Krill fishery

Krill fishery is the commercial fishery of krill, small shrimp-like marine animals that live in the oceans world-wide. Estimates for how much krill there is vary wildly, depending on the methodology used. They range from 125–725 million tonnes of biomass globally. The total global harvest of krill from all fisheries amounts to 150 – 200,000 tonnes annually, mainly Antarctic krill (Euphausia superba) and North Pacific krill (E. pacifica).

Krill are rich in protein (40% or more of dry weight) and lipids (about 20% in E. superba). Their exoskeleton amounts to some 2% of dry weight of chitin. They also contain traces of a wide array of hydrolytic enzymes such as proteases, carbohydrases, nucleases and phospholipases, which are concentrated in the digestive gland in the cephalothorax of the krill.

Most krill is used as aquaculture feed and fish bait; other uses include livestock or pet foods. Only a small percentage is prepared for human consumption. Their enzymes are interesting for medical applications, an expanding sector since the early 1990s.

Technology
Krill are small animals, considered part of zooplankton, and hence need to be fished with very fine-meshed plankton nets. Such nets pose several problems: they tend to clog fast, and they have a very high drag, producing a bow wave that deflects the krill to the sides. Trawling must hence be done at low speeds. Additionally, fine nets are also very delicate, and the first krill nets designed exploded while fishing through the krill schools. Furthermore, fine nets increase unwanted bycatch, such as fish fingerlings, which might have unforeseen side-effects on the ecosystem, even though large krill aggregations tend to be monospecific.

Yet another problem is bringing the krill catch on board. When the full net is hauled out of the water, the organisms compress each other, resulting in great loss of the krill's liquids. Experiments have been carried out to pump Antarctic krill, while still in water, through a large tube on board. This method has already been used by the small fishing boats in Japanese waters.

Krill must be processed within one to three hours after capture due to the rapid enzymatic breakdown and the tainting of the meat by the intestines. They must be peeled because their exoskeleton contains fluorides, which are toxic in high concentrations.

Products
Most krill is processed to produce fish food for use in aquariums and aquacultures. The krill is sold freeze-dried, either whole or pulverized. Krill as a food source is known to have positive effects on some fish, such as stimulating appetite or resulting in an increased disease resistance. Furthermore, krill contains carotenoids and is thus used sometimes as a pigmentizing agent to color the skin and meat of some fish. About 34% of the Japanese catch of E. superba and 50% of E. pacifica are used for fish food; the Canadian catch is used almost exclusively for this purpose.

Some 25% of the Japanese catch of E. superba is used in the form of fresh frozen krill as fish bait; and 50% of the E. pacifica catch is used as chum for sport fishing. About 43% of the Japanese catch of E. superba is processed for human consumption. The Japanese industry produces boiled, frozen krill and peeled tail meat. Other uses include krill pastes or processed krill as food additives, e.g. in the form of krill oil gel capsules.

Medical applications of krill enzymes include products for treating necrotic tissue and as chemonucleolytic agents. Of the 376 krill-related patents that had been registered world-wide until 2002, 17% related to medical uses. Most of these medical patents had been registered after 1988.

Antarctic krill fishery
Krill fishery in the Southern Ocean targets the largest species of krill existing, the Antarctic krill (Euphausia superba), which can grow to about 6 cm. Fishing began in the early 1960s, when the Soviet Union launched its first experimental operations. All throughout the decade, preparatory activities were carried out, resulting in small catches of a few tens of tonnes per year. Scientists mapped the locations of krill swarms to determine the best fishing grounds, and engineers developed and improved the equipment necessary to fish and process krill. In 1972, the Soviets set up a permanent fishery in Antarctic waters, landing 7,500 tonnes in 1973 and then expanding quickly. The Japanese began experimental krill fishing operation in the area in 1972 and started full-scale commercial operations in 1975.

Krill catch increased rapidly. In the 1980s, a few additional nations started operating in the area: Poland, Chile, and South Korea. Their catches amounted to a few thousand tonnes annually; the lion's share went to the Soviet Union, followed by Japan. A peak in krill harvest was reached in 1982 with a total production of over 528,000 tonnes, of which the Soviet Union produced 93%. In the following two years, production declined. It is unclear whether this was due to the discovery of fluorides in the krill's exoskeleton or to marketing problems. The trade recovered quickly, though, and reached more than 400,000 tonnes again in 1987.

With the demise of the Soviet Union, two of its successor nations, Russia and Ukraine, took over the operations. Russian operations and catches dwindled, and were abandoned altogether in 1993. Since then, Japan, Poland and Ukraine are the largest krill-fishing nations; since 2000, the small South Korean Antarctic krill fishery has also expanded considerably. A U.S. company entered the market in 2001.

In 1982, the CCAMLR (Convention on the Conservation of Antarctic Marine Living Resources) came into force, as part of the Antarctic Treaty System. The CCAMLR was originally signed by fifteen states; as of 2004 it had 24 members. Its purpose is to regulate the fishery in the Southern Ocean to ensure a long-term sustainable development and to prevent overfishing. In 1993, the CCAMLR set forth catch quotas for krill, which amount to nearly five million tonnes per year.

The annual catch of Euphausia superba since the mid-1990s is about 100,000 tonnes annually, i.e., about one fiftieth of the CCAMLR catch quota. Still, the CCAMLR is criticized for having defined its catch limits too generously, as there are no precise estimates of the total biomass of Antarctic krill available and there have been reports indicating that it is declining since the 1990s.

Fishing for Antarctic krill is commonly done from large stern trawlers using midwater trawls. For scientific purposes, vertical trawls using, for example, a bongo net, are also employed.

Krill fisheries around Japan
The krill fishery in Japanese waters primarily targets the North Pacific krill (Euphausia pacifica), which reaches a size of about 2 cm. The annual catch is of the order of 60 – 70,000 tonnes. Minor fisheries for Euphausia nana (a few thousand tonnes) and Thysannoessa inermis (a few hundred tonnes annually) also exist. The fishing ground are all above the continental shelf close to the coast and at most 200 m deep. E. nana reaches only 1.2 cm, and T. inermis can grow to 3 cm.

E. pacifica was fished as early as the 19th century. Fishing is done with small boats. The traditional technique uses bow-mounted trawls, augmented by fish pumps since the 1980s. A bow-mounted trawl can exploit only surface swarms of krill up to a depth of about eight metres. In the 1970s, the krill fishery expanded drastically and began to use also one- or two-boat seines, which can catch swarms as deep as 150 m. A peak in the krill production was reached in 1992 with over 100,000 tonnes. The following year, catch regulations were enforced, and since then the annual catch has been reduced by about 30%.

Experimental fisheries
Small-scale fisheries for krill also exist in other areas. In Canada, fishing for E. pacifica takes place in the Strait of Georgia off British Columbia; there is a government-imposed catch limit of 500 tonnes per year. Fisheries targeting the Northern krill (Meganyctiphanes norvegica), a medium-sized krill reaching body lengths of more than 4 cm, as well as Tysanoessa raschii (2 cm) and T. inermis in the Gulf of St. Lawrence and on the Scotian Shelf have been proposed, but didn't get beyond early experimental stages. They are limited to harvesting a few hundred tonnes of krill per year, and Nicol & Foster consider it unlikely that any new large-scale harvesting operations in these areas will be started due to the opposition from local fishing industries and conservation groups.