The hunt is on in Custer State Park, both for trophy elk and for a disease that might be causing a 50 percent decline in elk-calf numbers.

The calf crop has dropped sharply in the park during the past two years, to an average of about 20 calves per hundred cow elk. A more typical level in the park is 40 to 45 elk calves per 100 cows.

Park officials are getting help from hunters in the elk seasons that began in the park this fall. Along with the regular requirement that bagged elk must be checked in with Game, Fish & Parks officers, elk hunters in the park are also being given needles and vials to use to take blood samples immediately after they shoot an elk.

The blood is then tested for a variety of diseases that could be affecting reproductive rates and calf survival.

"We've had a couple years of poor calf production, so we're going to look first at the bulls and later on at the cows," park resources program manager Gary Brundige said. "We don't have an idea that we have a disease issue, other than the fact that we've had poor calf production. We want some idea of why that production is down."

The herd in the park is down dramatically from a high of more than 1,100 elk a decade ago to about 450, based on a survey last February. The 1,100 level was considered to be too many elk, based on the management plan for the herd and carrying capacity of the habitat in the park.

The state Game, Fish & Parks Commission issued more cow-elk permits for the park to reduce the herd to a management goal of 750. When the herd dropped below that, park elk licenses were reduced, particularly on cow tags.

"At one point, when that population was up, we were issuing as many as 150 cow tags," Brundige said. "We've dropped that back to 20. We didn't want to reduce it further, because we wanted to ensure some samples to work with."

There is still a good population of bull elk in the park, where hunters lucky enough to draw a permit have a good chance at a trophy.

But the hunt for the cause of declining calf crops is the most important hunt this year. Mountain lions are one source of elk mortality, but they aren't considered the major factor.

"Yes, we know lions are killing some calves," park wildlife biologist Chad Lehman said. "We believe the bigger issue lies with pregnancy rates, abortion or poor calf health after being born."

State biologists evaluate pregnancy rates by checking elk ovaries found where the animals have been field dressed by hunters during the elk season. A cow-elk season in October will give biologists another chance to check the pregnancy rates, which has dropped in recent years, too.

"The pregnancy rate last year was down to about 38 percent, and we had evidence that about 80 percent of the cows ovulated," Brundige said. "Based on that, we expected a higher cow-calf ratio."

In Wind Cave National Park, a 28,000-acre preserve adjoining Custer State Park on the south, the winter elk population also is down, from about 850 five years ago to 650 last winter. The park doesn't allow hunting. But the elk move in and out of the park, so the herd is affected by state seasons outside its boundaries, which are considered the main reason for the reduction in the Wind Cave herd.

Park spokesman Tom Farrell said the calf-to-cow ratio in Wind Cave is estimated at 30 to 35 per 100. Farrell said the park doesn't have much historical data on the cow-calf ratio, so it's difficult to determine whether there has been a drop.

But Wind Cave biologists believe the current ratio produces a "slowly growing herd," he said.

Outside the two parks in the rest of the Black Hills, the ratio is estimated at 50 elk calves to 100 cows, GF&P regional game specialist John Kanta of Rapid City said. Last year, the calf number was 42.

GF&P estimated the Black Hills elk population outside the two parks last year at 3,500. This year, the pre-season count looks like about 3,300, Kanta said. That's less than half the population level recorded five or six years ago, when GF&P responded to landowner concerns about elk numbers and began issuing more licenses to trim the herd.

"We heard loud and strong from the producers in the Black Hills area that they were sick and tired of elk and the damage they were causing," Kanta said. "So the department's direction was to bring that elk herd down. And we did it."

Landowner complaints have declined with the elk herd. And some ranchers are even calling to say that elk are scarce on their property, Kanta said.

"We're essentially going back into a building mode with the elk herd," he said, adding that some areas continue to have an abundance of elk, while others have dropped off.

Brundige and Lehman hope for a herd increase in Custer State Park, too. But first, they have to figure out what's happening to the calves.

"We hope our tests will help," Brundige said.

Contact Kevin Woster at 394-8413 or kevin.woster@rapidcityjournal.com