Gray wolves in the U.S. Northern Rockies are showing resilience even as states adopt increasingly aggressive tactics to drive down their numbers through hunting, trapping and government-sponsored pack removals.

A minimum of 1,691 wolves roamed the six-state region at the end of 2013, according to figures released Friday by state and federal agencies.

That’s little changed from the prior year, despite continued political pressure from hunters and ranchers who want the population significantly reduced.

A total of 627 wolves were counted in Montana at the end of 2013, compared to 625 the previous year, according to Montana Fish, Wildlife and Parks. That’s a minimum confirmed number.

Montana had 152 wolf packs (up from 147) but breeding pairs dropped to 28 in 2013 from 37 in 2012.

Northwest Montana has the bulk of Montana’s wolves: a minimum of 412 wolves in 104 verified packs and 16 breeding pairs, compared to 400, 100, and 25 in 2012.

Across Montana, hunters and trappers took 231 wolves during 2013 compared to 175 in 2012.

Idaho in recent months put government wildlife agents in helicopters to shoot entire packs that were preying on big game herds. Montana officials last year lifted wolf hunting and trapping quotas, increased the bag limit to five wolves per hunter and lowered the fees for out-of-state licenses.

As hunting and trapping efforts have intensified, wildlife advocates have warned the population could crash, but that hasn’t happened: Wolf numbers are down just 6 percent since the animals lost federal protections in 2011.

“Wolves are very tenacious, they’re very prolific,” said Mike Jimenez, federal wolf recovery coordinator for the Rockies and a biologist with the U.S. Fish and Wildlife Service. “The population is very secure, but it doesn’t remove the controversy.”

Jimenez says he expects the population to gradually decline over time in the face of the states’ efforts but remain healthy overall.

The only state to see a significant drop last year was Idaho, down 63 wolves to at least 659.

On the livestock side, wolves in the Northern Rockies killed at least 143 cattle and 476 sheep in 2013. That’s 51 fewer head of cattle and six fewer sheep than the prior year.

Government-sponsored campaigns exterminated gray wolves across most of the Lower 48 states early last century.

They’ve come back strong in the last three decades.

Wolves naturally began to repopulate Northwest Montana starting in the 1980s.

In other areas such as Yellowstone and Central Idaho, wolves were reintroduced almost two decades ago.

Wolves now occupy large parts of Montana, Idaho, Wyoming, Washington and Oregon. Part of a sixth state, Utah, falls within the Northern Rockies region but has no wolves.

The Great Lakes are home to a second major population of roughly 4,000 wolves.

Amid a pending proposal to lift protections across much of the remaining Lower 48 states, the success of restoration efforts to date hasn’t quieted the intense debate over whether there are too many or too few wolves.

A new rule adopted last month makes it easier for Montana livestock owners to shoot wolves without a permit.  State officials said that’s expected to have limited impact.

“Among the best news is that confirmed wolf depredations on livestock took a significant drop in 2013,” Montana Fish, Wildlife and Parks Director Jeff Hagener said in a news release. “And that comes on top of fewer overall agency control actions than the previous year.”

Overall, Hagener said Montana’s wolf population continues a stabilizing trend that’s likely a combination of suitable habitats being filled, smaller pack sizes, routine livestock-related removals and hunter and trapper harvests.

“When considered as a whole, it appears those factors are continuing to curb wolf population growth,” Hagener said.

Confirmed livestock depredations in Montana due to wolves included 50 cattle, 24 sheep, three horses and one goat in 2013, down 27 percent from 2012 loses of 67 cattle, 37 sheep, one dog, two horses and one llama.

Cattle losses were the lowest recorded in the past seven years.

A total of 75 wolves in Montana were removed via lethal control, down from 108 in 2012.