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Alien fish bully Lake Erie bass
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With millions of tons of cargo moving among the Great Lakes each season, it’s easy for certain small passengers to go unnoticed. One of those was the round goby, a small bug-eyed fish from Eurasia that now swarms the shallow waters of Lake Erie. An ongoing study, based at Ohio State University’s Stone Lab on Gibraltar Island, documents how the gobies jockey for a position in the lake’s changing ecosystem.
Chris Winslow and Sarah Norman are suiting up for a dive to the bottom of Lake Erie. Wet suits and SCUBA gear in place, they plunge into the water. Each carries a one-meter square frame built of PVC pipe. The squares define the area of the lake floor in which they will watch the gobies.
Sarah Norman, a senior at Wittenberg University, is a research assistant this summer. She says the lake bottom is an interesting place to work.
“It’s really not as bad as I thought it would be you get down there, get settled,” she said. “We went about 10-15 feet down, and gobies are everywhere. We went to a bed that was half cobble, half sand, and actually we had some partial sea grass there.”
As the divers look on, the fish return to their normal activities and twenty or thirty gobies dart about in each square.
Winslow, a Ph.D. candidate at Bowling Green State University and an instructor at Stone Lab, leads the study. He and Norman record their under-water data with pencil on a plastic arm-band
“So what we do is we watch a goby and count to a set time period and when you reach that time period you record what they’re doing are they active or are they sitting,” Winslow said. “And we do this multiple times, and we do it during the day and then we also come out at night.”
It turns out the gobies are most active during the day, especially at dawn and dusk. When the goby first arrived in the Great Lakes from the Black and Caspian seas in the early 1990′s, nobody knew this, and it makes a difference to how gobies affect native fish.
Winslow studies the goby’s interaction with smallmouth bass, whose numbers declined when the goby arrived.
The gobies eat bass eggs, but adult bass eat the gobies. Winslow wants to find out what happens in between– with gobies and very young bass. Could they compete for the same food? Or did they interrupt each other, indirect, ways?
So he watched the fish in aquaria, analyzed their stomach contents, and, now, he documents their activity patterns in the lake throughout the day to see how it compares to bass activity.
“Basically what we’ve been able to show is that it’s not necessarily a diet overlap,” he said. “So they’re not eating the same things but the gobies are pushing the small mouth up in the water column when they would prefer to be down towards the bottom close to their food.”
With the implementation of a new catch-and-release policy during spawning season, the bass population appears to be recovering. Nonetheless, Winslow says that the introduction of new species like the gobies to the Great Lakes is risky– because of the dramatic effects it can have on the native species.
At the same time, it’s an opportunity. He says the disruption gives scientists the chance to watch how newly interacting species reach an equilibrium, something they can’t see in ecosystems that are stable and established.
“I like the idea that with invasive species you can look at things like competition happening in the here and now,” Winslow said. “And I think it’s cool because we can now see new novel competitive interactions and see how they work themselves out.”
For Norman, it’s a glimpse of an easily forgotten underwater world.
“It’s pretty interesting to think all that stuff’s going on down there when we’re up here, you know,” she said.
Elsa Youngsteadt WOSU News