This report is a contribution to the Strategic Environmental Assessment (SEA6) conducted by the Department of Trade and Industry (now Department of Energy and Climate Change). Cephalopods are short-lived molluscs, characterised by rapid growth rates, and are important predators and prey in oceanic and neritic environments. They are active predators at all stages of their life-cycle and generally regarded as opportunistic, taking a wide variety of prey. Cannibalism has been frequently recorded in cephalopod species. Cephalopods also sustain a number of marine top predators such as fish, birds and marine mammals, especially whales. Many species are powerful swimmers and carry out vast feeding and spawning migrations, thus influencing prey and predator communities strongly on a seasonal and regional basis.
As cephalopods are important elements in food webs they interact with commercial fisheries of finfish. Evidence exists that fishing pressure has changed ecological conditions and shifts in community structures have occurred with cephalopod stocks slowly replacing predatory fish stocks. Their commercial significance to world fisheries is of relatively recent, but growing, importance. From a commercial point of view, the most important cephalopod species in the SEA6 area is Loligo forbesi, which is landed as a by-catch of the demersal trawl fishery (82 tonnes in 2002). But the species Alloteuthis subulata, although of no commercial value, has an important ecological role in the coastal food webs, since it is the most commonly recorded cephalopod species in the stomach contents of demersal fish in UK waters.