Whale sharks face deadly threats in shipping lanes

New research on whale sharks reveals that heavily trafficked shipping lanes intersect with critical feeding grounds of this endangered species, posing significant risks.

The researchers identified areas where these species are most vulnerable to collisions with large shipping vessels. The team mapped whale shark aggregations and overlaid them with shipping traffic data.

Lead author Dr. Freya Womersley from the Marine Research and Conservation Foundation (MARECO) and the University of Southampton emphasized the severity of the threat to these marine giants.

“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.”

Whale sharks and the growing threat of shipping lanes

The global merchant fleet has doubled in size over the past 16 years, with over 100,000 ships now transporting goods worldwide. This number is expected to grow by as much as 1,200 percent over the next 27 years.

Ship strikes, collisions between vessels and marine wildlife, are a leading cause of death for large marine animals, affecting over 75 species and posing population-level threats.

Whale sharks spend nearly half of their time in surface waters, often in coastal areas frequented by shipping vessels.

Dr. Gonzalo Araujo, director at MARECO, noted the difficulty in quantifying collision-related threats due to the nature of these species.

“Collisions with large ships are likely to be fatal for whale sharks, but evidence is scarce because whale sharks are slightly negatively buoyant, so their bodies sink. To inform conservation efforts, it’s important to quantify collision-related threats even when direct evidence is lacking,” said Dr. Araujo.

Identifying high-risk shipping sites

Whale sharks, primarily solitary creatures, gather at specific sites around the world known as constellations to feed. Protecting these high-density areas is crucial.

The researchers leveraged insights from over 75 experts worldwide to map these constellations. The team identified 107 areas across 26 countries with frequent whale shark sightings, based on over 13,000 individual observations.

Using data on large ship positions from Global Fishing Watch, the experts pinpointed regions where collisions are most likely. The most dangerous areas include the coast of mainland Ecuador, Isla Mujeres and La Paz in Mexico, Ewing Bank in the Gulf of Mexico, Kota Kinabalu and Redang Island in Malaysia, Pintuyan in the Philippines, Musandam in Oman, and regions around the Seychelles and Taiwan.

The researchers identified 39 sites where high shipping activity overlaps with peak whale shark occurrences.

“Many of these sites had more than one vessel per square kilometer in core habitats. For example, the constellation in Isla Mujeres in Mexico has an average of 56 ships passing through the core habitat monthly. These sites require urgent action to reduce the threats posed by shipping,” said Dr. Chris Rohner, principal scientist at MMF.

Mitigating collision risks for whale sharks

The research team explored mitigation strategies, including simulating vessel movements within the whale shark constellation at Ewing Bank in the northern Gulf of Mexico. Reducing vessel speeds by 75% led to a minor increase in transit time – about 5% – but significantly lowered the risk of collisions.

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

Rerouting ships around core habitats had an even smaller impact, with only a 0.5 percent increase in total transit time (about 2.4 hours per vessel) and a 1.1 percent increase in total distance traveled.

“Rerouting is the most direct way to reduce the risk of collision, and our results suggest that this will often be more cost-effective than speed reduction, mainly because whale shark core sites are small. Movements of as little as 12 nautical miles (22.2 km) away from a core whale shark habitat could mean fast transiting ships avoid the site entirely,” noted Dr. Araujo.

Amy Fraenkel, executive secretary of the Convention on the Conservation of Migratory Species of Wild Animals (CMS), emphasized the importance of these efforts.

“CMS plays a pivotal role in securing the long-term survival of the whale shark – a globally endangered species. Ensuring the safety of this highly migratory species from vessel collisions within its migratory range, particularly at aggregation sites, is a key goal under CMS,” said Fraenkel.

The study is published in the journal Science of The Total Environment.

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