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Sea
Otter
Enhydra lutris
Sea
Otter Behaviour
Feeding, Hunting & Foraging Behaviour of the Sea Otter
Sea
otters eat mostly marine invertebrates but also dine on other
animals that they hammer, tear, pick or snatch from the seabed
during brief dives. Among the diet are
sea urchins,
mussels, crabs, abalones, worms, fish and their eggs, and octopus.
The sea otter stays close to shore where it will commute several
kilometres to feed. Most of their food is
taken in water less than 30 meters deep. The daily routine in
California involves alternate snooze and groom bouts with a feeding
bout. A feeding and grooming bout begins at sunrise and lasts for
several hours followed by snoozing until mid afternoon when a second
feeding bout occurs. Resting follows until about midnight when a
third feeding bout and slumber. This routine is followed closely
each day and seems to be only disrupted by storms. In Alaska, the
routine is probably different especially in winter where they spend
up to 70% of the time feeding. Otters open prey items by cracking
the shells with their flattened molar teeth combined with hammering
against a rock balanced on the belly. They also use rocks underwater
to hammer shellfish free from the seabed. The sea otter is well
known for its ability to limit the distribution and abundance
invertebrate prey. They have been described as keystone species for
their ability to influence the presence of other species in an
ecosystem.
Aggressive, Defensive & Territorial Displays of the
Sea Otter
Sea otters are
highly sociable animals that form rafts of tens to a few thousand
individuals. Rafts of males are the largest; female groups seldom
exceed 30 animals. During the breeding season, adult male otters
defend territories against other males. In California, these
territories are about 40 hectares. Young males leave groups of
females and pups soon after weaning to establish their own
territories. Adult females tend to stay close to where they were
born seldom traveling more than 50 kilometers. They will seek out
males during the breeding season.
Sea Otter Courtship & Breeding Behaviour
Female otters become
sexually mature when they are about 3 years old. When they enter
estrus, females will swim to male territories where they briefly
reside while they are mating. Males
without territories reside in rafts with females where they attempt
to find mates, likely with low success. Male territorial otters
approach females in estrus by nuzzling them that leads to fondling
if a female is interested in him. After about an hour of this
behavior, pairs will attempt to mate. She takes up a rigid position
on her back while the male positions himself below her by holding on
with his paws in her armpits and her nose in his mouth. Nose biting
is painful and likely stimulates release of her unfertilized egg.
These bites can lead to bleeding wounds that form into distinctive
scars. Most Russian otters breed in June and July, and September and
October, Alaskan otters breed in September and October, and
California otters breed from July to October.
Gestation takes about six months and a single pup is born. Twins are
unusual and triplets are rare: among 1360 fetuses examined, 5 were
twins, 1 was a triplet, and the balance were singletons.
The pups are usually born in water at any
time of year in
California but mostly in January to March, most
probably in April to July in British Columbia and Alaska. Birth
takes place at sea although there are records of sea otters giving
birth on land. Pup birth weight is about 2 kilograms. Pups are
groomed extensively at birth to dry the fur. Suckling bouts last
about 9 minutes and occur about 6 times a day. Sea otters, and
particularly mothers with pups, spend most of their time floating in
kelp canopies. Sea otters rarely come ashore.
Captive-raised otter pups begin to dive when they are
a month old. At 6 weeks it begins to eat food, they can swim on
their back at about 8 weeks, and at 12 weeks, a young otter is
capable of prolonged dives with its parent. Pups are independent at
about 6 months of age.
Mature
females can reproduce each year. Male otters are sexual maturity at
about 5 years of age.
Sea otters, and particularly mothers with pups, spend
most of their time floating in kelp (macrocystis)
canopies.
Sea Otter Calls & Vocalizations
Marianne Reidman and
her co-workers identified ten types of vocalizations that they
describe as screams, whines, whistles, squeals, whimpers, squeaks,
hisses, growls, coos, and grunts. The calls are mostly for
short-range communication among familiar individuals.
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