Global blue whale populations assessed after whaling

Blue whale populations are slowly recovered from whaling, but Earth’s largest animals now confront new challenges from global warming, pollution, shipping and disrupted food sources.

On average, blue whales are 27m long can weigh more than 130t. The longest ever was 33.58m, while the heaviest weighed 199t. Despite their immense size, keeping track of whale numbers and migration is no mean feat.

The animals are currently listed on the IUCN Red List of Threatened Species as “Endangered.”

A major new study has assessed the number, distribution and genetics of blue whale populations from around the world. It is the largest global genomic dataset for blue whales.

World map showing the distribution of blue whale populations
Distribution of blue whale populations. Credit: Flinders University.

Results published in the journal Animal Conservation show the greatest differences between the subspecies in the Pacific and Antarctic Oceans compared to the pygmy subspecies of the eastern Indian and western Pacific.

“Each of these groups need to be conserved to maintain biodiversity in the species, and there are indications that natural selection in different environments contributed to driving genetic differences between the high-level groups,” says study first author Dr Catherine Attard, from Flinders University in South Australia.

No evidence of inbreeding within the populations was found – good news for potential recovery.

“The recovery of baleen whales is threatened by multiple human sources, including underwater noise (from shipping, oil and gas exploration activities and sonar), changing availability of food driven by human-induced effects on ocean productivity, environmental contaminants, ship collision and entanglement in fishing gear,” the authors write.

But the species is not out of the oceanic woods.

“Our findings build on decades of work to improve the management of endangered blue whales under the International Whaling Commission,” says Dr Attard.

The researchers used 276 samples to test single-nucleotide polymorphism and 531 samples to analyse mitochondrial DNA.

Currently, there are 5 classified blue whale subspecies.

Migration rates – the percentage of individuals within a subspecies’ geographical area who come from another subspecies – were estimated to be 1–4% across the groups. An unexpected similarity was found in the population structure of eastern South Pacific and easter North Pacific blue whales, suggesting they are in fact the same subspecies contrary to current classification.

“Genomics is a vital tool that has unparalleled power to determine population differentiation, connectivity, and other characteristics to inform the conservation management of biodiversity,” says co-author Professor Luciano Beheregaray.

“Whole-genome population studies and comparisons with environmental conditions are needed to better understand adaptations in blue whales and other baleen whales. Localised depletion of blue whales could occur if these threats are concentrated in areas containing populations with limited connectivity to animals in surrounding regions.

Blue whales became protected from commercial whaling in 1966. The International Whaling Commission (IWC) implemented a global moratorium 20 years later. The authors call for national management bodies to minimise human activities which may impact on blue whale conservation efforts.

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