The whale shark is the world’s largest fish and is globally assessed as Endangered on the International Union for the Conservation of Nature (IUCN) Red List, and Largely Depleted on the IUCN Green Status of Species. This negative outlook is largely the consequence of targeted fisheries and non-targeted fisheries induced mortality across much of their tropical to warm-temperate distribution. With long generation times, they are susceptible to anthropogenic threats. While direct fisheries have now largely stopped, an additional source of cryptic mortality that could be hindering the recovery of the species was recently attributed to ship strikes.

Whale sharks spend around half of their time in the top 20 m of the water column, and as such are prone to vessel collisions. Collisions with large vessels are likely fatal, yet due to the negative buoyancy of their cartilaginous skeletons, dead whale sharks sink and thus go unreported. To ensure the species recovery, we need to mitigate their main threats, including ship strikes.

Whale sharks are likely to be most at risk from ship strike in major shipping routes as they travel far distances across the ocean, and within small, predictable hotspots where up to 400 individuals aggregate, often to feed. Over 340 satellite tracks have identified the key areas where whale sharks are at high risk from shipping during their migrations. These included areas in all oceans, such as in the Gulf of Mexico, the Gulf of Panama, between Australia and Indonesia, and in the Red Sea. Some of the tagged whale sharks also revealed potential mortality events, where the tracks stopped right in the middle of busy shipping lanes.

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