|OverviewDriftnetting for shark and associated species is a passive fishing method. The technique being often associated with shark drift longlining (drifnet-cum-drifting longline), being this combination of gears carried-out mainly by small-scale and advanced artisanal fisheries in tropical and sub-tropical countries, targeting at the same time sharks, tuna like and other associated species.Species EnvironmentMany of the sharks taken by driftnets in directed fisheries or as a bycatch are also likely to have been the subject of fisheries elsewhere. Pelagic sharks are an important component of the same fisheries such as: the mako Spp, hammerhead and bigeye thresher shark. Blue shark, is also taken as bycatch in the offshore fisheries targeting tuna with longlines and driftnets beyond the slope of the continental shelf.|
In Ghana and neighboring countries of West Africa, the catch is composed of large pelagic species, such as shark ( Carcharhinus spp.), manta ray (Mobula and Myliobatis spp.), tunas (Thunnus albacares and Thunnus obesus), sailfishes (Istiophorus albicans), swordfishes (Xiphias gladius), skipjack (Katsuwonus pelamis) and little tuna (Euthynnus alletteratus).
In the western countries, a deep-water fishery has recently developed along and beyond the continental slope, targeting, black tip, silky shark, blue shark and associated species, generally in depths greater than 200 m, in response to declining catches of whitefish species such as cod (Gadidae), hake (Merluccius merluccius) and pollack (Pollachius pollachius), which are usually caught in shelf seas (ICES 1993).Fishing GearIn Sri Lanka and India, the driftnets consist of a number of panels joined together to form a wall of netting suspended vertically in water. Each panel is 1 000 meshes long and 120 meshes deep. In the case of the 150 mm mesh stretched meshes, the most popular in Sri Lanka, panels measure 83 m in length (hanging ratio 0.55) and 12.6 m in depth. The length of the float line may range from zero to 3 m, implying that the effective fishing depth could be 12.6-15.6 from the surface. A standard net would consist of 12 panels; each panel being 1 500 meshes long and 40-60 meshes deep.
In Benin, from 82 shark-fishing nets in 1982, to 128 in 1993, they reached the number of 406 in 1996, among them we identified 234 bottom set nets for sharks. Traditionally, they are using shark fishing driftnets called Nifa-nifa nets. This is a surface driftnet with mesh size ranging from 100 to 240 mm stretched meshes. Fishing is carried out at night and a round trip takes about 1 620 hours.
In Ghana, (Anifa-anifa or Nifa-nifa) is an offshore large mesh driftnet measuring 100-450 m long and 15-20 m deep. The mesh size varies from 100 to 200 mm. The yarn size is R 390 to 620 or 950 Tex, as per netting availability. In general, Ghanaian migrant fishermen used to fish with drift gillnets combined with attached longlines set out at the sunset and pulled out the next morning.Vessel OverviewVessels as small as six meters in length fish commercially for sharks elsewhere in the world. In their vast majority they are non-mechanized fishing units relying on man hauling power to paid out and haul their fishing gears.
In South-East Asia, driftnets are often stored under deck for security reasons in adverse weather conditions. However, it is not uncommon to see the whole gears stored on deck.
In the western world gillnetters targeting sharks are generally fishing boats with length ranging from 10 meters to more than 30 meters LOA. These vessels are well equipped in electronic positionning and fish detection materials (radar, GPS, echosounder, radio transmitter etc.) They are propelled with powerful diesel engines allowing speed of >10 knots as a minimum with a fishing trip lasting from one week up to nearly one month.
In West Africa, artisanal fishers operate with larges and small undecked dugout or planked canoes ranging from say 10 to more than 12 meters manned by 4 or more than 6 fishermen. They are generally propelled with outboard engines of 25 to 40 HP. (Benin, Ghana and few other coastal States).
In Asia, the diverse types of fishing crafts operating for sharks can be broadly categorized into the following: inboard motorized crafts - the coastal boats of 9 m 3.5 G.T. class and the offshore boats of 9-17m LOA. 5.5 m GRP (glass re-enforced plastic) flat bottom boats powered by outboard motors (between 8-20 hp).
With the development of the offshore multi-day fishing, the offshore boats now land more sharks than all the coastal boats. 11.6-12.3 m joined the offshore fishing fleet in later years. The industry has consolidated around this class of boat, displacing the previously dominant 9.0-10.3 m class of boat.
The large Taiwanese gillnetters are steel vessels of 160 to 380 t, 30 to 45 m long. They included converted Taiwanese longliners and stern trawlers as well as purpose built gillnetters. Millington and Walter (1981).
A minimum crew of four is required on a boat of 9-12 meters length. A minimum of two in the smaller coastal fishing canoes propelled with outboard engines. Fishing gears are often stored under deck for security reasons in adverse weather conditions. However, is not uncommon to see the whole gears stored on deck, or simply on the bottom of the undecked canoes.Handling ModeIn the warm waters of the tropics, drift gillnets are shoot before the sunset, for a soaking time of 9 to 10 hours. A shortest soaking time will however provide a better fish quality. Greater attention is given to fish handling in biggest gillnetters. Immediately after hauling session is completed, care is given to the fish catch, which is progressively cleaned up and /or iced. However, too often, in small fishing canoes, (elsewhere in the world where shark fishery is operated by small to medium size boats), because of limited freezing/storing areas, handling process is still to be improved. Often, ice quantity is not enough, advanced fish processing knowledge is insufficient, and limited storage capacity implies that most of the time, catch of sharks is kept on deck, only protected from the sun by a tarpaulin.Fishing OperationsA technique which works very well in one area may be ineffective somewhere else. The success or failure of a particular method in a given area depends on a host of conditions particular to that area. Therefore, if one is considering the development of a shark fishery, it is valuable to examine diverse methods, which have been tried in different places. Most of these experiences and observations apply mainly to fishing for large sharks, a practice that presents special challenges.
Catches are in general better from new moon to the first quarter in the driftnets, then decline progressively toward the full moon.
In the meanwhile, toward full moon, it may appear that in some areas, shark catches become generally low in the driftnets (some boats may even remain ashore during this period). However, it has been often noted that in moonlight period, the drifting longlines generates good catch of shark.
Trolling lines used on board during this kind of combined fishing operation give often insignificant catch results, and most of the time, fish caught is used as a bait fish.
|1. Selection of the fishing areaFor the smallest boats non equipped with navigationaids, the selection of the fishing area depend on reference to the landmarksand manual sounding devices, and knowledge of the zone recognized as good for his particular period of the year. |
For the bigger fishing boats, the use of electronic positionning materials such as radar, GPS, echosounder, etc.,facilitates the selection of the fishing zone by a progressive mapping of the working area.
|2. Setting driftnetsDriftnets are paid out before the sunset. A minimum of four fishers is required on a boat of 9-12 meters length. (13Â°/ the Team leader/steering man being on the tiller, orientates the boat down wind. Boatspeed is slow (1.5-knots) as per the wind and current speed as well as crews skill. 23Â°/ two fishers pay out progressively the markers flag and buoys equipped with storm light or flashing light, markers ropes and bridles. 33Â°/ the same two fishers then start to shoot out the driftnets progressively (one paying out the floatline and the second the leadline). 43Â°/ the fourth man islocated at the stern of the boat, watching for net entanglements and if needed helping on shooting the nets properly. |
Once the last part of the nets is in the water, the last end bridles are paid out, as well as the drifting/pulling rope. The skipper put the engine in neutral position. The rope is fitted to the bow of the boat, and the engine is stopped. The boat orientates itself toward the wind direction and the drifting operation goes on progressively up to 4:00 to 5:00 a.m. next morning (that is 8 to 10 hours drifting). In some drifters, drifting time is shorter, which allow a better quality fish.
NOTE: In the case of a fishing operation with combination gears, drifting longlines are paid out first, then, the last end of the drifting longlines ist ied out to the floating line of the driftnets. Immediately after, the gillnets are set out.
Fishery OverviewIn many fisheries combined fishing techniques are often used such as drift netting cum longlining with association of trolling lines while sailing to and from fishing grounds, and also while changing of fishing area.Fishery OverviewIn Benin, West Africa, from Cotonou fishing port, and adjacent beach landing sites, seasonally, fishers operates at the limit of the continental shelf that is less than 20 nautical miles from shore. As the coastline of several West African countries is generally limited in length, often fishermen cross the limit of the territorial waters to operate shark fishing activities. Target species are composed of Dusky shark, Bull shark, Requiem shark, Black tip shark, Skipjack, Yellowfin and associated species. Ghanaian fishers use to fit directly some branchlines on the lead line of the same type of driftnets. Their driftnets for sharks and associated species are operated offshore. They are large mesh driftnet measuring 100-450 m long and 15-20 m deep. The stretched mesh size varies from 100 to 200 mm. Fishing is carried out at night and a round trip takes about 16-20 hours. In western Europe, in the summer months, blue sharks move north to cooler waters, as far as the south coast of England and southern and western coasts of Ireland, where a directed fishery using longlines and gillnets (which also takes spur dog and hake) commenced in 1991. Fishing boats are operating at the limit of the continental shelf. Water depth in these areas is generally from 100 to >500 metres. Target species are composed of blue shark, thresher shark, mako, hammerhead, tope, porbeagle an associated species. In Europe, trawlers are catching (as by-catch) important quantities of sharks species. In the Azores, the kite fin shark, Oxynotus paradoxus, has been targeted for over 20 years by both gillnets and handlines which tend to catch mostly males and females respectively. In Australia, with the introduction of power-hauled gillnets, longlines began to decrease in popularity and by the end of the 1980s few longliners remained. By the mid-1990s there were no full-time shark fisherman using longlines, being the fishery dominated by gillnets fishing. Taiwanese drifters fleet, use surface set gillnets. The net length increased from about 8 km in 1979 to about 16 km in late 1985, with some nets longer than 20 km. The off-shore drift gillnet fishery for shark, tuna and tuna like species in Sri Lanka has developed rapidly since the mid-1980s. There are presently some 1 200 off-shore vessels referred to as multi-day boats, which are operated with drift gillnets. Most are between 36 and 45 feet in length and carry crews of 4-8 persons. The annual catch has risen continuously to the present 55 000 tons, comprised mainly of skipjack, tunas, shark and billfish.SeasonalityElsewhere in the world, sharks species can be caught all year round. However, adverse weather conditions may affect negatively the fishing operations, either in wintertime with frequent storms in Europe as well as strong winds during strong monsoon in tropical areas affected by cyclones.
|3. Hauling driftnetsIn small scale fishing boat, hauling operation start by pulling the driftnets out either manually or mechanically depending of the boat type and size. To be able to get a better quality fish with a limited soaking time, it would be preferable to start the hauling operation at the earliest (that is around 02:00 a.m.). But, in practice, fishers prefer to start this operation around 4:00 to 5:00 a.m. |
Depending of the weather conditions, current force and catch, the operation could last from one up to more than three hours.
While hauling, the catch are separated from the gillnets, but icing is done only at the end of the hauling operation. After the last extremity of the driftnets is on board, the marker rope and marker flag/lights are embarked.
Assuming that the catch was good, the boat will probably remain drifting in this area, ready for fishing again at the end of the day. However, if there was a poor catch, the boat may move to another fishing ground several miles away.
Trolling lines will be used on the way.
NOTE: In the case of a fishing operation with combination gears, driftnets are hauled first, since they are the closest to the boat, being the nets pulling rope tied up to the bow of the boat. Once all the driftnets are on board, the fishermen start to haul the drifting longlines without delay.
In Ghana, it is a year-round operation with a peak season in August and September.
In the Maldives, shark driftnetting tends to be carried out on a more seasonal basis. Fishermen carry out more pelagic shark driftnetting during the latter part of the north east monsoon season (when the weather tends to be calm) than at other times of year. However, they will go shark driftnetting at any season when shark catch rates are high, especially if tuna catch rates are low.IssuesOverexploitation
Responsible fishing practices
In the Gulf of Benin, West Africa, shark resource potential is still unknown. Studies should continue especially for the coastal species the most frequently caught (C. obscurus, C. leucas, C. limbatus, S. leroini) which constitutes the most accessible and vulnerable stocks, with about 80% of the total catches. Oceanic whitetip shark (C. longimanus) and Hammerhead sharks seem to be more abundant in the offshore waters. (Cf. P. S Änouvo, Marine Biologist, DOF, Benin,1997).Conflicts Due to the increasing price paid for shark fins elsewhere, however, the difference between target and bycatch species in these fisheries is becoming less clear.Possible solutions
Possible solutions: Gears restriction
In the Maldives the use of purse seines, trawls of any sort, and pelagic (drifting) gillnets is prohibited, as is the use of spear guns, explosives and poisons for fishing. These bans are effective since these gears are not imported. Nevertheless, they do indirectly limit shark fisheries activities.
In Seychelles, The most important regulation directly relevant to the management of the shark fishery for the artisanal fleet is the ban on fishing for sharks with nets that has come into effect on 1 August 1998. There are no regulations on shark catches by other fishing techniques nor have any effort limitations or closed season been introduced.
The Health Department of Western Australia has a regulation, which specifies that no shark with a cleaned weight (head, gut, and fins removed) greater than 18 kg can be sold for human consumption because of the mercury content of sharks caught in the fishery.
In the Maldives, shark fishing by purse seines, trawls of any sort, and pelagic driftnets is prohibited. Two species of sharks are protected: the whale shark Rhincodon typus and the white shark Carcharodon carcharias. In the majority of the countries dealing with shark fishing, no accurate statistics exist of shark catches from both the artisanal and industrial fisheries. It would be advisable to develop an accurate statistic system that include shark fishing.