The eggs, which were made into tiny black pearls, prized by the gastronomic world for their salty flavor profile, have been identified by state fisheries officials as necessary for research into the Wisconsin sturgeon population.

However, prosecutors say the state biologist overseeing the traditional sturgeon spear season at Lake Winnebago and its watershed, a winter rite for fish enthusiasts in the state, has acquired an expensive and illegal taste for the caviar made from the eggs.

Ryan P. Koenigs, a biologist at the Wisconsin Department of Natural Resources since 2008, accepted at least $ 20,000 in jars of caviar in exchange for delivering eggs to a caviar processor that had been collected under the guise of research, a criminal complaint last week filed in Winnebago County, said.

The caviar processing is operated by a former state biologist, according to prosecutors, who said it was one of several caviar processors who received sturgeon eggs as part of the barter. The former employee, who, according to prosecutors, received 65 pounds of roe in 2015 that produced $ 100,000 caviar, was not charged.

Wisconsin law requires that eggs be returned to the person who skewered or discarded the sturgeon upon request. Prosecutors found that caviar made from sturgeon eggs can sell for more than $ 100 an ounce.

The sea sturgeon, some of which can live up to 150 years but are listed as threatened in North America by the American Fisheries Society, is part of the state’s rich and peculiar fisheries heritage.

Mr. Koenigs’ arrest last week, along with three other people who were not government employees, followed a three-year investigation by the state and the US Fish and Wildlife Service. A former fisheries manager told investigators that staff would accept caviar and eat some during team meetings, take for personal use, and give something to bars, prosecutors said.

“Caviar is in high demand in both legal and illegal markets, and significant efforts have been made around the world to conduct this type of study to protect caviar-bearing sturgeon species,” the complaint said.

Mr. Koenigs, 36, of Appleton, Wisconsin, was charged in Calumet County last Wednesday of obstructing a conservation officer investigation. Prosecutors said he lied to investigators about the system that started before he began monitoring jamming spear season in 2012. He also reset a government-issued cell phone to hide evidence, according to a criminal complaint.

He was charged with theft in Winnebago County last Thursday, prosecutors said.

Scott Ceman, a lawyer for Mr. Koenigs, said in an email that his client would plead not guilty. He declined to comment on the case.

A spokeswoman for the Ministry of Natural Resources said Sunday evening that Mr Koenigs had been taken on administrative leave, but that she could not discuss the matter with the agency beyond his status.

Mr. Koenigs, who some news outlets referred to as a “sturgeon general”, was arrested just days before the start of sturgeon spear season in Wisconsin on Saturday.

The tightly controlled program requires that every sturgeon caught be logged at a state-run registration station, which gathers information on length, weight and gender, as well as tagging details. The season usually lasts 16 days or until gender-specific harvest caps are reached for a particular fishery.

Inspectors sometimes remove reproductive glands that contain eggs from adult female sturgeon so that they can be examined.

“Lake Sturgeon and many sturgeon species are rare and are currently threatened, endangered and even extinct in parts of the US and the world, making the harvest season unique in Wisconsin,” the Winnebago County complaint said.

Prosecutors said previous investigations linked caviar to organized crime and traffickers repackaging roe as higher quality, more expensive caviar that was exported to the Asian and European markets and resold in the US.

“For this reason, it is important to ensure accountability to all aspects of our laws in order to prevent the illegal marketing of our natural resources,” said the criminal complaint.