Sperm whales, the largest of the toothed whales and among the deepest-diving mammals on Earth, present a formidable challenge for conservation planners. They travel enormous distances across national jurisdictions and the open ocean, moving between feeding grounds, breeding areas and migration corridors that can span thousands of kilometres. Alexander Lomas, from the University of Exeter and lead author of the study, emphasized that this mobility is precisely why protection must cover extensive areas. By identifying core habitats, the study provides a baseline from which such protection can begin to be built, but the researchers also found a shifting patchwork of suitable areas as the climate changes, which they say highlights the need for dynamic protection rather than static, fixed boundaries.

To understand where sperm whales live today and where they are likely to live in the future, the team employed ensemble ecological niche models, a technique that combines multiple statistical modelling approaches to predict species distributions. These models were trained on whale survey data gathered by nine research groups working across the western Indian Ocean, including the Marine Megafauna Conservation Organisation, GLOBICE, the African Aquatic Conservation Fund and the IndoCet Consortium, alongside work by governments and non-governmental organisations from countries around the region. Ensemble approaches are considered more robust than single models because they average out the biases and uncertainties of individual methods, producing more reliable predictions of where environmental conditions are suitable for a species.

The study’s projections of future habitat loss are striking, and they vary considerably depending on which greenhouse gas emissions pathway humanity follows. Under the so-called optimistic scenario, known as SSP1-2.6, in which global emissions decline rapidly, 40 percent of suitable sperm whale habitat in the south-west Indian Ocean is projected to be lost by the year 2100. Under the intermediate scenario, SSP2-4.5, the projected loss is 37 percent. Perhaps counterintuitively, the pessimistic scenario, SSP5-8.5, projects a smaller direct habitat loss of 20 percent, but the researchers caution that this figure comes with a major caveat: in that scenario, stronger ocean currents predicted under extreme warming appear to offset some of the damage caused by rising temperatures, although the team did not assess the wider ecosystem impacts of such extreme climate change, which could prove harmful to the whales.

The physical structure of the seafloor emerged as a critical determinant of sperm whale presence. The findings suggest that underwater topography, particularly steep slopes, is key for the species, because these slopes promote the upwelling of nutrient-rich waters from the depths into sunlit layers where the whales’ prey can thrive. Sperm whales feed almost exclusively on deep-sea squid, hunting them in the darkness hundreds or even thousands of metres below the surface using powerful echolocation clicks. Where nutrient delivery sustains productive waters, squid populations flourish, and the whales follow. The study identified long-term core habitat, places that remain key for the whales despite warming, particularly off the Seychelles and Mauritius and along the steeply shelving ridges that lie between them, including areas around the vast Saya de Malha bank.

Dr Jeremy Kiszka, a Professor at Florida International University in Miami who was involved in the study, noted that climate change is predicted to substantially reduce suitable habitat for sperm whales in the south-west Indian Ocean, but that the team also identified places that could remain important refuges for these animals through the end of the century. These refugia, where suitable conditions are projected to persist even as the surrounding ocean changes, represent natural anchors for conservation planning. Protecting such areas could safeguard breeding females and their calves, which tend to occupy predictable ranges, while ensuring that the wider network of habitats the whales depend upon remains connected across the region.

The historical context of the region adds urgency to the findings. Sperm whales in the south-west Indian Ocean were targeted by the whaling industry in the past, and evidence on their numbers and movements has been limited since then. The new study draws on data from a series of research expeditions carried out over the last two decades, representing some of the first systematic scientific attention these populations have received since the whaling era. Dr Kirsten Young, who leads the Exeter Cetacean Research Group, described the experience of encountering the whales hundreds of kilometres from land around Saya de Malha bank as incredible, noting that the team is among the first to study these animals since the days of whaling. She added that the threats they face are a reminder of how far human influence reaches into the natural world, and of the urgent need to reduce human impact.

The implications extend well beyond a single charismatic species. Dr Young argued that extensive, dynamic protection will not only benefit iconic species like sperm whales, but that protecting large, interconnected swathes of the ocean would allow the wider ecosystem, and the multitude of species within it, to recover and thrive. Large marine protected areas that encompass the full range of a wide-ranging predator inevitably capture the habitats of countless other organisms, from the deep-sea squid at the base of the whales’ diet to the tuna, seabirds and sharks that share the same productive waters. In this sense, sperm whales can function as an umbrella species, with conservation measures designed around their needs delivering benefits that cascade through entire food webs.

The international collaboration underpinning the study offers a model for future ocean science. Lomas stressed that the paper highlights the benefits of international scientific collaboration, noting that it depended on data from nine research groups and on work by governments and non-governmental organisations from different countries around the Indian Ocean. Violaine Dulau, chair of IndoCet, the Indian Ocean network for cetacean research, said that by bringing together data and expertise from across the western Indian Ocean, researchers can finally see the bigger picture, and that thinking at the scale of the ocean is essential to understanding the habitats sperm whales depend on and what their future may look like. This pooling of survey effort across national boundaries mirrors the scale of the animals themselves and the scale of the threats they face.

As the ocean continues to warm, the study’s central message is that conservation planning must anticipate the future rather than merely record the present. Dr Young concluded that in a rapidly changing ocean, scientists need to know not only where animals are today, but where suitable habitat is most likely to persist in the future. Static protected areas drawn around current whale distributions could inadvertently protect waters that become unsuitable within decades, while missing the refugia that will matter most by 2100. The combination of long-term core habitat identification and climate-informed projections offers policymakers a template for adaptive management, one in which protection networks can expand, contract and shift in step with the moving mosaic of suitable conditions. For a species that survived industrial whaling but now confronts a warming ocean, the difference between static and dynamic conservation may determine whether the south-west Indian Ocean’s sperm whales endure through the century ahead.

Subject of Research: Climate-driven shifts in sperm whale habitat and conservation planning in the south-west Indian Ocean

Article Title: Sperm whale study highlights need for ‘extensive & dynamic’ conservation

Article References: Sperm whale study highlights need for ‘extensive & dynamic’ conservation. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: sperm whales, climate change, marine conservation, south-west Indian Ocean, habitat modelling, High Seas Treaty, Endangered Species Research, ecological niche models, Seychelles, Mauritius, deep-sea squid, ocean warming