Once nearly wiped out by overfishing (caviar is sturgeon eggs) and habitat alteration from dams, sturgeon have been staging a steady comeback in the Upper Midwest for decades. For the first time this year, Minnesota offers a statewide catch-and-release season for them, and subcultures of anglers target them with heavy tackle on the St. Croix River in the east metro and the Rainy River along the Canadian border. But they’re still a curiosity for most, including Yerhart and his two boatmates, who motored up the Mississippi River north of Winona on Friday morning in search of more traditional quarry: walleye. (Although the statewide walleye opener was Saturday, the season is year-round on that stretch of the Mississippi.)