Those who ply the sea know floating things attract or aggregate fish. Fish aggregating devices, known as FADs, are often thought of as manmade objects, but that is not always the case.
For most of history, the fad in FADs was natural, in the form of forest products: a branch or a tree falls into a river and makes its way to the sea. Any Tico captain knows to be ever watchful for floating branches and tree trunks that can damage a prop or hull, especially during the high runoff of rainy season, even when far offshore. But jump in with a piece of tree in the sea and you may be shocked.
Vast clouds of marine life will surround floating things that are smaller than you. When you jump in, all the life will often surround you like moths to a flame. Sometimes people jump right back in the boat when they realize there is no reef to dive down to. But you are the reef, and there may be so many fish surrounding you that you cannot see someone right next to you.
FADs offshore of southwestern Costa Rica’s Osa Peninsula often draw diver favorites like silky sharks and manta rays, two species recently declared endangered. Super- and megapods of dolphins become natural FADs, and they check out other FADs.
Why do many whales and dolphins, more than 300 species of fish like sharks, rays and billfish, all sea turtle species and countless crustaceans, seaweeds, invertebrates and other marine life hang out at natural and manmade FADs? Structure, protection, food and social opportunities seem to be the big attractions. Life like seaweed and barnacles quickly starts growing on almost all floating things. Other life shows up to eat what’s there. Still others may come for a bit of shade or a place to hide. Then come bigger things, and then even bigger things. A lot of marine life seems programmed with the instinct to check out FADs, probably because of the good chances to find lunch or a mate, or to not be eaten.
So where you have FADs, you have a lot of marine life. The longer the FAD is in the water, the more life it accumulates. Places with a lot of rivers and forests produce many natural FADs year-round, but mostly during rainy season and severe weather. The rivers of Costa Rica run full of FADs that will later drift many kilometers out to sea and grow their own clouds of marine life.
Natural FADs probably increase Costa Rica’s marine biodiversity and bioproductivity more than most people realize. Other places that are not so blessed with natural FADs make their own for local artisan and sport fishers and divers. Hawaii put in a system of FADs offshore of the islands in the 1970s. Today, each one of these many manmade FADs produces thousands of kilograms of fish a year with no by-catch, as well as recreation for local communities.
The purse seine commercial fishing industry also deploys manmade FADs, but on a massive scale over the entire Pacific. After the FADs grow their clouds of life, the ships put it all in a net. If they find a natural FAD, they do the same thing. This has a rather different outcome than the Hawaiian method.
The Hawaiian way kills no marine life other than food fish, and the local communities get the food and money the FAD generates. The Costa Rican purse seine netters’ way destroys the entire marine chain of life around the FAD, and no money or food goes to local Costa Ricans.
That is one fad I hope will end soon.