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Is it best to protect whale habitat where it once was, or where it is now?

Scientists discover that today’s sperm whale habitat is shaped by the ghost of human hunting, hinting at the peril of ignoring the past when working to change the planet’s future.
March 1, 2023

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Scientists of all sorts struggle to resurrect the past. Archaeologists create portraits of ancient societies from bits of pottery, coins and the remains of buildings. Paleontologists piece together the lives of dinosaurs from isolated fossils, a tiny sliver of the life that once roamed the earth. 

So too, ecologists and conservationists trying to restore long-damaged habitats or revive nearly-extinct species are challenged to piece together accurate pictures of the natural world from decades or centuries ago. A flawed understanding of how natural systems once worked can stymie recovery. Scientists in Washington state, for instance, turned to 150-year-old survey records from early colonists to get a better picture of what the region’s river habitat once looked like. The hope was that it could better guide how millions of dollars are spent to recover flagging salmon runs.

Now, scientists working far from the evergreen forests of the Pacific Northwest have discovered that today’s picture of the habitat of sperm whales – some of Earth’s largest animals – doesn’t match with where these creatures once dwelled. The findings could help guide future efforts to boost whale numbers. And it points to the potential perils of ignoring the past when working to change the planet’s future. “In the case of the sperm whale, understanding not only where the species is found today, but also where it once thrived, is key for effective, science-driven conservation planning and action,” said Samuel Turvey, a scientist at the Zoological Society of London (ZSL) who took part in the research.

Ironically, the very source of the whales’ woes provided the clues Turvey and his colleagues needed. Sperm whales get their name from spermaceti, a massive pocket of oily wax in the whale’s head thought to aid with buoyancy and echolocation. It also made them the 19th century equivalent of oil tankers. Whale hunters, many hailing from the New England coast, plied the world’s oceans in search of sperm whales. The oil helped fuel the Industrial Revolution, lighting lamps and lubricating machinery (and providing the raw material for Herman Melville’s Moby Dick). The pursuit of profit and light took a heavy toll. Today, some 360,000 sperm whales are thought to exist, roughly a third of the numbers before the era of commercial whaling.

While those Nantucket whalers were hell on whale populations, they were also meticulous record keepers. The researchers turned to old ship logbooks to try to reconstruct sperm whales’ preferred habitat in the part of the Indian Ocean that flanks Africa’s east coast. The scientists pinpointed 543 sperm whale encounters recorded by whalers in that stretch of ocean, as well as 219 sightings by modern-day scientists. To create a picture of the whale’s prime habitat, they collected information about the characteristics of the ocean around these sightings, including the water depth, the topography of the ocean floor, and its location to nearby land masses.


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It turns out that today’s whales prefer different habitat than the whales of old. Models of prime whale habitat in the region based on contemporary sightings show whales prefer deeper water in more remote areas. By contrast, models using the whaling logbooks showed that 19th century whalers were finding the richest hunting grounds in shallower waters closer to the coast, the scientists reported Feb. 9 in the journal Biological Conservation.

Tom Letessier, a ZSL scientist who helped lead the research, thinks these differences are partly because whale numbers were driven down where hunting was concentrated. But he suspects whales also learned to avoid the most heavily-hunted areas, developing a preference for more remote areas in the quest for refuge from the whalers’ harpoons. “It’s remarkable to consider that the distribution of the sperm whale, the world’s largest toothed animal, could still be being shaped by the ghost of human hunting from several generations ago,” said Letessier.

The insights could have implications for future conservation efforts. Today, there is a push among environmentalists and some world leaders to establish habitat protections for 30% of Earth’s land and ocean by 2030—the so-called 30 by 30 campaign. One thorny question is which habitat is the most important. In the case of sperm whales in the Indian Ocean—and potentially other species in other places—the answer might depend on whether scientists are using a snapshot from today or one culled from old archives.

To test this, the researchers looked at where patches of territory in the Indian Ocean are protected today. While the boundaries of these marine reserves weren’t set with sperm whales in mind, it was possible to see how they overlapped with today’s sperm whale habitat, versus the preferences of 19th century whales. It turns out these protected areas have more in common with historical habitat. Roughly 40% more ocean within the protected areas was prime historical whale territory, compared to modern whale habitat.

There are pros and cons to using such historical data to guide conservation decisions, the scientists note. On the one hand, weighting past habitat preferences could result in people protecting areas that don’t matter very much for a species today. On the other hand, if today’s populations are confined to marginal “refuges,” focusing just on those areas could overlook prime real estate where a species could thrive, if it can find its way back.

“It’s crucial to address any current threats that are pushing a species towards extinction, but we must also recognize that some species now survive only on the very edges of their ideal habitat,” said ZSL’s Turvey. “Our study shows the power of utilizing historical records to unlock important information for modern-day conservation that would otherwise be lost to the past.”

Letessier, et. al. “Contrasting ecological information content in whaling archives with modern cetacean surveys for conservation planning and identification of historical distribution changes.” Biological Conservation. Feb. 9, 2023.

Photo: Sperm whales, NOAA Northeast Fisheries Science Center.

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