Commercial fisheries have traditionally sustained the global population as a protein source. Coastal fishing communities were among the first organized coastal societies and remain an important source of revenue and cultural heritage sometimes beyond their viability as a commercial fisheries center. The economy supported by commercial and recreational fishing stretches well beyond the men and ships that go to sea. Communities have experienced boom and bust due to the availability of fishery stocks and these resource fluctuations are a complex mix of natural responses to climate patterns and the intensity of the fishing pressures. Countries have tried to manage the fish stocks in their national waters and, through international convention, to manage highly migratory species that pass through both international and national waters. Studies of historical catch and estimations, based on recent data collection, support most management plans. The effectiveness and success of this management is mixed.
Currently, the effects of resource extraction on the robustness of fish populations is a more pressing issue globally than the potential impacts of climate. Climate change and the potential effects on freshwater inflow to coastal waters, sea level, ocean currents, upwellings, storm frequency and intensity, and habitat alteration and sustainability will become increasingly the dominant features influencing both fishermen and the composition and survival of the fish stocks. Within recent history, some areas have experienced warming and others have experienced decreased temperatures. The projection of changes in the North Atlantic currents could threaten the survival of some species of fish. For instance, when the atmospheric circulation in the 1880s changed and drove the ocean currents differently, ship captains reported sailing through miles and miles of dead fish in warm water. Shifts in the 1920s, brought warm currents and a substantial amount of cod to the coast of Greenland, where few had been seen before. More recently over the past 20 years, Sea bass from around the British Isles have drifted north towards Norwegian waters.
It is very difficult to determine the impact of global climate change, and indeed if there is climate change, because there is so much natural variability in the earth's climate. In the chart at left, it is clear that some physical processes on the Earth are highly correlated with the abundance of some species of fish. Sediment records show that this variability has been going on for at least thousands of years. The chart is from FAO Fisheries Technical Paper 410, Climate change and long-term fluctuations of commercial catches, by Leonid Klyashtorin of the Russian Institute for Fisheries and Oceanography.

In the 2000 report of the Intergovernmental Panel on Climate Change, scientists from each continent and the island nations projected potential effects on national fish stocks as a result of the physical, chemical, and biological changes anticipated with a warming climate. Most predicted changes in population dynamics, poleward migration of some species to cooler waters, loss of some species, and adaption of some species to live at their physiological limits. Such changes place a stress not just on individual species but on the habitat and community structure in which they are a component. Man, as a top carnivore, must necessarily adjust to such changes in their fisheries by searching farther for traditional catch or adapting locally to a new mix of catch that may have a different economic value. Infrastructure may have to be adapted as well, requiring different gear, different processing, and even relocation of coastal structures such as wharves and fish processing houses to accommodate rising sea levels. Refrigeration and energy requirements to maintain high quality may be of greater emphasis and expense. Management of such a commercial effort may necessarily have to change also, with governments having to reconsider the basis on which they form new policies and shifting the foundation away from data based on historic catches.

Summary of IPCC Fisheries Chapter

This summary is taken from recent USA Congressional testimony. The full statement is available at Statement of Dr. John Everett.

<![if !supportLists]><![endif]>Freshwater fisheries and aquaculture at mid to higher latitudes should benefit

<![if !supportLists]><![endif]>Saltwater fisheries should be about the same

<![if !supportLists]><![endif]>Fishery areas and species mix will shift

<![if !supportLists]><![endif]>Changes in abundance more likely near ecosystem boundaries

<![if !supportLists]><![endif]>National fisheries will suffer if fishers cannot move within and across national borders (Subsistence/small scale fishermen suffer most)

<![if !supportLists]><![endif]>Climate change impacts add to overfishing, lost wetlands and nurseries, pollution, UV-B, and natural variation

<![if !supportLists]><![endif]>Inherent instability in world fisheries will be exacerbated by a changing climate

<![if !supportLists]><![endif]>Globally, economic and food supply impacts should be small.In some countries, they could be large

<![if !supportLists]><![endif]>Overfishing is more important than climate change today; the relationship should reverse in 50-100 years (as overfishing is controlled)