Blue shark, Prionace glauca. A female blue shark swimming close to the surface off Southwest Cornwall, UK. Blue sharks are easily recognisable by their slender form, long pectoral fins and vivid blue colour. Like many shark species they are counter-coloured, blue on their backs and white below. Blue sharks are found off Southwest Britain between July and October. For reasons that are still not fully understood it is most females that are seen in British waters. Female blue sharks can be recognised by the absence of of claspers on their belly; sexually mature female blues will often have prominent scars of their head, neck and back. These are mating scars causing by bites from the male blue shark during mating. Blue sharks are found in all major oceans, in temperate and tropical waters.