Development of a Single Buoy Anchored Fish Aggregating Device in Mauritius

The development of the Mauritius FAD Fishery started in 1985. The designed FAD is the rosary type comprising trawl floats mounted on a single or double-string polyamide rope, anchored in the open sea with polypropylene ropes, at depths ranging from 400 to 3500 m. Yet, FAD losses are high and mostly due to damages caused by navigating vessels and entanglement of fishing lines and hooks with the mooring rope of fishermen boats fishing close to the FADs. Moreover, it was observed that the rosary type FAD sinks to >200 m during strong surface current; hence, the use of trawl floats, which are resistant to pressure and resurfaces during slack current. Consequently, these FADs can neither be fixed to a light device for easy detection at night nor can they be equipped with satellite buoys as these would implode due to high pressure during sinkage. To reduce FAD losses, a sturdy, unsinkable and traceable fibreglass reinforced plastic single buoy FAD has been designed, equipped with a solar-powered flashlight, and a satellite buoy to track and collect biological and oceanography information. The mooring line consists of a mixed of steel wire (Ø 14 mm) and of polypropylene rope (Ø 20 mm). Based on the law of static equilibrium, the buoyant force on the buoy was calculated at 2,441.0 N. Turbulent flow models with speed of ocean current at 1, 2 and 3 knots were used to calculate the overall drag force (52,656.6 N) on both the mooring rope and the submerged portion of the buoy. Additional improvements made on the single buoy FAD were the (a) net-wrapping technique that proved to reduce the surface tension by as much as three times; and (b) shackle connection coupled with the formation of the catenary loop that provided full scope for rotation, thereby, reducing significantly the tensile force on the main line. Assuming a contingency anchorage of 130% on the total drag force, the minimum anchorage weight was 2,080.2 kg for metal and 3,578.4 kg for concrete.