Basking Sharks occur in temperate and boreal oceans. In the North Atlantic, the species occurs from the transition between Atlantic and Arctic waters (including the Gulf of Maine, south and west of Iceland and off the North Cape of Norway and Russia) to the Mediterranean, and occasionally as far south as Senegal and Florida. In the North Pacific, around Japan and off the Chinese coast, and from California north to British Columbia. In the southern hemisphere, recorded from South Africa, Brazil to Ecuador in South America, southern Australia and New Zealand (Compagno 1984a). Most records are from surface waters during spring and summer, with some reports from deep water in winter (Francis and Duffy 2002, Sims et al. 2003). A seasonal migration may occur, either from deep to shallow water or from lower to higher latitudes in warmer weather (the latter is not supported by recent UK observations (Sims et al. 2003)). Most records occur within a narrow range of water temperatures: 8°?14°C in the UK, Japan and Newfoundland, but up to 24°C in New England, USA. Records in warmer waters are generally of moribund or stranded specimens. At least some populations are migratory (Sims et al. 2003) and possibly seasonally segregated by sex; the winter distribution of most populations and locations used by pregnant females are unknown, although it seems likely that wintering sharks occur mainly in deep shelf water (Francis and Duffy 2002, Sims et al. 2003). The different morphological characteristics of basking sharks in the Pacific and the North and South Atlantic oceans are not thought to indicate separate species (Compagno 1984a), but geographically isolated populations.