Sperm Whales Learned to Avoid Nineteenth-Century Whalers
Reference: Whitehead, H., Smith, T. D., and Rendell, L. (2021). Adaptation of sperm whales to open-boat whalers: Rapid social learning on a large scale? Biology Letters, 17, 20210030. https://doi.org/10.1098/rsbl.2021.0030
Whaling in the 1800s
It’s the early 1800s. An American whaler has spotted a pod, or group, of sperm whales in the distance. The whaler quickly jots down the sighting in a logbook and sends smaller boats to hunt down the whales. Sperm whales have a special oil in their head and blubber that is a major commodity at the time. Depletion of whales near the shore has forced the nineteenth-century whalers to explore the open North Pacific Ocean. The whaler watches from the ship as the small boats return empty-handed, disappointedly logging the failed strike. Successful harpoon strikes are far fewer than they used to be when they first started whaling the North Pacific.
Whaling during the 1800s and 1900s caused sperm whale populations to plummet. Since the 1970s, sperm whales have been classified as endangered under the Endangered Species Act. While populations are recovering, sperm whales face many threats, including noise from shipping and drilling, climate change, pollution, and collisions with ships. Commercial whaling has been banned for several decades, but understanding how whales responded to whaling may help us protect whales from todays’ threats.
Nineteenth-century whalers of the North Pacific used logbooks to keep detailed records of their open sea voyages, including the number of sperm whales sighted, struck, and killed. Today, the digitization of these logbooks allows researchers to travel back in time to find insight into early whaling practices and how whales reacted to whalers. Observations that whalers recorded 200 years ago could provide new insights into protecting endangered sperm whales today.
Learning from Logbooks
Data from the logbook entries suggest that successful harpoon strikes of sperm whales declined drastically (58%) during the first few years of whaling in the North Pacific. After this initial drop, success rates stayed consistently low. Researchers Dr. Hal Whitehead and his colleagues tested several potential hypotheses for the decrease in strike success:
- The first whalers of the North Pacific Ocean may have been exceptionally skilled at whaling, and those skills became less polished over time.
- Perhaps the most vulnerable whales – including the young, old, and sick – were captured first, leaving the more challenging whales to catch.
- The whales might have learned to escape whalers’ harpoons based on their own experience with whalers.
- Lastly, the whales that experience whalers may communicate to whales from other pods how to escape whalers.
Using American whalers’ logbooks, the researchers examined 77,749 daily entries. From the 2405 entries that included sperm whale sighting, they determined when the first sperm whales were spotted in areas across the North Pacific. Every day that a sperm whale was sighted within 1000 kilometers of that spot, the researchers determined the whalers’ success rate at striking the whale. They used equations to estimate how strike success would change over time based on the different hypotheses above. The most similar estimate to the data collected from the logbooks is the most likely explanation for the sharp decline in strike success.
Between 1819 and 1844, American whalers spotted sperm whales for the first time in regions across the North Pacific. The researchers found that the loss of whaling skills and capturing the most vulnerable whales were insufficient explanations for the lower strike success. Individuals learning from their own experience with whalers was also not enough to explain such declines. Instead, information sharing between pods of sperm whales is the most likely reason whalers were failing to strike whales.
Spread the Word!
Sperm whale pods are made up of two family units (on average) consisting of females and their young. Considered to be the loudest animals on earth, sperm whales use “clicks” to communicate within and between pods. These loud clicks can travel at distances of several hundred kilometers (about the length of Nebraska, USA).
The equation that considered long-distance communication between pods was the best estimate for the cause behind the declining strike success. The researchers concluded that sperm whales that encountered whalers (and lived to tell the tale) were most likely communicating how to avoid whalers to other sperm whale pods. Nineteenth-century whalers even noted that sperm whales might be communicating danger to other whales causing all nearby whales to flee. The fleeing whales were frequently observed moving against the wind so the whaling ship could not catch up.
As the word spread rapidly amongst North Pacific sperm whale pods, whalers had an increasingly difficult time harpooning sperm whales. This transfer of information between individuals is called social learning and may be a mechanism for animals to adapt to human threats. Learning how life-saving information is shared at such a large scale between members of endangered species can help maximize conservation efforts.
While social learning between sperm whales led to disappointing outcomes for nineteenth-century whalers, it could lead to a promising future for sperm whale populations.