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

The smooth-coated otter (Lutrogale perspicillata) is listed as Vulnerable on the IUCN Red List and as Endangered on Nepal’s National Red List of Mammals. Across its range, which stretches from the lowland rivers of the Indian subcontinent to Southeast Asia, the species has been squeezed by habitat loss, degradation of prey resources, direct persecution and illegal trade. In Nepal, the animal is recorded from the major river systems, including the Karnali, but remains sparsely distributed across the Terai lowlands and poorly documented outside a handful of surveyed stretches. Because otters sit at or near the top of the aquatic food web, changes in their distribution and diet integrate shifts across the entire riverine ecosystem, making them practical sentinels for tracking river health.

The research team, working with approval from Nepal’s Department of National Parks and Wildlife Conservation and Bardiya National Park, surveyed both banks of the lower western branch of the Karnali River below Chisapani Bridge. The stretch cuts through a Terai floodplain mosaic of braided channels, sand bars, riverine forests and grasslands that also support gharial and Gangetic river dolphins. Fieldwork ran from early January to late February 2024, deliberately timed before the monsoon so that floodwaters would not wash away the indirect signs the survey depended on. The river was divided into consecutive one-kilometre segments, and at the midpoint of each segment on both banks, the team established nested sampling plots measuring 100 metres by 10 metres.

The survey covered 70 transects in total. Latrine sites turned up at just 15 plots, roughly 21 percent of those examined, meaning that for every transect with otter evidence, about three had none. In all, the researchers documented 32 latrine sites, some inside the nested plots and others beyond them. The distances of these sites from the active river channel ranged from 13 to 1,021 metres, with a median of 200 metres. A striking pattern emerged when the team correlated spraint counts with distance from the water: the farther a latrine sat from the active channel, the more spraints it contained. The positive correlation, quantified with Spearman’s rank correlation coefficient of 0.531, suggests that otters favour marking sites where deposits are less likely to be erased by daily water-level fluctuations or shoreline wash.

Substrate mattered too. Sandy banks supported the highest and most variable spraint counts, averaging 4.75 per site, compared with means of just 2.00 at stone and mould sites. Statistical testing confirmed that spraint counts were significantly higher on sand than on stone. The finding echoes work from India’s Cauvery River system, where loose sand was a defining feature of otter sites used for grooming and territorial marking. Sand appears to offer a better grooming surface for these semi-aquatic carnivores and improves the persistence and detectability of their marks, a combination that makes sandy banks disproportionately important for otter communication along the Karnali.

To understand what drives latrine placement, the researchers measured a battery of environmental variables at each plot: bank height and slope, river velocity measured with a floating stick, river width recorded with a laser rangefinder, the presence of braided bars and retaining walls, vegetation cover, escape cover distance, proximity to settlements and graded levels of human disturbance. After screening out collinear predictors using variance inflation factors, ten variables entered a generalised linear model with a binomial error structure. Six predictors emerged as statistically significant, and all pointed in the same direction: latrine occurrence declined with increasing distance to escape cover, increasing distance from settlements, increasing river width, faster flow velocity, the presence of islands and the presence of retaining walls.

Model simplification sharpened the picture. From 176 candidate models restricted to a maximum of three predictors, two competitive models survived Akaike’s information criterion corrected for small sample size. Both contained distance to settlement and river width, each carrying the maximum summed Akaike weight of 1.00. The effect sizes were substantial. A one-standard-deviation increase in distance from settlements was associated with roughly 53 percent lower odds of latrine occurrence, while the same increase in river width corresponded to about 92 percent lower odds. In plain terms, otters mark most intensively near human settlements and along narrower, slower sections of the river, where stable marking surfaces and predictable access points between channel and bank are easiest to find.

The proximity-to-settlement result deserves careful reading. It should not be interpreted as a preference for disturbance, the authors caution, but as evidence that otter marking activity overlaps with river sections that experience fishing, foot traffic, livestock use and riverbank modification. That overlap sets the stage for conflict, and the dietary analysis supplied a dramatic confirmation of just how entangled the two species’ fortunes have become. When the researchers dissected 32 spraint samples under a binocular microscope, comparing scales and bones against reference slides prepared from fish caught in cast nets and mounted in permanent slides, fish remains appeared in nearly every sample, 31 of 32, or 96.88 percent. Crab remains appeared in 18.75 percent of samples and bird remains in a single sample, confirming the species’ predominantly piscivorous diet with opportunistic forays beyond fish.

Within the fish component, Labeo dero dominated, appearing in 65.62 percent of spraints, followed by Tor putitora at 31.25 percent. Both are locally important food fishes that communities along the Karnali harvest for subsistence, meaning otters and people are drawing on the same prey base. But the most alarming laboratory finding had nothing to do with prey at all: fishing net material was found wrapped within 15 of the 32 spraints examined. This is direct evidence that otters are regularly interacting with gill nets, most likely while removing or consuming entangled fish. Elsewhere in the species’ range, smooth-coated otters have been reported taking fish directly from nets and damaging gear, fuelling negative perceptions among fishers. Abandoned and lost nets compound the hazard, entangling and injuring wildlife long after they stop catching fish for anyone.

The study arrives at a moment of real conservation opportunity. Rajapur and Tikapur municipalities have jointly declared Nepal’s first Fish Sanctuary, covering 3.9 square kilometres in the very stretch of river the researchers surveyed, a move intended to rebuild prey populations and regulate fishing pressure. The authors argue that practical action should include reducing destructive fishing practices and the safe disposal of damaged nets, implemented through local governments in collaboration with community-based organisations and the river-dependent Tharu and Sonaha communities. Their broader message is that otter conservation cannot be confined to remote, apparently undisturbed river sections, because the animals themselves mark, forage and raise their young in the human-dominated reaches where rivers are most at risk. In the spraints of the Karnali’s otters, scientists have found both a baseline for protecting a Vulnerable species and a blunt record of the pressures bearing down on one of Nepal’s great rivers.

Subject of Research: Latrine site selection and diet of the smooth-coated otter in the Karnali River, Nepal

Article Title: Determinants of Smooth‐coated Otter (Lutrogale perspicillata) Latrine Occurrence and Diet in the Karnali River, Nepal

Article References: Kathariya, R., Sapkota, R. P., Sada, R., Kapali, A., Kathariya, M., & Thapa, K. (2026). Determinants of Smooth‐coated Otter ( Lutrogale perspicillata ) Latrine Occurrence and Diet in the Karnali River, Nepal. Ecology and Evolution, 16(9), Article e74322. https://doi.org/10.1002/ece3.74322

Image Credits: AI Generated

DOI: 10.1002/ece3.74322

Keywords: smooth-coated otter, Lutrogale perspicillata, Karnali River, Nepal, latrine site selection, spraint analysis, diet composition, river conservation, human-wildlife conflict, fishing nets, habitat modelling, freshwater biodiversity