In February, March, April, and July, troopers found dead wolves.
The animals were killed by poisoning. The state police are asking the public for help with the case.
After months of investigating the killings, the Oregon State Police last week urged anyone with information to contact them.
The State Police said in a news release on Thursday that five wolves from the Catherine Pack and three wolves from other packs were among the animals killed.
The police wouldn't say what substances were used. They didn't say if they believed the poisonings were intentional or not.
It is illegal to shoot wolves in Oregon if you want to defend human life or if you want to destroy livestock, according to a spokeswoman for the Oregon Department of Fish and Wildlife. Penalties for wildlife crimes could include thousands of dollars and jail time, depending on the charges, she said, adding that Oregon does not allow hunting of wolves at this time.
The poisoning of an entire pack is significant. She said her department would have a better idea of how wolves will be affected by the deaths next year after biologists complete their winter surveys.
The deaths of wolves in Wisconsin, where hunters killed more than 200 wolves in less than 60 hours this spring, caused concern among wildlife advocates. Federal officials and wildlife advocates are fighting in the courts.
The executive director of the WolfConservation Center said the Oregon case was unusual and that the illegal killing of wolves every year remains a big concern.
As wolf populations have slowly increased over decades of protection, debate has returned over the extent of their recovery, the laws about them and their effect on ranching and hunting.
Ms. Howell said that wolves were sometimes treated as a political predator. People love them. She said people hate them. They evoke a lot of emotions.
The delisting of the wolf from Oregon's list of protected animals in 2015 and from the federal list this year could have played a role in the case.
She said that peer-reviewed research shows that legal protections for wolves are relaxed.
The decision to take wolves off the federal list was condemned by environmentalists. The gray wolves have reached their goals and are able to survive some hunting, according to federal officials.
The number of wolves counted in Oregon last winter was 173, a 9 percent increase over the previous year, according to the Fish and Wildlife spokeswoman. The gray wolf population has been increasing since the discovery of a pack in 2008, but only three wolf packs are in the northeast corner of the state.
The Oregon State Police Fish and Wildlife Division received information from the Oregon Department of Fish and Wildlife about a wolf that might have died.
The wolves that were found dead by the troopers were members of the Catherine Pack, which is located in northeastern Oregon. A dead bird was found.
The animals were taken to a forensic lab to determine their cause of death.
On March 11, troopers learned that another wolf's collar had pinged a "mortality signal:" Its collar had been still for many hours, suggesting the animal was likely dead. There was a dead wolf, a dead skunk, and a dead bird nearby. The remains were taken to a lab.
The troopers found evidence that they suspected was linked to poisoning and submitted it for testing.
The police said that poisoning was the cause of death for six wolves, a skunk, and two magpies. A wolf was found dead from another group. A female wolf from another pack was found dead.
The police said that different types of poison were found in both wolves.