A novel study in Palau has used a combination of Fish Aggregation Devices (FADs) and trackers to monitor how yellowfin tuna move, and where they can be caught by local fishermen.

Fisheries biologist Alexander Filous, in collaboration with the Palau International Coral Reef Center (PICRC), has implemented this new technology to pinpoint locations around the islands where these pelagic fish are most likely to group.

In a presentation of his findings on July 28 at PICRC, Dr. Filous explained how his research, which began in 2016, suggests that deeper waters are more likely to attract groupings of tuna.

“Basically, we’re finding that good-sized tuna are more likely to aggregate in waters that are at least 1,000 meters deep,” Dr. Filous said. “But, for small scale fishers, we also want to take into account how close these places are to land, so that fishers don’t overspend on fuel. So, if we’re talking about places most accessible by small motorboats, we’re looking at the waters off of Peleliu and the waters off of Ngardmau.”

FADs are buoys that act as magnets for pelagic fish, which, along with transmitters that are implanted in tuna, help to establish not only where the tunas go but also how long they stay in certain areas. Dr. Filous has used the data provided by these tags to determine preferred temperatures, depths, and yearly patterns of the pelagic fish.

“Although we’re using a lot of high-tech equipment, some of what we do is pretty simple,” he said. “For instance, FAD’s are just buoys in the water, but for some reason masses of fish are drawn to them. Being a scientist, I really want to understand why they behave the way that they do.”

Dr. Filous is also studying otoliths, bones located underneath the brains of the fish with growth rates reliant on the temperatures of the waters. By comparing otoliths of tuna from Palau, Hawaii, and French Polynesia, he hopes to determine if the tunas in Palau are migratory, or if they are spawning here.

He explained that the fish which aggregate around these FADS are mostly juvenile yellowfins, smaller than 60 cm, generally not big enough to sell to international markets. Due to changing feeding habits, adult tunas are much more mobile and harder to catch.

“Although we won’t be exporting the tuna we find in these FADS to Japan, they sell really well locally,” he said, stressing that the technology can be an important stepping-stone in establishing food security for the islands. The catching of exportable fish, he said, is less sustainable with the equipment available to local fishermen. 

“Pelagic fish are an excellent source of protein for the islands,” he said. “Tunas grow and reproduce quickly, as opposed to rabbitfish which might take 12 years to grow, so by relying on them we’re not completely plundering Palau’s marine resources.”

He added, “We’re using all this new technology, but rather than using it to feed the rest of the world, we’re feeding ourselves. Otherwise, Palau will remain reliant on canned tuna imported from other places.”

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