Commercial whaling led to loss of genetic diversity | Polarjournal
Whale bones next to the former whaler’s pier in Grytviken. On South Georgia, whale bones are still shattered along the coast, relatively well preserved because of the low temperatures. However, rising temperatures due to climate change could destroy the DNA in the bones. (Photo: Julia Hager)

During the 20th century, large whales had become so depleted by commercial whaling in the Southern Hemisphere that a loss of genetic diversity appeared to have occurred.

On the beaches of South Georgia, and especially near the former whaling stations, there are still countless whale bones today. For scientists, these are not only evidence of the merciless commercial whaling that began in earnest in Grytviken in 1904.

An international research team led by Oregon State University’s Marine Mammal Institute used the bones of blue, fin and humpback whales to compare the DNA of whales living at the time with the DNA of whales living today, some of them survivors from back then. Their goal was to better understand how commercial whaling may have affected the genetic diversity of the current population.

The researchers found that genetic diversity among cetaceans is still high. However, the team published clear evidence of maternal DNA lineage loss in blue and humpback whales in the Journal of Heredity . For Southern Hemisphere fin whales, the team found no differences in diversity between pre- and post-whaling DNA samples, presumably because there are very few post-whaling samples.

“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,” Angela Sremba, assistant professor at Oregon State University’s Marine Mammal Institute and lead author of the study, explained in a university news release. “If a maternal lineage is lost, that knowledge is likely also lost.”

This is supported by the fact that after the end of commercial whaling in the 1960s, whale sightings around South Georgia were very rare, while whale populations in other areas of the South Atlantic slowly recovered – an indication that local populations were extirpated, with knowledge of the rich feeding grounds around South Georgia also lost. It is only in the recent past that whales are again frequenting the waters around the sub-Antarctic island.

Angela Sremba analyzing DNA samples (left, photo: Marine Mammal Institute, Oregon State University) and Scott Baker on South Georgia with the jawbone of a large baleen whale (photo: Scott Baker, Marine Mammal Institute, Oregon State University).

“For 60 years, the whales have been absent from the South Georgia feeding grounds, suggesting that cultural memory was lost,” Scott Baker said, associate director of the Marine Mammal Institute and co-author of the study. “The numbers of whales returning to this region today are still not large, but there is a sense that they may be rediscovering this habitat.”

The killing by the whalers had reached an inconceivable scale: More than two million whales had been killed in the southern hemisphere, including 345,775 Antarctic blue whales (Balaenoptera musculus intermedia), 215,848 humpback whales (Megaptera novaeangliae), and 726,461 fin whales (Balaenoptera physalus). Around South Georgia, a total of more than 175,000 whales were taken.

There could be further loss of maternal DNA in blue and humpback whales as the whales die that survived the whaling of the past and are now slowly coming to the end of their lives. Sremba therefore stresses the importance of preserving the whales’ genetic information now.

“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,” Sremba says. “This work provides an opportunity to reconstruct the history of these whale populations and help us understand what was truly lost due to whaling activities.”

Julia Hager, PolarJournal

Link to the study: Angela L Sremba, Anthony R Martin, Peter Wilson et al. Diversity of mitochondrial DNA in 3 species of great whales before and after modern whaling. Journal of Heredity, 2023; DOI: 10.1093/jhered/esad048.

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