How many blue whales are there left in the world?

Scientists are assessing the current state of blue whale populations around the world using the largest global genomic data set to date

The Blue Whale (Balaenoptera musculus), the world’s largest living animal with an average length of 27 meters, has slowly recovered from whaling to meet the growing challenges of global warming, pollution, disruption of food sources, shipping and other human threats.

In a major new study, Flinders University has taken stock of the numbers, distribution and genetic characteristics of blue whale populations around the world, finding the greatest differences between the Eastern Pacific and Antarctic subspecies and the East Indian and Western Pacific dwarf subspecies.

“Each of these groups must be conserved to maintain the biodiversity of the species, and there is evidence that natural selection in different environments has helped drive genetic differences between high-level groups,” says Dr. Catherine Attard, lead author of the study, in an article recently published in Animal Conservation.

“Within these regions, there were differences between the eastern North Pacific and the eastern South Pacific, as well as between the eastern Indian Ocean, the western South Pacific and the northern Indian Ocean, but not in the Antarctic group,” he adds.

The blue whale is still threatened with extinction

The study found no signs of inbreeding, which is good news for the potential recovery of subspecies and populations. However, this endangered species continues to face challenges.

The recovery of baleen whales, including endangered blue whales, is threatened by numerous human-caused factors, including underwater noise, changes in food availability due to anthropogenic impacts on marine productivity, pollutant impacts on the environment, collisions with boats and entanglements in fishing gear.

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

Estimated migration rates were between 1% and 4% in each of the high-ranking groups, with migrants (i.e., people who move without necessarily interbreeding) and hybrid (i.e., interbreeding) individuals among the high-ranking groups.

In reconstructing whale population structures, researchers found an unexpected similarity between blue whales in the eastern South Pacific and eastern North Pacific, suggesting they are part of the same subspecies rather than their current classification as a separate subspecies.

The problem of genetic diversity in blue whales

“This finding was unexpected because blue whale populations are thought to have opposite breeding seasons when their populations exist on both sides of the equator,” adds lead author and Associate Professor Luciana Möller from the Laboratory of Molecular Ecology and the Laboratory of Cetacean Ecology. Behavior and Evolution at Flinders University.

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“While blue whales in the eastern Indian Ocean and western Pacific have the lowest genetic diversity of the high-ranking hierarchical groups, likely due to climate-driven diversification rather than anthropogenic influences, our study identified the ocean in the eastern Indian Ocean, western South Pacific and in the western South Pacific possibly the western Indian Ocean as distinct populations within the Indo-West Pacific,” says Associate Professor Möller.

In addition to generating the largest global dataset of blue whale genomes to date, the study incorporated information from recent satellite tagging, acoustic and stable isotope research to correlate genetic results with the calls of blue whale populations and their typical migration and breeding patterns.

Blue whale population

Experts at Flinders University have taken stock of the numbers, distribution and genetic characteristics of blue whale populations around the world and have identified the greatest differences between the East Pacific subspecies, the Antarctic subspecies and the Indian East Pacific pygmy subspecies. Photo credit: Flinders University

Another co-author, Professor Luciano Beheregaray, who founded Flinders University’s Molecular Ecology Laboratory in 2009, added: “Genomics is an important tool with unrivaled power in determining population differentiation, connectivity and other characteristics for reports on the management of the Protection of biological diversity.”

“To better understand the adaptations of the blue whale and other baleen whales, it is necessary to conduct population studies across the genome and compare these to environmental conditions.” If these threats are concentrated in areas where populations have limited connectivity to the animals in the If we live in surrounding regions, there could be a localized decline in blue whale populations.

“Describing the spatiotemporal patterns of population differences within a species and its geographical boundaries can therefore inform management decisions about the timing and location of human activities to minimize impacts on these large cetacean species.”

Although the blue whale was protected from commercial hunting in 1966, the International Whaling Commission (IWC) imposed a global moratorium 20 years later.

The Flinders University-based research group is calling on the IWC to use the results to refine the delineation of blue whale populations for conservation and management purposes.

“We recommend that national management authorities minimize human activities that could affect these management groups when blue whales are within their jurisdiction,” the researchers conclude.

REFERENCE

Global conservation genomics of blue whales challenges subspecies taxonomy and refines knowledge of population structure

Experts at Flinders University have taken stock of the numbers, distribution and genetic characteristics of blue whale populations around the world and have identified the greatest differences between the East Pacific subspecies, the Antarctic subspecies and the Indian East Pacific pygmy subspecies. Photo credit: Flinders University

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