For World’s Biggest Shark, Ship Strikes an Increasing Problem
Increasing numbers of whale sharks are showing up with scars and wounds caused by encounters with ships.
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Every March, off the northwest coast of Australia, whale sharks gather in the hundreds to bask in the shallow tropical waters at Ningaloo Marine Park. But at this UNESCO World Heritage Site, the number of whale sharks showing up with major scars and lacerations from ship strikes is a cause for concern.
Emily Lester, a doctoral candidate working with the Australian Institute of Marine Science, has been studying the wounded fish. “It looks like this threat has been increasing,” she says.
Lester and her colleagues recently completed a study analyzing images of 913 whale sharks taken between 2008 and 2013 by tour boat operators and research organizations working in the park. Almost one-fifth of the whale sharks documented showed major scarring or fin amputations. While some scars were from predator bites, most were the marks of blunt trauma, lacerations, or amputations arising from encounters with ships. The number of major injuries recorded in 2012 and 2013 was almost doubled that of 2011.
But even such striking numbers likely underestimate the true toll. Only sharks that survived their injuries and came back to Ningaloo to be photographed are documented in the study. Whale sharks that died and sank to the ocean floor weren’t accounted for in the statistics.
Increasing global shipping traffic, which grew fourfold from 1992 to 2012, causing more frequent ship strikes could explain the rise in the number of injured whale sharks. Some of the jump could also be attributable to better reporting with greater awareness from tour operators, who are required to photograph the sharks for research purposes, says Holly Raudino, a researcher with Western Australia’s Department of Biodiversity, Conservation and Attractions (DBCA), and a collaborator on the study.
Raudino is confident that licensed tour operators in Ningaloo Marine Park are complying with the code of conduct set by the DBCA, which outlines how boats must move around whale sharks to avoid collisions. In addition, tour boat operators use spotter planes to guide their approach toward whale sharks. “It’s more likely that the collisions are occurring outside the marine park or potentially with recreational boaters,” she says.
Whale sharks swim for thousands of kilometers on their annual migrations—well beyond Ningaloo’s park boundaries—crossing major shipping channels as they go. Exactly where they sustain their injuries is unknown.
Beyond Ningaloo, it is difficult to follow whale sharks’ movements, given the animals can dive as deep as two kilometers and tracking devices can be lost. As more data comes in from tracking studies, Raudino says they could overlay composite satellite data of whale shark migrations with global shipping tracks to identify hotspots where collisions are likely occurring.
Vanessa Pirotta, a marine wildlife conservation scientist from Macquarie University in Australia who was not involved in the study, says that with the right data, shipping traffic could be diverted around important migratory corridors to protect whale sharks in international waters.
She says in the North Atlantic there has been success with the Ship Strike Rule, a US regulation introduced in 2008 that reroutes ships around seasonal habitats of North Atlantic right whales. Both right whales and whale sharks are large, surface-active animals that are vulnerable to shipping activity, Pirotta says, so “that’s a similar approach that could be looked at or adopted.”