Tracking an invasive species

BGSU researchers collaborate to study Asian carp spawning in Sandusky River


By Jen Sobolewski 

Asian carps—it’s an invasion that has both people who make their living on the Great Lakes, and those who work to keep the ecosystem balanced, concerned.

A just-completed study from the U.S. Geological Survey (USGS), the Ohio Department of Natural Resources (DNR), and Bowling Green State University has clearly shown that one of the species, grass carp, has spawned in the Sandusky River, a tributary of Lake Erie. The study is the cover story in next month’s Journal of Great Lakes Research and is available online.

Jeremiah Davis, a graduate student in biology from Sandusky, led the BGSU portion of the study with assistance from Drs. Jeffrey Miner, an associate professor and chair of the biology department, and John Farver, an associate professor of geology.

A commercial fisherman captured the four grass carp last fall. The USGS analyzed the fish and determined they were at least a year old and had the capability to become spawning adults; that is, they were fertile. Bones in the fish’s heads, called otoliths, were then sent to BGSU for analysis to obtain a chemical fingerprint of the fish.

Davis examined the otoliths, which provide a history of the chemistry of the water the fish has inhabited over its lifetime. His analysis showed that the four grass carp had lived in the Sandusky River their entire lives, demonstrating that they had come from spawning in the Sandusky River.

“Jeremiah really perfected how you analyze these otoliths to get that chemical fingerprint necessary for understanding where the fish come from,” said Miner. “The USGS biologists sent out tissue samples to their genetics people to find out if these fish were fertile. Then they had to know if they were recently introduced or was there actual spawning going on in the Sandusky River. That’s where Jeremiah was able to show that they were indeed spawning in the river.”

“The geology of the region around the Sandusky River is unique due to strontium, the element we track the most in the otoliths,” said Farver. “The idea is that the fish is growing and will incorporate the strontium in the otolith from the concentration of the river in which it is living. It (strontium) is substantially higher in the Sandusky River. It made such a strong case when we showed that they had a relatively high level of strontium in their otoliths throughout their entire life.”

Grass carp eat large amounts of aquatic plants. This is why people stock infertile (triploid) grass carp in their private ponds. If they do establish themselves in the Great Lakes, there is a concern that they will have a negative effect on plants in the few remaining coastal wetlands and near shore areas, affecting ducks and the spawning and nursery habitats of native fish like yellow perch, walleye, northern pike and bass.

Miner said if the grass carp can reproduce in the Sandusky River, then other, even more harmful, species of Asian carp could potentially do the same.

“The grass carp are vastly different species from silver and bighead carps,” said Davis. “However, finding that these grass carp spawned here is very important. Even though these species are different, they have similar spawning habitat requirements. Previously, scientists thought you needed a longer stretch of undammed river for the eggs to survive. Finding that the eggs could survive in the Sandusky River leads to a concern that the other species could do the same.

“However, just because we found several fish that were born there doesn’t mean that there is an established population, or that we will be overrun next year.”

Researchers say 2011, when these grass carp hatched, was a high flow year for the river and may have played a significant part in their survival.

“If you have global warming occurring and changes in rainfall patterns, you don’t know if that will lead to more frequent high flow conditions and thus lead to more years when you might get successful reproduction,” Miner said.

“People are freaked out about the silver and bighead Asian carps,” Davis said. “They are scary. They will jump in your boat and knock you out. The grass carp don’t do that. The silver and bighead carp feed on a lot of plankton and food a lot of other important fish in Lake Erie rely upon.”

Miner says the next step for BGSU is to see how they can help manage the situation. The Lake Erie Protection Fund has approved a proposal by Davis, Miner and Farver to take the chemical fingerprint for species that are already in the river systems and determine the chemical signature for those rivers.

“What are we trying to do is better calibrate what the actual strontium level would be in order to be indicative of the Sandusky River, or the Maumee or Grand rivers,” Farver explained. “We will use the common carp as the closest relative to these Asian carps. You can find them everywhere, occupying all sorts of water masses. We will look at a number of different otolith samples from different water masses for strontium and barium concentrations and develop a calibration curve. So, when an Asian carp is caught we can say ‘ah-ha, that is indicative of that river’ — that’s the Maumee signature, or that’s another river signature.”

“From a biological perspective, the best way you could ever stop these invasives is if you found, almost instantly, where they got into the system so you can focus your management efforts to eliminate the small population at that point. If you wait until they disperse and go through a couple of generations in the lake, usually there are so many there are too many to control,” Miner said.

The Ohio DNR has recently established an Ohio Asian Carp Tactical Plan to further prevent natural introductions and to consistently monitor the bays and rivers where first introductions might be observed.

Updated: 07/13/2020 03:14PM