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An Introduction to the Fast Food Restaurants of the Ocean (FADs)

*This post was originally uploaded on December 31st, 2018 on a website that has since been deleted. Posts from that website will be re-uploaded here at a later date.

The Pacific coast of Costa Rica is home to a diverse and valuable (ecologically and economically) array of oceanic predators including billfishes (sailfish, marlins, etc.), tunas, sharks, and sea turtles. Sustaining commercial and recreational fisheries in this region is challenging because of limited data, the wide variety of competing interests, and perhaps an increasing influence from ocean climate variation. Marine animals live in a highly dynamic habitat, but humans have begun to interfere with these dynamics by installing Fish Aggregating Devices, or FADs, to attract these fast-moving pelagic predators to stationary locations. These underwater structures are attractive to smaller baitfish because they provide cover and are attractive to predators because they become localized "hot-spots" of food. Think of these FADs like fast-food restaurants. This theoretically reduces the amount of searching a pelagic predator needs to do to find their next meal as they could hop from FAD to FAD (or fast-food joint to fast-food joint if you will) to fill up. In addition, FADs are fascinating from an ecological perspective because they concentrate predator species (like marlin and sailfish) that would otherwise partition habitats and resources in order to avoid competing with each other. Our project hopes to better understand the basic predator-predator and predator-prey relationships around these fast-food hot-spots, in order to inform management decisions regarding how FADs affect commercial and recreational fisheries resources, as well as potentially protected species resources off of Costa Rica.

While we understand the general idea of these fast-food FADs, we still do not know much about the fish community that was established at FADs. The underwater structure is usually anchored around 60ft (~20m) below the ocean’s surface, and out of view of humans. To understand the predator-predator and predator-prey relationships that form at these fast-food hot-spots, we need to start with some basic observations. We propose to use an underwater ROV to try and assess the fish communities around the FADs. An ROV has several benefits over human divers. These FADs are often located 12-15 hours run time from shore which is dangerously long time to get help in the case of a scuba diving emergency. In addition, the small size of the ROV and lack of bubbles will be less disruptive of the fish’s natural behavior and allow for observations un-influenced by the presence of humans. Video observation is also a non-lethal technique to survey the fish communities around the structures, as opposed to more traditional fish surveying techniques like net trawling, or hook and line fishing. Therefore, an ROV provides an opportunity to spy on rare behaviors and ask the question- "how does everyone behave in the fast-food restaurant when no one wants to wait in line for their food, and what's on the menu?"

We just completed our first preliminary work in Costa Rica! Our team of researchers recently spent a little over a week in on the water in Costa Rica, working with private boat owners and charter boat captains to get on the ground (or on the water) experience fishing for marlin and sailfish, and deploying tags to track their movements. Most of the fishing was centered around these FADs, although what the fish community around the FADs looked like remained a mystery. We have many future trips planned and will hopefully be able to bring an ROV out with us to help answer some of these.

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