Citizen science and its role in marine species ID on Koh Tao

Citizen science has been playing an ever-increasing role in data collection and ecological research worldwide. With advances in technology and communication these non-scientists have been able to provide invaluable information. It is something we have been doing here on Koh Tao since 2015 when we started our Sea Turtle ID program. The program has proven to be incredibly successful and has resulted in over 70 turtles around the island being identified, recorded, and named.

After the success of the Koh Tao Turtle Project, we decided to set up Koh Tao Whale Sharks - to collect photos that are used to identify whale sharks visiting Koh Tao and submit them to Whaleshark.org to be part of a global ID program. This project enables anyone who sees a whale shark to submit photos of their sighting, along with additional information about these amazing creatures.

So, how do you ID a whale shark? Whale Sharks have a unique set of markings formed by their spots and stripes, these markings, not unlike a human fingerprint, are different for every individual. When we ask for ID photos we look for a nice clear image of the left hand side of the shark with a focus on the area between the gill slits and the dorsal fin. We also ask for additional photos or information regarding scaring, sex, size, behavior and location.

Research like this is important, as very little is known about the migration patterns or mating preferences of whale sharks. By having a global coalition of divers acting as citizen scientists, individuals can be tracked as they move around the globe. By gathering behavioural and information and plotting times and locations when whale sharks gather together more can be discovered about their reproductive habitats. It is important to know when and whale sharks bred so that effective conservation and protective measures can be taken to limit fishing at those times.

Little is also known about the brooding of whale shark pups, the information that has been gathered from 2 encounters. The first involved a pregnant female that was caught by fishermen in Taiwan and had 300 pups in her womb. This finding gave scientists the evidence needed to confirm the brooding strategy of the whale shark. The species is live bearing however like nurse sharks they produce egg cases within the body where the embryos develop until which time they are ready to hatch and are born as fully developed miniatures. The second comes from a baby of 38cm that was found tied to a stake in shallow water in the Philippines.

The smallest whale shark ever recorded alive (Photo credit to WWF - Philippines)

 2017 brought with it some unusually high numbers of whale sharks here on Koh Tao, especially throughout the early months of the year. For much of the year it seemed as though at least a few groups of divers would see one every day. A total of 90 sightings were reported to the project, 6 of which came from NHRCP/New Heaven only 13 of which were from years prior to 2017. There were undoubtedly more sightings, however in some instances there were no cameras with the dive groups, so photos so could not be used for the project itself.

For the most part, the individuals that were reported were different, only in a few instances whale sharks moved between dive sites and were recorded several times. One such individual, easily recognised for the scarring around her tail, stayed in the area for 2 weeks and moved between Sail Rock and South West.

The whale sharks preferred areas of deeper water, the best sites to observe them were Chumphon Pinnacle (26 sightings) and Sail Rock (18 sightings). We can assume that this is due to their feeding habits, with deeper water and stronger currents bringing planktonic food for these immense filter feeders (An adult whale shark can filter feed as much as 600,000 litres of seawater a day).

The length of the whale sharks ranged between 2 meters and 5 meters, and the small size of the claspers in the males suggests that there were primarily juveniles. There was a higher proportion of females to males, and the best time to see them was between March and May.

Whaleshark abundance by month

We do not know why 2017 was such an amazing year to see whale sharks around Koh Tao, but it made for a great year to kick off this new program, and will prove to be an interesting study moving forward. We hope that this trend continues in 2018, and we are all looking forward to spending more time with these incredible animals and finding out what is bringing so many of them here.