Oceanic (pelagic) sharks are mostly taken by longline. The pelagic longline fishery appears to have started in the
1960s (Anderson and Ahmed 1992, 1993). Traditional open wooden fishing boats of about 10-15m (masdhonis) are used in this fishery. The numbers of hooks set varies between about 40-200 per night.
The main species taken in the pelagic longline fishery (accounting for perhaps 70%-80% of the catch by numbers)
is the silky shark Carcharhinus falciformis. Several other species are taken in smaller numbers, including oceanic whitetip C. longimanus, tiger Galeocerdo cuvier, blue Prionace glauca, silvertip C. albimarginatus, bignose C.
altimus, shortfin mako Isurus oxyrinchus, threshers and hammerheads. Sizes of oceanic sharks caught by longline
Table 1. Elasmobranch species currently known from the Maldives. (Modified from Anderson and Ahmed 1993, Randall and Anderson 1993, Adam, Merrett and Anderson 1998, unpublished data.)
English name Frilled shark*
Sharpnose sevengill shark Bluntnose sixgill shark Bramble shark*
Taiwan gulper shark Leafscale gulper shark Mosaic gulper shark Kitefin shark Cookiecutter shark*
Tawny nurse shark Zebra shark Whale shark
Smalltooth sand tiger Crocodile shark Gray reef shark Silky shark Blacktip shark Oceanic whitetip shark Blacktip reef shark Spottail shark Tiger shark Sliteye shark
Sharptooth lemon shark Blue shark
Whitetip reef shark Scalloped hammerhead Great hammerhead*
Bowmouth guitarfish Whitespotted guitarfish Electric ray
Bluespotted faintail ray*
Fantail stingray
Thickspine giant stingray Pink whipray
Mangrove stingray Feathertail stingray Porcupine ray Spotted eagle ray Ornate eagle ray Manta
Daiy dhigu miyaru
? miyaru Kandi miyaru Kandi miyaru Kandi miyaru Woshimas miyaru Hikandhi thun miyaru Boathuni miyaru Falhu mathi dhon miyaru Dhon miyaru
are mostly within the range 1.7-2.5m (see Figure 1 for silky shark lengths). Longlining is normally carried out during trips of one or two nights duration. Sharks are usually processed when the boat returns to its island.
In addition to the longline fishery, some oceanic sharks are taken as bycatch by tuna fishermen. These fishermen occasionally catch sharks by pole and line, but they more commonly take them by handline or by hand. Sharks are taken by hand when schools of juvenile silky sharks are encountered with surface tuna schools; a tuna carcass held overboard brings the sharks alongside where they are grabbed by the dorsal or pectoral fin and swung inboard.
Most are within the length range 0.9-1.5m (Figure 1).
Tuna fishing is carried out on day trips only. Any sharks caught are processed on the island. Whole juvenile silky shark carcasses were bought from tuna fishermen by specialised processors on one island (B. Thulaadhoo) for MRf100 (US$8.45) in August 1995, and about MRf75 (US$6.35) in June 1997.
The main products from all oceanic sharks are dried fins and salt-dried meat. Some crude liver oil may be collected for treating boats, and some jaws are kept for sale as tourist curios (especially from large specimens or prized species such as tiger and mako sharks). Exports of shark fins and salt-dried shark meat are listed in Table 2. These export data do not distinguish
Figure 1. Length
frequency distribution of silky shark Carcharhinus falciformis catches in the Maldives.
Figure 2. Annual catches of shallow water (i.e.
oceanic and reef) sharks in the Maldives, 1963-1996. (Estimated from dried fin export data.)
Figure 3. Annual average price of dried shark fins (FOB Male'), 1974-1996.
(Customs data, compiled by Ministry of Fisheries and Agriculture.)
between products from the oceanic shark and reef shark fisheries. Estimated catches for the two fisheries combined are illustrated in Figure 2. Average fin prices are shown in Figure 3. Fin prices in the Maldives closely follow international trends (Cook 1990, Anderson and Ahmed
1993).
The Maldives is a tuna fishing nation. Nearly 90% of the total recorded fish catch is of tunas, and over 90% of the tuna catch is made by livebait pole and line (Anderson et al. 1996). The main oceanic shark species caught is the silky shark, and it is well known that silky sharks associate with tunas (Au 1991, Anderson and Ahmed 1993). In the Maldives, adult silky sharks are known as ainu miyaru (school shark) because of their close association with tuna schools. Thejuveniles are known as oivaalimiyaru (drifting object or flotsam shark). Drifting objects, and their associated fishes, are carried to the Maldives by the monsoon currents, so tend to appear off the west coast during the south-east monsoon (May to October) and off the east coast during the north-east monsoon (December to March). Maldivian fishermen search for flotsam, in order to catch the tunas associated with them. The most commonly caught varieties are juvenile yellowfin tuna Thunnus albacares and skipjack tuna Katsuwonus pelamis, but other target and bycatch species can also be found, including juvenile silky sharks.
Despite the fact that some tuna fishermen take silky sharks, they nearly all believe that doing so reduces tuna catches. They continue to take them because "everybody else does" and because of the economic incentives.
Fishermen say that tunas follow silky sharks, and that if the sharks are removed the tuna schools will disperse or dive. For this reason most tuna fishermen are strongly opposed to pelagic longlining. For the same reason any type of fishing other than pole and line tuna fishing is banned in the vicinity of fish aggregating devices. This conflict between shark fishing and tuna fishing interests is a serious issue in the Maldives where tuna fishing is such an important industry.
A second potential problem with the oceanic shark fishery is that the species involved are believed to be highly
migratory and, as such, to be subject to fishing mortality over a wide area. The oceanic sharks caught in Maldivian waters are likely to be also taken by:
• Longliners and gillnetters operated by fishermen from other coastal countries.
• Distant water tuna longline fleets, notably those from Japan, Taiwan and Korea. Japanese longliners first entered the Indian Ocean in 1952, with other fleets building up in the following decades.
• Tuna purse-seine fleets, notably those from France and Spain, which have a major operations base in the Seychelles. Although there had been some purse-seining in the Indian Ocean before, large-scale operations started in 1984.
Reliable shark catch data from these fleets are not available.
Bonfil (1994) estimated that distant water longline fleets may have caught about 2,000,000 oceanic sharks (i.e.
about 75,000t) per year in 1987-1989. From preliminary bycatch data provided by Lablache and Karpinski (1988), we estimate that the purse-seine fishery may be catching about 5,000t of oceanic sharks per year at present. These estimates are very crude, and the extent to which such catch levels may have caused stock depletion is unknown.
However, this should be a cause for concern since Indian Ocean stocks of bigeye tuna Thunnus obesus and yellowfin tuna (which are often caught at the same time as oceanic sharks) may both now be being exploited at levels in excess of their estimated maximum sustainable yields (IPTP 1995). Some rough indication of the likely recent increase and current magnitude of oceanic shark fishing mortality by Indian Ocean tuna fleets may be given by the catch of those shallow water tropical tunas with which these sharks often associate (Figure 4).