A team of researchers studying the photo-identification database of Indian Ocean whale sharks (Rhincodon typus) say the sharks — at least the young males — don’t go very far. In short: the world's largest fish are homebodies.

Studies suggest that seasonal aggregations of whale sharks at coastal sites in the tropics — including some of the most popular spots in the world for snorkelers to get close to the majestic animals — may be linked by migration.

“While these sharks spend the majority of their lives in the open ocean, they also form predictable seasonal aggregations of mostly juvenile males on the coastal shelves of warm temperate and tropical regions worldwide in certain locations,” say the study’s researchers. Their report was published by the Royal Society Open Science.

Researchers focused on Ningaloo Reef in Western Australia, where young male whale sharks turn up every March. What was poorly understood was where the sharks went after departing the region in July. Ningaloo Reef is one of the areas popular with snorkelers hoping to swim with the world's largest fish.

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“Once departing their seasonal aggregation sites, the individual movements and ranges of whale sharks are largely unknown,” says the researchers in citing why they conducted the study, which consisted of reviewing 6,519 photos taken over several years.

The sharks tend to aggregate where food is seasonally abundant in the Indian Ocean – at Ningaloo, the Maldives, Mozambique and the Seychelles – but scientists did not know whether it was the same population that migrated between these sites.

The new research suggests that the sharks don’t go very far at all, and return to the same sites year after year. Researchers concluded ”that although it was possible for whale sharks to move over entire ocean basins, many sharks appear to remain close to single aggregation sites for several months or years."

Whale sharks have distinctive spot patterns — they are unique to the individual shark, much like human fingerprints — and by running a database of more than 6,000 images through a semi-automated matching program, the team of seven scientists identified about 1,000 individuals. Of these, 35 percent were seen at the same Indian Ocean site in more than one year, and none were found to move across the ocean.

Photographs were taken by researchers, tourism operators and tourists, who swim alongside individual whale sharks and record their flanks with still or video cameras. Ideally, say the researchers, "photos were taken on both of the right and left flanks of the shark although this was not always possible."

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One shark was tracked between Mozambique and the Seychelles, but generally, the populations in the two destinations appear to be isolated, with juvenile males returning regularly to the same sites. Juveniles photographed at Ningaloo in 1992 were seen up to 19 years later, with many sightings in between and some returning in up to six consecutive years.

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Researchers found that females and adult males were rarely spotted at these sites, leading the scientists to theorize that they don’t necessarily behave in the same way as juveniles.

Whale sharks are listed as Endangered on the IUCN Red List. Whale sharks face threats from fisheries, bycatch losses, and collisions with ships. These dangers — combined with the long life span and late maturation of whale sharks (it can take whale sharks up to 30 years to mature) — makes it critical to understand their behavior and migratory patterns, in order to better protect them. The study authors say that when the young males stay close to home, it allows conservation and management efforts to be concentrated in more localized areas.

The scientists now want to increase the number of study sites and photographs taken to boost their knowledge of migration patterns further. “Understanding the movements, connectivity patterns and demography of populations are critical goals of management and conservation strategies for these animals,” say the scientists.

Read the report: The Ecological Connectivity of Whale Shark Aggregations in the Indian Ocean: a Photo-Identification Approach