AfricanDiver.com

Bryan Hart’s posting about Dull days in Durban contained an item about a great white that had drowned after being caught in a fish attracting device (“FAD”). The Natal Sharks Board’s Geremy Cliff gave us some additional information about the incident:

“We received a call from NSRI late Sunday morning with the news that a large white shark had entangled itself in a FAD off Umdloti. Yesterday (Monday) morning we went out to investigate. The GPS co-ords indicated that it was about 4 nm offshore. We couldn’t find anything at the spot but did find another 2 FADs closer inshore. Apparently there are at least 3 FADs in the area; presumably deployed by local skiboaters to improve catches, esp. Dorado. The positions of each one are well known to the local anglers. One of the anglers who saw the shark estimated that it was about 4.5 m long, but I don’t think it was anywhere near that, probably about 3.5 m.

I jumped in on both FADs, but only saw small triggerfish and tiny kingfish. The one has tassels of strapping case bands as an attractant, the other horizontal strips of material.

I suspect that the weight of the dead white shark, which appeared to be very fresh on Sunday morning, must have pulled the FAD down below the surface. It is difficult to work out exactly how a white shark would have entangled itself, unless it already had a trace in its mouth, which then snagged the FAD.”

Geremy added “we did hear that an angler had removed the head, presumably to take out the jaws, which is illegal in that white sharks are fully protected species. EKZN want to remove these FADs, which like all others are illegal”

Tunas and other pelagic species are often attracted to floating objects such as coconuts, logs, seaweed, and plastic bottles. These are often found at current boundaries and up-wellings, which are areas of the ocean that are usually very productive and therefore good places for tuna to search for food. Local fishers generally know about such areas, but current boundaries, and the fish that feed around them, are never stationary. Fishers may have to search a large area to locate them, in order to take advantage of the good fishing. FADs are floating objects that are specifically designed and located to attract tunas and pelagics, and therefore allow fishers to find them more easily. No one understands exactly why tunas are attracted to FADs, but the ropes, floats and the other materials used presumably mimic the build-up of driftwood and seaweed found naturally in the sea. A FAD comprises a large anchor (up to 1mt), a heavy-duty mooring chain (usually about 30m in length) and mooring rope, with about 50 purse-seine floats strung at the surface. The ropes and chain are joined using various shackles, rope connectors, splices and thimbles. A flag-pole is attached to facilitate finding the FAD. FADs may be placed in shallow (50-100m) or deep (500- 1,500m) waters. Deep-water FADs attract or aggregate Skipjack (Katsuwonus pelamis), Yellowfin (Thunnus albacares), and Bigeye tunas (T. obesus) and also sharks, Dolphin-fish, Rainbow-runner and other smaller fish. FADs anchored a few kilometers off the coast, and in depths of over 500m are generally more successful in attracting schools of tunas than shallow-water FADs. FADs aggregate the smaller tunas (Skipjack and immature Yellowfin, for example) at the surface and larger tunas (such as mature Yellowfin and Bigeye) at depths of 300-400m. A key point to recognize is that FADs do not increase the biomass of fish (i.e. they do not increase size of a fish population). All they do is aggregate them in one place, making them easier to catch. Schools of tuna never actually ‘live’ under FAD’s, but they associate with it for a few days or weeks, often ranging some kilometers away searching for good, before moving on. Fishing captains have reported finding individual schools of tuna that exceeded, 500 mt in total weight and may hold more than a million individual fish.