Why Whales Disappeared off South Georgia Island

By Jessica Boswell

Jessica Boswell is a senior in the Environmental Studies Department at the University of California, Santa Barbara. She is specializing in species conservation policy and ecology with an outside concentration in marginalized community politics. She is researching terrestrial and marine community dynamics on the Palmyra Atoll as it undergoes various conservation projects.

The waters of South Georgia in the Southern Atlantic Ocean were once teeming with whales, but local populations were driven to near extinction after decades of commercial whaling. Recovery of these important large cetaceans has been particularly slow in South Georgia, and scientists have just discovered why.

In the early 20^th century, whaling operations began in South Georgia, a small remote island in the South Atlantic. Platforms were established in surrounding waters to catch, kill, and process whales, and discard the remains back into the ocean. The industry lasted more than 50 years during which 175,250 whales were reported killed. The official statistics do not include whales that were struck by harpoons but lost in the depths, nor does it include any baby whales who were left behind and starved to death.

In the greater Southern Hemisphere, from the turn of the 20^th century until the 1986 whaling moratorium, commercial whaling operations slaughtered more than two million whales. Since 1986, Japanese whalers have continued to kill whales under the guise of “scientific research,” with annual expeditions to Antarctica, but little research was ever published, and the whale meat was sold commercially in Japan.

The South Georgia population of Antarctic blue whales (Balaenoptera musculus intermedia) was estimated to be around 250,000 just before the exploitation by the commercial whaling industry. By 1972, that number dropped to under 1,000. The Brazilian humpback whale (Megaptera novaeangliae) population also dropped from over 25,000 to a shocking 440 individuals by 1958. Fin whales (Balaenoptera physalus) were also victims of the slaughter, but their populations have yet to be thoroughly studied. While blue whales, humpback whales, and fin whales are beginning to recover elsewhere in the South Atlantic, their recolonization in South Georgia specifically, has been underwhelming.

Scientists from Oregon State University and the Marine Mammal Institute set out to understand why recovery was significantly slower compared to other regions. They compiled existing DNA data from current populations of blue whales, humpback whales, and fin whales inhabiting the South Atlantic, and compared the diversity of mitochondrial DNA (mtDNA) to pre-whaling populations.

South Georgia offers a unique opportunity to study pre-whaling populations because of the collection of whale remains found onshore. Not long after whaling began, the practice of discarding the remains, bones in particular, into the ocean stopped, so the limited samples along the South Georgia shores are essentially time capsules from the period of exploitation.

The results of the study were two-fold. mDNA sequencing revealed that genetic diversity for all species was relatively intact. However, further analysis of rare genetic markers indicated that whaling has had population-wide impacts on distribution, most notably for blue whales and humpback whales.

The preservation of genetic diversity in these species is unsurprising. Whales have a long lifespan, particularly when compared to the length of exploitation in South Georgia. Estimates for surviving individuals were also in the hundreds. The longevity of whales and the abundance of surviving individuals, though nothing like before, is likely why genetic diversity has been maintained.

Although genetic diversity survived, the scientists found evidence that maternal lineages were lost. Maternal lineages include the genetic and behavioral identities passed from mother whales to offspring. Mother whales pass on complex cultures to their offspring including communication (possibly language), behavior, identity, information on foraging areas, and migratory patterns. The authors suggest, “a local extirpation may have led to a cultural loss of known feeding areas and migratory routes within the wider distribution of each species”. This explains why South Georgia is no longer a hub for whale activity – too many local whales were extinguished.

The International Marine Mammal Project spoke with Dr. Scott Baker, co-author of the study, who revealed concerns for the larger ecosystem.

Dr. Baker noted: “Baleen whales are the primary consumers of krill and a critical link in the food web of the Southern Ocean. The loss of fidelity to feeding grounds and the near-extinction of several species of whales are likely to have had an impact on this ecosystem”.

In a more positive light, Dr. Baker pointed out that recovery efforts of whales in the South Atlantic will provide scientists with an interesting case study that will expand the understanding of how climate change can impact species in the region.

Now that whale species are returning to South Georgia, scientists can also observe the recolonization process and how the presence of these key species will impact an ecosystem that has been without them for decades. It will be interesting to see if the individuals returning to South Georgia are related to pre-whaling populations or if the return of whales is entirely a rediscovery of habitats that are sadly vacant.

The lost lineages of South Georgia serve as a prime illustration of how commercial whaling can have tremendous impacts on cetaceans and their futures. The case also represents the importance of using science to enhance future decision-making regarding the protection of marine mammals, their culture, and entire ecosystems.

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The International Marine Mammal Project is working to end commercial whaling and dolphin hunting around the world. Thousands of whales and dolphins are slaughtered or captured every year, threatening the survivability of the species and the ecosystems they inhabit. Your donation to our campaign will help end whaling and dolphin hunts for good. Thank you for your support!