These animals are remarkable!
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Begin forwarded message:
From: Curiosity Correspondent <info@xxxxxxxxxxxxxxxxx>
Date: September 23, 2021 at 11:44:15 AM PDT
To: cfrench1366@xxxxxxx
Subject: SAN MIGUEL ISLAND ELEPHANT SEALS
Reply-To: Curiosity Correspondent <info@xxxxxxxxxxxxxxxxx>
SAN MIGUEL ISLAND ELEPHANT SEALS ~
NORTH TO THE FISH; SOUTH TO THE BEACH
As previously noted [Curiosity Correspondent #19], Advisory Council Member
Dr. Brent Stewart, Senior Research Scientist at Hubbs-SeaWorld Research
Institute (and All 8 Member #15), has been researching Northern Elephant
Seals at the Channel Islands since 1978. He began tagging them on San Miguel
Island in 1980, pioneering the use of radio and satellite telemetry. Through
his work on their diving patterns, the world learned that the animals
routinely dive to 1700 feet in dives of more than 80 minutes at a time. Dives
depths over 5,000 feet have been recorded, making them second only to Sperm
Whales in diving deeper and longer.
On San Miguel Island in late February 1988, Brent Stewart, assisted by Robert
DeLong (NOAA Fisheries), successfully developed a method to attach electronic
data recorders to the heads or backs of adult male elephant seals, using
5-minute epoxy, with hose clamps embedded into the epoxy to hold the
instrument in place. Identifying letters and numbers were also harmlessly
bleached onto the tagged animal’s side.
In the first study, eight adult male elephant seals were tagged using this
method. Each animal was first immobilized by sneaking up on it while it was
sleeping, and administering an intramuscular injection of short-term
anesthetic while the tag was set. These pioneering efforts were twofold in
purpose: to learn of the elephant seals’ vertical depth of foraging habits;
and to learn where they go when they leave the island.
Top to bottom: Radio transmitter measuring tape for reference; tag
electronics;
titanium tube housing; assembled instrument (vertical).
One of eight transmitter-tagged adult male elephant seals, San Miguel Island,
1988.
Photo by Brent S. Stewart
Within a week, the tagged male seals had departed the island. The radio
transmitters would allow each tag to be relocated should they return to San
Miguel Island. Much to everyone’s delight and surprise, about six months
after having been tagged, seven of the eight seals returned to the island in
July to molt. Using the same stealth anesthetizing methods, Stewart and
DeLong recovered the instruments. One of the tags had flooded; six were
viable.
Photo by Howard Hall, Natural History Magazine, February 1996
Data recovered showed that once these seals left San Miguel Island, they dove
continuously, and to great depths. In further studies, using more advanced
tags, it was learned the seals traveled north in blue ocean to the Aleutian
Islands, while continuously diving. They then returned south to San Miguel
Island. Dive depths recorded on seal #666 reached an astounding 5,150 feet!
In addition, it was a ground-breaking discovery to learn these seals make not
one, but two long distance trips north each year. Tracked females did the
same thing, but going to different areas than the males: north to the fish,
south back to the beach. Ninety percent of their time is spent underwater
diving for food. They come ashore only to mate, give birth, and nurse, and
later to molt.
As Stewart recently explained to this Curiosity Correspondent: “By late
January, the coastlines of San Miguel, San Nicolas, Santa Rosa and some of
the other islands seem to strain against the sheer weight of elephant seals.
Then by early March, the seals are gone. The females are the first to leave,
abruptly abandoning their fattened pups. They are followed by the adult males
and then, about a month later, by the pups. In late spring and summer, the
seals return, this time for their annual molt—juveniles first, then adult
females, then sub-adult males, then adult males. After molting, the seals
disappear a second time, leaving behind tons of shed patches of sloughed skin
and hair. Beginning in December, adult males return first, followed by
pregnant females. All juveniles and last years’ pup stay away until the
spring molt. Pups are born; females breed, and the annual cycle continues.”
Molting season for female and juvenile elephant seals on San Miguel Island.
Photo by Brent S. Stewart.
In January 1996, in a special issue of Discover Magazine on the world of
science, Brent Stewart’s San Miguel Island elephant seal research was deemed
one of the top 100 science stories of the year.
THE CALIFORNIA ISLANDS—
SAVING THEIR HISTORY, TELLING THEIR STORIES.
Respectfully submitted by,
Your Faithful California Islands Curiosity Correspondent
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