UCLA biologists have found that whaling in the 20th century wiped out 99% of the Eastern North Pacific fin whale breeding population. This percentage is 29 percent higher than prior assessments. The alarming revelation is a stark reminder of human impacts on the environment.
“When you look at whaling records, you can only tell how many were killed. You can’t tell how many there were to begin with,” said study co-author Meixi Lin. “We know 20th century whaling was severe, but we didn’t know how severe it was for fin whales.”
However, the researchers also found a silver lining. They determined that genetic diversity among the remaining fin whales of the Eastern North Pacific is still rich enough to ensure that – with adequate conservation measures – these whales can recover without facing the threats of inbreeding.
The UCLA study is a significant advancement from previous research, which was restricted to whaling records or mitochondrial DNA. With the entire genome at their disposal, the researchers now possess a comprehensive understanding of the current size and genetic diversity of these whales.
While most whale species faced devastation due to 19th-century whaling, the larger species, particularly blue and fin whales, managed to remain largely unaffected.
However, industrial whaling in the subsequent century flipped this scenario, leading to the near extinction of fin whales, especially in the Eastern North Pacific.
The methods employed in the research were not only innovative but also challenging. Gathering DNA samples from the whales was not easy.
“Getting samples from live whales is hard, because you don’t know where they’re going to be – and when they come up, you only have a moment to take the sample before they go back underwater,” said study co-author Nigenda-Morales. “It is a humbling experience to conduct field research and interact with the second-largest animal on the planet.”
Overall, 50 whales were studied, including fin whales from the Gulf of California. These whales were not targeted by whalers, but belong to a small, isolated group.
“Nevertheless, this population has been small with limited gene flow from and to the Pacific for thousands of years,” noted the study authors. “In contrast, the Eastern North Pacific population was large, interconnected, and overexploited.”
The analysis revealed that the Gulf of California fin whales diverged about 16,000 years ago, maintaining a population of around 114 adult breeders.
The Eastern North Pacific population remained stable at around 24,000 individuals for millennia. However, 20th-century whaling caused a catastrophic reduction from 24,000 individuals to only 305 in just 26 to 52 years.
While earlier studies estimated a 70% decline, the current data illustrates the contrast. The severe drop made the genomic reduction distinctly evident, as noted by Nigenda-Morales.
“It’s usually hard to detect such strong recent reductions in the genome. But in this case, fin whales were really abundant before, which made the sudden reduction very obvious in our data. If the reduction hadn’t been so strong, we wouldn’t have been able to detect it,” said Nigenda-Morales.
The research also revealed the significance of the Eastern North Pacific fin whale population for the fin whales in the Gulf of California.
While the Gulf of California population has faced its set of challenges, including the amplification of harmful genes, occasional visits from Eastern North Pacific whales have introduced new genetic material, ensuring their survival.
However, the situation remains fragile. While current protections appear adequate, they need to be sustained for an extended period, ensuring the continued recovery of these whale populations.
External threats, including climate change and human disturbances like ship strikes, could still threaten this progress.
“With improvement in computational models, we can incorporate factors like climate change and relate the risk of extinction from human-mediated processes with what’s happening at the genomic level,” said study co-author Kirk Lohmueller. “Continuing to develop such models is as important as collecting more data.”
The research, which was conducted in dedication to the late UCLA Professor Robert Wayne, represents a significant step forward in understanding the complexities and challenges faced by fin whales.
The study is published in the journal Nature Communications.
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