How healthy are the oceans? Ask a whale shark

Observer

2 days ago

On a calm morning in May, Brianna Beaulieu, a master's student in marine biology at the University of Western Australia, and several researchers from around the world boarded two research vessels bound for Ningaloo Reef on Australia's west coast.
The scientists have invested months of planning to spend just a few minutes in the water collecting data on one of the ocean's most mysterious animals. Whale sharks are not whales. They are fish, the largest in the sea, growing up to 60 feet long. Yet, surprisingly little is known about their life cycle. Researchers still don't know where whale sharks mate, how often they breed or where they go to give birth.
Beaulieu and her colleagues hope to gain at least some insights into these giants. A whale shark can easily be spotted from the air, cruising just below the surface of the crystal-clear waters of the Indian Ocean. In May, they gather off the reef in numbers so high that, for the half-dozen spotter planes overhead, finding them is simple.
For 20 years, a team from the University of Western Australia has conducted annual fieldwork at Ningaloo Reef. Ningaloo is one of the world's longest fringing reefs, formed unusually close to shore, and is listed as a Unesco World Heritage site.
At the reef, the scientists measure the lengths and dimensions of the animals and collect tissue samples for chemical analysis. They also use drones to assess the body condition of the whale sharks: Are they getting fatter? Thinner? 'Whale sharks can live for over 100 years and grow very slowly,' Meekan said.
'By monitoring them, we're not just learning about the sharks, we're learning about ocean health more broadly,' he said.
'These animals travel thousands of kilometres, so each one is like a sentinel or autonomous sampling unit moving across the Indian Ocean and returning to Ningaloo each year to tell the tale.' Much of Beaulieu's research focuses on measuring the overall health of whale sharks and the impact of human-made threats on them, including boat strikes and 'forever chemicals' in the water.
Whale sharks gather at Ningaloo Reef to feed on plankton that appear each year when coral spawn. Beaulieu dives into the water, taking a compact underwater camera to document a whale shark's appearance. Her colleague Sophie Jones often joins her in the water, gripping a yard-long reference pole that provides a crucial scale to help researchers precisely determine the animal's size, while a drone captures the scene from above.
The whale shark typically remains relatively calm as Beaulieu swims beneath it and holds a small ultrasound device above the surface of its skin, just behind the dorsal fin. The data, which measures skin depth and the condition of the muscles, is sent to a veterinarian to assess the whale shark's internal health and reproductive status.
The encounter lasts just a few minutes, before the whale shark disappears again into the deep blue. Beaulieu and the other researchers then swim to the surface and signal for pickup.
Then they do it all again. The team repeated the sequence 11 times that day: spotting, diving, documenting and collecting data. These few minutes with the whale sharks are the culmination of a year's planning, a gigantic logistical effort to shadow a giant. In the 12 days of fieldwork, the researchers documented 101 whale shark encounters — a bumper year. In 2023, after their boat broke down, they had only four.
Researchers have developed tools that allow the public to contribute to whale shark science. Platforms such as Shark Guardian and Wildbook for Whale Sharks invite divers, tour operators and marine tourists to upload their photographs of whale sharks, ideally with a clear view of the area just behind the gills, where the spot patterns are most reliable.
Sophisticated pattern-matching algorithms then compare these images with an international database of more than 8,000 individual whale sharks, improving the ability of scientists to monitor their movements, residency, growth and health.
— The New York Times