More Than Half  of St Helena's 2021 Whale Shark Sightings Were New to Science

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Male and female whale sharks gather around St Helena in equal numbers (Photo: Shutterstock)

Scientists from the remote South Atlantic island of St Helena have discovered that more than half of the whale sharks identified in its waters this year have never been recorded anywhere in the world before.

Since January 2021, the St Helena National Trust Marine (SHNT) team has been conducting boat surveys across the island’s Marine Protected Area, which, at 444,916 square kilometres, spans an area almost size of France. During that time, 21 of the whale sharks – known locally as 'bone sharks' – identified by the scientists at SHNT were found to be new to the global Wildbook for Whale Sharks database.

Whale sharks have spot patterns behind their gills which, like human fingerprints, are unique to each individual animal. Studying the markings helps researchers identify and track the sharks, helping them to understand where the sharks are travelling, and how many are present around St Helena at any given time.

Whale sharks gather around St Helena each year between December and March. Historical whale shark population data collected by the St Helena Government has shown that the male and female sharks are present in almost equal numbers, the only known location in the world where such an aggregation occurs. The near 50/50 split, together with anecdotal reports from local experts, very strongly suggests that whale sharks gather in St Helena's waters to mate, although the behaviour has yet to be officially recorded.

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More than half of the 2021 whale shark sightings were new identifications (Photo: EMD Marine, St Helena)

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From 2021 onwards, whale shark research on St Helena has been led by the SHNT under the Bone Shark Research Project (BSRP). Supported by the Blue Marine Foundation (BLUE), the team is now leading a 'comprehensive research intitiative' to learn more about the endangered species and better inform the protection and management of St Helena's marine protected area. The team will continue to work closely with a network of citizen scientists from St Helena Island, including local fishermen, divers and boat operators, who provide insights into the number and locations of whale sharks that are present around the island.

This year's sightings brings the total number of whale sharks identified around St Helena to 312, although sightings were down compared to previous years. Just 37 sharks were spotted during the most recent season, 21 of which had never been identified before, although the number is significantly lower than the 127 sharks identified in 2019. In addition to the new sightings, the BSRP's findings also indicate that the sharks prefer certain sites to others, including the shallow sea-mounts known as 'The Caps', located off St Helena's north-eastern shore.

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The bait ball vortex is a rare event where small fish swirl around the whale sharks (Photo: SHNT Marine Team)

'As abundance data is gathered across consecutive seasons, more individual sharks are recorded returning to St Helena, and shark behaviour is monitored further, the Marine Team hopes to identify patterns in whale shark activity that reveals the services that St Helena's Marine Protected Area provides to the world's largest fish,' said SHNTs Marine Officer, James Wylor-Owen. 'Such insight will allow the St Helena Government to refine marine management actions and enact more bespoke protections for whale sharks, sheltering them from the threats they face around the world and facilitating an upcoming blue-tourism boost for the island's economy. The SHNT Marine Team will help to ensure St Helena remains a haven for whale sharks through strong, evidence-driven conservation measures and public engagement.'

The waters of St Helena are a treasure-trove of species, many of them endemic to the island. In addition to the whale shark research, the SHNT Marine Team also identified Chilean devil rays, a small pod of bottlenose dolphins and secured the first evidence of a third turtle species in St Helena’s waters – the leatherback turtle. The team also witnessed a rare ‘bait ball vortex’, which occurs when small fish swarm in a tightly packed spherical formation, and which completely engulfed a 9m long male whale shark.

'Encountering St Helena’s famous Whale Sharks was an absolute highlight of my career in conservation,' said Wylor-Owen, who only recently moved to St Helena and was experiencing the annual gathering for the first time. 'As if swimming alongside the world’s largest fish wasn’t incredible enough, being joined by Chilean devil rays and a pod of bottlenose dolphins was a stunning snapshot of St Helena’s pristine marine environment.'

For more on St Helena, its marine life and whale sharks, check out our Essential Guide to Scuba Diving St Helena

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