Samples from 136 humpback whales Megaptera novaeangliae, representing 5 feeding aggregations in the North Atlantic and 1 in the Antarctic, were analyzed with respect to the sequence variation in the mitochondria1 (mt) control region. A total of 288 base pairs was sequenced by direct sequencing of asymmetrically amplified DNA. Thirty-one different haplotypes were identified. The nucleotide diversity for the total sample was estimated to be 2.6 %, w h c h is high relative to other North Atlantic cetaceans. The degree of genetic differentiation in various subsets of the samples was estimated and tested for statistical significance by Monte Carlo simulations. Significant degrees of heterogeneity were found between the Antarctic and all North Atlantic areas, as well as between Iceland and the western North Atlantic samples. A genealogical tree was estimated for the 31 haplotypes and rooted with the homologous sequence from a fin whale Balaenoptera physalus. The branching pattern in the genealogical tree suggests that the North Atlantic Ocean has been populated by 2 independent influxes of humpback whales. The combined results from the homogeneity tests and the genealogical tree indicate that behaviour (in this case maternally directed site fidelity to a foraging area) can influence the population structure of marine cetaceans on an evolutionary time scale.

Ventral fluke patterns of humpback whales Megaptera novaeangliae were assessed to determine if pigmentation shows geographical variation across different breeding areas. Fluke photographs (n = 3854) were collected from 7 major breeding grounds worldwide and were ranked into categories 1 (white) through 5 (black) based on the proportion of white and black pigment on the ventral surface. Average coloration varied primarily between oceanic populations, with the Southern Ocean stocks (Area IV, western Australia, and Area V, eastern Australia) characterized by significantly more light-colored flukes, while the North Pacific subpopulations consisted of individuals with significantly more dark-colored flukes. Results of statistical analyses revealed that all populahons differed significantly from one another in the distribution of pigmentation classes, with the exceptions of Hawaii vs Japan, Mexico vs Japan, Mexico vs Hawaii, eastern Australia vs western Australia, and West Indies vs Colombia. Results of pigmentation analyses reveal historic and current interactions among oceanic subpopulations of humpback whales and reflect population sub-division in this species.

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The demography of baleen whales and their prey during the past 30 thousand years was assessed to understand the effects of past rapid global warming on marine ecosystems. Mitochondrial and genome-wide DNA sequence variation in eight baleen whale and seven prey species revealed strong, ocean-wide demographic changes that were correlated with changes in global temperatures and regional oceanographic conditions. In the Southern Ocean baleen whale and prey abundance increased exponentially and in apparent synchrony, whereas changes in abundance varied among species in the more heterogeneous North Atlantic Ocean. The estimated changes in whale abundance correlated with increases in the abundance of prey likely driven by reductions in sea-ice cover and an overall increase in primary production. However, the specific regional oceanographic environment, trophic interactions and species ecology also appeared to play an important role. Somewhat surprisingly the abundance of baleen whales and prey continued to increase for several thousand years after global temperatures stabilized. These findings warn of the potential for dramatic, long-term effects of current climate changes on the marine ecosystem.One Sentence SummaryThe effects of past global warming on marine ecosystems were drastic, system-wide and long-lasting.