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

A new study of sperm whales highlights the need for ocean conservation that covers large areas – with boundaries redrawn as our climate changes.

The research team, led by the University of Exeter, combined sperm whale surveys in the south-west Indian Ocean with predictions of how climate change will shift where the whales are found in future.

Suitable whale habitat is expected to shrink as temperatures rise – although the stronger currents predicted by more extreme warming may benefit whales.

The study also found “long-term core habitat” – places that remain key for the whales despite warming – particularly off the Seychelles and Mauritius, and the steeply shelving ridges in between.

“Sperm whales travel great distances, so protection must cover extensive areas to allow them to feed, breed and migrate,” said Alexander Lomas, from the University of Exeter.

“By identifying core habitats, our study provides a baseline to begin building this protection.

“But we also find a changing patchwork of suitable areas as the climate changes – highlighting a need for dynamic protection.”

Initiatives including the recently agreed High Seas Treaty aim to bring about global-scale conservation – addressing threats including overfishing, noise, pollution and climate change.

Dr Kirsten Young, who leads the Exeter Cetacean Research Group, said: “Extensive, dynamic protection will not only benefit iconic species like sperm whales.

“Protecting large, inter-connected swathes of the ocean would also allow the wider ecosystem – and the multitude of species with it – to recover and thrive.”

Sperm whales in the south-west Indian Ocean were targeted by the whaling industry in the past.

Evidence on their numbers and movements has been limited since then, but the new study uses data from a series of studies carried out in the last two decades.

The findings suggest underwater topography, particularly steep slopes, is key for sperm whales, as slopes promote nutrients coming from the depths into the area where their prey – deep-sea squid – can thrive.

The projected percentage of habitat lost by the year 2100 under different climate scenarios is:

• 40% for an “optimistic” scenario (called SSP1–2.6) where humanity’s greenhouse gas emissions decline rapidly.
• 37% for an “intermediate” scenario (SSP2-4.5).
• 20% for a “pessimistic” scenario (SSP5-8.5). The study projects that damage caused by extreme climate warming would be offset by stronger currents. However, the authors stress that they did not assess wider ecosystem impacts, which could be harmful to whales.

Dr Jeremy Kiszka, a Professor at Florida International University, in Miami, and involved in this study, said: “Climate change is predicted to substantially reduce suitable habitat for sperm whales in the southwest Indian Ocean, but we also identified places that could remain important refuges for these animals through the end of the century.”

Commenting on seeing the whales during a research trip to the Indian Ocean, Dr Young added: “Meeting these sperm whales hundreds of kilometres from land, around Saya de Malha bank, was incredible – we are some of the first people to study them since the days of whaling.

“But the threats they face are a reminder of how far human influence reaches into the natural world, and the urgent need to reduce our impact.”

Lomas added: “This paper highlights the benefits of international scientific collaboration.

“It depended on data from nine research groups – and work by governments and non-governmental organisations – from different countries around the Indian Ocean. For example, the Marine Megafauna Conservation Organisation, GLOBICE, African Aquatic Conservation Fund and the IndoCet Consortium.”

Violaine Dulau, chair of IndoCet, the Indian Ocean network for Cetacan research, said: “By bringing together data and expertise from across the western Indian Ocean, we can finally see the bigger picture. Thinking at the scale of the ocean is essential to understanding the habitats sperm whales depend on and what their future may look like.” 

Dr Young concluded: “In a rapidly changing ocean, we need to know not only where animals are today, but where suitable habitat is most likely to persist in the future.”

The paper, published in the journal Endangered Species Research, is entitled: “Using ensemble ecological niche models to predict long-term core habitat of sperm whales (Physeter macrocephalus) in the southwest Indian Ocean under future climate scenarios.”