| Home: Special status species: Southern sea otter: Natural history |
SPECIAL STATUS SPECIES: SOUTHERN (CALIFORNIA) SEA OTTER (Enhydra lutris nereis)
NATURAL HISTORY |
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| General |
| Taxonomy: |
Order
Carnivora; Family Mustelidae (weasels). There are
three subspecies of sea otter Enhydra lutris;
the southern (Californian) E. l. nereis,
the northern (Alaskan) sea otter E. l. kenyoni,
and the Russian E. l. lutris,
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| Appearance: |
Adult males
typically weigh about 30 kg (65 lb) and reach a length
of about 135 cm (4.5 ft).1
Adult females typically weigh about 20 kg (45 lb)
and reach a length of about 125 cm (4 ft).1
Sea otters are covered by dense brown or golden brown
fur, which is the highest density fur of any mammal.
At the surface, sea otters are most often seen floating
on their backs and either sleeping, grooming, or feeding.
Grooming is needed to keep the fur clean and to trap
air bubbles for insulation. There is little subcutaneous
fat and no layer of blubber for insulation. The elongated
and webbed hind paws are used for swimming while the
small front paws are used in feeding and grooming.
The long tail may be used as a rudder when swimming. |
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| Feeding Behavior |
| Overview: |
A sea otter must consume
approximately 25% of its body weight each day to maintain
its high metabolism. Stones are often used as hammers
to dislodge prey and as anvils to smash the hard shells
of certain prey items. Though this species has a highly
diverse diet, individual sea otters typically specialize
on a few main prey types.16
Three general "diet types", representing
distinct foraging specializations, have been described:
the first type consumes prey of large size but low
abundance (abalone, crabs) and these individuals often
surface from a feeding dive without a prey item; the
second type consumes more abundant small to medium
size prey (clams, mussels, worms) and these individuals
often capture multiple prey items per dive; the third
type consumes very small prey (primarily marine snails)
and these individuals capture many items per dive.11 |
| Prey Items: |
Many different types
of benthic invertebrates are consumed including crabs,
sea urchins, mussels, clams and other bivalve mollusks,
abalone, marine snails, marine worms, sea stars, octopus,
and squid. |
| Method of
Capture: |
Sea otters
are able to dive to a maximum of 100m, but most
dives
are less than 20m.11
Dives lasting up to 5 minutes have been recorded
for this species, but most dives are less than 2
minutes. Some animals occasionally forage in the
surface canopy
of kelp
(primarily on kelp crabs and snails) diving only
a
meter or two. Otters sometimes pry
mussels from rocks while at the surface or while
climbing around on the rocks. The front paws
are used to locate and capture prey, which is then
either grasped
in
the forepaws or stored in “pockets” of
loose skin under the forelegs during the ascent
to
the surface. Prey items are handled and processed
at the surface using forepaws and teeth, often with
the aid of tools (rocks, shells or other prey items). |
Feeding sea otter in the Monterey Harbor. Photo: Lonhart / MBNMS. |
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| Reproduction |
| Overview: |
Many adult males hold
aquatic territories and attempt to mate with all
estrous females
inside the territory while excluding other adult
males. Territoriality is not a universal male strategy:
other males appear to employ an alternative “sneaker”
strategy, consisting of extensive range-wide movements
and opportunistic mating at multiple locations.
Mating
occurs in the water. During mating attempts, males
often bite the female's nose, occasionally inflicting
significant wounds. Typically pups are born in the
water, but occasionally pups are born on the shore
and then carried to the water. The mother carries,
nurses,
and grooms the pup on her chest and belly
while floating in the water. Pups begin to dive
and collect food at about two
months,
although nursing continues until weaning. |
| Time to Maturity: |
Females: 3 years; males:
5 years1 |
| Longevity: |
Probably 11-18 years in the wild
(females live longer than males); captive animals
can live to 28 years |
| Breeding
Season: |
Females can give birth
throughout the year; birth rates peak in January-March,
with a secondary peak in late fall (October). |
| Frequency
of Breeding: |
Most adult females produce one
pup per year; premature death of a pup may cause the
female to come into estrus. |
| Gestation
Period: |
4-6 months; it takes
4 months for the fetus to develop, but delayed implantation
(of approximately 2 months) almost always occurs. |
| Number of
Offspring per Pregnancy: |
One (twins are extremely
rare and in such cases one pup is always abandoned).1 |
| Parental
Care: |
Maternal; females
nurse their pup for an average of 6 months. |
| Mating
System: |
Polygamy |
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