Bycatch is not automatically a problem in all fisheries. If bycatch is minimal, does not deplete populations of vulnerable species or undermine the productivity of fish stocks, it doesn't necessarily cause ecological harm. Unfortunately, on a global scale, bycatch is significantly exacerbating the threats posed by the commercial over-exploitation of the oceans. According to the latest estimates of the UN Food and Agriculture Organisation 7.3 million tonnes of bycatch are discarded annually by the worlds fisheries.

This was not always the case. The tremendous growth of the fishing industry in the last few decades has meant not only expanding fishing fleets, but the development of vessels which are larger, faster and able to cover greater areas of ocean. Unfortunately, these vessels are often less selective than their predecessors. And as fisheries are rapidly reaching their limits of exploitation, wastage of marine life is coming under greater scrutiny.

High levels of bycatch can affect entire marine communities, reducing biomass and altering the ecological structure and diversity of the oceans. The impacts of bycatch on vulnerable "charismatic" species have been particularly well documented, and have perhaps received greatest public attention. Often long-lived and slow to mature with low natural mortality and low reproductive output, populations of several marine mammals, sea turtles, sharks and sea birds (amongst others) have declined due to incidental capture. Some species in these groups are highly endangered, for example the vaquita porpoise of the Gulf of California.

As those species vulnerable to high levels of mortality are selectively removed, food chains and predator-prey relationships are affected. The long-term consequences of these changes are not fully understood.

Fishing supports the livelihoods of 450 million people and, as the global population expands, pressure on fish stocks is likely to increase. Over-exploitation will lead to an eventual loss in profit and job opportunities for fishing companies and their employees. Yet for artisanal and subsistence fishers in developing nations, declines in fish stocks can mean hunger and a loss of livelihood where few other options exist.

Industrial vessels operating in shallow coastal areas of developing countries can have considerable impacts on food security. Even when targeting different stocks altogether, high incidental capture of artisanal fish species can quickly undermine the productivity of traditional fishing grounds.

Bycatch not only affects marine ecosystems but also the millions of people who rely on healthy fish stocks for food and employment. The economic costs of discarded bycatch for the fishing industry can be considerable. Bycatch may contain commercial species: often juvenile individuals with little market value. High juvenile mortality due to incidental capture has implications for the productivity of stocks (both target and non-target) potentially leading to declining yields and premature closures of fisheries. In several cases this has caused conflict between fishermen.

Shrimp fisheries are an important part of the European Union's fishing industry. However, the fine meshed trawl nets used to capture brown shrimp (Crangon crangon) also incidentally catch high levels of non-target species. Bycatch often consists of juveniles of other commercial species. Indeed, these brown shrimp fisheries have caused losses of 6-16% of the North Sea spawning stock of plaice. Because these non-target fish are discarded, potential landings lost are calculated to be around 12,000 tonnes a year, with a market value of €17.9million. Annual losses of sole and cod are estimated at €3.9 million and €2.7 million respectively.

This incidental capture can be reduced through the use of "bycatch reduction devices" (BRDs), which retain shrimp, but allow more fish to escape from nets unharmed. BRDs have been used very successfully to reduce bycatch in the cold-water shrimp fisheries of Canada, Iceland and Norway.

Due to concerns about the impacts of any contact between tuna fisheries and dolphins, alternative methods of capturing tuna have also been developed. However, some of these, including the use of artificial fish aggregating devices (not only used in tuna fisheries) have resulted in high bycatch of other species including mahi-mahis, yellowtails, sharks and rays, as well as juvenile tuna.

Tuna purse-seining (where a net is used to encircle the targeted shoal of fish and then closed tight) can be used in three different ways that correspond to three means of detecting tuna:

1. on free-swimming schools of tuna;


2. on tunas associated with floating objects (naturally occurring or artificial);


3. on dolphins (mainly in the Eastern Tropical Pacific - ETP).

The capture of dolphins that were deliberately targeted in tuna purse-seine nets in the Eastern Pacific Ocean caused an outcry when first brought to pubic attention. Tuna's association with dolphins makes detection at the surface easier, but dolphins deliberately encircled by the purse-seiners were frequently captured and killed in the process. Dolphin mortalities reached hundreds of thousands every year, and populations declined rapidly until the mid-1990s when technological and operational changes to reduce dolphin bycatch were successfully introduced. The efficacy of these measures, in conjunction with management actions to limit dolphin deaths per vessel, has lowered mortality levels for all dolphin populations to less than 0.1%.

Mortality levels for all dolphin populations in the ETP was lowered considerably, from an estimated 133,000 in 1986 to around 1,877 in 1998. Nevertheless, serious bycatch concerns regarding the fishery still persist, as bycatch of immature tunas and other fish species have now increased due to the popularity of alternative fishing practises designed to avoid contact with dolphins, particularly the use of fish aggregating devices (FADs).

This case study therefore presents a clear-cut example of the folly in taking a single-species approach to bycatch reduction; by focussing solely on reducing impacts on dolphin populations, the problem of bycatch has not been eradicated, it has merely been displaced onto another set of marine fauna.

Fish Aggregating Devices (FADs) are artificial floating structures that attract pelagic species, including tuna. These devices are now widely distributed in tropical and subtropical waters globally, contributing more than half of the worldwide tuna catch (estimated at around 3.5 million tons a year). This trend is increasing, with the use of FADs being particularly prevalent in the Indian Ocean. EU purse seiners fish for tuna using FADs in the Indian, Pacific and Atlantic Oceans under all of the 17 Fishing Agreements with developing countries.

Data from the Eastern Tropical Pacific indicates that levels of bycatch using FADs can be up to 50%, composed of dolphin fish, billfish, wahoo, triggerfish, barracuda, rainbow runners, sharks, rays and sea turtles. Skipjack are the main target species but increasingly large numbers of juvenile tunas - yellowfin and bigeye (the latter is classed as a "vulnerable" species by the IUCN) are also caught. One study reported that almost 20% of the tuna catch can be discarded in these types of fisheries because it is below the market minimum requirement for size or condition.

For many areas there is little data on the levels and composition of bycatch associated with FAD fisheries, or on the status of non-target species' populations. In general, the use of FADs is regarded as a non-sustainable practice for which solutions are urgently needed; at present there are few well-established technical or operational means to reduce bycatch in these fisheries. Innovative bycatch reduction measures need to be devised, and the EU should take a principal role in funding and directing this research.

Shrimp is typically caught by trawling the oceans with fine-mesh nets. Unless adequately managed, these trawl fisheries are particularly indiscriminate in their capture of non-target marine life or "bycatch".

• Shrimp trawl fisheries alone are responsible for around one third of the world's discarded bycatch, despite producing less than 2% of global seafood.


• In the tropics, up to 20kg of non-target marine organisms can be caught (and are often discarded) to obtain just 1kg of shrimp.


• 150,000 marine turtles are killed by shrimp trawlers each year. Trawling also poses a significant threat to seahorses.

Populations of many "bycatch" species have declined rapidly in areas where shrimp trawlers operate, including commercial and artisanal fish species that have supported fishing communities for centuries. Left unmanaged, these fisheries will lead to a decline in marine biodiversity and productivity, along with increased poverty in the developing world where food security is often already in doubt. It is imperative that the excessive bycatch levels often associated with tropical shrimp trawl fisheries are reduced.