A fish aggregating device, or FAD, is any floating object placed in the ocean to attract fish. Hundreds of marine species, from tuna to sharks to small baitfish, naturally gather beneath floating debris in open water. FADs exploit that instinct by giving fishers a predictable spot to find concentrated schools of fish, dramatically increasing catch efficiency.
The concept is centuries old. Coastal fishers across Southeast Asia have long used structures called “payaos,” bamboo rafts with palm fronds dangling underneath, to draw in small pelagic fish and tuna. What started as a simple artisanal technique has scaled into a global industrial practice. Today, tens of thousands of FADs dot tropical oceans, and they account for a significant share of the world’s tuna catch.
Why Fish Gather Around Floating Objects
Scientists have proposed several explanations for why pelagic fish cluster beneath floating objects, but no single theory fully accounts for the behavior. One idea is that floating structures mimic natural shelter like driftwood or seaweed mats, offering small fish a place to hide from predators. Those small fish then attract larger predators like tuna, creating a food chain in miniature. Another hypothesis suggests the objects serve as orientation points in the otherwise featureless open ocean, giving fish a reference to navigate by. A third theory proposes that fish simply follow a deep evolutionary instinct to associate with any floating structure, whether or not it provides a direct survival benefit.
Whatever the mechanism, the effect is reliable and powerful. A single FAD can attract hundreds of species, building an entire temporary ecosystem beneath what might be nothing more than a raft of bamboo and rope.
Anchored vs. Drifting FADs
FADs come in two basic types. Anchored FADs (sometimes called aFADs) are fixed to the seafloor with mooring lines and stay in one location permanently. Drifting FADs (dFADs) float freely with ocean currents, sometimes traveling hundreds of miles over their lifespan. Both types attract fish effectively, but they serve different purposes and create different problems.
Anchored FADs are commonly used in coastal and artisanal fisheries. In the Philippines, payaos originally supported small-scale fishers using ring nets and handlines near shore. Because anchored FADs use long mooring lines stretching from the surface to the seabed, they pose a particular risk to marine mammals, which can become entangled or injured in the cables.
Drifting FADs dominate the industrial tuna fishery. Large purse seine vessels deploy dozens or even hundreds of them across vast stretches of ocean, then circle back to haul in whatever has gathered underneath. Drifting FADs have become the bigger environmental concern in recent years because of their sheer number and the volume of non-target species they attract.
Modern FAD Technology
Industrial FADs have evolved well beyond bamboo and palm fronds. A modern drifting FAD typically consists of a floating surface raft (made from synthetic materials, foam, or old netting) with a “tail” of material hanging below it to create an underwater profile that attracts fish. Attached to the raft is a satellite-linked buoy that transmits the FAD’s GPS coordinates back to the fishing vessel in real time.
Many of these buoys now include built-in echo sounders, essentially small sonar units that scan the water beneath the FAD and send back rough estimates of how much fish biomass has gathered. This lets a vessel operator sitting on a bridge monitor dozens of FADs remotely, checking each one’s location and fish load before deciding which to visit. The result is a highly efficient system: instead of searching for fish, the vessel simply deploys FADs, waits, and harvests whichever ones have accumulated enough tuna to justify a set.
Bycatch and Environmental Concerns
The efficiency of FADs comes with a significant ecological cost. Because floating objects attract virtually everything in the water column, fishing on a FAD means catching far more non-target species than fishing on a free-swimming school of tuna. Data from the Western and Central Pacific Fisheries Commission shows that drifting FADs accounted for the majority of shark and ray bycatch from 2008 onward, reaching over 55% of all shark bycatch by 2017. Billfish bycatch followed a similar pattern, with drifting FADs responsible for roughly 30% to 60% of billfish catch in most years after 2008.
The species most commonly caught as bycatch around FADs include juvenile bigeye tuna (a vulnerable species often too small to be the target), silky sharks, oceanic whitetip sharks, mahi-mahi, and various billfish. Sea turtles are also caught, though the data suggests unassociated sets (fishing on free schools) actually account for a higher proportion of turtle bycatch in most years.
Beyond bycatch, abandoned or lost drifting FADs create marine debris. Traditional designs using synthetic netting in their underwater structures can continue to entangle marine life long after they stop being tracked, a problem known as “ghost fishing.” Thousands of FADs wash ashore on reefs and coastlines each year, damaging coral and polluting beaches.
Limits on FAD Numbers
Regional fisheries management organizations have imposed caps on how many active FADs a single vessel can have in the water at once. In the eastern Pacific, rules finalized for 2025 set limits based on vessel size. The largest purse seiners (with well volumes of 1,200 cubic meters or more) can have no more than 340 active FADs at any one time. Mid-sized vessels are capped at 210, and the smallest at 50. Similar limits exist in the Indian Ocean and western Pacific under their respective management bodies.
These caps represent a significant shift. Before regulation, some industrial vessels were deploying and tracking well over a thousand FADs simultaneously. The limits aim to reduce the total number of FADs in the ocean and, by extension, the volume of bycatch and marine debris they generate.
The Shift Toward Biodegradable Designs
The biggest design change happening now involves materials. Regulations in the eastern Pacific already require all FADs to be “non-entangling,” meaning they cannot use netting materials in any part of their structure, surface or subsurface. This eliminates the ghost-fishing problem caused by traditional mesh designs.
Starting January 1, 2026, new rules will require that at least the surface or subsurface portion of every FAD deployed in the eastern Pacific be made from fully biodegradable materials. Approved options include plant-based materials like cotton, jute, manila hemp, bamboo, and natural rubber. By January 1, 2029, the requirements tighten further: the entire FAD, except for flotation components like plastic buoys or foam, must be biodegradable. Any non-biodegradable materials like nylon rope can only be used to reinforce the structure, not as a primary building material.
The biodegradability standards are specific. Materials must meet international testing standards (ASTM D6691, ASTM D7881, or TUV Austria certification) confirming they break down in marine environments without releasing heavy metals or microplastics. The goal is that a lost or abandoned FAD will eventually decompose rather than persisting as ocean debris for years.
Artisanal vs. Industrial Use
It is worth noting that FADs play very different roles depending on who uses them. For small-scale fishers in the Pacific Islands, the Caribbean, and Southeast Asia, anchored FADs near shore can be genuinely beneficial. They concentrate fish close to home, reducing fuel costs and time at sea for communities that depend on fishing for food security. A single well-placed anchored FAD can sustain a small fleet of handline fishers.
The environmental debate centers almost entirely on industrial-scale drifting FADs, where the combination of massive deployment numbers, satellite tracking, sonar-equipped buoys, and purse seine nets creates a fishing system so efficient it raises serious sustainability questions for tuna stocks and ocean ecosystems alike. The regulatory push toward fewer, biodegradable, non-entangling FADs is an attempt to preserve the tool’s usefulness while reducing the damage it causes at scale.