|
White Sharks
Very few animals
generate the mixture of fascination and terror as does the
great white shark. Unfortunately, the terror-associated, anti-shark
sentiment has led to the unnecessary slaughter of many animals.
Fortunately, white sharks are now protected in California
waters and are listed as a threatened species in the Pacific
(appendix II of Convention on International Trade in Endangered
Species of Flora and Fauna, CITES).
Studies of these
powerful sharks
have been limited
by the difficulty
of gaining access
to them. They are
difficult to capture
or handle, and
working with free-swimming
animals has its
obvious complications.
Most information
is available from
dead specimens
or from shore-based
research stations.
While observations
of animals from
shore have provided
a wealth of information,
we are left wondering
where they venture
once they have
left these areas.
By combining long
term photographic
identification
of individual white
sharks from Guadalupe
Island, together
with long term
tracking of these
same sharks, the
rsearchers at the
Marine Conservation
Science Institute
have put together
the most comprehensive
study of white
sharks in the world.
Since January
2000, PIER and
MCSI have deployed
75 pop-up satellite
tags at Guadalupe
Island on sharks
ranging in size
from 8 to 18 feet
long. Tags are
inserted into the
backs of the sharks
(as close to the
dorsal fin as possible)
as they are lured
close to the boat
with large tuna
carcasses. The
tags have remained
on the sharks for
anywhere from 2
weeks to 1 year
and have given
us invaluable information
on the behavior
and movement of
white sharks including
swimming depths,
temperatures encountered,
daily patterns,
and migratory movements.
Dr. Michael Domeier
tags a white shark
off of Guadalupe
Island
The satellite
tagging data has
shown that sharks
remain at Guadalupe
Island for a portion
of the tagging
period, but they
leave the island
for as much as
half the year and
travel very long
distances. We have
found that they
are traveling towards
the middle of the
Pacific Ocean,
towards offshore
seamounts. This
suggests that even
away from shore,
animals may be
drawn to topographical
relief features
in the ocean. Such
features are frequently
gathering places
for a wide variety
of marine inhabitants.
MCSI has also
been studying the
sharks at Guadalupe
Island through
a rapidly expanding
photo-identification
project. Individuals
have been identified
using photos and
video taken by
our research team
as well as by photographers
and divers on cage-diving
expeditions at
the island. Using
physical features
such as: pigmentation
patterns, the sex
of the animal,
and any scars and
mutilations, 85
individual white
sharks have been
identified and
tracked at Guadalupe
Island. Many of
these sharks have
been tracked around
the island every
year since 2001
and 65 of the identified
sharks have been
photographed at
the island over
multiple years.
It is clear that
great white sharks
are drawn to the
area around Guadalupe
Island. The challenge
remains to determine
why they have selected
this spot. Perhaps
they are taking
advantage of the
local seal colonies
on the steep rocky
shores. Guadalupe
is also known as
a prime fishing
spot for recreational
anglers. The large
tuna and yellowtail
that are found
here may also attract
one of the oceans
largest predators.
Through additional
research, MCSI
hopes to learn
more about why
the sharks are
attracted to Guadalupe.
We gratefully acknowledge the support of The George
T. Pfleger Foundation and the Offield Family Foundation. |
