Transcript Elephant Seals

Elephant Seals
Named for trunk-like nose of adult males
among the largest of all pinnipeds
Mirounga angustirostris
Two species
• The term Mirounga is derived from an
Australian aboriginal name for the elephant
seals and represents two species in the genus
• Our is the Northern (Mirounga angustirostris)
from Baja and as far north as Point Reyes on
shore, but feed up to Alaska.
• angustirostris means having a narrower snout
than the southern elephant seal
• Southern Elephant (M. leonina) seals are subAntarctic, and larger then the northern species.
• Both nearly hunted to extinction and now
recovering
Adult males (bulls) measure 14-16 ft long & can weigh 4,000- 5,000 lbs
Females are about 1/3 the size of males
• elephant seals migrate twice a year from CA and Mexican beaches to Alaska
or west to open ocean
• adult males range to Gulf of Alaska
• adult females range as far west as Hawaii
• leave the water twice a year: once to molt and once to breed & give birth at
the same beaches where they were born!
a tracked male’s route from
Southern CA to the Aleutian
Islands of Alaska
A male’s route tracked from Southern CA to the
Aleutian Islands of Alaska
Breeding
Mating and birthing occur Dec.- March in places called rookeries…
• in CA, males arrive at beaches in Dec.
• engage in violent battles to establish dominance
• the victor wins mating rights to a harem of females
•unlike other seals, which may have harems averaging 40 cows, a dominant
bull elephant seal may have only a dozen cows within his territory.
What’s with that snout??
• Mostly for vocalizations to defend territory and harem
• May Filter
• Helps to condense fresh water from breath
Elephant seals do not eat or drink the entire time they
are at the rookery!
(Dec- March)
• live off their fat for energy and water
•on land, males can lose as much as 1,500 pounds
• females give birth, nurse, and mate without ever eating! -she will loose about 40% body weight
• when females leave the rookery in March, they are weak and unhealthyimmediately swim for the continental shelf to search for food
delayed implantation
• although mating occurs in Jan/Feb, the fertilized egg doesn’t implant in
uterus until May/June after the female has fed for several months
• helps to ensure a healthy pregnancy
• Females arrive in Dec. & Jan.- give birth to
a pup within 6 days of “hauling out”
• Female nurses pup for about 1 month with
milk that is 55% fat!
• Pups weigh approx. 75 lbs. at birth and
within one month, weigh 250-350 lbs
• Females then leave pups on their own
some pups sneak off and nurse from multiple females
“super weaners” can weigh up to 600 lbs
Weaning
• After 1 month, moms abruptly leave pups
• Weaned pups congregate safely in "weaner
pods” for protection.
• Pups fur changes from black to silver
• Pups live off of their fat stores for 8- 12
weeks until they get hungry
Learning to
swim and
forage
• can't swim at birth
• after weaning, learn to swim by venturing
into the water for short periods, learning to
swim and feed
• In late April- pups go to sea and disperse
north - feed off coast of WA & BC
Molting – all at once!
• Have a “catastrophic” molt – loose all fur
and outer skin layer
• On land warm blood circulate to skin, in
cold water skin has little blood flow
Female Maturity
• Females give birth for the first time at an
average age of 3-4
• Females have an average life expectancy
of about 20 years.
Male Maturity
• Males are mature at five years
• Males don't reach high rank until 8 with prime
breeding years between 9-12.
• Males have a life expectancy of 14 years.
Males
• The older males develop a "cornified chest" - a
thick calloused skin on the chest with numerous
creases that is often pink, white and brown in color.
• It is used in the fights for dominance and establishing
territories and harems.
• The enlarged proboscis begins to form at sexual
maturity about five years and it is fully developed by
age seven to nine years
• around the 19th day of lactation, female goes into estrus (receptive to mating)
• the dominant bull mates with all females in his harem
• while the alpha bull is busy mating, defending the harem, or sleeping, other
bulls (“sneaker males”) will try to sneak in and mate with some females
Summer molting
• Return to same beaches in summer for a
month- called “hauling out”
• With out skin, fur they can not enter the
water or they get too cold.
• Don’t eat or drink for the month they grow
new skin
• Other seal molt, but only the elephant and
monk seals have a catastrophic molt.
Dates vary by group:
Año Nuevo Molting:
• April to May for females and juveniles
• May to June, sub-adult males
• July to August, adult males.
Año Nuevo
• The first elephant seals on Año Nuevo Island were
sighted in 1955, and the first pup was born there in
1961. In 1978, 872 were born there. Males began to
haul out on the mainland in 1965. A pup born in
January 1975 was the first known mainland birth of a
northern elephant seal at Año Nuevo; 86 pups were
born there in 1978. By 1988/1989, about 2,000
elephant seals came ashore at Año Nuevo, and the
number of seals breeding and giving birth on the
mainland is still increasing. During the 1994-95
breeding season, approximately 2,000 pups were
born on the mainland.
- from park website
Dives
• Elephant seals dive longer and deeper
than most other marine mammals
• Dive for food- mostly squid, rays, skates,
crabs (& minimize predation..)
• At sea, spend 80-95% of their time in dives
– may even sleep while diving below predators
• Average dive time = 20 minutes-- can be 12 hours
• Dives are typically 300 - 1500 ft. & deepest
recorded = 5,015 in 1991
Deep Dives
• Avoid predators – great white sharks,
Orcas
• Deep water food is concentrated at these
depths
• Even most of the whales can’t get at the
food source this deep – little competition.
• Allowed for speedy recovery?
• Shorter life span- “crushing physiology”
Ranging & feeding differences between sexes
FEMALES
• range west to open ocean
• ranges more variable than males- pursuing moving prey
• dive profiles are jagged- show females are following swimming prey (squid)
MALES
• range north along continental margin to Alaska
• range routes highly consistent
• dive profiles are flat-bottomed – feeding off sea floor (skates, rays, ratfish)
Dive physiology
heart rate drops by 65% (110  40 beats per min)
(also on land - 30%)
metabolism slows
high hemoglobin, myoglobin holds large amounts of O2
as they dive, exhale to collapse lungs – decreases chance of nitrogen entering
bloodstream which could cause “bends” when dissolved gas out of solution
bloodstream carries oxygen only to vital organs
Conservation Status
• hundreds of thousands of northern elephant seals once inhabited Pacific Ocean
• from mid-1800s to the early 1900s, elephant seals were hunted for blubber (oil )
• by 1890, only 50-100 seals remained
• only remaining colony was on the Guadalupe Island (Baja California)
• 1922, Mexican gov’t gave protected status to elephant seals- U.S. followed suit
• elephant seals have continued to multiply exponentially & have extended breeding
range as far north as Point Reyes
• today  approx. 160,000 northern elephant seals
• http://www.biosbcc.net/ocean/marinesci/05
nekton/esbody.htm