(DRAFT) - Taxonomy
Species otter, sea
Species Id M120031
Date 26 AUG 96
TAXONOMY
NAME - otter, sea
OTHER COMMON NAMES -
ELEMENT CODE -
CATEGORY - Marine Mammals
PHYLUM AND SUBPHYLUM - Animalia,
CLASS AND SUBCLASS - ,
ORDER AND SUBORDER - ,
FAMILY AND SUBFAMILY - Mustelidae,
GENUS AND SUBGENUS - Enhydra,
SPECIES AND SSP - lutris,
SCIENTIFIC NAME - Enhydra lutris
AUTHORITY -
TAXONOMY REFERENCES - 125
Taxonomy - 1 (DRAFT) - Status
Species otter, sea
Species Id M120031
Date 26 AUG 96
STATUS
Coded Status
Marine Mammal
Furbearer
REFERENCES FOR STATUS - 125
Status - 1 (DRAFT) - Distribution
Species otter, sea
Species Id M120031
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
COMMENTS ON HABITAT ASSOCIATIONS -
Sea otters spend much of their lives in the coastal zone, where they haul
out in or near the intertidal zone and swim, feed, and socialize in
nearshore waters. Much of the habitat essential to the sea otter
population is State-owned tidal and submerged lands; this was the habitat
most severely affected by the T/V Exxon Valdez oil spill.*280*
ANIMAL/PLANT SPECIES ASSOCIATIONS -
Ecological Interactions
In some areas sea otters may be a "keystone predator" (as defined by Paine
[1966]), and have a major influence on the composition and diversity of the
nearshore marine communities of which they are a part (Estes and Palmisano
1974; Estes et al. 1978, 1982; Simenstad et al. 1978; Duggins 1980; Breen et
al. 1982). It has been proposed, for example, that in at least parts of
Alaska and California, macroalgae (kelps) will be abundant if substantial
numbers of sea otters are present, and, conversely, that epibenthic
herbivores, particularly sea urchins, will be abundant if sea otters are
absent or present only in low densities (Rosenthal and Barilotti 1973; Estes
and Palmisano 1974; Estes et al. 1978, 1982; Simenstad et al. 1978; Duggins
1980). However, most of the information suggesting more complex
interactions is indirect. Other factors such as water temperature and
currents, storm surges, the season in which disturbances occur, and a number
of other variables in addition to sea otters can also play important roles
in determining the structure and dynamics of nearshore marine communities
(Foster 1982, Dayton 1984).*125*
Habitat Associations - 1 (DRAFT) - Food Habits
Species otter, sea
Species Id M120031
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
CARNIVORE
REFERENCES FOR TROPHIC LEVEL - 125
LIFESTAGE FOOD FOOD PART
Adult Bivalve Molluscs Not Specified
Adult See Comments; Food
General Snails Not Specified
General Sea/Heart Urchins Not Specified
General Molluscs Not Specified
General Squid, Octopus Not Specified
General Crustaceans Not Specified
General Fish Not Specified
REFERENCES FOR GENERAL FOOD - 125
COMMENTS ON FOOD -
The flat molars and rounded, blunt canines of sea otters are more suited
for crushing the exoskeletons of shellfish than for cutting flesh (Kenyon
1969). Sea otters eat a variety of sessile and slow-moving benthic
invertebrates, including sea urchins (Strongylocentrotus spp.), abalone
(Haliotis spp.), razor clams (Tresus nuttalli), horse clams (Tresus capax),
soft-shell clams (Mya arenaria), pismo clams (Tivela stultoreum), Washington
clams (Saxidomus nuttalli), mussels (Mytilus spp.), basket cockles
(Clinocarddium nuttallii), rock scallops (Hinnites giganteus), Dungeness
crab (Cancer magister), rock crabs (Cancer spp.), kelp crabs (Pugettia
spp.), spiny lobsters (Panulius interruptus), sea stars (Pisaster spp.),
and turban snails (Tegula spp.). Sea otters also eat octopuses (Octopus
spp.) and squids (e.g., Loligo opalescens), and, in some parts of Alaska,
sluggish epibenthic fishes.
Sea otter food habits may vary depending on habitat type, duration and
density of sea otter occupancy, season, and individual characteristics
(Ebert 1968, Vandevere 1969, Wild and Ames 1974, Calkins 1978, Estes et al.
1981, Garshelis et al. 1986). Sea urchins, abalone, and certain species of
clams and crabs appear to be preferred prey and are eaten when and where
they are present and accessible. Such species are inaccessible only when
they are in deep water or in cracks and crevices in rocky substrate where
sea otters cannot reach them (Lowry and Pearse 1973). Thus, populations of
these preferred prey species increased as sea otter populations were
extirpated by commercial hunting from 1740 to 1911. They may decline and
become less frequent in the sea otter diet as sea otters repopulate their
historic range.*125*
Food Habits - 1 (DRAFT) - Environment Associations
Species otter, sea
Species Id M120031
Date 26 AUG 96
ENVIRONMENTAL ASSOCIATIONS
Environment Associations - 1 (DRAFT) - Life History
Species otter, sea
Species Id M120031
Date 26 AUG 96
LIFE HISTORY
General Morphology
Adult males can attain lengths of at least 148 cm and weigh 45 kg or
slightly more (Kenyon 1969; Schneider, pers. commum.). Adult females can
attain lengths of at least 140 cm and weigh up to 32.5 kg (Kenyon 1969).
Within an area, both weight and length can vary to some extent as a function
of age (Garshelis 1984). Substantial differences were found in the average
weights of animals in different areas of the central and western Aleutians.
The differences are not a result of age biases, since animals of the same
ages were compared. This variation may result from differences in the
available food supply (Kenyon 1969; Schneider, pers. commumn.).
Within a given population, adult sea otters are slightly sexually
dimorphic. Kenyon's (1969) analysis of 79 adult males and 254 females
harvested at Amchitka Island from 1959 to 1963 probably provides the least
biased averages of weight and length available for a given population. Mean
weights were 28 kg and 135 cm and for adult females were 22 kg and 125 cm.
Older males generally have thicker, more massive heads and necks than
females. Young males and females, however, are similar in overall
appearance and the only conclusive characters upon which to distinguish sex
in the field are the penile bulge in males and the abdominal mammae in
females (Barabash-Nikiforov et al. 1947, Kenyon 1969, Estes 1980).
Additionally, only females are known to carry pups (Kenyon 1969).
Pelage
Because sea otters lack an insulating layer of blubber, they depend
entirely upon their fur for protection from the cold. Sea otter pelage
comprises a sparse outer layer of guard hairs and an extremely dense wooly
underfur. The underfur, which averages about 100,800 hairs/cm squared
(Kenyon 1969, Tarasoff 1974), is the densest mammalian fur. It was for
their extremely warm, dense fur that sea otters were hunted nearly to
extinction. Interest in the fur is the basis for the increasing harvest of
sea otters by Alaska Natives today. It is also because of their dependence
on their fur for insulation that sea otters are highly vulnerable to oil
contamination.
Sea otter skin is loose and can be pulled toward the midline to facilitate
grooming. Regular grooming is critcal in order to maintain the insulating
properties of the fur.
The normal adult pelage can vary considerably in color, from a light
golden-tipped color to a dark, almost chocolate brown (Kenyon 1969). Young
sea otter pups have a woolly, light brown to yellowish natal pelage (Fisher
1940) which changes gradually to a dark, unifornly brown "cub" pelage by 13
weeks (Payne and Jameson 1984). Despite the apparent similarity of otter
pelts, Kenyon (1982) reported that they are difficult to match for
commercial purposes.
The head, neck, and chest of some adults become lighter with age, due to
loss of pigment. By classifying head color as either brown, intermediate,
or white and comparing the head classification to age estimated from annuli
in tooth sections), Garshelis (1984) was able to differentiate several age
classes of individuals. Hence, head color can be used as a crude estimator
of age.
Sea otters molt throughout the year (Ognev 1931, Kenyon 1969), which
Life History - 1 (DRAFT) - Life History
Species otter, sea
Species Id M120031
Date 26 AUG 96
historically resulted in their being hunted in all seasons (Maynard 1898).
However, data from a captive adult otter showed that fewer fur fibers were
shed in January than in August (Kenyon 1969, 1982).*125*
Life History and Movements
Better information of the basic life history and movements of sea otters
in Alaska is necessary to more reliably predict the outcome of alternative
management strategies, and, more generally, to predict response to
disturbance. With respect to basic life history, specific emphasis should
be placed on determining the average age of first reproduction (both sexes);
length of pup dependency and its effect on the future reproductive success
of females; average life expectancy and reproductive life (both sexes);
average pupping interval; age-specific survival rates (both sexes);
effective population size; breeding sex ratios; and the influence of
density-dependent and density-independent factors on these variables.
Sea otters are very mobile and, as noted earlier, their movement patterns
appear to vary by age, sex, reproductive status, and season of the year.
The results of alternative management stategies will depend, in part, upon
how the boundaries of management units are established with respect to
available habitat and the distribution, densities, and movement patterns of
different age and sex classes of otters. Identification of the optimal
management strategy therefore will require better information on the
movement patterns of different age and sex classes. Studies should focus on
the movements of adult females, with and without pups, and of recently
independent individuals. Research should be carried out in recently
repopulated areas where densities are increasing, and in areas with
long-established populations near carrying capacity. Within an area, data
need to be gathered over a long period. To establish a data base on
individuals of known age, capture and marking programs should concentrate on
young animals. When possible, animals should be recaptured in subsequent
years. Two issues that should be emphasized using radiotelemetry are (1)
dispersal patterns of young individuals over their first year and (2)
habitat use as a function of age, reproductive status, sex, time of year,
and habitat status. Community studies should be conducted concurrently to
determine the relationship between resources and life history
characteristics.*125*
Behavior:
Sea otters have many complicated behaviors associated with grooming,
feeding, and mating. Common behaviors include rolling, somersaulting,
repeated shallow diving, blowing of bubbles, and intensive rubbing and
working of the fur with the mouth, forepaws, and hind flippers. These
behaviors may be misinterpreted as indicators of stress by inexperienced
observers. Healthy sea otter fur can be recognized by the characteristic
"beading" or rapid "wicking away" of water when the animal is on the
surface. In the case of rescue of otters in oil slick situations, sea
otters in the water should be considered for capture if the fur retains a
slick, wet appearance even after the animal has been on the surface for 10
seconds or more. Other signs of possible oiling include frequent head
shaking, obvious shivering, tolerance of close approach by a boat, lethargy,
or obvious emaciation. However, none of the above are certain indicators
that the animal is in fact oiled. In addition, sea otter pups frequently
are quite vocal, and their high-pitched called are easily mistaken for
Life History - 2 (DRAFT) - Life History
Species otter, sea
Species Id M120031
Date 26 AUG 96
signals of distress. A mother-pup pair should never be pursued simply
because the pup is vocalizing frequently.*280*
REFERENCES FOR LIFE HISTORY- 125
Life History - 3 (DRAFT) - Management Practices
Species otter, sea
Species Id M120031
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Restricting/regulating human use of habitats
Beneficial Restricting/regulating human disturbance of populations
Beneficial Controlling pollution [thermal, chemical, physical]
Adverse Shoreline modification/development
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 125
REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 125
COMMENTS ON MANAGEMENT PRACTICES -
Present and foreseeable conservation issues regarding sea otters involve (1)
increasing conflicts with commercial, subsistence, and recreational
shellfisheries; (2) incidental take in gillnet and other fisheries; (3)
hunting by Alaska Natives; (4) coastal and offshore development; (5)
increasing interest in commercial harvest of sea otters; (6) the growing
importance of sea otters to the Alaska tourist industry; and (7) the live
capture and removal of sea otters for public display and scientific
research.*125*
Impacts on commercial, subsistence, and recreational shellfisheries may
increase as sea otters continue to repopulate their former range in Alaska.
Similarly, conflicts between fishermen, Native hunters, coastal developers,
the tourist industry, and other possible users of sea otter habitat can be
expected to increase.
Some form of zonal management, whereby sea otters and various activities
are afforded priority in certain designated areas, may offer the only
practical way to effectively protect sea otters and avoid or minimize
impacts from conflicting activities. Under such a management program,
certain areas might be designated "otter-free" zones (in which otters would
be absent, or at least, afforded low priority) or as "otter" zones (area
where otters would be given high priority). In this context, it is
important to note that the use of the terms "otter" and "otter-free" zones
is not intended to indicate that there are only two types of possible
management zones or that no otters would ever be present or tolerated in
designated "no-otter" zones. Both logistically and politically, it may be
more feasible to achieve "otter-reduced" zones, rather than strictly
"otter-free" zones.
The Copper River Delta is one example of an area where some form of zonal
management might be useful. Sea otters from Prince William Sound are
expanding their range into the Copper River Delta and may impact the
Dungeness crab fishery there (Garshelis and Garshelis 1984). In addition,
sea otters are caught incidentally (Matkin and Fay 1980) or killed
deliberately in the salmon gillnet fishery in the area (Simon-Jackson 1986).
To judge the potential utility and feasibility of zonal management,
studies should be designed and conducted to evaluate the geographic and
genetic relationships of sea otters within and between selected management
units; relevant biological, ecological and socioeconomic information should
be compiled and evaluated to identify possible management conflicts and
management zones; and field experiments should be designed and conducted to
Management Practices - 1 (DRAFT) - Management Practices
Species otter, sea
Species Id M120031
Date 26 AUG 96
evaluate the likely cost-effectiveness of various methods for regulating sea
otter distribution and abundance.*125*
Sea otters are considered one of the most highly sensitive of marine mammals
to oil pollution. When oiled, the insulative quality of the pelage of sea
otters is lost, resulting in hypothermia and eventually death. Toxic effect
of exposure to crude oil through inhalation of vapors or ingestion are also
likely, although they were undocumented for sea otters before the T/V Exxon
Valdez oil spill.
Recommendations for sea otter rescue efforts:
1. Begin response efforts immediately.
2. Heavy initial oiling and mortality suggest that preemptive capture may be
warranted in front of the leading edge of an oil spill. Effective
preemptive capture would require accurate assessement of oil movements and
otter distribution and abundance.
3. Capture vessels and equipment, including skiffs, outboards, nets and
tackle need to be cataloged and available on short notice. Good
communications networks must also be available as well as a list of
qualified personnel.
4. Standardize data collection and recording methods.*280*
Management Practices - 2 (DRAFT) - References
Species otter, sea
Species Id M120031
Date 26 AUG 96
References
125* Lentfer, J.W. (ed.). 1988. Selected Marine Mammals of Alaska,
Species Accounts with Research and Management Recommendations.
Marine Mammal Commission Washington, D.C pp 275.
280 * Bayha, Keith, Kormendy, Jennifer. 1990. Sea Otter
Symposium: Proceedings of a Symposium to Evaluate the Response
Effort on Behalf of Sea Otters After the T/V Exxon Valdez Oil
Spill Into Prince William Sound, Anchorage, Alaska, 17-19 April
1990. 90(12)Bayha, Keith and Jennifer Kormendy (ed.). National
Fish and Wildife Foundation Washington, DC:485.
References - 1