SHAWANO, Wis. -- The surgery was over in seconds.
The patient was on her back, head covered with a sheet of plastic on the operating stretcher, as a small slit was made in her belly, a sonar device implanted and then she was rapidly stitched up.
As she scooted back into the flowing water below the Shawano dam, No. 16442 began pinging, sending out a code that Wisconsin Department of Natural Resources fisheries biologists hope soon will explain a few mysteries of the prehistoric creature.
Although Wisconsin's lake sturgeon population is among the most heavily monitored and protected in the world, there are still quite a few questions biologists would like to answer, such as: How often do they spawn, and where do they go from day to day and from season to season?
Now, thanks to $300 sonar transmitters that look like small black flashlights, the Wisconsin DNR plans to follow the whereabouts of hundreds of lake sturgeon.
"It'll be like little light bulbs going off all the way; it's really cool," DNR fisheries biologist Ron Bruch said as he watched the 63-inch female sturgeon he had just implanted with No. 16442 sonar transmitter swim away.
After she finished spawning, an exhausted No. 16442 would head back to Lake Winnebago, a 125-mile trip, as the needle on her internal compass swung south, said Bruch, who has led Wisconsin's sturgeon management program since 1990. Bruch estimated her age at mid- to late 40s.
Sonar transmitters give off a ping recorded by 27 Wisconsin listening stations along the lower Wolf River between Shawano and Oshkosh and the upper Fox River between Oshkosh and Montello, plus one in Appleton. Many are suspended from bridges, where they won't get crunched by ice in the winter and can listen for the pinging sturgeon across the body of water without obstructions such as islands.
Each time a sturgeon carrying a sonar transmitter passes a receiver, the date and time are recorded by computer chips. The information is downloaded twice a year, giving scientists an incredibly accurate and complete picture of just where the fish are hanging out and heading.
The Wisconsin DNR began implanting sonar transmitters in 2002, but the early devices wore out after four years. Now they last 10 years. By the end of this spawning season, about 100 of the latest longer-lasting transmitters will be in lake sturgeon -- roughly 85 females and 15 males. In total, about 350 sonar transmitters have been implanted since the program started.
Biologists believe females, which don't begin to spawn until their mid-20s, procreate every three to five years. Males are believed to spawn yearly. What Bruch and other scientists have learned already through sonar tracking is that some males are spawning at multiple sites among several rivers each year.
"That's an interesting thing we've learned. This is all brand new -- we never knew this before," said Bruch, as he mended a large hole in a fish net caused by a writhing sturgeon.
Expenses for sturgeon monitoring are paid with spearing license fees, which are $20 for a resident permit. Last season, 10,860 spearing licenses were sold, said Bruch.
Friday appeared to be the peak sturgeon spawning day at Shawano dam, the farthest point north on the Wolf River, which is also the ancestral spawning site of the lake sturgeon until the dam was built by a paper company in the late 1800s, said Dave Paynter, a DNR fish technician.
Hundreds of people turned out, including a few school classes, to snap photos and watch DNR technicians wearing chest waders wield large nets to catch sturgeon to measure length and insert rice-grain-sized tags under the dorsal fin, another tracking device that will be recorded again when the fish is caught. Spurred by higher than usual temperatures, the sturgeon began spawning a week to 10 days earlier than normal.
Hundreds of sturgeon swam toward the dam and flopped together in a frenzy, drawn each spring to this spot and elsewhere along the Wolf and Fox rivers. Water levels were fairly low for this time of year, and dorsal fins stuck up from the river like a shark convention. A few leapt out of the water, which biologists call porpoising.
Scott Wirtz and Kevin Hartmann had driven their Harleys from Sheboygan to see the sturgeon show. Wirtz heads out to Lake Winnebago every February for the annual sturgeon spearing season. In 2009 he speared a 53.5-inch female and a decade earlier he caught a 43-inch sturgeon.
As he sat on a rock next to the river watching the show, he was asked if he was sizing up next season's catch.
"If only it was that easy," Wirtz joked.