CHAMPAIGN, Ill. - Every spring, fishermen wait for a peculiar-looking relic to swim up the Wabash River between southern Illinois and Indiana.

The shovelnose sturgeon, a prehistoric fish covered in bony plates and with a strip of barbs down its back, is plentiful in these waters, where they can live up to 60 years.

Ronnie Harrington says he has roamed the waters of the Wabash for just about all his 70 years. "You put a couple, three or four nets out, and if you catch them, you know they're running," he said.

But scientists worry that the decline of another type of sturgeon half a world away could mean trouble for the shovelnose, North America's smallest sturgeon.

It has become increasingly popular in the caviar trade as the beluga sturgeon, a much bigger cousin that produces the king of caviar, has declined due to overfishing in the Black and Caspian seas. That prompted the U.S. and other countries to restrict or ban the import of beluga caviar.

So U.S. fishermen are turning to the shovelnose to help feed the world's appetite for the delicacy - and states are beginning to look for ways to protect the fish.

"The concern is if you keep taking out those big females from the population, what you can do is cause that population to begin to decline," said Purdue University researcher Trent Sutton, who has studied shovelnose on the Wabash, its stronghold.

Illinois' Senate is considering restrictions on shovelnose fishing, already passed by the House, including establishing a commercial season and size limit. Indiana will establish similar restrictions this summer and Wisconsin is considering them.

A number of other states - from Missouri to the Dakotas - where the fish is less plentiful than on the Wabash, have restrictions of varying degrees.

In North Dakota, "they're only found in the Missouri river system. They're producing and doing OK," state fisheries chief Greg Power said. Anglers who catch shovelnose sturgeon must release them, he said.

Some people mistake them for the endangered pallid sturgeon, but there are thousands of shovelnose sturgeon for every pallid, Power said.

Commercial anglers in North Dakota have other fish to fry, he said.

"This is a walleye state. People are happy with walleye," he said.

Between the Wabash and Mississippi rivers, Illinois fishermen took a steady 65,000 to 70,000 pounds of shovelnose a year from 2000 through 2004, according to the Department of Natural Resources. Preliminary figures from 2005 - the most recent year available and the year the U.S. began its beluga ban - show the harvest shot up to 97,000 pounds.

In Missouri, the harvest has increased since 2000 from a few thousand pounds to about 35,000 pounds annually.

Because shovelnose are slow to reproduce - females mature between ages 6 and 9 - and don't spawn every year, scientists worry that without restrictions it wouldn't take long to damage the Wabash population and, in the worst case, push it toward collapse.

Some fishermen support regulation, if only as a precautionary measure. But others don't believe it's needed.

"We've done proved to them that all these rules and regulations that they're trying to put into effect is a bunch of malarkey," said John Radloff, a former fisherman in West Union, Ill., who now buys sturgeon roe from Wabash fishermen and sells it to wholesalers and retailers.