Technology: Did You Hear That?

A Hawai‘i-based researcher uses a new kind of transmitter to figure out when sharks are eating, and where.

photo: Dave Fleetham/Pacific Stock

Kim Holland, intense and fast spoken, walks over to one of the natural saltwater ponds at his Coconut Island wet lab in Kane‘ohe Bay and points to a white-tip shark lazily swimming in circles. “Today we’re testing the first-ever pinging pH meter,” says Holland, who heads the Hawai‘i Institute of Marine Biology Shark Research Group, affiliated with the University of Hawai‘i at Manoa. “When the shark eats, the meter in his stomach records the change in acidity level and transmits it.” Holland tosses a few pieces of fish, the shark picks them up effortlessly and sure enough, the numbers on the meter connected to the hydrophone start inching up.

Holland is at the cutting edge of a technology that is revolutionizing marine science. Electronic tags placed in fishes, turtles, seals and whales are telling scientists with increasing accuracy what the marine animals are doing under water. By recording depth, temperature, position and salinity, these objects—about the size of a cell phone—disclose the outlines of previously secret lives: how deep the marine creatures dive and how far they travel. Due to these tags, “We’ve seen an explosion of knowledge in the past 10 years,” says Ellen Pikitch, the director of the Pew Institute for Ocean Science in Miami.

Some tags ping under water, allowing an observer at a console connected to a hydrophone to follow a creature’s movements in real time. By placing Holland’s acidity transmitter in the belly of a tagged shark, biologists will know for the first time where and when it feeds.

Another type of transmitter, called an archival tag, accumulates data for years but must be recovered, so it is used on heavily fished species like tuna. The latest models, called pop-ups, record the data for up to a year and then pop up to the surface to transmit it to satellites, which then send it to scientists by e-mail.

The information gathered using the tag has already saved Hawaiian tiger sharks, recalls Holland. In the 1990s, tags proved that these sharks are constantly on the move, traveling from one end of the archipelago to the other. “Until then, whenever there was a shark attack, entire flotillas would go out and catch as many sharks as they could, because they thought they could catch the attacker,” he says. “Once we showed them that the likelihood of catching that particular fish in the same area the next day was about zero, the practice stopped.”

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