Crabs of the British Isles (29,193 t), various swimming crabs (3,180 t), the spider crab "Maja squinado" (1,565 t), the shore crab or green crab "Carcinus maenas" (553 t) and the velvet crab "Necora puber" (193 t). Around 77% of the catch is landed in the United Kingdom, 19% in Ireland, 4% in the Channel Islands, and 1% in the Isle of Man. 62 species have been directly observed in the waters of the British Isles: Three deep-water species have also been recorded near the British Isles, and are likely to occur in the area. These are: Crabs of the British Isles Around 65 species
Introduced species of the British Isles are susceptible. The grey squirrel is a carrier of the squirrel pox virus which kills red squirrels but not grey squirrels. The European crayfish is susceptible to crayfish plague which is spread by the introduced signal crayfish. Unlike some other environmental problems such as pollution, the effect of an introduced species is not a single event. Once a species has been introduced to an island, the problems may persist and escalate as the species spreads further. Coypus "(Myocastor coypus)", large semi-aquatic rodents native to South America, were introduced to the British Isles in 1929 when fur farms were set up