Migrating whale sharks make pit stops at oil and gas rigs

Like rolling into a gas station during a road trip, whale sharks use oil and gas rigs as a pit stop during their migrations of thousands of kilometers across the oceans. The human-made structures attract marine life — including the sharks’ favorite snack: plankton. But experts worry that this lure could put the endangered behemoths at risk of ship strike or chemical pollution.

Satellite tracking of whale sharks off the coast of western Australia shows how oil and gas platforms influence the movements of these gentle giants, marine ecologist Ben D’Antonio and colleagues report January 18 in Diversity and Distributions. “As they migrate across the ocean, they are stopping over and moving between features to presumably grab an easy meal before continuing with their migration,” says D’Antonio, of the Australian Institute of Marine Science (AIMS) and University of Western Australia in Perth.

The biggest fish on the planet (Rhincodon typus) — reaching up to 18 meters long — munch through 20 kilograms of plankton daily. Oil and gas rigs act like artificial reefs, creating plenty of prey to draw the sharks in.

“Think of seafloor features like a truck stop on a highway,” D’Antonio says. “On a family vacation, we often pull into truck stops to fuel up and grab a quick bite before [heading] to our final destination. Whale sharks seem to be using seafloor features in a similar way.”

Over 14 years, the researchers tagged 78 whale sharks, tracked their movements and cross-checked the location of geomorphological features to see how these affect the sharks’ routes. While natural pinnacles, canyons and seamounts also act as pit stops, this lure towards oil rigs — possibly bolstered by plankton’s attraction to the platforms’ beams of light — could put the huge filter feeders at risk of being hit by a ship or pollution from oil spills or discharges. It’s impossible to know exactly how many are being killed by vessels because their bodies sink without a trace.

The authors hope this finding will help decision makers managing marine protected areas and raise awareness of the potential impact on marine life when human-made platforms are decommissioned or new structures, like offshore wind turbines, are built. “This will become more relevant as developments for renewable energy begin to add additional structure to many areas along continental margins,” D’Antonio says.