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Echoes of the past: Whaling's long-term impact on genetic diversity

The impacts of 20th-century commercial whaling continue to linger today, according to research led by by Angela Sremba of Oregon State University (OSU). The study reveals a significant loss in genetic diversity among surviving whales. 

“The 20th century commercial whaling industry severely reduced populations of great whales throughout the Southern Hemisphere. The effect of this exploitation on genetic diversity and population structure remains largely undescribed,” wrote the study authors. 

“Over 2 million whales were killed by commercial whalers in the Southern Hemisphere during the 20th century. This included 345,775 Antarctic blue whales (Balaenoptera musculus intermedia), 215,848 humpback whales (Megaptera novaeangliae), and an astounding 726,461 fin whales.”

Focus of the study

The researchers set out to investigate genetic diversity changes among great whales in the South Atlantic. They examined DNA from whale bones found near abandoned whaling stations on South Georgia Island.

The bones, some of which are over a century old, were compared to DNA from contemporary whale populations. The study showed a pronounced loss of maternal DNA lineages among blue and humpback whales. 

Loss of cultural memories

“A maternal lineage is often associated with an animal’s cultural memories such as feeding and breeding locations that are passed from one generation to the next. If a maternal lineage is lost, that knowledge is likely also lost,” said Sremba.

South Georgia Island, situated approximately 800 miles southeast of the Falkland Islands, was an active hub for whaling from the early 1900s to the 1960s. The aftermath of this extensive hunting is still visible, with the island scattered with whale bones, preserved due to the region’s cold temperatures.

Rediscovering their habitat

Although commercial whaling has ceased, and South Atlantic whale populations are gradually recovering, the number of whale sightings near South Georgia is notably low. This indicates possible localized extinction, or extirpation, in the area’s whale populations, according to study co-author Scott Baker, associate director of OSU’s Marine Mammal Institute.

“For 60 years, the whales have been absent from the South Georgia feeding grounds, suggesting that cultural memory was lost.” However, Baker noted that there are signs of whales gradually returning to the region, potentially “rediscovering” the habitat after the loss of cultural memory.

DNA analysis

To assess the impact on genetic diversity, Sremba extracted and analyzed DNA from whale bones on South Georgia Island, comparing the findings to genetic data from current whale populations. 

The analysis, encompassing humpback, blue, and fin whales, showed that while there is still high genetic diversity, there is evident loss of maternal DNA lineages in blue and humpback whales. The team couldn’t discern diversity differences in fin whales due to the scarcity of post-whaling samples.

Maternal lineages 

Sremba, now affiliated with the Cooperative Institute for Marine Ecosystem and Resources Studies at OSU’s Hatfield Marine Science Center, emphasized that some whales alive today might have lived during the whaling era, given their lifespan can reach a century. 

As these older whales pass away, further maternal lineages could be lost. Thus, preserving current genetic information is crucial.

Understanding the past

“It’s remarkable these species survived. In another 100 years, we don’t know what might change, and we can’t measure any change now if we don’t have a good understanding of the past,” said Sremba.

The research offers valuable insights into the history and losses of whale populations due to whaling.

Baker noted that rising temperatures due to climate change could also lead to deterioration of the DNA in the bones on South Georgia Island. “This work is a way to preserve this history indefinitely.”

The study is published in the Journal of Heredity.

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