shown that increasing surface temperatures cause localization and reduction of upwelling, leading to fragmentation of feeding areas critical to pelagic species. We test our hypothesis by genetic analyses of populations of two closely related baleen whales, the Antarctic minke whale (Balaenoptera bonaerensis) and common minke whale (Balaenoptera acutorostrata) whose current distributions and migration patterns extent are largely determined by areas of consistent upwelling with high primary production. Phylogeographic and population genetic analyses of mitochondrial DNA control-region nucleotide sequences collected from 467 whales sampled in four different ocean basins were employed to infer the evolutionary relationship among populations of B. acutorostrata by rooting an intraspecific phylogeny with a population of B. bonaerensis. Our findings suggest that the two species diverged in the Southern Hemisphere less than 5 million years ago (Ma). This estimate places the speciation event during a period of extended global warming in the Pliocene. We propose that elevated ocean temperatures in the period facilitated allopatric speciation by disrupting the continuous belt of upwelling maintained by the Antarctic Circumpolar Current. Our analyses revealed that the current populations of B. acutorostrata likely diverged after the Pliocene some 1.5 Ma when global temperatures had decreased and presumably coinciding with the re-establishment of the polar-equatorial temperature gradient that ultimately drives upwelling. In most population samples, we detected genetic signatures of exponential population expansions, consistent with the notion of increasing carrying capacity after the Pliocene. Our hypothesis that prolonged periods of global warming facilitate speciation in pelagic marine species that depend on upwelling should be tested by comparative analyses in other pelagic species.

North Atlantic humpback whales (Megaptera novaeangliae (Borowski, 1781)) migrate from high-latitude summer feeding grounds to low-latitude winter breeding grounds along the Antillean Island chain. In the winters and springs of 2008 through 2012, satellite tags were deployed on humpback whales on Silver Bank (Dominican Republic) and in Guadeloupe (French West Indies) breeding areas. Whales were monitored, on average, for 26 days (range = 4-90 days). Some animals remained near their tagging location for multiple days before beginning their northerly migration, yet some visited habitats along the northwestern coast of the Dominican Republic, northern Haiti, the Turks and Caicos islands, and off Anguilla. Individuals monitored during migration headed towards feeding grounds in the Gulf of Maine (USA), Canada, and the eastern North Atlantic (Iceland or Norway). One individual traveled near Bermuda during the migration. This study provides the first detailed description of routes used by North Atlantic humpback whales towards multiple feeding destinations. Additionally, it corroborates previous research showing that individuals from multiple feeding grounds migrate to the Antilles for the breeding season. This study indicates that North Atlantic humpbacks use an area broader than the existing boundaries of marine mammal sanctuaries, which should provide justification for their expansion.