About the author
Angie Sremba is an Assistant Professor (Sr Res) at the Cooperative Institute for Marine and Ecosystem Research Studies at Oregon State University. She is also an affiliate of the Marine Mammal Institute at OSU where she completed her PhD studying the impact of the commercial whaling industry on the genetic diversity great whales working with Dr. C. Scott Baker.
A new study, recently published in the Journal of Heredity, utilizes DNA from bones left over from whaling in the last century to investigate how exploitation impacted the genetic diversity of great whales.
During the 20th century, humans killed over two million whales in the Southern Hemisphere, bringing many populations near extinction. Although international protection was agreed upon in the early 1960s, the former Soviet Union and Japan still engaged in large-scale illegal whaling. One species severely impacted by commercial whaling was the Antarctic blue whale. This population once spread throughout the Southern Ocean and estimates suggest it dwindled from over 250,000 whales to fewer than 400 in just over 60 years. Researchers have explored the impact of this exploitation on the genetic diversity of many surviving populations using small biopsy samples from living whales, but few studies have surveyed the diversity of the pre-whaling populations using historical sources of DNA (e.g., Sremba et al. 2012).
Although commercial whaling ended with a moratorium in 1986, the remains of this era, in the form of innumerable whale bones, still litter the beaches near abandoned whaling stations in the Southern Ocean. These bones serve as a silent testament to the industry’s excesses during its peak. The epicenter of this slaughter was the South Atlantic Island of South Georgia, where the first whaling station was established in 1904. Over the next 61 years, more than 175,000 whales were killed, before the station closed due to the extirpation of local populations. These early whaling stations essentially functioned as ship-board processers, with the carcass of the whale discarded into the harbors following processing. Thousands of bones remain scattered along the shores over 100 years later. We used the DNA from this “molecular archive” to estimate pre-whaling diversity in the South Atlantic populations of blue, humpback, and fin whales. We then compared our results to previously published data on the contemporary diversity in these same populations.
This research was originally inspired by a collection of nearly 400 whale bones from South Georgia by one of our co-authors, Professor Tony Martin. The DNA extracted from these bones allowed not only species identification (Sremba et al. 2015), but also direct estimates of mitochondrial DNA (mtDNA) diversity in pre-whaling populations. Among those samples, we identified 158 humpback whales, 48 fin whales and 18 blue whales. To increase the number of blue whale bones in our study, our team collected nearly 100 additional bones from South Georgia and other early whaling stations around the West Antarctic Peninsula.
We found strong evidence for the loss of mtDNA lineages in the blue and humpback whales, and evidence of differentiation in the pre- and post-whaling haplotype frequencies of both species. For blue whales, we attribute this loss of haplotypes primarily to a population bottleneck, resulting from the near extinction of this species. For the humpback whales, the change in haplotype frequencies is potentially due to a loss of maternal fidelity in the local feeding grounds of South Georgia, followed by a replacement from other subpopulations as the whales slowly recover. These hypotheses could be further tested by collecting genetic samples from the contemporary populations around South Georgia. Previously, this direct comparison was not possible because the whales had essentially been extirpated from the local waters of South Georgia. It is encouraging that after nearly 60 years of protection, these populations are finally showing evidence of recovery (Kennedy et al. 2020).
For now, the bones scattered along the shorelines of South Georgia preserve the genetic diversity of the once-abundant great whales of the Southern Ocean. The cold temperatures of the Antarctic maintained this remarkable archive, but with the rapidly increasing temperatures in this region, the future preservation of these bones is in jeopardy. There is an urgent need for further non-destructive sampling and whole-genome sequencing to permanently preserve the molecular legacy of whaling.
References
Sremba AL, Martin AR, Baker CS (2015) Species identification and likely catch time period of whale bones from South Georgia. Marine Mammal Science. https://doi.org/10.1111/mms.12139.
Sremba AL, Hancock-Hanser B, Branch TA, LeDuc RL, Baker CS (2012) Circumpolar diversity and geographic differentiation of mtDNA in the critically endangered Antarctic blue whale (Balaenoptera musculus intermedia). Plos One. https://doi.org/10.1371/journal.pone.0032579.
Kennedy AS, Carroll EL, Baker CS, Bassoi M, Buss D, Collins MA, Calderan S, Ensor P, Fieldin, S, Leaper R MacDonald D (2020) Whales return to the epicentre of whaling? Pre-liminary results from the 2020 cetacean survey at South Georgia (Islas Georgias del Sur). Report (SC/68B/CMP/22) to the Scientific Committee of the International Whaling Commission.