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Fishing Techniques

Shark Bottom Set Gillnetting

Main Components

Aquatic species

Target Species
Shark market species

Target Species
TrevaillesTarget Species
Rayfish

Gear types: Set gillnets

Set gillnets

A set gillnet consists of a single netting wall kept more or less vertical by a floatline and a weighted groundline.

Vessel types: Set netters

Characteristics

OverviewBottom set gillnets for shark is a passive fishing method. This method is considered as a unique fishing technique.Species EnvironmentFishing EnvironmentThe small toothed sand tiger shark, is caught in both the deep benthic fishery and, occasionally, in the reef fishery. Both the silvertip sharks, and the scalloped hammerhead, are taken in both the reef fishery and the oceanic shark fishery. The cosmopolitan tiger shark can be caught almost anywhere.Sand tiger shark is a demersal marine species living by depth range 0-191 m. This large coastal species of shark has one of the lowest reproductive rates known among elasmobranchs, giving birth to one or two large young every two years. As a result, annual rates of population increase and ability to sustain fishing pressure are very low.

Silvertip shark is a marine reef-associated species leaving in depth ranging between 0-800 m. It is an inshore and offshore shark found over or adjacent to continental and insular shelves and offshore banks. Prefers offshore islands, coral reefs and banks. Feeds mainly on benthic and midwater fishes, also rays, and small sharks and occasionally cephalopods.

Scalloped hammerhead is a marine pelagic species (depth range 0-275 m) occurring over continental and insular shelves and adjacent deep water, often approaching close inshore and entering enclosed bays and estuaries. Readily available to inshore artisanal and small commercial fisheries as well as to offshore operations. This widely distributed species is extremely commonly taken in fisheries, both as a target species and as utilised bycatch (fins are highly valued).

Bigeye thresher is a marine pelagic species (depth range 0-500 m). It occurs in coastal waters over continental shelves, sometimes close inshore in shallow waters, and on the high seas far from land. Feeds on pelagic and bottom fishes and squids. Utilized for human consumption, liver oil for vitamins, skin for leather, and fins for shark-fin soup.Fishing GearIn South-East Asia, in various countries, large mesh bottom set gillnets are targeting sharks, queen fish, trevally, etc., operating from traditional crafts and FRP boats. Nets of 120-180 mm mesh made of PA multifilament twine R450-600 Tex, are set in the evenings or are left for 2-3 weeks at the same fishing grounds, (although hauled every day or second day). A standard net would consist of 5 to 12 panels; each panel being 1 500 meshes long and 40-60 meshes deep.

In the Caribbean, the gillnets are made of polyethylene or nylon twine (multifilament as well as monofilament material is used) and range in size from 1 000 m to 1 600 m in length. They are generally 4 m deep with 200 mm stretched mesh. Nets are generally anchored at one end and marked by a buoy at the floating end.

In West Africa, Gulf of Benin, large mesh bottom set gillnets (called "Agbla"), with stretched meshes of 220-240 mm, (made of multifilament mainly, R390-620 tex) are directed to shark fishery by depth inferior to 50 m.Vessel OverviewIn western countries, fishing vessels are generally fishing boats with length ranging from 8 meters to more than 15 meters LOA. That type of fishing boat is well equipped in electronic positionning system, fish detection materials and sturdy hydraulic hauling devices. They are propelled with powerful diesel engines allowing speed of 10 knots as a minimum, with at least two weeks fishing trip range. Although, in some areas, Set netters may come back to port every evening, according to the distance of the fishing ground.

In the developing countries, artisanal fishermen operate bottom set gillnets with small and larges undecked, planked or dugout canoes ranging from say 6 to more than 18 meters, especially along the west coast of Africa. In their vast majority, they are non-mechanized fishing units, relying on man hauling power to cast and haul their fishing gears. The bottom gillnets are stored either directly in the bottom of the hull, or separated from the bottom of the hull by a tarpaulin.

In some islands of the Caribbean, there is two types of artisanal gillnet boats: large gillnetters 12-15 m in length which conduct trips of up to 12 days duration and small gillnetters of 6-12 m length which conduct daily trips. The areas of operations of both vessel types overlap.Handling ModeWhile on the modern gillnetters great attention is given to fish handling, yet to often, in small-scale fishing units, (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 or simply not available.Fishing OperationsSet net fishing does not need bait and, apart from a few areas with strong tidal flow, is much more efficient than longlines for catching various species of bottom dwelling sharks and associated species. The method has also the advantage in that set net can be designed to catch a particular size range of sharks. The set nets consist of a stationary fishing gear, anchored and buoyed at each end.

In the tropical warm waters, bottom set gillnets for sharks are paid out before the sunset, and the hauling activities start at 5:00 to 6:00 a.m, giving a soaking time of 9 to 10 hours. Once cast out, the boats will either come back to shore and return to haul their gears next morning before sunrise. This is frequently the case for the small-scale set netters, where, in some parts of tropical areas, fishing boats will remain nearby the fishing ground, watching the nets for preventing eventual theft, and operating handlines from time to time. On undecked canoes, set gillnets are generally stored on the bottom of the hull. For the bigger set netters, operating a multiday shark fishery, they will operate also with handlines for a few hours. Then the crew will rest, and alternatively watch the fishing gears until the hauling time has arrived. A soaking time of three to four hours is generally better for good quality bottom shark fishing especially if the area is rich in associated species of high commercial value such as trevallies, groupers etc. However, often the fishermen seems to prefer a longer soaking time, that is up to ten hours before hauling their set nets. In advanced artisanal fisheries, a light is fitted to the dahn pole (flag buoy), but this is hardly the case in small-scale bottom set nets fishery. For advanced artisanal fisheries, operating further offshore, there could be a multi day fisheries operation, involving hanlining, while carrying ice on board.

1. Shooting of the bottom set gillnetsOn board of the small artisanal fishing canoes, once arrived in the selected fishing area, the skipper orientates the canoe down wind. Then, the marker flag buoy and ropes and the sinker or a small anchor iscast out. This is followed by the veering line and bridles, then, the net setis paid out over board. Once the last part of the gillnets is in the water, the skipper decrease the boat speed, then the edge rope [PPâPE or PA, with Å 10-12mm with about 30-40 meters in length] is paid out together with the last endanchor, and the bottom extension rope will follows. Next, the marker rope is paid out together with the marker float. On the bigger boats, having localized the fishing ground, shooting the bottom gillnets start when the skipper orientates the boat down wind. (However, this may vary also according to the local working habits, currents and wind direction as well as proximity of rocky areas for a better positioning of the nets). The boat steaming at speed of about 2 knots (this may vary slightly according to the wind andcurrent speed). Flag buoy and marker float are paid out. This is followed by the sinker/anchor, and the veering lines and bottom extension rope. Then the bridles and the gillnets are paid out. A crew of four as a minimum, (skipper included) is required on a boat of 9-12 meters length. (1A°/ the leader/steeringman being on the tiller, 2A°/ two fishers dealing with the shooting of the gillnets, 3A°/ another watching and preventing that the gillnets are not shotout twisted).

2. HandlingWhile hauling, the catch is removed from the nets in the biggest boats. Fishes will be subsequently processed and iced on board. While in the smallest canoes which return to shore almost every day, fishers will either remove the catch from the nets and stock it under atarpaulin on the bottom of the canoe, or haul the entire net set, and keep it on board. Once arrived ashore, fishers will be assisted by local people to remove the catch from the nets. According to local traditions and kind of market demand for sharks, fishes will be gutted or not. Gills will be most ofthe time separated and dried out. Carcasses will be processed appropriately and subsequently sold locally, or exported to another area or neighboring country. In some cases, carcasses will be discarded.

3. Hauling gillnetsStarting with the up-current end, the hauling activity could start. The skipper keeps the boat up on the gear from his position on the tiller. Fish are taken from the nets by two or three men immediately on the bigger netters. They are put behind the hauler before the cleaned net is pulled astern, and spread, ready for shooting to the next fishing ground.

Fishery OverviewVery limited fisheries is now conducted using bottom-set nets for sharks. Demersal sharks in the total shark catches have become insignificant in recent years in several parts of the world. In the western Europe, set netters using bottom gillne are not targeting specifically bottom sharks, which are considered mostly as a by-catch.Fishery OverviewIn Sri Lanka, large mesh bottom-set gillnets, targeting sharks, queenfish, trevally, etc., are operated from traditional crafts and FRP boats. Nets are set in the evening and visited the next morning, but could be left for 2-3 weeks at the same fishing grounds. However, a very limited fishery is now conducted using bottom-set nets. Demersal sharks (small toothed sand tiger shark, silvertip sharks, and the scalloped hammerhead. The cosmopolitan tiger shark can be caught almost anywhere. In the total shark catches these species have become insignificant in recent years, particularly in the face of increased landings of other pelagic sharks from the rapidly developing and expanding drift gillnet cum drift longline fisheries in both the coastal and offshore sectors. In Trinidad and Tobago the artisanal gillnet and line fishery is the most widespread fishing method accounting for over 85% of artisanal shark landings. In the Maldives, bottom set netting for reef sharks requires larger investments in gear (and greater specialist knowledge) than other shark fisheries, and so fishermen on relatively few islands have adopted this technique. Despite this concentration of fishermen in just a few islands, shark gillnetting is carried out throughout the country because the fishermen undertake 10-14 day trips and visit all atolls for fishing. The number of fishermen engaged in shark gillnetting is decreasing. The fisheries which contribute most to shark landings in Dominica are the bottom gillnet and line fishery and the trolling fishery which operates in inshore areas off the north west, north and east coasts of Dominica (Guiste et al. 1996). In the Caribbean islands in general, the multispecies nature of the fisheries and the fact that most shark landings are by catches of other fisheries poses special challenges to the management process. In some islands, the flesh is used as bait for other higher priced species. Shark catches in the region are primarily taken, as bycatch, though a few directed fisheries exist most of which are both occasional and seasonal. This means that at certain times of the year some fishers may specifically target sharks. In West Africa, Gulf of Benin, large mesh bottom set gillnets (called Agbla), are directed to shark fishery by depth inferior to 50 m. In this area, this kind of fishery is most of all practiced by Ghanaian and Beninese fishermen. Continental shelf rocky/patchy appropriate fishing areas for bottom sharks are limited in both countries. Ghana and Benin have continental shelfs of 20 900 square km, and 3 100 square km respectively. In both countries, less than 10% is composed with rocky patches areas, the rest being of sandy/muddy substrate. The number of canoes/fishers involved in this fishery is not available. However, this type of bottom set gillnet (although visited every day or second day) is kept into the water for about a week, until the magnitude of the damages in the netting force the fishers to return the fishing gear ashore for further repairs. Hauling devices are seldom available on board, and sets of bottom gillnets for sharks are most of the time hauled manually. 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. There are two styles of fishing employed in the fishery:
- Extended trips that last from 3 to 14 days. These vessels have refrigerated holds and operate large distances from their homeport. These vessels are the largest in the fleet. Set times for gillnets are short, typically 3 to 8 hours, with the gear being worked around the clock. Practically all fishers in determined areas, but very few fishers in the other areas carry out this style of fishing.
- Day trips. Fishers operating in this manner return to port each day after clearing and moving their net(s). The nets remain set overnight, with set times ranging from 15 to 24 hours. The vessels rarely have refrigeration.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.Responsible Practices
Responsible fishing practices
Very few countries enforce size limits in their management plan in relation to any species of the shark caught. However, some nations have a regulation that specifies that no shark with a cleaned weight (head, gut, and fins removed) greater than a certain size can be sold for human consumption because of the mercury content of sharks caught in the fishery.

Selectivity: Gears restriction
For the artisanal fishery of Trinidad and Tobago and Dominica, there are regulations under the 1916 Fisheries Act and the 1961 "Laws of Dominica, Fisheries, Chapter 79" respectively. Gillnets are limited to 900 ft in length and 15 ft depth with mesh sizes not smaller than 3½ in stretched mesh. Net dimensions and minimum mesh sizes are specified for seine nets which also land sharks. In Australia, according to the areas, a maximum net length of six kilometers is allowed per fishing unit duly registered by Fisheries Authorities.

Possible solutions
Advanced fish processing training would benefit to artisanal fishers dealing with shark fishing with bottom set gillnet. In the majority of the countries dealing with shark fishing, the information available is poor on species composition of shark catches in the bottom-set gillnet fishery or bottom longline demersal fisheries. 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. Damage to traps caused by certain sharks, in particular the Nurse shark (Ginglymostoma spp.) is a serious problem for fishermen. Hence from a fishermen's perspective, shark capture is necessary as an element of pest control and others would go further to state that it would reduce danger of shark attack to swimmers.IssuesEnvironmental Shark fishing with bottom set gillnets are regulated or prohibited in several countries, as they may cause damages to the environment. 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.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.Bibliography

Anderson, R.C. & A. Hafiz 1997 “Reef Fish Resources Survey in the Maldives, Phase 2.” Madras BOBP/WP/80: 1-51.

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