Fish aggregating device
A fish aggregating (or aggregation) device (FAD) is a man-made object used to attract pelagic fish such as marlin, tuna and mahi-mahi (dolphin fish). They usually consist of buoys or floats tethered to the ocean floor. FADs attract fish for reasons that vary by species.
Fish tend to move around FADs in varying orbits, rather than remaining stationary below the buoys. Both recreational and commercial fisheries use FADs.
Before FADs, commercial tuna fishing used purse seining to target surface-visible aggregations of birds and dolphins, which were a reliable signal of the presence of tuna schools below. The demand for dolphin-safe tuna was a driving force for FADs.[1] In the past, people in the Pacific islands used bamboo rafts to make it easier to catch tuna that gathered below. FAD use has made fishing much easier.[2]
Fish behaviour[edit]
Fish are fascinated with floating objects, which they use to mark locations for mating activities. They aggregate around objects such as drifting flotsam, rafts, jellyfish and floating seaweed. The objects appear to provide a "visual stimulus in an optical void",[3] and offer refuge for juvenile fish from predators.[4] The juvenile fish, in turn attract predators. A study using sonar in French Polynesia, found large shoals of juvenile bigeye tuna and yellowfin tuna aggregated closest to the devices, at distances of 10 to 50m. Further out, 50 to 150m, a less dense group of larger yellowfin and albacore tuna gathered. Yet further out, to 500m, was a dispersed group of mature tuna. The distribution and density of these groups was variable and overlapped. The FADs were also used by other fish, and the aggregations dispersed after dark.[5]
Types[edit]
Drifting FADs float with the currents, are not tethered to the bottom and can be man made, or natural objects such as logs or driftwood. They can include sonar and GPS capabilities so that operators can contact it via satellite to assess associated populations.[6]
Moored FADs occupy a fixed location and attach to the sea bottom using a weight such as a concrete block. A rope made of floating synthetics such as polypropylene attaches to the mooring and in turn attaches to a buoy. The buoy can float at the surface (lasting 3–4 years) or lie subsurface to avoid detection and surface hazards such as weather and ship traffic. Subsurface FADs last longer (5–6 years) due to less wear and tear, but can be harder for fishers to locate. In some cases the upper section of rope is made from metal chain so that if the buoy detaches from the rope, the rope sinks and thereby avoids damage to passing ships.[7]
Applications[edit]
Fisheries[edit]
Drifting FADs are widespread in the Atlantic, Pacific and Indian Ocean purse seine fisheries. They attract over 1 million tons of tuna (nearly one-third of the global tuna total) and over 100,000 tons of by-catch as of 2005.[8] Skipjack (Katsuwonus pelamis), bigeye tuna (Thunnus obesus) and yellowfin (Thunnus albacares) tuna are the three primary tuna species that FADs target. Other targets include albacore, dolphin fish, wahoo, blue marlin, striped marlin, mako shark, silky shark, whitetip shark, galapagos shark, mackerel, and bonito.[7]
Before FADs, pelagic purse seiners targeted free-swimming schools of tuna. Increasing FAD since 1990 increased the productivity of the fishing fleet, but has significant side-effects. The average FAD-caught fish is smaller and comes with relatively large bycatch, raising concern about populations of pelagic sharks.
The U.S. state of Hawaiʻi operates 55 surface FADs around its islands to support sport fishing and marine research.[7]
Marine Protected Areas[edit]
Blue water FADs can enhance the effectiveness of marine protected areas by retaining fish within MPAs (where fishing is prohibited) long enough to benefit local fish populations. One study reported that even a small number can meaningfully expand populations.[6]
Removal[edit]
In the Indian Ocean some NGOs want to reduce the impact of pollution and coral degradation by removing FADs that have drifted onto and damaging corals. Oceanika, a UN registered NGO, launches regular removal missions.[9]
See also[edit]
References[edit]
- ^ Armstrong WA and Oliver CW (1996) Recent use of fish aggregation devices in the eastern tropical Pacific tuna purse-seine fishery: 1990-1994 Administrative report LJ-96-02, Southwest Fisheries Science Center, NOAA.
- ^ Gupta, Alex Sen; Pilling, Graham; Phillips, Joe Scutt; Escalle, Lauriane. "Tens of thousands of tuna-attracting devices are drifting around the Pacific". The Conversation. Retrieved 2020-08-10.
- ^ Hunter, JR; Mitchell, CT (1966). "Association of fishes with flotsam in the offshore waters of Central America". Fishery Bulletin. 66: 13–29.
- ^ Kingsford, M. J. (1993). "Biotic and abiotic structure in the pelagic environment: importance to small fishes". Bulletin of Marine Science. 53 (2): 393–415.
- ^ Josse, Erwan; Laurent Dagorn; Arnaud Bertrand (2000). "Typology and behaviour of tuna aggregations around fish aggregating devices from acoustic surveys in French Polynesia". Aquatic Living Resources. 13 (4): 183–192. doi:10.1016/S0990-7440(00)00051-6.
- ^ a b "Research Explores Use of Commercial Fishing Gear as a Conservation Tool". The Nature Conservancy. December 11, 2023. Retrieved 2024-02-19.
- ^ a b c "The FAD FAQ". Retrieved September 2, 2009.
- ^ "Does fishing on drifting fish aggregation devices endanger the survival of tropical tuna?". Science News. 15 May 2008. Retrieved September 3, 2009.
- ^ "Oceanika calls for industrial fishing vessels to do more to remove FADs in Seychelles' waters".
External links[edit]
- FADs in Hawaii, USA
- FADs in New South Wales, Australia
- FADs in the Commonwealth of the Northern Mariana Islands, USA
- Bhavani, V (2004) Fish Aggregating Devices Information Sources FAO: Information document: BOBP/INF/2, Rome.
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