Short description: Drifting longlining is a passive fishing method used by the artisanal fisheries in tropical areas for targeting sharks and tunas species. The technique is seldom considered as a unique fishing technique, being often coupled with driftnets targeting also large multi pelagic species (especially in tropical areas).Species EnvironmentBlue shark, is taken on drifting longlines as far south as the west coast of Africa by European longliners. Other pelagic sharks that are an important component of the same fisheries are the mako, hammerhead and bigeye thresher sharks. |
Blue sharks are also taken in tropical waters, elsewhere, as bycatch in the offshore fisheries targeting tuna with longlines and driftnets beyond the slope of the continental shelf. A deepwater fishery has recently developed along and beyond the continental slope, in the Far East in particular. The target species of the deep benthic fishery are limited to just a narrow strip of habitat, i.e. the outer atoll slopes between the depths of about 200 m and 1 000 m.
In some tropical island nations like the Maldives in the Indian Ocean, fishes do have a particular type of habitat. According to Anderson and Hafiz, 1997, the marine environnement is composed of oceanic atolls and so has no continental shelf. However, it does have a narrow atoll slope and a broader shelf area between the double row of atolls in the centre and north of the country. As a result there is a gradation in the oceanic shark species composition from inshore to offshore. The true offshore pelagic fishery, which may start no more than 1-2 km outside the atolls, catches mainly silky sharks as well as other highseas varieties such as oceanic white tip sharks, and blue sharks. The inshore pelagic fishery, which takes place close to, and between, the atolls, catches the same highseas varieties plus an assortment of other species such as the bignose shark, the silvertip shark, and the scalloped hammerhead.Fishing GearDrift longlining for sharks species in the western world, is practised seasonally (this is the case of the porbeagle, blue shark and associated species in western Europe for example).
In tropical areas due to the size of the fishing boats drifting longlines composed by 100-300 hooks are utilized (about 3 to 9 km long). As an example, for baiting 200 hooks on a drifting longline, about 80 kg of bait is required, that is around 300-400 grams of bait per hook. Often, trolling lines are operated on the way to, and from the fishing ground, to target additional fish that will be used as additional bait.
At small-scale and artisanal fishing boats level, the mainline is very often made of polypropylene (PP) and polyethylene (PE) [cheaper to buy than polyamide material], with Å: 6 mm, green or blue color. However, as this is a floating material, lead olive of 150-200 gf are fitted in between each branchline, to allow the gear to remain submerged even with strong winds and currents. A marker float 10-15 kgf is fitted every five hooks or one basket, (that is each 200-240 metres distance between marker float).
On board of bigger longliners the drifting longlines as well as the upper part of the branchlines are made of polyamide and kuralon materials. However, starting from a few years ago, monofilament polyamide is replacing progressively the multifilament materials of the drifting longlines, especially in the western fishing fleets and modern vessels of Europe, Asia and America.
NOTE: in the smallest boats, space between branchline is reduced to 20-30 meters instead of 40 to 50 meters in the larger vessels. Clips are often not used, the branchlines being knotted to the mainline, and arranged in such a way that the fishing gear is paid out without entanglement.
Drifting longlines for sharks and associated species, generally use a shorter type of branchline than those fitted for tuna drift longlining (around 12 meters overall length instead of < 22 meters for tuna drifting longline). On board of small-scale and artisanal fishing boats, branchlines is often made of Polypropylene (PP) or Polyethylene (PE), Å: 4,5 mm, [which is cheaper to buy than polyamide material]. The length of the branchline is composed of PP or PE with 10 meters in length. At the lower extremity about 1,50-2 meters of SS wire, Å: 2,5 mm is added. Both elements are separated by a leaded swivel 80 kgf. The type of hooks used is generally the hollow point Mustad-tuna hook © Ref. 9202B NÂ° 6/0-7/0-8/0-9/0. The bait used is usually little tuna species or other associated species locally available.Vessel Overview Longliners ranging from 6 to more than 17 meters LOA are operated.
It should be noted that until recently, the majority of these small scale fishing vessels were not mechanized. Although today some countries are mechanizing progressively their fishing units, the vast majority of the smallest longliners does not use shooting nor hauling devices. They are still shooting and pulling manually up to 9 km of longlines. In the western world, midwater longliners are generally fishing boats with length ranging from 12 meters to more than 30 meters LOA. These vessels are well equipped in electronic positioning and fish detection materials. A line drum is generally fitted behind the wheelhouse. 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 the developing countries, artisanal fishermen operate drifting longlines with small and large undecked, planked or dugout canoes ranging from say 10 to more than 18 meters. In their vast majority they are non-mechanized fishing units, relying on man hauling power to cast and haul their fishing gears. The longlines are stored either directly in the bottom of the hull, or separated from the bottom of the hull by a tarpaulin.Handling ModeA shortest soaking time will provide a better fish quality. In drifting longlines, catch rates are generally not as high as in gillnetting, but the sharks are more often alive when caught, and the product is therefore in better condition. 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 earlier, which is around 02:00 a.m.
The smallest longliners, often one night fishing canoe, don't carry ice at sea. Space is lacking on board, or ice supply simply not available. Bigger boats operating from harbours are carrying ice blocks and seldom flake ice, while operating these fishing gears.Fishing OperationsIn the tropical warm waters, drifting longlines are shoot before the sunset, and the hauling activities start at 4:00 to 5:00 a.m, giving a soaking time of 9 to 10 hours. However, often, fishers prefer to keep longer the fishing gears into the water expecting a higher catch rate while covering a bigger drifting time/distance.
A minimum of four fishers is required on a boat of 9-12 meters length. (1A°/ the Team leader/steering man being on the tiller, 2A°/ a fisher dealing with the shooting of the mainline, 3A°/ another preparing the branchline (per basket of five hooks) and 4A°/ the fourth man baiting the hooks and presenting the branchline to the fisher dealing with the mainline, which will clip the branchline to the mainline).
On decked boats, fishing gears are often stored in drums on deck or under deck for security reasons in adverse weather conditions. However, it is not uncommon to see the whole gears stored on deck. In some countries, undecked fishing boats use to store their fishing gears in the bottom of the fishing canoes.
In small scale and artisanal fishing boats, shooting and hauling techniques are quite similar than for tuna longlining fishing operation.
|1. Fish school detectionFor the smallest boats non equipped with electronic materials such as echosounder, GPS, etc., the selection of the fishing area depend on visual observations such as the presence of seabirds, jumping fish, information on the local currents, or knowledge of the zone recognized as good for this particular period of the year. The presence of several other longliners in this area could be a good indication for selecting the fishing area. For the bigger fishing boats, the use of electronic positioning materials facilitates the selection of the fishing zone by a progressive mapping of the working area.|
|2. Shooting longlinesShooting the drifting longline start before the sunsetat 5:00 to 6:00 p.m. when the skipper orientates the boat down wind. The boat steaming at speed of 2-3 knots (this may vary slightly according to the wind speed). The flag buoy and marker floats of about 20-25 kgf are paid out, followed by a PP/PE rope with 10-12 mm in diameter and 30-40 meters in length.|
Next, the longline is paid out progressively. Each branchline if clipped out to the mainline by the means of a SST clip every 20 to 40 meters,according to the general feature of the longline used and boat size. A markerf loat of about 8-10 kgf is fitted between each basket (5 hooks). If the boat is a small one, say 6 to 8 meters approximately, branchlines are knotted to the mainline through a loop, thus, clipping activity is avoided. Free space on deck is an important aspect of this fishery.
In South-east Asia, bait usedby small-scale and artisanal fishery for drifting longline is generally pieces of little tuna, skipjacks and associated species. In other part of the world, as per availability, frozen squids are used as bait, as well as any other fishbait available. Branchline are baited progressively in order to keep the bait fresh until the moment it touches the water. Once the last branchline is in the water, the skipper decrease the boat speed, then the edge rope (PP PE or PA, with Å10-12 mm and 30-50 meters long) is paid out and tied to the bow of the boat. The engine gear box is put neutral, and stopped until the moment of hauling the fishing gear is arrived. The boat orientates itself progressively toward the wind direction, and the drifting activity begins. Depending of the length of the whole gear, it will take between 1 to 1.5 hours to deploy the drift longlines.
Fishery OverviewAlthough the high mobility of the offshore fleets targeting shark market species allows it to harvest resources well beyond the EEZ all over the world, the declining total catches and catch/boat for sharks raises doubts regarding the sustainability of the resource in the face of increased and sustained fishing pressure.
|3. Hauling longlinesWhile hauling, the catch are removed from the hooks, but iced only at the end of the hauling operation. During the whole process, the skipper manages to keep the boat forward at low speed, to facilitate the work of the deck hands and avoid, as far as possible, the branchline to twist around the mainline. Assuming that the catch was good, the boat will probably remain in this area, ready for fishing again from the sunset. However, if there was a poor result, the boat may move to another fishing ground several miles away, looking for natural elements indicating a possible good fishing area.Trolling lines will be used on the way.|
The development of an independent drift longline fishery directed exclusively for shark has occurred in recent years; driven by the lucrative export market for shark fins. In drifting longlines, catch rates are generally not as high as in shark driftnetting, but the sharks are more often alive when caught and the product is therefore in better condition.Fishery Overview
South-East Asia, offshore multidays artisanal boats undertake fishing trips lasting 10 to 15 days and venture well outside the EEZ waters. These boats target mainly pelagic sharks, using drifting longlines. Some of the larger boats make only one trip a month. In Japan, the fisheries that catch sharks are classified into three groups in terms of the method of capture: (1)tuna longline fisheries, (2) trawl fisheries, and (3) other fisheries. The third group includes the high seas drifnet fishery, other gillnet fishery, bottom longline, and set net fisheries. The major sources of batoids landings are: (1) the trawl fishery operating in the East China Sea, (2) other trawl fisheries operating around northern part of Japan, and (3) other fisheries. In Seychelles, in 1997, has also emerged a locally based semi-industrial fishery targeting swordfish and tuna using monofilament longlines, hence catching shark as by catch. 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. According to the information available, within the Taiwanesedrifters fleet, drifting longlines and the surface-set gillnets of multifilament nylon were in use in Asian seas in 1986. In the Maldives, there are three distinct types of shark fishery: (1) A fishery for deepwater benthic sharks. (2) A fishery for reef sharks. (3) A fishery for oceanic sharks. In 1994-96 only Far Eastern style longliners were operated in the Maldives, but in 1997 Indonesian longliners were added to the fleet.SeasonalityElsewhere in the world, sharks species can be caught all year round. However, adverse weather conditions may affect negatively the fishing operations, either in winter time with frequent storms in Europe as well as strong winds during the monsoon in tropical areas affected by cyclones.
In the Maldives, shark longlining tends to be carried out on a more seasonal basis. Fishermen carry out more pelagic shark longlining during the latter part of the northeast monsoon season (when the weather tends to be calm) than at other times of year. However, they will go shark longlining at any season when shark catch rates are high, especially if tuna catch rates are low. Shark longlining and gillnetting is carried out by at least some fishermen in nearly every atoll. Also, these fishermen are now carrying out shark longlining year round, rather than just in periods of calm weather and/or poor tuna fishing as before.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 (Carcharhinus obscurus, Carcharhinus leucas, Carcharhinus limbatus, Sphyrna lewini) which constitutes the most accessible and vulnerable stocks, with about 80% of the total catches. Oceanic white tip shark and Hammerhead sharks seem to be more abundant in the offshore waters.
Two species of sharks are protected in Western Australian waters the whale shark Rhincodon typus and the white shark Carcharodon carcharias.
The most important source of mortality on blue sharks probably arises where they are taken as a bycatch in the longline and driftnet fleets targeting tuna and billfish, particularly from nations with high seas fleets such as Japan, Taiwan, Korea and Russia. Because there is usually no requirement for these fisheries to record their blue shark catch, its magnitude (and the consequent mortality) is not reflected in catch statistics.Conflicts Marketing problems in the sale of shark meat have hindered expansion of the fishery in some country, while in others shark meat is not consumed, but only caught for export, as well as the shark fins. In recent years the escalating price of shark fins has changed the global characteristics of the fishery such that revenue from fins now approaches that of the meat in some areas. 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.Selectivity Selectivity: Gears restriction
An important development in longline fisheries in several parts of the world, is the use of machines which attach baits to the hooks and facilitate rapid automatic attachment of the snoods to the mainline when setting the gear and facilitate removal of the snoods when hauling the gear. These labour saving devices are currently prohibited in some states for shark fishery, because they would inevitably increase the number of hooks set, and the period a vessel can operate each day.
In the Maldives, gear restrictions that apply to the shark fisheries have been adopted because of interference with the pole and line tuna fishery. They apply to specific areas or to tuna schools. These gear restrictions were introduced to protect the traditional pole and lines tuna fishery and the reef environment. 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. Since 1997, however, there has been practically no landing of sharks by longliners in Seychelles.
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.Bibliography
Anderson, R.C. & A. Hafiz . 1997 “Reef Fish Resources Survey in the Maldives, Phase 2.” Madras BOBP/WP/80: 1-51.