Global warming and rising sea temperatures are contributing to a decline in cod and wild salmon stocks in northern waters, according to a leading British marine scientist.
Climatic "uncertainty" needs to be taken into account in the management and assessment of fish stocks, Dr Chris Reid, director of the Sir Alister Hardy Foundation for Ocean Science, told an EU-sponsored, two-day conference on cod recovery in Edinburgh, Scotland.
Dr Reid said evidence was accumulating that the North Sea and the seas around these islands were experiencing a "pronounced change" since the 1980s at all levels of the ecosystem, and global change was at a rate not witnessed in the last 1,000 years.
He said such changes were first observed in plankton which act as the marine equivalent of the "canary in a mine". Cod do not like warm water, but stock levels have also been affected by a decline in plankton which Dr Reid links to climate change.
The Sir Alister Hardy Foundation for Ocean Science in Plymouth has been studying plankton in the northern Atlantic and North Sea for over 70 years. The long-term survey has involved monthly analysis of samples collected by merchant ships.
Dr Reid said findings show that the most abundant zooplanktonic organism in the north Atlantic and a major food for larval cod, a crustacean copepod known as calanus finmarchicus, has decreased by over 80 per cent in the northeast Atlantic over the last 40 years.
He said not only had cod been affected by the plankton decline, but salmon returns have also fallen due to changes in abundance of planktonic food. Overfishing was still a significant contributory factor to stock levels, but the added pressure of environmental change made stocks under pressure more vulnerable.
Irish and British fishermen have been participating in EU cod-recovery programmes, and the two-day conference attended by EU officials, scientists and fishing industry representatives has focused on why the initiatives are not proving as successful as anticipated.