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Issue In the process of producing food, economic resources, employment, livelihood and recreation, fisheries have to potential to modify ecosystems because fishing may alter or affect: the target resource (especially if there is overfishing of the target resource); species associated with or dependent on the targeted resource (such as predators or prey); trophic relationships within the ecosystem in which the fishery operates; and habitats in which fishing occurs. Sometimes the impacts are reversible, and sometimes the impacts are difficult to reverse, but Under the Code of Conduct for Responsible Fisheries, the fishing sector is expected to reduce theire impacts to a minimum in ways that are also compatible with its own sustained existence.
Some of the more well-documented fishing activities that can have potentially negative impacts on the environment include:
- Overfishing and excessive fishing can reduce the spawning biomass of a fishery below desired levels such as maximum sustainable or economic yields.
- When there is sustained overfishing, changes in species composition and biodiversity can occur with progressive reduction of large, long-lived, and high value predator species and the increase in small, short-lived, and lower value pelagic and demersal prey species, a process described as "fishing down the food chain". Important macroscopic changes have been observed in many ecosystems such as the North Sea, Yellow Sea, North Atlantic (e.g. George's Bank and Barents Sea), Gulf of Thailand, and southeastern Australia. Intensive fishing can also reduce genetic diversity of wild populations (e.g. rapidly depressing the proportion of fast growing and late spawning individuals) and changes in species composition or dominance can also be provoked through competition for food between fisheries and marine apical predators.
- Non-selective fishing gear that is not modified to exclude or otherwise deter the entanglement of fish, turtles, or seabirds, and as a result may take a significant bycatch of juvenile fish, benthic animals, marine mammals, marine birds, vulnerable or endangered species, etc. that are often discarded dead. While bycatch and discard problems are usually measured in the potential loss of human food, the increased risk of depletion for particularly vulnerable or endangered species (e.g. small cetaceans, turtles) can be significant. In the North Sea, for example, the impact of discarded fish on the food chain and species composition is consequential because the discards can represent up to 30% of what some birds' would otherwise consume.
- Ghost fishing can occur when certain gear such as pots or gillnets have either been lost or abandoned at sea and, although untended, continue to catch and kill fish until the gear falls apart.
- Impacts on the bottom can result from the intense use of trawls and other mobile bottom gear (e.g. dredges) can change bottom structure, microhabitats, and benthic fauna. The effect is particularly obvious when these gears are used in sensitive environments where there are sea grass and algal beds, coral reefs, sponges, and tube worms. Where fishers work the same area year after year much like a farmer's fields, the long-term impacts of such repeated activities are less obvious on soft bottoms, although the scraping or ploughing the bottom to depths of as much as 30 cm can seriously disturb the substratum habitat and productivity.
- Fishing entailing the use of dynamite and poisons can have severe and broad-reaching impacts, particularly on coral reefs.
There are also other less conspicuous or debated environmental impacts of fisheries-related activities. Some relate to the direct dumping of debris (gear, twine, food containers, plastic bands, etc.) or the unintentional dumping and accidental introduction of unwanted organisms, pathogens, and non-indigenous/foreign/alien species by fishing vessels. Other impacts include the organic pollution from at-sea processing and the pollution caused by unregulated wastes and effluents from coastal processing plants. Finally, fishing vessels and processing plants also have the potential to contribute to global warming through exhaust fumes and refrigerant gases.
Solving the problem of overfishing - and, thus, the impacts of overfishing on the environment - is a longstanding regulatory challenge that requires fishers to have clear financial reasons to not overharvest in their efforts to fish. Additional data and research on the environmental impacts of fishing on the ecosystem can help managers and fishers, alike, to make more informed decisions regarding the impacts of fishing and, in particular, on species composition and the environment.
When coupled with measures to avoid overharvesting, technologies to increase harvesting selectivity can similarly help to reduce bycatch and subsequent discarding. The problem of ghost fishing can be decreased through greater awareness raising, the prohibition and control of dumping of damaged gear at sea, and with active at-sea programmes for the retrieval of lost gear. Gear technology (e.g. biodegradable material, collapsible traps, etc.) can also diminish the ability of lost gear to continue catching fish. Improved gear technologies can be used to reduce the impacts of fishing on various habitats and on the bottom. Finally, the adoption and enforcement of measures to prohibit destructive fishing practices can also help to reduce the impacts of fishing on the environment.
Countries have been tackling the problem of overfishing - and, thus, the impacts that overfishing can have on the environment - for a long time (although with limited success in many instances). However, under the International Plan of Action (IPOA) for the Management of Fishing Capacity (IPOA-Capacity) that was adopted at FAO in 1999, countries are currently working to address overcapacity and its many associated problems, including overfishing. In addition, under the 2001 FAO IPOA on Illegal, Unreported and Unregulated Fishing (IPOA - IUU), there are many efforts currently underway around the globe to address illegal, unreported, and otherwise unregulated fishing activities and, thus, also helping to counteract overfishing.
NGOs have become very active at uncovering and illustrating the problems of the environmental and ecosystem impacts of fishing activities, exerting considerable pressure on governments and fishery organizations from very local to very global levels. Consumers are also starting to exert pressure on fisheries management, and the progressive use of environmental ecolabels based on sustainable fishing activities is also providing additional incentives to consider and mitigate the environmental impacts of fishing. To limit international trade in endangered fish species, CITES is adding fish species that are subject to large-scale exploitation to its annexes. Some countries have regulated discarding, imposing severe discard limits or banning it altogether and forcing the landing of all unwanted bycatch (e.g. in Norway, Canada, Iceland, and the Faeroe Islands).
The fishing industry as a whole is working to address the operational side-effects of fisheries on the environment. The use of innovative gear modifications, including selective grids, panels and square meshes in several trawl fisheries is facilitating the escape of unwanted species or small-sized individuals. Special devices are currently used in tuna fisheries to successfully reduce dolphin catches. Longlines are being modified to reduce bycatch of birds, and an IPOA for Reducing Incidental Catch of Seabirds in Longline Fisheries was adopted by FAO in 1999. In some countries (e.g. Norway), programmes exist to retrieve lost gillnets lying on the bottom.
Zoning strategies, including Marine Protected Areas (MPAs) has been used to keep trawlers away from vulnerable habitats, although with little success in areas where there is ineffective enforcement and/or fleet overcapacity. Programmes for the development of integrated and more sustainable livelihoods are being implemented (e.g. by FAO in Western and Central Africa). Some countries (USA, Ireland) require the elaboration of an environmental impact assessment (EIA) and/or environmental impact statement (EIS) for their fisheries, whilst in other countries such as Australia, the fishing industry is voluntarily adopting and implementing environmental management systems.
Awareness of the environmental impacts of fishing activities has been greatly increasing since UNCED (1992) both in the fisheries sector and among the public. The current pressure for ecosystem-based fisheries management is pushing managers and fishers to more specifically address the environmental impacts of fishing activities. The fishing sector progressively adopting economical technologies and approaches to environmentally acceptable fishing practices. Progress made in fishing and processing technology is significant and the fisheries sector is increasingly recognizing the benefits of ecolabelling. As a consequence, while much remains to be accomplished, the prospects for improvement are optimistic.