Highly aquatic, the sea otter rarely comes ashore, both resting and feeding in coastal waters. Alaskan sea otters are more at home out of the water than their Californian relatives, often hauling out on sandbars and ice (8). Otters have a high metabolic rate (9) and these resourceful, opportunistic predators need to consume 25 percent of their body weight a day (6). Diving to depths of up to 75 metres they retrieve invertebrates such as mussels, snails, crabs and urchins from the seabed (6). Pouches of skin at the armpit of each forelimb can be used to store food whilst it is carried to the surface (6). Otters float on their backs, using their chest as a table whilst they attempt to prize open the shells. Sometimes rocks are used to smash open the hard shells and sea otters are one of the only mammals (apart from primates) to have developed tool use (6). Sea otters are considered a 'keystone species' in some parts of their range, as they appear to be vital in the maintenance of kelp forest ecosystems by suppressing the number of sea urchins that would otherwise overgraze the forests (4). These gregarious creatures can be found in large same-sex groups known as 'rafts'. Rafts in California rarely exceed 50 individuals but in Alaska, where the population density is higher, up to 2,000 otters can gather (2). Sea otters probably spend more time and energy grooming their fur that any other mammal; an important activity required to maintain the insulation of their fur, as it cleans and replenishes air to the under fur (4). Grooming involves rubbing, rolling and blowing air into the fur (4). Trapped air in the under fur is heated by the body to provide insulation and gives otters a silvery appearance underwater (5). Sea otters are polygynous, with adult males generally defending territories that encompass the ranges of several females (2) (4). While mating, the male will grip the female's nose with his teeth and she is often left with a bloody souvenir of their encounter (4). Females usually give birth to a single pup and carry them on their chest, nursing them and grooming them meticulously to ensure the fur remains buoyant and insulated (9). Young pups are left on the surface whilst their mother dives for food, but as they mature they follow her, learning to forage by watching her technique (5). Pups will stay with their mother for around three to six moths (6).
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