The aftermath of whaling past: Impending genetic extinction of the eastern North Atlantic humpback whale breeding population

Commercial whaling from the mid-19th Century to the early 20th Century dramatically reduced the North Atlantic (NA) humpback whale populations. Post-whaling protection appears to have facilitated population recovery in the western NA breeding grounds but not in the eastern NA. The underlying cause for this disparity remains unknown. The most recent abundance estimate of the eastern NA breeding population was at ~300, indicating little, if any, post-whaling recovery. In contrast, the western NA breeding population has reached an estimated abundance at ~12,000 individuals. Gabualdi et al. (unpublished ) employed microsatellites to infer that only ~20% of the Cabo Verde breeding population had pure eastern NA ancestry, while the remaining ~80% were either immigrants from the western NA breeding population or descendants thereof. Considering the very different recovery rates in the western and eastern NA breeding populations, we expect a further continued increase in effective migration into the eastern NA breeding population from the western NA. This introgression of western NA genomes into the eastern NA breeding population will eventually result in the replacement and extinction of the eastern NA breeding population; a legacy of the long ranging impacts of whaling. We employed Approximate Bayesian Computation to assess the posterior probabilities of different post-whaling scenarios in order to elucidate the population dynamics and estimate rates of recovery and migration. Our model selection was based upon data from 19 microsatellite loci and mtDNA control region sequences in 245 samples. The ABC model selection suggested a whaling-bottleneck scenario generating source-sink dynamics, confirming that the eastern NA breeding population will eventually be supplanted by immigrants from the western NA breeding population. Our results underline the importance of management plans where genetic diversity is considered along with population abundance.