Study finds whaling decimated whale populations and genetic diversity

New research from Oregon State University reveals that 20th-century commercial whaling not only significantly reduced large whale populations but also left a lasting mark on the genetic diversity of today’s surviving whales.

By comparing DNA samples obtained from whale bones found near abandoned whaling stations on South Georgia Island in the South Atlantic Ocean with DNA from contemporary whale populations, scientists detected compelling evidence of the loss of maternal DNA lineages in blue and humpback whales.

Lead author Angela Sremba, during her doctoral studies at Oregon State University’s Marine Mammal Institute, pointed out that maternal lineages often carry crucial cultural knowledge, such as feeding and breeding locations, passed down through generations. Losing a maternal lineage likely means losing this valuable knowledge.

The study’s findings were recently published in the Journal of Heredity.

South Georgia, a remote island located approximately 800 miles southeast of the Falkland Islands, was home to several whaling stations operational from the early 1900s to the 1960s. Within a little over six decades, over 2 million whales were hunted and killed in the Southern Hemisphere, with 175,000 of them near South Georgia.

Evidence of this devastating whaling history remains on the island, where thousands of whale bones, some over a century old, were left behind during commercial processing. The region’s cold temperatures contributed to the preservation of these remains.

While South Atlantic whale populations have begun to recover since the end of commercial whaling, whale sightings around South Georgia have remained scarce. This suggests the possibility of localized extinction, as described by study co-author Scott Baker, associate director of OSU’s Marine Mammal Institute. Baker last visited South Georgia Island as part of a research expedition in early 2020.

Baker noted, “For 60 years, the whales have been absent from the South Georgia feeding grounds, suggesting that cultural memory was lost. The current whale numbers returning to this region are still relatively low, but there is hope that they may be rediscovering their habitat.”

Credit: Bob Pittman, Oregon State University

To gain a deeper insight into how whaling might have impacted the genetic diversity of today’s whale populations, Angela Sremba conducted a comprehensive analysis. She extracted DNA from bones discovered on South Georgia Island and compared this genetic information with previously published data from contemporary living whales post-whaling.

Sremba and her team unearthed bones from humpback, blue, and fin whales. Their findings indicated that while genetic diversity among these whales remains relatively robust, there are signs of a decline in maternal DNA lineages within the blue and humpback populations.

Southern Hemisphere fin whales, however, didn’t display noticeable differences in diversity between pre- and post-whaling DNA samples. This could be attributed to the limited availability of post-whaling DNA samples for this species.

Notably, some whale species can live up to a century, raising the possibility that some of today’s whales might have coexisted with the whaling era. As these whales eventually pass away, there’s a risk of losing more maternal lineages. This emphasizes the importance of preserving the genetic information of current whale populations.

Angela Sremba, now a researcher at OSU’s Hatfield Marine Science Center, highlights the significance of this effort: “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. 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.”

Additionally, the rising temperatures associated with climate change could threaten the preservation of DNA in the whale bones on South Georgia Island, according to Scott Baker.

In essence, this research serves as a vital means of indefinitely preserving the history of these magnificent creatures, as undertaken by the Marine Mammal Institute, which is part of Oregon State’s College of Agricultural Sciences and is situated at Hatfield Marine Science Center in Newport.

Source: Oregon State University

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