Bycatch

Commercial fishing Bycatch is inevitable wherever there is fishing. The incidental catch is not limited to only fish species: dolphins, sea turtles, and seabirds are also victims of bycatch. Bycatch happens most commonly with the use of gillnetting, longlines, or bottom trawling. Longlines with bait hook attachments can potentially reach lengths of dozens of kilometres, and, along with gill nets in the water and bottom trawls sweeping the sea floor, can catch essentially everything in their path. There are thousands of kilometres of nets and lines cast into the world's oceans daily. This modern fish gear is robust and invisible to the eye, making it efficient at catching fish and bycatching everything that happens to be in the way. Hook-and-line fishing could limit bycatch to a certain extent as the non-target animals can be released back to the ocean fairly quickly. Shrimp trawling hauling in nets|alt=Photo of boat moving forward at sea. On each side, the boat has one pole pointing away from boat with nets attached bycatch|alt=Photo of hundreds of dead fish lying on ship deck The highest rates of incidental catch of non-target species are associated with tropical shrimp trawling. In 1997, the Food and Agriculture Organization of the United Nations (FAO) documented the estimated bycatch and discard levels from shrimp fisheries around the world. They found discard rates (ratio of bycatch to catch by mass) as high as 20:1 with a world average of 5.7:1. When bycatch is discarded (returned to the sea), it is often dead or dying. Recent sampling in the South Atlantic rock shrimp fishery found 166 species of finfish, 37 crustacean species, and 29 other species of invertebrate among the bycatch in the trawls. or untargeted insects) and control of introduced vertebrates which have become pest species like the muskrat in Europe (where the bycatch in traps may be European minks or waterfowl). == Victims ==

Sharks and rays Longlines, trawls and purse seine nets are driving factors in the endangerment of no fewer than fifteen shark species. Bycatch may also affect reproduction of populations as juveniles are also victims of bycatch. Cetacean Cetaceans, such as dolphins, porpoises, and whales, can be seriously affected by entanglement in fishing nets and lines, or direct capture by hooks or in trawl nets. Cetacean bycatch is increasing in intensity and frequency. Albatross hooked on a long-line|alt=Photo of bird struggling to fly away Of the 22 albatross species recognised by IUCN on their Red List, 15 are threatened with extinction, six species are considered as Near Threatened, and only one of Least Concern. Two species, the Tristan albatross and the waved albatross, are considered as Critically Endangered. because albatrosses and other seabirds which readily feed on offal are attracted to the set bait, after which they become hooked on the lines and drown. An estimated 100,000 albatross per year are killed in this fashion. Unregulated pirate fisheries exacerbate the problem. A research study examined the impact of illegal longline fishing vessels on albatrosses, by using environmental criminology as a guiding theoretical framework. The results indicated that potentially illegal longline fishing activities are highly concentrated in areas of illegally-caught fish species, and the risk to bycatch albatrosses is significantly higher in areas where these illegal longline fishing vessels operate. The speed and length of the trawl method is significant because, "for a tow duration of less than 10 minutes, the mortality rate for sea turtles is less than one percent, whereas for tows greater than sixty minutes the mortality rate rapidly increases to fifty to one hundred percent". Sea turtles can sometimes escape from the trawls. In the Gulf of Mexico, the Kemp's ridley turtles recorded most interactions, followed in order by loggerhead, green, and leatherback sea turtles. In the US Atlantic, the interactions were greatest for loggerheads, followed in order by Kemp's ridley, leatherback, and green sea turtles. ==Mitigation==

|alt= Concern about bycatch has led fishers and scientists to seek ways of reducing unwanted catch. There are two main approaches. One approach is to ban fishing in areas where bycatch is unacceptably high. Such area closures can be permanent, seasonal, or for a specific period when a bycatch problem is registered. Temporary area closures are common in some bottom trawl fisheries where undersized fish or non-target species are caught unpredictably. In some cases fishers are required to relocate when a bycatch problem occurs. The other approach is alternative fishing gear. A technically simple solution is to use nets with a larger mesh size, allowing smaller species and smaller individuals to escape. However, this usually requires replacing the existing gear. In some cases, it is possible to modify gear. Bycatch reduction devices (BRDs) and the Nordmore grate are net modifications that help fish escape from shrimp nets. Bycatch reduction devices BRDs allow many commercial finfish species to escape. The US government has approved BRDs that reduce finfish bycatch by 30%. Spanish mackerel and weakfish bycatch in the South Atlantic was reduced by 40%. A rock shrimp fishery off Florida found the devices failed to exclude 166 species of fish, 37 crustacean species, and 29 species of other invertebrates. Turtle excluder devices In 1978, the National Marine Fisheries Service (NMFS) started to develop turtle excluder devices (TED). A TED uses a grid which deflects turtles and other big animals, so they exit from the trawl net through an opening above the grid. US shrimp trawlers and foreign fleets which market shrimp in the US are required to use TEDs. Not all nations enforce the use of TEDs. For the most part, when they are used, TEDs have been successful reducing sea turtle bycatch. However, they are not completely effective, and some turtles are still captured. NMFS certifies TED designs if they are 97% effective. In heavily trawled areas, the same sea turtle may pass repeatedly through TEDs. Recent studies indicate recapture rates of 20% or more, but it is not clear how many turtles survive the escape process. Conservation engineering of trawl nets The size selectivity of trawl nets is controlled by the size of the net openings, especially in the "cod end". The larger the openings, the more easily small fish can escape. The development and testing of modifications to fishing gear to improve selectivity and decrease impact is called "conservation engineering". s chase longline fishing vessel|alt=Photo of hundreds of seabirds on water surface around boat Longline fishing is controversial in some areas because of bycatch. Mitigation methods have been successfully implemented in some fisheries. These include: • weights to sink the lines quickly • streamer lines to scare birds away from baited hooks while deploying the lines • setting lines only at night with minimal ship lighting (to avoid attracting birds) • limiting fishing seasons to the southern winter (when most seabirds are not feeding young) • not discharging offal while setting lines. However, gear modifications do not eliminate bycatch of many species. In March 2006, the Hawaii longline swordfish fishing season was closed due to excessive loggerhead sea turtle bycatch after being open only a few months, despite using modified circle hooks. Seabirds Seabirds get entangled in longlines by flocking around vessels, this eventually leads to drowning because they try to catch baits on the hooks. Fisheries had been using "streamer lines" as a cost effective solution to mitigate this type of bycatch, and it has dramatically reduced seabird mortality. These streamer lines have bright colors and are made of polyester rope, they are positioned alongside the longlines on both sides. Their bright colors and constantly flapping of water frightens the seabirds and they fly away before reaching the baited hooks. A successful example would be the use of streamer lines in Alaskan groundfish longline fisheries, as the deaths of seabirds declined by about 70% after the deployment of these lines. ==Retention==

Some fisheries retain bycatch, rather than throwing the fish back into the ocean. Commercialization of bycatch Sometimes bycatch is sorted and sold as food, especially in Asia, Africa and Latin America, where labour is cheaper. Bycatch can also be sold in frozen bags as "assorted seafood" or "seafood medley" at cheaper prices. Bycatch can be converted into fish hydrolysate (ground up fish carcasses) for use as a soil amendment in organic agriculture or it can be used as an ingredient in fish meal. In Southeast Asia bycatch is sometimes used as a raw material for fish sauce production. Bycatch is also commonly de-boned, de-shelled, ground and blended into fish paste or moulded into fish cakes (surimi) and sold either fresh (for domestic use) or frozen (for export). This is commonly the case in Asia or by Asian fisheries. Sometimes bycatch is sold to fish farms to feed farmed fish, especially in Asia. No discards policy A 'no discards' policy has been adopted by Norway as a way to reduce bycatch. This means that the fishermen must keep everything they catch. This policy has helped to "encourage bycatch research", which, in turn has helped "encourage behavioral changes in fishers" and "reduce the waste of life" as well. == See also ==