Several thousand minks that vandals freed from a central Minnesota farm have been recovered, but “the vast majority” of those died soon after recovery, authorities said Tuesday. Under cover of darkness late Sunday or early Monday, perpetrators invaded Lang Farms near Eden Valley and set loose about 38,000 fur-bearing minks valued at more than $750,000. Stearns County Sheriff Don Gudmundson said he’s convinced that animal rights militants are responsible for the crime.

As of midafternoon Tuesday, the farm’s recovery effort has collected 5,500 of the minks, said chief sheriff’s deputy Jon Lentz. “The vast majority are expiring shortly after being recovered,” Lentz said. “It may be due to stress, but the owners are not certain.”

Michael Whelan, executive director of the fur-raising industry association Fur Commission USA, said Tuesday afternoon that “mink ranchers from around the Midwest continue to arrive to assist in the recovery efforts.” “As domesticated livestock,” Whelan said, minks “are not equipped to live outside the farm environment, where they are fed, watered and cared for daily.”

Lentz said no one has contacted the Sheriff’s Office claiming responsibility. He said his agency continues to cooperate with state and federal authorities in the investigation. Gudmundson has classified the suspects as “nitwits” for thinking they were doing the minks a favor by carrying out a deed that has ended up killing them by the thousands. Whelan concurred, saying, “Anyone who thinks they are helping animals by doing this are severely misinformed.”

Along with the risk of the minks biting humans, Gudmundson said there is concern for wildlife that come into contact with any minks still on the loose. The animals are capable of traveling many miles. The vandalism falls under the Federal Animal Enterprise Terrorism Act, said Whelan, adding that his group is offering a $10,000 reward for information leading to the arrest and conviction of those responsible. The vandals targeted a farm run by the Lang family, which has been raising minks since 1936, spanning four generations.

Lang Farms asks that anyone who spots the minks call the operation at 1-320-453-4750 so its personnel can try to capture them. Anyone with information about the minks’ release is urged to call the Sheriff’s Office at 1-320-251-4240 or Tri-County CrimeStoppers at 1-800-225-1301. In October 2013, animal rights radicals set loose hundreds of minks from a southeastern Minnesota ranch in Grand Meadow.

Minnesota ranks among the top states in mink production year in and year out. Last year, there were 204,580 pelts produced in the state, ranking it No. 5 in the United States, according to the U.S. Department of Agriculture. Leading the way by a large margin is Wisconsin, which last year produced 1.2 million of the nation’s yield of 3.2 million pelts, the federal agency reported.