OVER-FISHING

The single greatest threat to marine ecology is over-fishing. Catch sizes now regularly exceed sustainable levels, a trend that could have devastating consequences for the health of our oceans.

In 'The State of World Fisheries and Aquaculture 2002' the UN Food and Agriculture Organisation (FAO) states: "About 47% of the main stocks or species groups are fully exploited and are therefore producing catches that have reached, or are very close to, their maximum sustainable limits...Another 18% of stocks or species groups are reported as overexploited...10% of stocks have become significantly depleted, or are recovering from depletion." [1] By these figures, 75% of major fish species are either at or below sustainable levels.

Depleted fish populations mean smaller catches, but fishing fleets have not responded by allowing species time to recover; instead they continue to increase ship sizes and carrying capacity. In August 2000 the world's biggest fishing vessel ever was launched. The Atlantic Dawn measures 473 feet by 79 feet, and carries purse seine nets 3,600 feet in circumference and 550 feet deep. Its trawl nets are 1,200 feet wide and 96 feet high and it has storage capacity for 7,000 tonnes of frozen fish.

The problems caused by fishing fleets are not limited to the fish species they target. The marine environment is little understood and the effect on the ecosystem of the removal of thousands of fish every day is difficult to estimate. However, some consequences of large-scale commercial fishing are obvious. The Whale and Dolphin Conservation Society states: "The introduction of increasingly destructive fishing methods and the staggering growth of many modern commercial fisheries - particularly since the 1950s - have spelt disaster for whales and dolphins around the world." [2]

All net types cause problems for fish and marine mammals, but the most environmentally harmful are driftnets, purse seine nets and trawl nets.

The most notoriously destructive type of fishing is the use of driftnets. These can be anything up to 50km long and they hang in the water, like 'curtains of death' catching everything in their path: sea turtles, seabirds, sharks, whales, dolphins, seals - driftnets do not discriminate. They are now illegal in the European Union, although lobbying from Sweden, Denmark and Finland ensured that this method was allowed to continue in the Baltic Sea.

Purse seine nets are also known for injuring and killing marine mammals, especially dolphins. Several million dolphins have been killed by tuna fishermen who use their presence to find tuna shoals and all too often sweep the dolphins underwater, drowning them in their nets. Recent consumer pressure has encouraged more prudent use of these nets, but casualties still abound.

Trawler nets are held open by heavy metal trawl boards or weighted down by a long metal beam. They often have 'tickler' chains, which hang from the bottom of the net, dragging across the sea floor to encourage more sea creatures into the trap. Trawlers are thought to be responsible not only for the deaths of thousands of non-target species, including fish, mammals and birds, but also for the destruction of the ocean floor. In the UK, the damage to cold water coral reefs that have survived for more than eight millennia has been blamed on trawler fishing. [3]

The industrial pillage of our oceans for food continues to cause serious environmental problems and a number of species of both fish and mammals now face extinction. Only time will reveal the full scale of the upset this will cause to the delicate balance of the marine ecosystem.

FISH FARMING

With wild fish populations crashing because of over-fishing, attention has turned to fish farming to try to pick up the shortfall and aquaculture is now the world's most rapidly expanding area of animal production. This has led to enormous problems.

Far from being the saviour of wild fish populations, salmon farming has been blamed for further decline in wild salmon populations. Every year, thousands of farmed salmon escape from their sea cages. They compete with wild salmon and transmit the diseases and parasites that their overcrowded sea cages have helped foster. In many salmon farming areas, populations of wild salmon have plummeted. Catches of escaped farmed salmon now outnumber catches of wild salmon by seven to one. [4]

Even without these problems, aquaculture cannot be seen as a sustainable form of food production. Farmed fish are fed on meal made from wild fish. More than 3 tonnes of wild-caught fish are needed to produce 1 tonne of farmed salmon. For the newly farmed marine species such as halibut and cod, the ratio of wild fish used in feed to farmed fish produced is about 5 to 1. Far from helping to prevent wild fish stocks from plummeting further, aquaculture actually exacerbates the problems of over-fishing. [5]

This is not the only environmental problem caused by intensive fish farming. In its assessment of wild salmon, grilse and sea trout numbers, the Scottish Executive states:

"Disease and water pollution in particular may be partially attributed to fish farming practises. Nitrogen and phosphorus from fish food, faeces and urine may cause eutrophication and algal blooms. The high prevalence of sea-lice in fish farms is treated with chemicals that poison other aquatic life. In addition, farmed fish may escape to the wild where they may compete and breed with local stocks." [6]

By continuing to eat fish, whether farmed or wild-caught, humanity continues to contribute to the destruction of ocean environments. It may well be too late for some species, but by switching to a diet free from animal products we can help to save marine ecosystems from further assault.