British Columbia residents authorized to hunt big game in parts of the province that are adjacent to the Yukon routinely cross the territorial boundary to kill animals, says a Whitehorse conservation officer.

Kris Gustafson was the lead investigator in the case against Abe Dougan, a Kamloops, B.C., guide facing a dozen federal wildlife charges related to allegations that he illegally killed a Dall sheep in the Yukon in 1999.

Gustafson, who has spent the last 35 years patrolling the Yukon wilds for illegal hunting, is now testifying at Dougan's poaching trial in provincial court in Kamloops.

Dougan has said the sheep was killed in northwestern B.C., where he was licensed to hunt sheep.

One of two photos entered as evidence at his trial shows him with a sheep near a mountain that is in the Yukon — 18 kilometres north of the B.C.-Yukon boundary.

Gustafson, who is director of conservation officer services for Environment Yukon, said outside court that cross-boundary poaching is a big concern.

"We have concerns respecting any illegal harvesting of wildlife — and that's a big one."

He told court he was the driving force behind a Yukon conservation campaign set up in the 1980s to keep B.C. hunters in their own province.

It included a program that involved setting up signs along the boundary and on the shores of float-plane-friendly lakes warning hunters they were no longer in B.C.

Court has heard that in 1999, Dougan received special authorization via lottery to hunt sheep in a specific part of northwestern B.C. between the Yukon and Alaska borders.

Sheep recorded as B.C.'s 2nd largest

He bagged a Dall sheep, which was the second-largest ever recorded in B.C. The score made its way into the pages of the fifth edition of "Big Game Records of British Columbia," when it was published in 2003.

In 2011, conservation officials in the Yukon received a tip from an anonymous tipster telling them to look closely at the B.C. record book — specifically at the picture of Dougan with his record sheep.

The person said the photo was taken in the Yukon, court heard.

A mapping specialist with Environment Yukon then created a three-dimensional computer model of the Yukon mountains and searched until he found what looked like the matching spot.

In July 2011, a team of three investigators, including Gustafson, flew by helicopter to the site, 18 kilometres north of the B.C.-Yukon boundary.

They took photos from what the Crown says is the exact location the photographer who shot Dougan's picture would have been standing.

The Crown maintains the mountains depicted in the backgrounds are identical, and prosecutor Lesley Ann Kilgore called the area geographically "unique."

Court has heard after hunting the sheep, Dougan was required to tell B.C. officials where it was killed. He gave them a location in the section of northwestern B.C., where he was authorized to hunt.

Defence lawyer Kevin Church has questioned the authenticity of the photos and said investigators failed to visit the location where Dougan claimed to have killed the sheep.

"They don't ever go to where Mr. Dougan says he shot this sheep," he told court. "They never even try."

Lawyers will meet this week to set a date for the trial to resume.