A small bone in the heads of fish could reveal to researchers where important sport and commercial fish have spawned and where they are spending their adult lives.
BGSU biologists and geologists are collaborating on a study of yellow perch in Lake Erie to see if the otolith—a small bone that helps fish maintain their balance—is a reliable source of encoded information on their spawning and migratory habits. The results could help the Ohio Department of Natural Resources focus its conservation and management efforts on the critical habitats of yellow perch and other sport fish such as walleye, white bass and smallmouth bass.
Sport fishing is a major recreational activity on Lake Erie and a prime economic driver of the coastal tourism industry. Lake Erie fishing traditionally has contributed about $500 million per year to Ohio's economy, according to Ohio Sea Grant data. A 1999 Sea Grant study of recreational boating in Ohio estimated that over half of Ohio's $1.3 billion boating-related spending was connected to Lake Erie fishing. But the industries supported by Ohio's sport and commercial fisheries have experienced economic declines in recent years, due in part to ecological changes in Lake Erie that have affected food supplies and altered fish distribution and behavior. BGSU has several research projects aimed at helping to identify and solve those problems.
In one of them, Dr. John Farver, geology, and Dr. Jeffrey Miner, biology, have devised a series of experiments in the lake and laboratory to look for a chemical signature in yellow perch otoliths. The project is funded through a three-year grant from the Sea Grant program of the U.S. National Oceanic and Atmospheric Administration for nearly $270,000 in total funding.
“We don’t really know where the fish come from and where they are going,” according to Todd Hayden, a second-year doctoral student from Mechanicsburg, Ohio, who is heading up the project.
Yellow perch spawn throughout the western basin of Lake Erie and near shore areas of the central basin near Cleveland, and then distribute themselves throughout the lake, where they seek an area with plentiful food supply in which to live out their lives. “If we can discover which are the most fertile spawning grounds, that information can help the DNR set better fishing limits on those areas in the spring in order for the area to continue to be a strong provider of fish,” Hayden said.
“The otolith is really more of a rock than a bone,” he explained “It is made up of elements like strontium, magnesium and manganese, but mostly calcium as in bone. The analytical technique we use was developed by geologists and involves using a laser ablation inductively coupled mass spectrometer.” Because BGSU does not own that instrument, the researchers are collaborating with the University of Windsor to analyze their samples.
“Otoliths are like the rings in a tree trunk,” Hayden said. “They grow more in summer and contain the chemical elements of the environments the fish pass through. If these rings turn out to be reliable indicators, we’re really onto something.”
The technique could be used by aquatic ecologists everywhere to track the movement of fish and help conserve habitat. In addition, the otoliths provide a record of when persistent bioaccumulating toxic metals such as lead and mercury were absorbed. Because consumption of those metals impacts human health, the otolith may also provide valuable information on water quality in critical habitats of important fish.
Hayden and a team of graduate and undergraduate students have placed cages holding young perch in nine locations around Lake Erie, leaving them in place for three weeks at a time to allow the otolith to grow enough to incorporate the chemical signature of the water.
On a recent hot, August day, he headed out to the lake with Christopher Winslow, a fellow doctoral student and instructor in biology, for the second round of checks on the perch cages. It takes several days to check all the cages, which range from near Rattlesnake Island to Sandusky Bay to close to the Canadian border near Detroit.
|Todd Hayden, left, transfers the baby perch from the cage to a bag held by James Verhoff. |
After locating the cages using a Global Positioning Satellite device and a sonar fish finder, Hayden and Winslow dived in to retrieve them. Swimming near the bottom—“like swimming blindfolded or with your eyes closed,” according to Hayden—they located the cages by feel and pulled them up and into the boat.
They were pleased to find that, again, a good number had survived. In the first round of experiments in July, 75 percent of the perch had survived, impressive since very young fish have a 99 percent mortality rate, Hayden explained. The tiny yellow fish were counted and placed into plastic bags to be taken back to the laboratory for removal of the otolith.
They also retrieved a sensor that had recorded water temperatures over the previous three weeks, and then collected water samples to see what the baby fish had been eating and how many zooplankton, or aquatic insects, are in each location.
They were dismayed, however, to find that a number of round goby fish had somehow made their way into some of the cages. The invasive species, carried to Lake Erie in the ballast water of ocean-going ships, are changing the ecology of the lake and threatening food supplies of native fish.
The dispersal of early juvenile round gobies in Lake Erie was the subject of Hayden’s master’s thesis and employed, among other things, the chemistry of their otoliths. The round gobies are the subject of another BGSU research project, headed by Miner and conducted by Winslow, which is studying their impact on smallmouth bass populations.