Campus: CSU Long Beach -- July 9, 2003
CSULB Grad Student's New Harmless Method of Studying
Shark Feeding Behavior Paves Way for Future Research
Popular thinking among those who frequent the ocean holds that sharks
tend to feed in the early morning or evening, often favorite times for
surfers and beachgoers to be in the water and thus more susceptible
to being bitten.
However, this idea remains largely unsupported by research, but a three
and one-half-year study recently concluded by a California State University,
Long Beach marine biology graduate student offers a novel new way to
study shark feeding behaviors.
Yannis Papastamatiou completed his M.S. in biological sciences in May
as a student of Marine Biology Professor Christopher G. Lowe, an internationally
recognized shark expert.
Papastamatiou begins his Ph.D. in marine biology at the University of
Hawaii in August. The dual British/Greek student did his undergraduate
work at the University of Southampton, England and then interned at
the International Shark Attack File before coming to CSULB.
“I’ve always been interested in when, how much and how frequently
sharks feed, especially because I used to work for the shark attack
file,” explained Papastamatiou. “We’d often hear recommendations
of not to swim during the hours of darkness because that’s when
sharks feed. When I started looking into this, there is actually very
little scientific evidence to support those theories, and in fact, we
know very little about when these animals feed, how often they feed
or how much they feed.”
He thought that if he could determine when and how much stomach acid
is secreted through studying stomach pH, a measurement of acidity, this
would help establish when and how much animals ate.
Since the nearby Long Beach Aquarium of the Pacific has a number of
leopard sharks as well as some nurse sharks, Papastamatiou decided to
begin his work with captive animals to see if his idea was feasible
and to compare data between the two species.
“I got a device which measures pH continuously and stores that
information on a data
logger,” he explained. Hidden in a piece of fish, “the device
is about 11 centimeters (4.3 inches) long, so it goes in the shark’s
stomach and just sits there. The shark swims around oblivious to the
fact that this instrument is there. It records the pH measurements and
then at a later date, I can recover the probe and connect the data logger
to a computer and I get all this data which has been recording over
the last 2 1/2 weeks.” Leopard sharks are about 130-150- centimeters
(4.26-4.9 feet) long, and both leopard and nurse species are largely
harmless to humans. He dove into a tank to feed them meals of squid
and kept precise records of when the animals ate and how much food they
consumed. At some point, the sharks regurgitated the instruments, and
Papastamatiou collected the devices from the tank.
But the beauty of this method is that it is harmless to fish being studied.
“Previous techniques to look at feeding basically involved killing
large numbers of sharks in the wild to cut open their stomachs and see
what they’ve eaten and how much food is in the stomach,”
he said. “I found out that there are marked changes in pH when
the animals fed, so by looking at how the pH had changed, I could see
when it had eaten. What’s more, based on how much the pH changed,
we are able to somewhat estimate how much the shark ate” Papastamatiou
He plans to expand this technique to study sharks and tuna in the open
sea for his doctoral work. “What we aim to do is to modify the
design so that rather than storing the data on the data logger, the
probe actually converts the electrical signal into an acoustic signal.
Then we can have automated listening stations set up in the ocean and
every time the shark gets within range, the pH probe will download the
data and we can know what the pH in the stomach is and how it has changed
over the previous few weeks. We’ll be able to get this data without
ever having to recover the device, which is important because the probe
will most likely be regurgitated and lost.”
This promising new technique is the subject of a research paper under
review by the Journal of Experimental Biology and a proposed article
is being developed for Nature. Papastamatiou’s work with the nurse
sharks was filmed for a documentary titled Sharks Under Glass for the
Discovery Channel’s forthcoming Shark Week series.