Assessing blue whale populations

Although the world’s largest living mammal was protected from commercial whaling in 1966 – 20 years before the 1986 global moratorium on whaling was implemented through the International Whaling Commission – the blue whale’s recovery has been slow. Researchers from Flinders University conducted a major new study to assess the status of blue whale populations (Balaenoptera musculus) now global warming, pollution, underwater noise, disrupted food sources, shipping and other human activities such as entanglement in fishing gear, present further threats to the species’ survival. The results were published in the journal Animal Conservation.

Scientists compared the number, distribution and genetic characteristics of blue whale populations from around the world. They found the greatest differences were among the eastern Pacific, Antarctic subspecies and pygmy subspecies of the Indian and western Pacific. For biodiversity to be maintained, first author Catherine Attard from FU’s College of Science and Engineering, said it was important that all whale groups were conserved since the study indicated natural selection in different environments contributed to driving genetic differences between the high-level groups.

            “Within these regions there were differences between the eastern North and eastern South Pacific, and among the eastern Indian Ocean, the western South Pacific and the northern Indian Ocean, but no differences in the Antarctic group,” she said, adding that despite no evidence of inbreeding being found significant environmental challenges for the endangered species remained.

            The study found an unexpected similarity between the eastern South Pacific and eastern North Pacific blue whales, which suggested they were part of the same subspecies, rather than their current classification as separate subspecies.

            Senior author Luciana Möller from FU’s Molecular Ecology Lab, and Cetacean Ecology, Behaviour and Evolution Lab, said the finding was unexpected given that blue whale populations were understood to have opposite breeding seasons when their populations existed on the other side of the equator.

            “While eastern Indian and western Pacific blue whales have the lowest genetic diversity of the high-level hierarchical groups, which is likely due to climate-induced diversification rather than anthropogenic impacts, our study identified the eastern Indian Ocean, western South Pacific Ocean and potentially western Indian Ocean as different populations within the Indo-western Pacific,” she said.

            In addition to generating the largest global genomic dataset to date for blue whales, the study also incorporated information from recent satellite tagging, acoustics and stable isotopes research to link the genetic results to blue whale population calls and typical migratory and breeding patterns.

            Co-author Luciano Beheregray, founder of FU’s Molecular Ecology Lab, said that genomics was a vital tool with unparalleled power to determine population differentiation, connectivity and other characteristics able to inform the conservation management of biodiversity.

            “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. Thus, describing the spatio-temporal patterns of population differences within a species and their geographic boundaries can inform management decisions on the timing and location of human activities to minimise impacts on these wide-ranging whale species,” he said.

            The study recommended that national management bodies minimise human activities that can impact these management groups when the blue whales are within their jurisdiction.

Anne Layton-Bennett

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