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Counting Fish the New Fashioned Way
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NOVEMBER 20, 2003 -- One fish, two fish . . . Counting sturgeon swimming upstream can be a tricky business. But if your life's work revolves around these strange, endangered, and oddly charming relics from another age, then finding out how many there are is a top priority.
Nancy Auer, a research assistant professor in the Department of Biological Sciences, and her team have been tracking lake sturgeon on the Sturgeon River for 15 years. Figuring out how many sturgeon make it up the river to spawn is critical for fisheries management, because those numbers tell if the species is rebounding or at risk. Traditionally, Auer's team has donned waders and hauled nets out into river, catching, counting and tagging sturgeon as they swim by.
This method has its problems for both fish and people. While most fish survive this treatment with few ill effects, it's still stressful. Plus, you can only count the sturgeon that are swimming by while you're there.
However, for the past two years Auer has been trying out a promising, new method. Using a specialized type of hydroacoustic equipment installed on the riverbank, they can track fish traveling upstream. It sends out a sound wave that bounces off the air bladders on passing fish, and since the sturgeon air bladder is so big, it has a characteristic signature. A printout shows a long, wavy line for sturgeon, compared to a shorter dash for other fish.
To make sure they weren't counting just any fish as a sturgeon, Auer's team got down into the river and dragged sturgeon and suckers through the sonar beam. "You could distinguish between them pretty well," she said.
The system, which has previously only been used to count salmon, seems to be working well. "We're finding out that we can find sturgeon," Auer says. "This is the first time this method has been used on a nongame species."
The acoustic system is behaving as hoped, counting fish when researchers can't. "And it's noninvasive; you don't have to clobber the fish," Auer notes.
"This is a brand new application," she adds. "If we can fine-tune it, we should be able to apply it to other systems."
As to whether more or fewer sturgeon are swimming up the river that bears their name, Auer says it's too early to tell. "We're making advances, but the problem with studying sturgeon is that it takes so long to see results," she says.
After hatching, the larval lake sturgeon (which look like miniature adults) drift down the river and spend 10 or 15 years knocking about Lake Superior's sloughs. Sturgeon tagged by Auer have been found as far away as Munising and Bayfield, Wis.
Then, as they reach maturity, they swim back up to their birthplace to spawn. Unlike salmon, they don't die, but return to the lake, and, if all goes well, live to spawn another day. And another. And another. "They can live quite long, up to 150 years," Auer notes.
Auer's hydroacoustic equipment and 2002-03 research program was funded by a $214,000 grant from the Great Lakes Fishery Trust.
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