The IUCN/SSC Shark Specialist Group
Shark News 7: June 1996
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Satellite tracking blue sharks
Andy Kingman (formerly Woods Hole Oceanographic Institution)
In 1993 Frank Carey (Woods Hole Oceanographic Institution) built
four ARGOS satellite tracking devices for a study on blue sharks
Prionace glauca. In 1994 three of them were deployed on adult male
blue sharks off Cape
Hatteras, North Carolina,
USA. They have provided
information on depth,
water temperature,
swimming speed and
location. One (shark #1)
transmitted only once, on
the first day; another (shark
#2) transmitted 93 times
over the course of 17 days;
and shark #3 approxim-ately
300 times over the
course of 36 days.
Satellite transmitter on the back of a blue shark. Photo: F.G. Carey.
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The transmitters are
modifications of a design
developed by the Sea
Mammal Research Unit
(SMRU), Cambridge, UK.
Two aluminium pressure
tubes house a transmitter,
a microprocessor, two lithium "D" cell batteries and depth, temperature
and speed recording equipment. The tubes are cast in a urethane
saddle, which is attached directly to the shark's back. A rotor for
measuring swimming speed, a wet/dry transmission switch and the
antenna are mounted on an eighteen inch (45 cm) mast. Transmissions
are initiated when the mast breaks the surface. At the latitude of the
study area (approx. 35°N), satellite coverage is close to 110 minutes/
day, during which period approximately 5% of the possible total
number of transmissions were successfully completed.
Data received included temperatures ranging from 8.4° to 22.2°C,
and depths ranging from the surface to over 500 m. During the 17
days it was tracked, shark #2 covered more than 400 nautical
miles, and shark #3 covered more than 1,100 nautical miles over
36 days. Both of these study animals received a significant boost
in speed from the Gulf Stream; mileages were higher than 30 miles/
day during periods when swimming was highly directional and
parallel to the current. At speeds like this, the sharks could easily
accomplish a trans-Atlantic migration over the course of a few
months.
Track taken by transmitting blue sharks overlain on false colour satellite
image showing surface water temperature. Graphic: J. Bisagni.
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Capsule tag studies have provided point-to-point data
demonstrating that blue sharks will cross oceans, but these studies
provide no information on course and behaviour between tagging and
recapture. Sonic tracking experiments have provided detailed
information on behaviour over a short time, but are impractical for
periods of more than one week. Satellite tracking offers a means of
collecting detailed data over an extended period of time. After ironing
out some of the technical difficulties experienced in this trial, and with
newer, more compact transmitters already available, tracking durations
of several months are easily within reach. Unfortunately, Dr Carey's
death in December 1994 has precluded the continuation of this study,
but the stage has been set for more satellite tracking of fish.
A paper on this study is currently in preparation, possibly for
Marine Ecology Progress Series, authors: F.G. Carey, A. Kingman, N.
Kohler, J. Bisagni and C. Hunter or M. Fedak.
Andy Kingman, 2253 Buttonwood Road, Berwyn, PA 19312,
USA. Email: lamna@aol.com
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