Both species of deer are a way down in south-central BC, the Shuswap, Thompson and maybe Kamloops area. The reports I hear are there are lots further south in the south Okanagan.
Our game department has no funds for inventory work, to even officially know about these things, so certainly no money or staff to look into the "why", of why they seem to be down.
Salmon Arm is a huge municipality, lots of smaller farms, tree lines, old growth and brushy areas, with no hunting having been allowed for years. In short, a haven for whitetail deer. My son lives on a small farm that used to be well populated with deer throughout the area. This year, I don't think he has seen one all year. We live on acreage much closer to town, but deer quite often wandered through our place. They haven't for about two years now.
This last fall we went many evenings on drives throughout the more thinly populated areas of the entire municipality, looking for deer. We didn't see a single deer all fall!
I suspect there has been a disease hit them. About three years ago our son and grandson brought a shot deer to our place. There was a huge, abnormal, growth on its neck and shoulder. I quickly told them to don't even think about eating it.
A year ago this fall on an evening drive thirty miles out, we saw a deer in an abandoned field. My camera has a long zoom lens and the deer very patiently let me take all the pictures I wanted to take. When I enlarged the pictures on the computer it could be seen that the deer had a large, abnormal growth down the entire inside of the one back leg, that was visible.
This past summer and fall, with many drives on back roads with the car, plus trips on really back roads with the quad, we didn't see a single deer.