This report is a contribution to the Department of Trade and Industry's (now Department of Energy and Climate Change) Strategic Environmental Assessment SEA2, which covers the mature oil and gas fields of the Southern, Central and Northern North Sea. The report reviews the impact of human activity on fish and fisheries in the North Sea and is relevant to both SEA 2 and SEA 3 areas. The North Sea is one of the world's most important fishing grounds. In the central and northern parts there is a mixed demersal fishery that targets cod, haddock and whiting; plaice and sole are trawled in the southern and southeastern North Sea; there are extensive pelagic fisheries for herring and mackerel; crustaceans fisheries for Norway lobster, crab and scallop; and industrial fisheries for sandeel and Norway pout. Commercial fishing itself has the highest impact on fish populations. The various impacts of the offshore oil and gas industry (e.g. seismic surveys, drilling discharges, produced water discharges) are classified as intermediate in scale. The biology of the commercially important fish and shellfish that occur in the offshore waters of the North Sea is discussed. Numerous maps, showing the location of spawning activity and the location of fishing effort, are included.