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Power to the people: citizen science shows occurrence & seasonality of Gulf of Thailand whale sharks

Koh Tao is a popular diving destination known globally for its shallow reefs and easy diving. However, there is something lesser-known about Koh Tao and its seasonal visitors; Endangered whale sharks.

New collaborative study “Citizen science reveals the population structure and seasonal presence of whale sharks in the Gulf of Thailand” by Magson et al., sheds light on both the seasonality and demographics of whale sharks visiting Koh Tao, neighbouring islands and seamounts in the Gulf of Thailand. The data used in the study were collected through a citizen science programme, originally known as ‘Koh Tao Whale Sharks’ after a call was made on social media following an increase in the number of sightings in 2017.

The results from the citizen science call were unexpected and provided much-needed insight into whale sharks in this data-poor region. The data shared were from 2004 to 2019 and yielded 179 different individuals from 249 reported sightings. Of those 179 individuals, only one had been re-sighted internationally, 700 km away off Peninsular Malaysia. Re-sightings usually occurred within a week or so of the first sighting, however, all of these sightings, combined with estimates of residency, indicated that the animals sighted were transient to the area and moving somewhere else. The Koh Tao and neighbouring islands' population of whale sharks is a juvenile one, with an average size of 3.7 m and a sex ratio of 2:1 female to male – a rather unusual find, highlighting the importance of collaborative research like this. In Koh Tao, whale sharks were encountered throughout the year with increases in sightings between Apr-May and again in Oct-Nov due to the changing of the monsoon winds. This seasonality may be linked to regional productivity and whale sharks moving to/from feeding grounds.

Projects and research like this highlight the importance of citizen science when studying elusive species, like the whale shark. Any person with a camera can help with data collection and reporting, which is in turn critical to population monitoring of Endangered species.

The project has since expanded to cover the whole of Thailand, and we are encouraging everyone encountering whale sharks to report them to ‘Thai Whale Sharks’ on social media, or through direct email submissions to Alternatively, sightings can also be directly uploaded on and they’ll make their way to us.

Access the full article here.

Thai Whalesharks Instagram: @Thaiwhalesharks

Article by Kirsty Magson.

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