Fishy Disappearance

hammerhead shark

Bright yellow signs like missing-child notices appear along the rivers of western Pennsylvania. "Have you seen this fish?" they ask in bold, black letters. An accompanying illustration depicts a strange, hybrid-looking creature—something like a duck-billed shark.

The paddlefish, which gets its name from its long, oar-shaped snout, or rostrum, is the oldest living animal in North America. According to Patrick Barry, a Penn State graduate student in wildlife and fisheries science, they're older than dinosaurs. They can grow to seven feet long, and like sharks, have skeletons made entirely of cartilage. The paddlefish's nubbly, slate-gray skin has no scales. "They swim like sharks, too," says Barry. "They kind of cruise."

Paddlefish are hard to catch. That's due, in part, to a set of highly receptive sensory organs, pinholes that dot the underside of the rostrum. These sensors detect the slightest motion and are key to the creature's survival. With their beady eyes, Barry explains, paddlefish can't see very well. "But they can sense the movement of plankton floating downstream. I even heard that the Navy is studying the paddlefish rostrum to develop navigation technology."

This sensitivity may also explain the fish's disappearance from Pennsylvania. By 1919, paddlefish were rarely seen in the state, though they continued to thrive in the main branches of the Mississippi River. According to Barry, 80 percent of paddlefish in the Mississippi tend to live in waters behind river islands where barges and large boats can't travel. Because Pennsylvania's rivers have fewer back-water areas, Barry speculates that turbulence from heavy boat traffic chased the ancient species away. To test the theory, he and the Pennsylvania Fish and Boat Commission are fitting hatchery-born paddlefish with radio transmitters, releasing them into the river, and tracking their movements.

Barry surgically inserts the plastic-coated transmitters into six-month-old fish. The fish is anesthetized, a transmitter battery is placed in the stomach, and the connected antenna protrudes about two inches past the pelvic fin, under the tail. After stitching the incision, Barry releases the fish into the river just outside Pittsburgh.

Each fish's transmitter sends a unique signal that Barry picks up with an antenna from his small aluminum boat. Barry and two fellow researchers spend up to eight hours a day tracking fish. They try to record the location of each implanted fish at least once a day. "If we have time, we'll do it twice," says Barry.

Some of the baby paddlefish Barry has tracked swim as far as 20 kilometers in two weeks, apparently in search of deeper, calmer water where a concrete retaining wall or a jutting embankment creates a peaceful pool and algae and plankton provide plenty of food.

For his most recent stint of tracking, which lasted three months, Barry prepared predictions of where 34 radio-implanted paddlefish would swim based on what he's seen so far. He released the babies in different places and plotted their daily movements and depths in the river. His findings should help the Fish and Boat Commission understand exactly where paddlefish thrive, and perhaps someday to release more hatchery-born fish to repopulate the state's rivers. "I think these fish are trying to get away from boat traffic," says Barry. "I think they basically want to get away from us.

Patrick Barry will receive an M.S. in wildlife and fisheries science in May 2004 from the College of Agricultural Sciences. His adviser is Robert F. Carline, Ph.D., 113 Merkle Bldg., University Park, PA 16802; 814-865-4511; rcarline@psu.edu. Barry's research is funded by The Pennsylvania Fish and Boat Commission.

Last Updated May 01, 2004