Sea otters are unusual among marine mammals in
that they live outside of their zone of thermal neutrality and
consequently have extremely high metabolic demands. As a result they
require a high rate of food intake, up to 30% of their body weight per
day, and they have limited capacity to cope with reduced food
availability or additional physiological challenges. Moreover, a large
proportion of their diet consists of filter-feeding benthic
invertebrates, which tend to concentrate both contaminants and
disease-causing pathogens that flow into near-shore waters from land.
With their elevated metabolic rates, sea otters must consume large
quantities of these invertebrates and thus they have high exposure
rates to the associated parasites and pollutants. The net result of all
these traits is that sea otters are especially susceptible to
human-induced stressors in their environment, and like the proverbial
"canary in a coal mine," they represent effective sentinels of the
health of coastal oceans. Their utility as a sentinel (or indicator) of
ecosystem health is further increased by their near-shore distribution,
their extraordinary appeal to the general public (a fact that generates
community support for monitoring efforts), and because they are
relatively easy to observe.
Sea OtterSea Otters dive to the seafloor to
obtain a variety of invertebrate animals. The most common prey of Sea
Otters are sea urchins, mussels, abalone, clams, scallops, crabs, sea
snails, chitons, octopus, and squid. An acute sense of touch, using
paws, nose, and whiskers, is very important for finding prey in
crevices or bottom sediments, and during dim light. Food items are
normally clasped between tough leathery pads of the two forepaws and
brought to the surface to eat. Several food items are often stored in a
loose pocket of skin in the armpit area for transportation and while
The ingenious Sea Otter uses rocks as tools to break open hard-shelled
prey or to dislodge prey such as abalone. It is the only mammal other
than the primates (monkeys, apes, humans) known to use tools. While
eating, Sea Otters float on their backs, using their chest as a dinner
table, and are often accompanied by gulls and small fish which scavenge
on leftovers. Items such as crabs and urchins are broken open with paws
and teeth; the teeth are modified for crushing hard foods. Hard-shelled
mussels and clams are bashed repeatedly against a stone on the otter's
chest. Their rock tools range from 6 to 15 cm across, and favourite
rocks may be carried in the armpit pouch on several successive dives.
Most foraging is at depths under 30 metres, but a dive to 100 m has
been recorded. Research on the west coast of Vancouver Island found
that food dives varied from 45 to 127 seconds, the longest interval
between food dives was 180 seconds, and individuals may spend up to two
hours diving for one kind of food.
Sea OtterSea Otters need unpolluted nearshore marine habitats, usually
having depths under 40 m, an abundant food supply consisting primarily
of shellfish, and freedom from excessive human disturbance. Complex
coastlines having many islands, reefs, bays, and points provide a
variety of feeding sites and shelter from storms, and appear to support
the highest numbers of otters. Habitats of this nature occur along most
of the outer coast of British Columbia. The reintroduced British
Columbia population, possibly with the help of animals from northern
Washington and southeast Alaska, may eventually expand their range into
this vacant habitat.
Females leave pups on the surface when they dive
for food. They share solid food with the pups shortly after birth, but
larger pups aggressively take food from their mothers. The young begin
to dive in their second month; the duration of dives and success in
finding food increases with age. There is much to learn during the
period of dependency.
Sea OtterIn contrast to whales and seals, which rely on their blubber
for insulation, the Sea Otter relies on its wellgroomed fur with many
tiny air bubbles trapped in it. They have the thickest fur of any
living animal, with an incredible 100 000 or more hairs per square
centimetre. Frequent grooming activity prevents soiling of the fur,
loss of insulation, and reduced buoyancy. The fur is rubbed
meticulously with front and hind feet, the flexible otter rolling
inside its baggy skin to reach the awkward parts. Folds of skin are
squeezed between the forepaws or with the tongue to remove moisture.
Finally the fur is aerated by blowing into it or churning the water to
a froth with the paws.
Sea Otters walk awkwardly on land and even in water do not have the
speed or agility of seals. When lying face-up they move slowly by
sculling the tail or paddling with one or both hindlimbs. Faster
movements are always belly-down and involve up and down undulations of
the entire body ("porpoising") with the hindfeet and tail held stiffly
as an extension of the body, and the forefeet held against the chest.
Normal speeds are 1 to 5 km an hour; the maximum about 9 km an hour.
When at rest, Sea Otters lie on their backs, usually entwined in kelp
to hold their position, feet held high in the air to prevent heat loss.