Submitted by Arthur Dahl on 5. June 2011 - 19:40
e-learning centre on sustainable development


Heading: Development    Topic: Fishing

The collapse of the North-west Atlantic cod fishery, among other ocean fishery crises and disputes, has only confirmed the concerns behind the oceans chapter of Agenda 21 (UNCED, 1992, para. 17.45 and 17.72). World fishery production has reached 122 million tones in 1997, a figure six times that of 1950 (FAO Fact File). Major ocean fisheries, most of which are within exclusive economic zones, are already using a high proportion of the total available primary production, amounting to 25 percent for upwelling areas and 24-35 percent in shelf systems, leaving little or no possibility for further increases in these most productive fisheries (Pauly and Christensen, 1995). On the contrary, 70 percent of marine fisheries are so heavily exploited that reproduction cannot or can just barely keep up (Garcia, 1995). For example, the swordfish in the North Atlantic Ocean has declined by about 70% over the past twenty years and populations of cod, hake, haddock and flounder have fallen by as much as 95% between 1989 and 1994 (Jackson, 1995). In addition, large oceanic driftnets and longlines harvest not only the targeted fish species but slaughter numerous other species, such as dolphins, sharks, sea turtles and sea birds. One quarter of the world's annual catch (20 million tonnes) is thrown back into the sea, dead or dying (Leong Ching Ching, 1998). With the continuing over-investment in fishing fleets, annual losses now amount to $50 billion, requiring cuts of 20 to 50 percent in the fishing industry capacity to achieve sustainability (FAO Fisheries Department, 1995; Garcia, 1995).

Marine fisheries piechart
Source: FAO fact file

Bottom trawling accounts for more of the world's catch than any other method, but due to its environmental impact, it is often compared to forest clear-cutting (Watling et al., 1998). The area trawled each year is about equivalent to 150 times the total forest area clear-cut yearly and corresponds to about an area twice the size of the contiguous United States (Norse, 1998). Until the 1950's, some areas were naturally protected from trawling, being too rocky, too deep or too remote to allow access (MCBI website), but today new technologies have permitted trawling almost everywhere. In intensive fishing areas, the bottom can be trawled 100 to 700% each year. Both bottom trawling and scallop dredging dramatically affect marine ecosystems. The large weighted nets not only catch all marine life in midwaters, whether targeted or caught incidentally, but also cause severe seabed habitat destruction. Sea creatures living on the bottom are crushed, buried or exposed to predators, and clouds of sediments rise, altering seabed biochemistry.

Trawler bycatch represents between 17-39 million metric tones of fish discarded unused each year (McAllister, 1998). Ecosystems, such as continental shelves and slopes, are more affected than other areas; they naturally suffer less disturbance (by storm waves for example) and have evolved for slower growth and other biological processes, which means that recovery takes places over a longer period of time (Watling et al., 1998). 

Scallops before dredging
After scallop dredge
Healthy cobble-shell bottom habitat for scallops before (left) and after (right) one pass of a scallop dredge.

Before photo: Peter Auster, National Undersea Research Center. After photo: Peter Auster, NURC. (AOC website)

Shrimp trawl catch. The 95% of the catch in this photo that was not shrimp died on deck and was shoved overboard. (Elliott A. Norse). (MCBI website).

A recent study shows that greater habitat complexity correlates with increased survival rates in young fish (Lindholm et al., 1999). Scientists therefore encourage fishery management programs to take the impact of trawling on sea habitats more into account, rather than focusing only on variations in fish populations. The adoption in 1995 of a global agreement on Straddling and Highly Migratory Fish Stocks and a Code of Conduct for Responsible Fishing, as significant outcomes of the Earth Summit in Rio in 1992, shows that States are now taking the risks to high seas living resources more seriously (FAO, 1995b). More than 1,600 marine scientists and conservation biologists from 65 countries have issued a call to turn 20% of the world's oceans into natural marine reserves by the year 2020 (Troubled Waters: A Call for Action, 1998). In a recent meeting regrouping 120 countries, three new action plans were designed for more sustainable fisheries to be implemented in the framework of the FAO Code of Conduct for Responsible Fisheries. The International Plans of Action for the Management of Fishing Capacity, for the Conservation and Management of Sharks, and on Incidental Catches of Seabirds in Longlines Fisheries, encourage countries to manage their fishing capacities, to protect affected fisheries as well as endangered shark populations, and to decrease bird bycatch (FAO Ministerial Meeting, 1999). Specialists encourage the emergence of share-based fisheries, in which rights or “shares” are allocated to the overall fishery and not for individual species. This would create a local-level management institution, in which fishers would be more cautious of marine ecosystems if their shares were at risk. It would also allow more rapid gathering of local ecological information at a minimum cost (Costanza et al., 1998).

The total world aquaculture production contributes to the global fish supply. Aquaculture is one of the fastest growing food sectors, with production increasing from 10 million tonnes in 1990 to 29 million tonnes in 1997 (FAO, 1999). More than 220 species of finfish and shellfish are farmed today.

However, carnivorous farmed fish are fed on high levels of fish meal and fish oil and require a fish biomass input superior to the fish biomass produced. For the ten species of fish most commonly farmed , an average of 1.9kg of wild fish is required for every kilogram of fish raised. Unfortunately, there is an increase in the production trend of carnivorous fish (such as salmon or shrimp), rather than herbivorous or filter feeder fish. Small pelagic fish mainly provide the fish meal and fish oils used for aquaculture feed. Aquaculture's growing needs increase pressures existing on wild fisheries for small pelagic fish, which already suffer from overexploitation and are strained by climate changes resulting from the El Niño warming effect.

Aquaculture activities also result in indirect pressures on wild fisheries. Aquaculture farms have replaced hundreds of thousands of hectares of mangroves and coastal wetlands, which naturally provide nurseries and shelter for wild fish populations. In addition to natural habitat destruction, some farms remove wild finfish or shellfish post-larvae to stock their ponds, instead of using hatchery-reared post-larvae, thus affecting wild population renewal. Another problem may arise from the escape of farmed fish, which can cause serious biological pollution. Wild population genetics may be altered through hybridization with farmed individuals, and movement of cultured stocks may increase the risks that pathogens will spread to wild populations. Aquaculture fisheries may finally damage the environment through effluent discharge of untreated wastewater. Specialists recommend farming expansion of low trophic level fish with herbivorous diets and a reduction of fish meal and oil input in aquaculture feed. Polyculture is encouraged as a mean of exploiting all available food and water resources of the pond ecosystem (Naylor et al., 2000).


Aquaculture's contribution to total food fish and shellfish supplies Annual contribution of aquaculture including plants
Fig 1: Data source: FAO website   Fig 2: Data source: FAO website


Watch a video about the effect of bottom trawling or visit the website of the AOC:

"What's a Fish Lover to Eat?" The Audubon Guide to Seafood by Carl Safina. MCBI website:


AOC (American Oceans Campaign) website:

Costanza, R., F. Andrade, P. Autunes, M. van den Belt, D. Boerma, D.F. Boesch, F. Catarino, S. Hanna, K. Limburg, B. Low, M. Molitor, J.G. Pereira, S. Rayner, R. Santos, J. Wilson, and M. Young. 1998. "Principles for sustainable governance of the oceans". Science, 281: 198-199.

FAO. 1995a. The State of World Fisheries and Aquaculture. Fisheries Department, Food and Agriculture Organization, Rome.

FAO, 1995b. Code of Conduct for Responsible Fisheries. Food and Agriculture Organization, Rome.

FAO Fisheries Department. 1999. "Aquaculture Production Statistics 1988-1997". Food and Agriculture Organization, Rome.

FAO Ministerial Meeting on the Implementation of the Code of Conduct for Responsible Fisheries (1999). The 23rd session of the Committee on Fisheries (COFI) convened at FAO headquarters in Rome from 15 to 19 February 1999. Press release, 11 March 1999.

FAO website:
FAO Fact File:
Figure 1:
Figure 2:

Garcia, Serge. 1995. (FAO) Quoted in "Too many fishermen chasing too few fish." Inter-Press Service, 24 May 1995.

Jackson, J.O. 1995. "The sea: tears for Neptune". Times, 30 October 1995.

Leong Ching Ching. 1998. "Oceans of the world: in troubled waters". Straits Times, 21 January 1998.

Lindholm, J.B., Auster, P.J, Kaufman, L.S. 1999. "Habitat mediated survivorship of juvenile (0-year) Atlantic cod Gadus morhua".  Marine Ecology Progress Series, 17 March 1999.
For a summary, see:

MacAllister, D. 1998. Quoted in Oceanspace issue 100, 22 December 1998.

MCBI (Marine Conservation Biology Institute) website:

Naylor, R.L., Goldburg, R.J., Primavera, J.H., Kautsky, N., Beveridge, M.C.M., Clay, J., Folke, C., Lubchenco, J., Mooney, H., Troell, M. 2000. Effect of aquaculture on world fish supplies. Nature, 405: 1017-1024.

Norse, E. 1998. Quoted in Oceanspace issue 100, 22 December 1998.

Pauly, D., and V. Christensen. 1995. "Primary production required to sustain global fisheries." Nature, 374:255-257.

"Troubled Waters: A Call for Action" Campaign, 1998.

UNCED. 1992. Agenda 21: Programme of Action for Sustainable Development, paragraphs 17.45 and 17.72. United Nations, New York.

Watling, L., Norse, E.A. 1998. Disturbance of the seabed by mobile fishing gear: a comparison with forest clear-cutting.  Conservation Biology, Dec. 1998.

Based partly on materials originally prepared for UN System-wide Earthwatch

Article last updated 28 July 2000

Return to IEF sustapedia


Return to e-learning centre

Last updated 30 August 2010