How Sperm Whales Outwitted Whalers By Devising Intelligent Evasive Tactics Against Deadly Harpoons
A research report published by the Royal Society in the Biology Letters journal on 17 March has found out that the rate at which whalers succeeded in harpooning ('striking') sighted whales fell by about 58 per cent over the first few years of exploitation in a region.
The researchers Hal D Whitehead, Tim Smith, and Luke Rendell argue that whales swiftly learned effective defensive behaviour. Sperm whales (Physeter macrocephalus) live in kin-based social units.
"Our models show that social learning, in which naive social units, when confronted by whalers, learned defensive measures from grouped social units with experience, could lead to the documented rapid decline in strike rate."
Some historians have suggested that the success rate of open-boat whalers in harpooning sighted whales—the second stage in these whaling operations—dropped substantially during the initial years of industrial exploitation and that this was due to socially learned changes in whale behaviour.
Quantitative data for the earliest years of any new exploitation of wildlife are usually few or absent, the development of pelagic whaling operations in the North Pacific by American whalers during the middle nineteenth century is well chronicled in digitised whalers' logbooks.
The results showed that the dataset included 77,749 operational voyage-days, with sperm whale sightings on 2,405 voyage-days. The descriptive model indicated a 58 per cent drop in strike rates over time lag scales of 2.4 years, after which they stabilised.
Talking to Live Sciences about the research Hal Whitehead, a professor of biology at Dalhousie University in Nova Scotia, said "At first, the whales reacted to the new threat of human hunters in exactly the same way as they would to the killer whale, which was their only predator at this time,"
"[The sperm whales] all gathered together on the surface, put the baby in the middle, and tried to defend by biting or slapping their tails down. [But against human whalers], that's the very worst thing they could do; they made themselves a very large target."
The whales seem to have learned from their mistakes, and the ones that survived quickly adapted — instead of resorting to old tactics, the whalers wrote in their logbooks, the sperm whales instead chose new ones, swimming fast upwind away from the whalers' wind-powered vessels.
It appears these clever tactics developed by individual whales soon spread across the whale community, with whales learning successful getaway techniques from each other, the research team found.
"Each whale group that you meet at sea typically comprises two or three family units, and the units quite often split off and form other groups," Whitehead said. "So, what we think happened is that one or two of the units that make up the group could have had encounters with humans before, and the ones who didn't copied closely from their pals who had."
"Sperm whales are divided into acoustic cultural climates," Whitehead further added. "They split themselves into large clans, each with distinctive patterns of sonar clicks, like a dialect, and they only form groups with members of the same clan."
Survival against hard conditions is a defining feature of the whales' history. However, now that commercial whaling is largely illegal, many great whale populations have rebounded, still, they face numerous environmental challenges.
Whitehead wants to delve deeper into the ways that different whale cultures are expressed, including the benefits that having one culture over another may help a clan survive.
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