Technology and warmer seas have hit cod population

Fishing technology that can pinpoint the position of a shoal, the overfishing of stocks before they have bred, and rising sea temperatures have all contributed to the near collapse of the North Sea fisheries.

Fishing technology that can pinpoint the position of a shoal, the overfishing of stocks before they have bred, and rising sea temperatures have all contributed to the near collapse of the North Sea fisheries.

The annual catch of the Atlantic cod species, for instance, reached a high in the 1960s but has suffered a decline in the last 40 years culminating in historically low levels in the 1990s.

Cod, the better half of the national dish, typifies what has happened to North Sea fish stocks. In 1970, the annual cod catch peaked at more than 350,000 tons. Last year, fishing boats had difficulty finding fish to fill the quota of 132,000 tons.

Like all marine fish, cod populations go through huge natural fluctuations. Numbers can rise and fall several times over due to environmental variations such as spring-time temperatures of the sea.

Colin Bannister, a senior fisheries science adviser at the Government's Centre for Environment, Fisheries and Aquaculture Science, in Lowestoft, Suffolk, says fishermen are catching more immature cod than ever before, reducing the breeding population.

"The story of the North Sea cod is that it's spawning population is at its lowest level ever recorded. It hasn't collapsed yet, but it's in considerable danger," Dr Bannister said.

The European Commission's proposal yesterday for massive cuts in quotas for cod, whiting and hake is largely based on what has happened to the Atlantic cod population in North Sea fishing grounds, which have an estimated 65,000 tons of breeding cod left.

Most cod in the North Sea spawn between January and April, with the eggs floating at the sea surface for about two or three weeks before hatching. It is during this stage and the later, larval stage that the cod is most vulnerable to high sea temperatures, which have been rising in the last two decades.

Research published earlier this year also demonstrated a link between sea temperatures and low stocks of spawning cod. When the number of spawning fish is low, there is less chance of them producing high numbers of fish that will survive for at least a year.

Since 1988, the average spring temperature in the North Sea has been warmer than the previous four decades and, except for in 1997, the "recruitment" of young cod has been well below average.

However, it is the continual search for fish by an increasingly sophisticated fishing fleet that has really put the pressure on cod stocks. "The primary cause of the fall in numbers has been quite a long history of exploitation," Dr Bannister said.

Fishing boats are faster than ever and have sonar and satellite gear for locating shoals. The improvements have significantly increased the catch rate for under-aged, but legal fish.