From the Marine Megafauna Foundation
A new collaborative study into the threats posed by the shipping industry to whale sharks has detailed how heavily used shipping lanes regularly pass through seasonal whale shark aggregations, and offers solutions on how to mitigate the impact on populations of the endangered species.
The global merchant fleet has doubled in size over the past 16 years, with around 105,500 vessels of at least 100 gross tonnes registered at the end of 2023, more than half of which are heavy vessels of more than 1,000 gross tonnes. Some studies suggest this could increase by as much as 1,200 per cent over the next three decades.
As a result, ship strikes on large animals have become increasingly common, and associated research into the scale of the problem by scientists from such organisations as the Marine Megafauna Foundation (MMF) has caused growing concern for the populations of whale sharks, which spend most of their time at or near the surface of the water.
Campaigns for the protection of Sri Lankan blue whales have seen some of the world’s major shipping routes redirected, but the impact of ship strikes on whale sharks is more difficult to quantify. While previous studies have shown that the number of incidents is grossly underestimated, exact data is difficult to obtain as whale sharks – like most sharks – are negatively buoyant and sink if killed, essentially hiding the evidence.
Published in the online journal Science of the Total Environment, the new study builds on previous research by mapping 107 different areas across 26 countries where whale sharks are known to be regularly present – including 57 core sites and 52 ‘constellation’ sites, where the sharks gather in the most numbers.
The study’s lead author, Dr Freya Womersley, a researcher at the Marine Biological Association (MBA) and University of Southampton, obtained survey data from more than 75 experts and scientists, with observations reported from 13,080 individual whale sharks.
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The scientists found that whale sharks were most in danger of ship strikes off the coast of Ecuador, Isla Mujeres and La Paz in Mexico, Ewing Bank in the northern Gulf of Mexico, Kota Kinabalu and Redang Island in Malaysia, Pintuyan in the Philippines, Musandam in Oman, and around Taiwan and the islands of Seychelles.
Of these sites, a total of 39 were determined to have peaks in shipping activity that coincided with peak seasonal occurrences of whale sharks, sometimes across several months.
‘Many of these sites had more than one vessel per square kilometre in core habitats,’ said Dr Chris Rohner, Principal Scientist at MMF. ‘The constellation in Isla Mujeres in Mexico had an average of 56 ships passing through the core habitat monthly.’
The researchers looked at how the impact of shipping could be mitigated to offer better protections, such as speed reductions or redirecting ships around core habitats. A simulated 75 per cent reduction in speed resulted in a five per cent increase in the vessel’s total transit time; a redirection around the entire area had even less of an impact, resulting in an average increase in journey time of just 2.4 hours per ship.
It is hoped the new study will provide enough evidence to persuade shipping companies to take action to protect whale sharks – and that it doesn’t need to be prohibitively costly.
‘The almost ubiquitous overlap of at least some large shipping vessel traffic with whale shark aggregations underlines the magnitude of the threat the shipping industry poses,’ said Dr Womersley. ‘Our findings highlight the need for targeted measures within these areas to reduce the risk of collision and improve the conservation status of endangered whale sharks.’
Read the original version of this edited article on the Marine Megafauna Foundation website. the complete study ‘Identifying priority sites for whale shark ship collision management globally’ by Freya C Womersley et al, is published in the online journal Science of the Total Environment
