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Protecting ocean giants from marine traffic

As our economies continue to grow, so does our dependence on maritime transport to move our merchandise around the globe which presents a growing threat to a broad range of marine megafauna species such as cetaceans, sea turtles and fish, including whale sharks. Not only are species affected by stressors such as anthropogenic noise pollution, but they face entanglement in fishing gear and fatal collisions from ship strikes. Information on fatal collisions for whale sharks is poorly understood across the whale shark’s distribution range, and as the species is listed as ‘Endangered and decreasing’ (IUCN, Red List) globally, there is a strong need to understand where shipping lanes are overlapping with whale shark aggregations.

A major challenge to understand the scale of impact from heavy marine traffic to whale sharks is the lack of data on species aggregations in shipping lanes. A new collaborative global paper which overlapped years of satellite tracking data from 348 whale sharks all over the world, with global shipping traffic data, has just been released. Data from tracked sharks shows that whale sharks have area-restricted movements, interspersed by long-distance travel and confirmed known aggregation hotspots such as the northern coast of West Papua, the north-western coast of Australia, the Pacific coast of Panama, Qatari waters in the Arabian Gulf and the north-eastern coast of the Yucatán Peninsula (Mexico). Using depth tracking tags it was also found that whale sharks spent almost half of their tracked time in surface waters (<20m), where ship strikes are more likely.

Images: Brooke Pyke @brookepykephotography

You can see from this image the impacts of shipping strikes on whale sharks, and whilst this particular shark may have survived, collisions with larger vessels travelling at higher speeds would likely be fatal. This collaborative research paper highlighted hotspots of potential collision risk in all major oceans, which mainly overlap with cargo and tanker vessels in gulf regions, where dense shipping traffic co-occurred with large seasonal whale shark aggregations (e.g. off Isla Mujeres in Mexico).

Collision risk estimates were also found to correlate with reported whale shark mortality from ship strikes, indicating higher mortality in areas with greatest overlap. The last known locations of tracked sharks coincided with busier shipping routes more often than expected, suggesting substantial ‘cryptic’ lethal ship strikes may be occurring, potentially impacting population recovery and highlighting the need for us to work with the shipping industry to protect the endangered whale shark and other marine megafauna species such as cetaceans who may be at risk from collisions.

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