Gray wolf populations in the Rocky Mountains have stabilized at a “robust” level, while their numbers are rapidly increasing in the Northwest, according to the U.S. Fish and Wildlife Service’s annual report on wolf recovery.

The report released April 1 shows that wolf numbers in Idaho, Wyoming and Montana have largely leveled off, but picking up momentum in Oregon and Washington.

Wolves were re-introduced into Yellowstone National Park and Central Idaho in 1994, joining a small number in Montana. Since then, wolves have expanded westward into Oregon and Washington.

Wildlife officials counted 1,904 wolves at the end of 2015, up from 1,802 wolves the year before.

Most of the population growth occurred in Oregon and Washington, even though those states have far fewer wolves than the other three.

Oregon’s wolf population increased to 110 from 77, a 43 percent increase. In Washington, the population grew to 90 from 68, a 32 percent increase.

The Rocky Mountain population grew by 2 percent. Idaho had the most wolves, 786, followed by Montana with 536 and Wyoming with 382. Minimum population targets are 150 wolves in each state, according to USFWS.

Here’s a closer look by state:

• Oregon: The state Fish and Wildlife Commission in November took wolves off the state’s protected species list. Wolves remain a federally protected species in Western Oregon. The state Department of Fish and Wildlife reported that wolves killed three cattle, 10 sheep and one dog. Seven wolves were known to have died, including three that were illegally shot.

• Washington: Breeding pairs increased to eight from five. Under current policy, wolves will remain a state-protected species until the state has at least 15 breeding pairs, including four in each of three recovery zones.

So far, wolves are mostly in the northeastern corner of the state and have yet to move in sufficient numbers toward the Cascades to come close to state recovery goals. The Washington Department of Fish and Wildlife confirmed seven cattle were killed and one sheep dog injured by wolves in 2015. Seven wolves were known to have died, including three that were legally harvested on the Spokane Indian Reservation by tribal members.

• Idaho: Wildlife officials recorded 358 wolf mortalities, including 256 that were legally shot by hunters. Wolves claimed 35 cattle, 125 sheep, three dogs and one horse. Wolves were taken off the federally protected species list in 2011 in Idaho, as well as Montana.

Montana: Wildlife officials recorded 276 wolf deaths, including 205 legally killed by hunters. Another eight wolves were killed illegally. Officials confirmed that wolves killed 41 cattle, 21 sheep and two horses.

• Wyoming: By a federal court order, wolves remain a federally protected species in Wyoming. The population grew by less than 2 percent. No hunting was allowed, but 54 wolves were lethally removed. Wolves killed 72 cattle and 62 sheep.