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“The whale sharks are a good omen for the fishers because they know when the whale sharks come, that means that lots of small fish or anchovies are around,” says Edy Setyawan, the lead conservation scientist of the Elasmobranch Institute Indonesia.
It is the relationship between whale sharks (Rhincodon typus) and fishers in Indonesia that has enabled marine biologists from Konservasi International and Elasmobranch Institute Indonesia to satellite tag more than 70 whale sharks for a decade-long study that has revealed previously unknown migration routes, feeding grounds and a whale shark nursery.
It is one of the biggest tracking data sets across the globe on whale sharks and is the first time such a detailed survey has been conducted in the Indo-Pacific.
While 60% of the global population of whale sharks can be found in the Indo-Pacific, it can be difficult for researchers to study them because the species travel such long distances. But the researchers experienced a breakthrough when they when found out about the relationship between bagan fishers and whale sharks.
Bagan fishers work on floating wooden platforms from which they lower an oversized net into the water to catch fish. Working at night with lights, the fishers attract shoals of ikan bilis (anchovies) into their nets. The whale sharks, which follow the small fish, have learned to gather around these platforms.
Marine biologist Mark Erdmann, who had been working in Indonesia since the 1990s, saw the arrival of the bagan fishers in 15 years ago. “Bagans were heavily prevalent around Jakarta, but as they overfished the west, they started moving further east. Eventually they got to Papua and Cenderawasih Bay,” he says.
At first the whale sharks, who long preceded the bagan fishers in these waters, kept their distance from the floating platforms. “By 2010, the whale sharks have become very used to the bagan lift net fishers, and that’s when you started seeing this interaction happening,” says Erdmann.
Occasionally, the whale sharks would swim into the nets and feed upon the fish inside them, which initially made the fishers nervous. Erdmann, who at the time was working with Conservation International, recognised this as an opportunity to safely tag them in the water.
Working together
In 2015, the researchers, with the help of different groups of bagan fishers, started tagging whale sharks in Cenderawasih Bay and Kaimana in West Papua, Saleh Bay in Sumbawa and the Gulf of Tomini in Sulawesi, using fin-mounted satellite tags capable of delivering up to three years of data.
Before and during the tag fitting, the team tested for stress levels in the whale shark. “[The team] measured the chemical compound of the blood [for] stress. But it shows that there’s no difference,” Setyawan says.
Initially, the fishers were reluctant to temporarily hold the world’s largest fish in their nets. “They were afraid to catch the whale shark because they’re big and they’re afraid the fishing platform could be broken,” says marine biologist and lead author of the study Mochamad Iqbal Herwata Putra. But the marine biologists showed them how the tagging could be done safely without hurting them or the whale sharks.
Previously, whale sharks had only been tagged by using a pole spear. The tag would last no longer than six months. But over the next 10 years, from 2015-25, the data from the new tags revealed previously unmapped movements of the whale sharks and helped highlight seamounts that are used as foraging sites and whale shark highways, which needed to be protected.
The team’s data are now being used by the Indonesian government to help establish a whale shark-based marine protected area in Saleh Bay this year. “The zoning considers critical habitats, including no-take zones that cover key whale shark areas [like] nursery or juvenile habitats as well as mangroves, which support prey availability, such as shrimp and [plankton],” says Putra, who is the focal species conservation senior manager at Konservasi Indonesia.
As they were able to capture multiyear data sets, the researchers were able to spot patterns in the data. The whale sharks, which operated as individuals, would take defined routes each year to suit their own agendas. Some would leave the bay for months at a time, then return. Putra says it appears they do this to change their diet. Each June, one whale shark would travel to the north of Papua just as the tuna spawned; another was observed traveling at the same time each year to the Timor Gap between Timor-Leste, Indonesia and Australia when the southern bluefin tuna are spawning. These were seasonal habits that the researchers were previously unaware of.
The data also revealed other habits, such as while some of the whale sharks might not leave the warm waters of Cenderawasih Bay, they would suddenly dive to 200 meters (650 feet), which the researchers believed could be temperature-control dives to cool their body.
Robert Harcourt, who is the facility leader IMOS animal tracking at the Sydney Institute of Marine Science & School of Natural Sciences, Macquarie University, questions the usage of fin-mounted tagging for long periods of time: “Short term fin mounted tagging of whale sharks is fine, but long term (four month plus) can cause permanent damage to the fin so should be avoided. There are some sharks off Ningaloo [in Western Australia] whose dorsal fins are now permanently bent.”
Harcourt, who is not connected to the project, adds: “Of course, with miniaturisation in future the impact can be lessened but it’s a delicate balancing act. The rationale for the study is key. If it will help improve protection for a population it may be justifiable.”
Putra says animal welfare is heavily thought through. “We carefully consider animal welfare and tag burden, but based on current experience, extended deployments provide far more robust scientific value without compromising the animal, when done properly,” he says. “Dorsal healing following tag recovery is rapid. After six months, the attachment site is almost fully covered.”
Erdmann says there is another aspect that can’t be overlooked. While the relationship between the whale sharks and the fishers has aided the research, Erdmann does have concerns about the bagans’ presence. “The concern I have is if the bagans continue to expand, we’ll eventually get to a point where there’s not enough food for the whale sharks.”
Banner image: Scientists from Konservasi International satellite tagging a whale shark. Image by Abdi Hasan.
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Citation:
Putra MIH, Wirasatriya A, Sianipar A, Hasan A, Setyawan E, Syakurachman I, Mambrasar R, Erdmann M, Supriatna J and Manessa MDM (2026) Integrating behavioral movement and environmental preferences to map critical habitat of whale sharks using long-term satellite tracking in the Indo-Pacific Ocean. Front. Mar. Sci. 13:1808805. doi: 10.3389/fmars.2026.1808805
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