FAD
General Background
A Fish Aggregating Device ( FAD) is a permanent, semi-permanent or temporary structure or device made from any material and used to lure fish. They have been used for thousands of years in various forms. The earliest surface/midwater FADs were elements from nature such as driftwood and trees.
Now surface and midwater artificial FADs are systematically used in a large number of countries. Present practices vary considerably, sometimes involving advanced technology. Generally speaking, buoys and floats close to the surface comprise the major part of the aggregating system but some models exist with the aggregating device in mid-water - so called midwater FADs – where the only surface component is a small marker buoy (which is less subject to stress from wind and waves and the risk of damage by ships).
The deployment and proliferation of FADs has influenced harvesting practices and become the concern of fisheries managers.
Installation
FADs can be used in either a single or multiple arrangement. Common practice is to use more than one with enough distance between each. The most suitable distance between each FAD depends on the abundance and type of species targeted: between several hundred and one thousand metres for small pelagic fish in coastal or shallow waters; or 5 to 10 nautical miles for deep-water tuna FADs.
Some FADs are permanent structures while others are moveable. The former are set mainly in deep waters and relocation is virtually impossible. Present experience shows that the expected life of a permanent FAD would be 2 to 3 years. The mobile, lighter structures can be moved to attract fish to a particular point. Still others can be removed from the water during certain seasons when the fish are not in the area or when the weather is rough, e.g. monsoon.
Aggregation Process
The process of aggregation (to be related to the fouling on the structures, at the surface and on the mooring line of the FAD) is often made in two steps: firstly small fish are attracted and secondly large fish arrive. The bulk of the aggregation can sometimes be at some distance from the FAD.
It is also important to note that, in many cases, the fish aggregation is found not only close to the buoy on the surface but also in deeper water where the species are generally different from those observed near the surface or at a distance from the FAD. In general, larger fish are found in deeper waters. In spite of intensive research the reason fish are attracted to these devices is still not known with certainty. However, the fact is that FADs play the role of offshore banks (moored FAD have to be set far enough from the coast).
Impact
Consideration must be given to the fact that fish behaviour around a FAD differs from one species to another and this determines the different aggregating ability of the FAD for the various species. The FAD may make different species to those generally caught available to the fishers and as a consequence different fishing methods might be needed. Methods used in the open sea may not be suitable for fishing around the FAD.
It has been observed that the use of FADs often alters the exploitation of the resources with more juvenile stocks of fish were being taken when fishing around the FADs.
