A fish aggregating device (FAD) is a floating structure that draws fish to a specific location, making them easier to catch. The basic design has three parts: a float at the surface, a mooring line running down to the bottom, and an anchor holding everything in place. Building one yourself is straightforward with the right materials, though the specifics depend on whether you want a simple drifting FAD or a permanently anchored setup.
Why Fish Gather Around Floating Objects
Fish are drawn to floating structures for reasons that aren’t fully settled among marine biologists, but two explanations hold the most weight. The first is evolutionary: natural debris like logs and seaweed historically accumulated in nutrient-rich waters and along ocean fronts, so fish developed an instinct to associate floating objects with food. The second theory focuses on social behavior. In open water with no visual landmarks, a floating object acts as a meeting point where fish can find each other, form schools, and reorganize. Both explanations likely play a role, and the practical result is the same: put something in the water and fish will show up, often within days.
Small baitfish and reef species arrive first, seeking shade and shelter beneath the structure. Larger predators follow the food. Over time, a well-placed FAD builds its own miniature ecosystem, attracting everything from juvenile jacks to tuna, mahi-mahi, and wahoo.
The Three Main Components
Every anchored FAD consists of the same three sections: upper floatation, a main line, and an anchor system. The upper floatation keeps the device visible at the surface and prevents the mooring line from tangling. The main line connects the surface float to the anchor on the bottom. And the anchor holds the whole system in position against currents and waves. How you build each section depends on your budget, your water depth, and how long you want the FAD to last.
Choosing and Building the Float
The surface float needs to be buoyant enough to support the weight of the mooring line below it and visible enough that you (and other boaters) can find it. Common options include sealed plastic drums, hard foam-filled buoys, or clusters of purse-seine corks lashed together. A single sealed 55-gallon drum works well for small-scale setups in moderate depths. For deeper deployments where the mooring line is heavier, you may need two or three drums or a purpose-built offshore buoy.
Attach a flag or radar reflector to the top of your float. This is both a practical necessity for relocating your FAD and, in many jurisdictions, a legal requirement for navigation safety.
Adding Attractors Below the Surface
Hanging material beneath the float dramatically increases how well your FAD holds fish. These “aggregators” create shade, mimic structure, and give small organisms a surface to colonize, which in turn draws baitfish and then larger species. Effective attractor materials include coconut palm fronds, synthetic streamers (strips of woven polypropylene or raffia), and bundled sections of old rope. Hang them from the underside of your float so they trail 3 to 10 meters into the water column.
Avoid using netting as an attractor. Loose netting beneath a FAD creates a serious entanglement hazard for sea turtles, sharks, and other marine life. Regulations increasingly prohibit it. NOAA now defines a “non-entangling FAD” as one that contains no netting materials in any part of the structure, surface or subsurface. Streamers and fronds accomplish the same fish-attracting goal without the bycatch risk.
Rigging the Mooring Line
The mooring line is the most failure-prone part of the system, so it deserves careful attention. Use a durable synthetic rope rated for marine use, such as polypropylene or polyester. The line needs to be longer than the water depth at your site to allow for tidal changes and current drag. A common rule of thumb for moderate depths (under 100 meters) is to use 1.5 times the water depth in rope length. In deeper water, specialized catenary calculations come into play, and published rope length tables exist for deployments in 700 meters or more.
Adding small floats (supplementary buoyancy) at intervals along the mooring line helps keep it from lying flat on the bottom and tangling around the anchor. These intermediate floats also reduce the overall downward pull on your surface buoy. Use hard foam floats or sealed PVC pipe sections, spaced every 20 to 50 meters along the line depending on depth.
Where the rope connects to the float and anchor, chafing is the primary killer. Wrap connection points with protective tubing or hose, and use stainless steel shackles or thimbles to prevent the rope from grinding against hard edges. Inspect these points on every maintenance visit.
Building and Setting the Anchor
Your anchor needs enough weight to resist the combined force of current dragging on the mooring line and surface float. For deep-water commercial FADs, the Pacific Community recommends a square concrete block weighing around 900 kilograms (roughly 2,000 pounds), which provides about 450 kilograms of holding power once submerged. That specification is designed for ocean deployments in hundreds of meters of water with strong currents.
For a small-scale, nearshore FAD in 15 to 50 meters of water, you can scale down considerably. A concrete block of 50 to 150 kilograms often suffices, depending on local current strength. The key design principle is the same regardless of size: make the base wider than the block is tall. A broad, flat bottom maximizes friction against the seabed, which is what actually prevents the anchor from sliding. You can cast your own concrete anchor using a simple plywood mold, embedding a stainless steel eyebolt or U-bolt in the top for the mooring line attachment before the concrete sets.
Adding a short length of chain (1 to 3 meters) between the anchor and the start of the rope absorbs abrasion from the seabed and adds weight right where it’s needed most.
Using Eco-Friendly Materials
FADs that break loose become marine debris, and any synthetic materials they carry can persist in the ocean for years. Regulations are tightening worldwide. Starting in 2026, FADs deployed in the eastern Pacific must have at least their surface or subsurface section built from fully biodegradable materials. By 2029, the entire structure (except flotation components like plastic buoys) must be biodegradable.
Even if you’re building a personal FAD outside commercial regulation, using natural materials where possible is good practice. Approved biodegradable options include cotton rope, jute twine, manila hemp (abaca), bamboo, and natural rubber. These materials work well for attractors and lashings. Cotton canvas strips or bundled palm fronds make excellent subsurface streamers that will eventually break down if the FAD is lost. The flotation itself is harder to replace with biodegradable options, so plastic buoys and foam are still generally acceptable, but everything else can and should be as natural as possible.
Where to Deploy and What to Expect
Location matters more than construction quality. Look for spots where currents create natural convergence zones, near drop-offs or ledges, or along the edges of reef systems where pelagic species patrol. Avoid shipping lanes, protected marine areas, and anywhere your FAD could become a navigation hazard. Water depth between 20 and 100 meters is manageable for a DIY anchored setup; deeper than that and you’re dealing with engineering challenges that benefit from professional guidance.
Check local and regional regulations before deployment. In U.S. waters regulated by the Inter-American Tropical Tuna Commission, FADs require unique identification codes and visible markings at least five centimeters tall on the buoy. Other regions have their own registration and marking requirements. Even in areas without specific FAD laws, unmarked floating structures can create liability if another vessel collides with one.
Once deployed, give the FAD at least one to two weeks before expecting significant fish activity. The colonization process typically starts with algae and barnacles growing on submerged surfaces, followed by small baitfish, then progressively larger predators. A well-placed FAD in productive waters can attract fishable concentrations of mahi-mahi, tuna, and other pelagics within a month.
Maintenance and Lifespan
Most FADs begin to physically degrade after about one year in the water. Rope chafes, floats lose buoyancy from barnacle loading, and attractor materials break apart. Plan to inspect your FAD every two to three months if conditions allow. Check the surface float for leaks or lost buoyancy, clear heavy barnacle growth, replace worn attractor streamers, and examine the top section of mooring line for chafe damage.
The mooring line connection to the float is the most common failure point. If you notice fraying, replace the top few meters of rope rather than waiting for a break. Carrying a spare pre-rigged section of line with shackles makes field repairs much faster. With regular maintenance, a well-built FAD can remain functional for two to three years before needing a major overhaul or full replacement.