(DRAFT) - Taxonomy
Species walrus, Pacific
Species Id M120100
Date 26 AUG 96
TAXONOMY
NAME - walrus, Pacific
OTHER COMMON NAMES - Pacific walrus
ELEMENT CODE -
CATEGORY - Marine Mammals
PHYLUM AND SUBPHYLUM - Chordata,
CLASS AND SUBCLASS - Mammalia,
ORDER AND SUBORDER - Pinnipedia,
FAMILY AND SUBFAMILY - Odobenidae,
GENUS AND SUBGENUS - Odobenus,
SPECIES AND SSP - rosmarus, divergens
SCIENTIFIC NAME - Odobenus rosmarus divergens
AUTHORITY - Illiger
TAXONOMY REFERENCES - 170
COMMENTS ON TAXONOMY -
The walrus is the only surviving species of the family Odobenidae. While
ancestral forms apparently flourished on to ten million years ago, all
except Odobenus were extinct by recent times. The walrus, like other
members of the Order Pinnipedia, is adapted for feeding and traveling in the
water while maintaining an association with ice or land as a substrate on
which to rest, socialize, give birth, and care for young.*170*
Taxonomy - 1 (DRAFT) - Status
Species walrus, Pacific
Species Id M120100
Date 26 AUG 96
STATUS
Coded Status
Marine Mammal
REFERENCES FOR STATUS - 170
COMMENTS ON STATUS -
Current regulation on harvest of walruses are based on provisions of the
MMPA. These regulations present several problems. The MMPA provides for
harvest of walruses by Alaska Natives, but prevents any regulation of that
harvest unless the species is declared depeleted or management is returned
to the State. This, in effect, prohibits regulation of the most significant
harvesters of walruses and precludes many management options. Although
Natives are allowed to harvest walruses without limit, they can sell to
non-Natives only those parts of the walrus that have been processed into
handicrafts. This may not allow for full utilization of the harvested
animals.*170*
Status - 1 (DRAFT) - Distribution
Species walrus, Pacific
Species Id M120100
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Marine RS1
Marine FL2
REFERENCES FOR NWI - 170
COMMENTS ON HABITAT ASSOCIATIONS -
The coastal locations used as hauling areas by walruses represent a variety
of physical types including rocky islands with steep cliffs and boulder
beaches, low-lying sand and gravel spits extending from islands or the
mainland, tundra-covered islands with gently sloping sand/gravel beaches,
and mainland coast with sand/gravel beaches backed by steep bluffs.
Although diverse in their physical characteristics, these areas undoubtedly
have some common properties which make them more suitable than other
similar appearing areas. The location of hauling areas in relation to
normal distribution and migraton patterns is certainly of significance.
Hauling areas, particularly those used in summer months, may be located in
close proximity to feeding grounds. Perhaps of greatest significance is
the fact that all areas used regularly by large numbers of walruses are
located where the animals are not subjected to frequent and regular
disturbances.*170*
Habitat Associations - 1 (DRAFT) - Food Habits
Species walrus, Pacific
Species Id M120100
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
CARNIVORE
REFERENCES FOR TROPHIC LEVEL - 170
LIFESTAGE FOOD FOOD PART
General Molluscs Adult stage
General Snails Adult stage
General Worms Not Specified
General Bivalve Molluscs Adult stage
General Sea Cucumbers Not Specified
General Crustaceans Not Specified
Juvenile Mother's milk Not Applicable
REFERENCES FOR GENERAL FOOD - 170
REFERENCES FOR ADULT FOOD - 170
REFERENCES FOR JUVENILE FOOD - 170
COMMENTS ON FOOD -
Walruses feed on several species of molluscs. The sensory and feeding
apparatuses of walruses are highly specialized to allow efficient location,
manipulation, and ingestion of clams. An average sized adult walrus will
consume about 60 kg of food per day. Since only certain parts of the clams
are eaten, the actual biomass destroyed per day probably is three to four
times that amount. Obviously, clams must be reasonably dense for a walrus
to find and eat an adequate amount in a day. Few data are available on
distribution and abundance of the clams eaten by walruses. Available data
indicate that clams are not uniformly distributed, so in at least some parts
of the walrus range, high density areas may not be very common or
extensive. In the Bering and Chukchi seas, the only groups eaten in
quantity are clams, snails, crabs, shrimp, worms, and sea cucumbers. Seals
are eaten occasionally. Of those groups, clams usually make up 85-95% of
the stomach content examined at a given locality. Only the soft parts of
the clams are found in the stomachs. Shells are separated and discarded
prior to ingestion.*170*
COMMENTS ON ADULT FOOD -
Similar prey species are eaten by both males and females. In the northern
Bering Sea, females tend to eat smaller species of clams and smaller
individuals of the large species. Males feed primarily on large individuals
of large species. Although age-related food differences have not been
rigorously examined, it appears that young animals feed on smaller items
than do adults.*170*
COMMENTS ON JUVENILE FOOD -
Walrus calves feed almost entirely on their mother's milk for the first
year of life. During their second year, they begin to eat invertebrates,
but many continue to suckle. They are usually fully weaned at two years of
Food Habits - 1 (DRAFT) - Food Habits
Species walrus, Pacific
Species Id M120100
Date 26 AUG 96
age, but a few may continue to nurse for another year. After weaning,
walruses feed almost entirely on benthic organisms.*170*
Food Habits - 2 (DRAFT) - Environment Associations
Species walrus, Pacific
Species Id M120100
Date 26 AUG 96
ENVIRONMENTAL ASSOCIATIONS
G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae
LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
G Substrate: Rocks
G Water Depth Preference: Specified in Comments
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 170
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
In Alaskan waters, two of the major factors influencing walrus distribution
are water depth and characteristics of sea ice. Since they are primarily
benthic feeders, they do not remain in water too deep for efficient
feeding. Walruses, therefore, are seldom seem in water more than 100m
deep. During much of the year, walruses are found in and around sea ice.
Although they can break through thin ice, they generally are not found in
areas where thick ice covers more than 80% of the sea surface.*170*
COMMENTS ON RESTING ADULT ENVIRONMENTAL ASSOC_ -
The coastal locations used as hauling area by walruses represent a variety
of physical types including rocky islands with steep cliffs and boulder
beaches, low-lying sand and gravel spits extending from islands or the
mainland, tundra-covered islands with gently sloping sand/gravel beaches,
and mainland sand/gravel beaches backed by steep bluffs.*170*
Because walruses require regular access to both air and water, some sea ice
conditions are not suitable. During cold months when ice is contiuously
forming, walruses are restricted to areas where winds, currents, and land
formations cause regular openings to occur in the ice cover. Walruses are
much more common in relatively dispersed ice at the edge of the main pack
than farther to the north in heavy, consolidated ice.*170*
COMMENTS ON FEEDING ADULT ENVIRONTAL ASSOC_ -
The range in water depths at which walrus feed is thought to be primarily
between 10 and 80 meters. It is unknown whether the observed range is a
function of the diving capacity of walurses or the depth distribution of
their prey.*170*
Environment Associations - 1 (DRAFT) - Life History
Species walrus, Pacific
Species Id M120100
Date 26 AUG 96
LIFE HISTORY
Morphology:
Walruses generally are similar to other pinnipeds. In outward appearance,
they most closely resemble sea lions. Both fore and hind limbs are modified
for swimming. Unlike seals and like sea lions, their hind limbs can be
brought beneath the body and the chest raised up by the front flippers,
allowing a sort of quadrapedal locomotion on land or ice. Their chests are
massive in comparison to the hindquarters, their necks are thick, and their
heads square. Their skin is covered with short, sparse hairs and overlies a
thick layer of blubber. Color generally is brownish. The most distinctive
feature of walruses, and the one from which their generic name is derived
(Odobenus meaning tooth-walker), is the development of massive canine teeth,
or tusks, in the upper jaw. These tusks, possessed by nearly all adults of
both sexes, begin to be visible at about age two. The broad snout, covered
with stiff short bristles below the nasal region, is also unique among
pinnipeds.*170*
Reproduction:
Newborn walrus calves are approximately 100-120 cm in standard length
(straight line distance from nose to tail) and weigh 45-60 kg. Subsequent
growth is quite rapid with the weight of one-year-olds about triple that of
newborns. Adult walruses are among the largest of pinnipeds. Average adult
males are approximately 320 cm long and weigh 1,200 kg, while adult females
are about 15% shorter and 30% lighter. Females and males are similar in
appearance, although they can be distinguished by characteristics of tusks,
head shape, and chest.*170*
Predation:
The only known walrus predators are polar bears, killer whales, and humans.
Polar bears apparently kill mainly calves, while killer whales take animals
of all ages. Although available data are inadequate to estimate rates of
mortality due to predation, the impact is probably slight in comparison to
other causes of death. Although numerous disease conditions and parasites
have been found in walruses, few deaths can be attributed to those factors.
Trauma caused by rock slides and crushing by other walruses have been
identified as mortality factors on hauling grounds.*170*
REFERENCES FOR LIFE HISTORY- 170
Life History - 1 (DRAFT) - Management Practices
Species walrus, Pacific
Species Id M120100
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Restricting/regulating human disturbance of populations
Beneficial Maintaining undisturbed/undeveloped areas
Beneficial Other management practices [specified in comments]
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 170 and 125
COMMENTS ON MANAGEMENT PRACTICES -
Low flying aircraft, vessel noises, reports from firearms, and other loud
noises regularly and predictably cause hauled-out walruses to move into the
water, disrupting the animals' normal behavioral routine and constituting an
additional and unnecessary expenditure of energy. When large numbers of
walruses are hauled out, especially on land, "stampedes" may cause death or
injury of numerous animals due to crushing. In addition, regular and
frequent disturbances on coastal hauling grounds can cause abandonment of
those areas, making it necessary to regulate access and types of activities
in and near walrus hauling areas, particularly terrestrial sites. The
effects of waterborne sounds on walruses are not known, but it seems likely
that sounds of certain frequencies and intensities would cause walruses to
avoid their source. Many activites associated with coastal and offshore
development have the potential to introduce deleterious substances into the
marine environment. Examples are human wastes, chemicals and heavy metals
from industrial and agricultural activities, thermal and radioactive
pollution from electrical generating facilities, and a variety of petroleum
products. Although it is unlikely that such substances would enter the
marine system in quantities adequate to cause direct mortality to walruses,
their presence could affect resistance to disease, successful production of
young, and the abundance and suitability of food.*170*
Any factor which causes a change in the relationship between food
requirements of walruses and abundance and productivity of their prey can be
expected to influence walrus numbers and productivity. Activities of other
species feeding on benthic animals undoubtedly affect clam populations and
therefore, walruses. Human activities such as commercial fishing for clams
(and perhaps other species) and dredging for gravel or gold probably would
cause reductions in clam numbers.*170*
The potential adverse effects of oil and gas exploration and development are
another threat to the walrus population. Disturbances from drilling
platforms and support vessels could impinge on major mating areas in winter,
calving areas and migration corridors in spring, nursery areas in summer,
and feeding areas and migration corridors in autumn. Environmental
contamination from drilling muds or oil spills could affect food supplies or
directly affect walruses through bioaccumulation. Future management plans
should include means to assess and monitor the extent of disturbance from
oil development as well as to mitigate adverse effects.*125*
Management Practices - 1 (DRAFT) - References
Species walrus, Pacific
Species Id M120100
Date 26 AUG 96
References
170* Burns, John, Kathryn Frost, Lloyd Lowry (eds.) 1985. (7).
Alaska Department of Fish and Game, 96.
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.
References - 1