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 remarked.
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.