Warming waters as a result of climate change are putting whale sharks on a collision course with commercial shipping lanes that will make them 15,000 times more likely to be struck by ships by the year 2100, a new study has found.

While whale sharks currently live in warm waters around the equator, it’s anticipated that their populations will begin to move into cooler regions as climate change brings average ocean temperatures up in the coming decades.

A new research paper co-authored by Camrin Braun, The Marine Biological Association and the Woods Hole Oceanographic Institution shark biologist, has combined satellite tracking data with global climate models and shipping maps to determine the future distribution of these ocean giants as they move away from the equator in search of more temperate waters.

Whale sharks already spend most of their time in surface waters near the coast, which are often areas of high marine traffic. One such area is offshore of New England, where Braun has observed ‘a rising incidence of whale sharks during the summer.’

His co-authored research suggests that habitat loss as well as the need to find food sources will eventually force the whale shark population into areas of high marine traffic. In a high emissions future, this predicted trend will make whale sharks up to 15,000 times more likely to be injured or killed by ship strikes. It suggests that the western coasts of the USA and Sierra Leone are set to become particular collision hotspots.

‘Global warming is one of the most pervasive facets of human-driven climate change, with the magnitude of projected temperature rises over the 21st Century comparable to that of the largest global changes in the past 65 million years,’ reads the paper, published in the journal Nature Climate Change.

‘Biological responses to warming are already apparent across terrestrial, freshwater, and marine taxa. As environments change, species must either adapt, tolerate, move, or face extinction. A series of commonly articulated hypotheses have emerged in relation to movement, whereby species are expected to shift their distributions under warming to greater elevations (altitude), higher latitudes, or deeper ocean depths to remain within suitable environmental conditions,’ the paper further states. 

Already classified as ‘Endangered’ in the International Union for Conservation of Nature (IUCN) Red List, it’s possible that even relatively small climate-induced changes in the habitat distribution of whale sharks could have a disproportionate impact on collision vulnerability. 

However, speaking with the Natural History Museum, Professor David Sims, a co-author of the research from the University of Southampton, has positioned that the predicted rise in ship strikes on whale sharks would ‘fall sharply if urgent action is taken to address climate change.’

“The shifts we predict are likely to be less extreme if we are able to slow warming and mitigate climate change, suggesting that even complex, multi-factor impacts of climate change can be somewhat alleviated by our actions,” he said.

Whale sharks live in all the world’s tropical waters, but their populations are divided in two. Around three quarters of the fish live in the Indian and Pacific Oceans, with the rest living in the Atlantic Ocean. Despite their size, surprisingly little is known about the life of a whale shark, with knowledge gaps around even some of the most basic details including reproduction, breeding grounds, and population structure.

To change this, scientists have been tracking the animals using satellite tags and combining this with reports to help identify around 25 aggregation sites where sharks come together in large numbers. These include areas off the coast of Australia, Mexico, and the Atlantic island of St Helena. 

In the current study, researchers worked out the kind of habitats the fish most often frequent by combining 15 years of satellite tracking data from almost 350 whale sharks with details of ocean conditions. This was then used to model where whale sharks might live in three future climate scenarios featuring low, medium, and high emissions.

In the highest emissions scenario, it’s predicted that almost 60% of countries will lose more than half of their whale shark habitat by 2100. The largest changes will occur in the eastern Pacific, where it’s estimated that as much as five million square kilometres of whale shark habitat – an area larger than the EU – will become unsuitable for fish to live in.

Couple this with the predicted continued expansion of the world’s merchant fleet – an industry that has doubled in size in the last 16 years to the more than 100,000 ships transporting goods worldwide, today – by as much as 1,200% over the next 27 years, and the outcome for whale shark populations around the world looks bleak.

Collisions with wildlife are a growing concern and can be a leading cause of death for large marine animals, with more than 75 species at risk of population-level consequences. It’s estimated that whale shark numbers have fallen by around 63% in the Indian and Pacific Oceans, and over 30% in the Atlantic. This is due to a combination of fishing bycatch, unsustainable tourism, and pollution.

Dr Freya Wormersley, a lead author on the most recent study has now called for action to limit the levels and impact of ship strikes by putting new mitigation measures in place. This could include reducing the speed of ships passing through whale hotspots by up to 75%, which previous research shows, would only increase a ship’s journey time by 5%.

“One of the benefits of speed reductions is that they can be temporarily introduced during whale shark peak seasons,” said Dr Wormersley. “These speed limits can also be applied to smaller vessels which are less deadly but can still damage the sharks.”

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