Overfishing: how many Dead Seas?

by Gregory Giuliani

Fishing activities have various negative impacts on marine ecosystems. The greatest cause for concern is the rapid depletion of fi sh population due to extensive commercial fi shing. In 2002 72% of the world’s marine fi sh stocks were being harvested faster than they can reproduce. Bycatch – the harvest of fi sh or shellfi sh other than the species for which the fi shing gear was set – accounts for a quarter of the total catch (27m tonnes in 2003) and much of it is lost.

For many scientists overfishing now ranks as one of the greatest impacts of human activity on oceans. It increases the vulnerability of ocean ecosystems and contributes to the decline of other elements of the marine food-chain, including birds and mammals. The record for total fi sheries production (captured and farmed) was around 100m tonnes and was recorded in 2000. But the apparent glut conceals a serious decrease in the productivity of many fi sh species.

The fi shing industry, ranging from subsistence fi shers to large-scale mechanised fi shing vessels, employs directly or indirectly some 200 million people worldwide. As an economic sector it is a crucial factor in the development of many countries. But fish depletion also threatens food security. In Asia alone more than a billion people depend on fi sh and seafood as their major source of animal protein. The UN Educational, Scientifi c and Cultural Organisation (UNESCO) warns that fi sh, long regarded as the “poor man’s protein”, is diminishing globally due to increasing market demand and overfi shing.

Modern fi shing technology is elaborate. Some trawlers are 170 metres long and can engulf catches equivalent in volume to 12 jumbo jets. Drift-nets may exceed 60 km in length. Fishing vessels stay at sea for several months and often prepare the catch for market distribution at sea. For bottom trawling powerful ships drag heavily weighed nets across the ocean fl oor, destroying the natural habitat. Each year they harvest an area twice the size of the continental United States! Sonars, aerial monitoring systems and satellite platforms help to locate fi sh schools and follow them more easily.

Bycatch may include low-value species but also large amounts of young or undersized fi sh of valuable commercial species. Almost 25% of all harvested fi sh never reach the market. Bottom trawling is particularly indiscriminate. For example, up to 95% of the take in halibut trawling can be bycatch, including various endangered or overfi shed species.

Although some countries have adopted fl eet reduction programmes, most fi shing nations have acknowledged that overcapacity is a serious problem. The FAO estimates that the world fi shing fl eet numbered about 3.8m vessels in 1995 of which nearly 1.2m included storage space. The fact that fi shing capacity reduction has often been achieved by relocating vessels in other countries’ fi sheries or in high seas’ fi sheries is of serious concern, as it does not contribute to a global reduction in fi shing capacity. Signifi cant reductions in fi shing capacity in highly populous and least-developed countries are not likely to occur due to increasing social pressure. At the same time the best way to reduce bycatch would be to lower the total fi shing effort as much as possible, and develop selective technologies, better regulations and stronger enforcement. So far only eight countries have imposed a total or partial ban on bottom trawling (New Zealand, Indonesia, Philippines, Scotland, Italy [Sicily only], Kenya, Seychelles and Greece). In all studies conducted in these countries it was found that pressure on fi sh resources had been alleviated and stock recovery had occurred.

Gregory Giuliani is a master of environmental sciences specialised in GIS and remote sensing. He works on early warning issues and the GEO project at UNEP/GRID-Europe.

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