Driftnets are a very simple method of fishing with a long history of use all around the world. They are currently used on many tens of thousands of fishing boats and make a significant contribution to world fish catches.
In recent years there has been an expansion of high seas driftnet fishing. This has apparently been prompted in part by the exclusion of distant water fleets from coastal EEZ's, and an increasing world demand for fish, and has been facilitated by a ready availability of cheap nylon twines for net construction. These factors have allowed the profitable exploitation of dispersed fish resources.
Of the existing driftnet fisheries, the largest is the North Pacific squid driftnet fishery, in which over 780 vessels participate seasonally, each deploying 40 km or more of netting. Some coastal driftnet fisheries may rival this fishery in terms of the amounts of netting being deployed.
In the North Pacific, the major high seas fisheries are those for salmon, squid and for tunas (large mesh fishery). There is also a large Japanese driftnet fishery for salmon inside the Japanese EEZ, a smaller driftnet fishery for swordfish and sharks in US waters, and many thousands of vessels using driftnets in Chinese, Japanese and US coastal waters. Catches of marine mammals, birds, and other non-target species have been monitored in the salmon and squid high seas fisheries. Reliable estimates of total catches and assessments of impacts on populations have only been made for Dall's porpoises taken by the Japanese mothership fleet. Dall's porpoises, northern right whale dolphins and Pacific white-sided dolphins are all taken in relatively large numbers by the high seas fisheries. Other species which may be adversely impacted include leatherback turtles and Laysan albatrosses.
The large mesh high seas driftnet fishery for albacore and skipjack in the southern Pacific Ocean is currently declining, and is due to be terminated by 1992. Common dolphins and southern bottlenose whales have been reported caught in this fishery. Other fisheries in the South Pacific include the Peruvian and Chilean fisheries for tunas, sharks and small cetaceans, and for swordfish. Dusky dolphins and Burmeister's porpoises are apparently the most frequent marine mammal catches in South American waters.
In the Indo-Pacific, there is a Taiwanese fishery operating in the Arafura Sea, and many tens of thousands of driftnet vessels operating in coastal waters of Thailand, Malaysia, Indonesia and other countries, targeting mainly small tunas and spanish mackerels. Information on non-target catches is lacking.
In the Indian Ocean, a Taiwanese large scale driftnet fishery operates in the Arabian Sea, north of the Seychelles, and in the southern Indian Ocean, mainly targeting albacore. There are very large coastal driftnet fisheries in India and Sri Lanka as well as Bangladesh, Pakistan, Iran and the Gulf states, again largely for tunas and spanish mackerels, but also for a variety of non-scombrid fishes in Bangladesh. The fishery in Sri Lanka may take several tens of thousands of small cetaceans, mainly spinner and striped dolphins. Non-target catches in the other fisheries are largely unknown.
In the Atlantic an undocumented Taiwanese driftnet fishery operates in the area around Tristan da Cunha and perhaps elsewhere. It is thought to target albacore, with non–target catches including unidentified small cetaceans and rockhopper penguins. Coastal fisheries in Brazil and in parts of West Africa also employ driftnets but are little documented.
There are reliable records of a small number of Taiwanese vessels also using driftnets in the North Atlantic, apparently for tunas. A French driftnet fishery operates in the eastern north Atlantic for albacore, and there are numerous small scale coastal driftnet fisheries for salmon and other pelagic fish around much of the North Atlantic. Non–target species caught include harbour porpoises, common dolphins, Brunnich’s guillemot, common guillemots, razorbills and shags.
A large Italian driftnet fishery for swordfish has recently been terminated. This was taking large numbers of striped dolphins as well as significant numbers of sperm whales. Some small scale driftnetting for tunas continues in other parts of the Mediterranean.
Much of the recent expansion of Taiwanese driftnetting on the high seas is not well documented and catches of non–target species by these fleets are largely unknown.
There are numerous concerns surrounding high seas driftnet fisheries, many of which are due to perceived or actual competition with existing fisheries. Attempts could be made to resolve most of these if effective regional fishery management regimes were established to manage high seas fishery resources.
There are also a range of environmental problems surrounding high seas driftnet fisheries which have been addressed by a recent UN resolution. Chief amongst these are the potential impact that driftnet fisheries may have on air breathing animals and some of the less numerous fish. If these concerns are to be addressed, and if high seas driftnet fisheries continue, then it will be necessary to implement regional fishery management regimes to cover the high seas, as has been proposed by the UNCLOS.
There are few important differences between driftnet fisheries which are operated inside EEZ's compared with those operated outside EEZ's, except that effective management and regulation of those in international waters may be more difficult. The environmental impact of numerous vessels each operating a few net sections in coastal waters may be equivalent to, or even greater than, a smaller number of high seas vessels each operating a greater number of net sections. Coastal states have been encouraged by the UN resolution (44/225) to co–operate in the management of driftnet fisheries taking into account measures taken on the high seas for the conservation of living marine resources.
If high seas driftnet fisheries do continue to operate after 1992, and if they are to be managed with the aim of minimising environmental impacts, then it would be necessary to adopt appropriate environmental objectives and resultant management measures. The most straightforward objectives would involve controlling the level of impact on individual non–target species. In this case it would be necessary to decide on the levels of impact, if any, which are acceptable, and to adopt management measures which enable the impact of the fishery to be monitored and controlled. This would require considerable technical, financial and logistical resources.