Back to ancestral waters
Written by Milwaukee Journal Sentinel   
Tuesday, 16 May 2006 16:00

The success of a 25-year commitment begun this spring to help restore lake sturgeon to their historic spawning range in the Milwaukee River, while boosting the ancient fish's population in Lake Michigan, rests on the shoulders of Carl John and a handful of other volunteers at Riveredge Nature Center.

The volunteers are raising newborn sturgeon in water from the Milwaukee River on the chance that this introduction to the stream will enable the fish to find their way back home many years from now, after being released in October and slowly growing to adulthood in the lake.

There are only a few thousand of the torpedo-shaped fish with shark-like tail fins now swimming in Lake Michigan, a near-total decline from the hundreds of thousands estimated to have roamed the lake in the early 19th century.

Restoring a larger population of this fish, which started swimming on the planet 100 million years ago in the age of dinosaurs, comes with the side benefit of helping to control two invading species - quagga and zebra mussels, said Rob Elliott, a Great Lakes fishery biologist with the U.S. Fish and Wildlife Service in Green Bay.

Though sturgeon have no teeth, they do have a crop. That large muscle smashes everything that the fish sucks out of the water or sediment at the lake's bottom, including the nuisance mussels, Elliott said.

The five dozen or so month-old lake sturgeon swimming in tanks at Riveredge likely will come to know the water of their natal stream so well that they will be able to pick out a unique scent from it when they search for a spawning stream as adults, according to Elliott and other researchers.

The scent could be from a type of soil, dissolved mineral or chemical not found in any other lake tributary.

Female sturgeon do not become sexually mature and participate in spawning runs until they are 20 to 25 years old.

"I don't think I'll be around to see them return," John, 77, said. "But that's OK. I'm watching them grow."

Eggs were collected from females spawning on the Wolf River near Shiocton in Outagamie County, then fertilized with sperm removed from males at the same location and delivered to Riveredge on April 14, said Marc White, director of research at Riveredge.

By April 25, larvae had hatched from eggs, and White began training volunteers to clean fish tanks and water lines in a trailer parked about 300 feet from the river. Water is pumped out of the river to the trailer.

The sturgeon are an inch long at this time. The fish will be released into the river at Lime Kiln Park in Grafton by early October, when they should be 6 to 8 inches long, White said.

Scientists do not know what specific scent or other cue will ring a bell with the fish when they encounter the river again later in life, Elliott said. It is certain, however, that it happens in a process known as imprinting.

This occurs early in a sturgeon's life, he said. It is how spawning Pacific salmon select the stream of their birth.

The U.S. Fish and Wildlife Service is working with the Wisconsin and Michigan Departments of Natural Resources in a three-year experiment to raise sturgeon in trailers adjacent to the Milwaukee and Manitowoc rivers in Wisconsin and the Cedar and Whitefish rivers in Michigan. The Manitowoc River trailer will be operating by June, but sturgeon will not be raised there for release to the river until next year.

The first three years of the effort to restore a spawning population to those streams are being funded with a $583,000 grant from the Great Lakes Fishery Trust in Michigan, said Brad Eggold, southern Lake Michigan fisheries supervisor for the Wisconsin DNR.

Within three years, the Riveredge and Manitowoc crews will be expected to raise 1,500 young sturgeon from eggs annually and maintain that production for up to 25 years, Eggold said. After grant funds are spent, the DNR intends to pay costs of operating the sturgeon trailers on the two rivers.

The first year's efforts at Riveredge showed White and his volunteers how difficult it can be to raise native fish from eggs in captivity. White estimates that fewer than 5% of eggs hatched. As sediment was siphoned out of the bottom of the tanks in which the larval fish live, some of them also were removed, further reducing the number of survivors.

The DNR traditionally relies on its large-scale hatcheries throughout the state to provide fish for stocking.

Since spring 2003, the department has released tens of thousands of sturgeon up to 1 year old from the Wild Rose hatchery into the Milwaukee River at Lime Kiln Park in an attempt to get some fish spawning in the river again, Eggold said.

All of them likely were too old to imprint to the unique chemistry of the river, however. That is one reason why the DNR has decided to stop placing hatchery-raised sturgeon in the Milwaukee River and is turning to volunteers.

"We could not be certain that the fish would return to the Milwaukee River," Eggold said of earlier stocking efforts. "They might stray to another stream."

Lake sturgeon have not spawned in the Milwaukee River in more than a century, and they do not spawn in the other three rivers targeted in the experiment.

The fish can be recognized by its long, tapering snout with four barbels, or feelers, dangling in front of its mouth, and its armor - five rows of bony plates along its body. A tubular mouth protrudes only when the fish is sucking up snails, crawfish, leeches, small clams and nuisance mussels.

Hundreds of thousands, perhaps several million, of the large fish roamed Lake Michigan in the early 1800s. By the 1880s, however, commercial fishing, water pollution and dam construction on tributaries had nearly eliminated sturgeon from the lake.

Today, researchers estimate there are between 2,000 and 5,000 adult sturgeon in the lake. Anglers and commercial fishers are not allowed to take them out of Lake Michigan or Green Bay.

Sturgeon are known to spawn in only eight of Lake Michigan's tributary rivers: the Fox, Oconto and Peshtigo in Wisconsin; the Menominee on the border of Wisconsin and Michigan; and the Muskegon, Manistee, Manistique and Kalamazoo in Michigan.

 
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