Wednesday, February 1st, 2023
Wednesday, February 1st, 2023

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DNR: Bear population not declining

Roscommon, Mich. —  Michigan’s bear population is not declining, nor has it been. If anything, the state’s bear population is increasing in response to reduced statewide bear license quotas during the past three years, according to the best scientific data available from the DNR, which was made public at a bear symposium, Dec. 6 in Roscommon.

DNR research specialist Sarah Mayhew gave a presentation during the symposium on the use of statistical reconstruction to estimate bear numbers across the state.

“We have sex and age data from our bear population since 1992 to the present,” Mayhew said. “We have the age at harvest for our bears from mandatory registration of animals taken by hunters. Those ages are determined by looking at the teeth from those bears. Hunting effort is determined by annual surveys of bear hunters.

“All of the information is plugged into the program and it goes through a number of scenarios to determine what the bear population was most likely to have been like to produce the harvest that we know we had, given the other data that is known.”

Based on that science, Mayhew said there were an estimated 11,000 bears that were more than a year old in the areas open to bear hunting on Sept. 9, 2014, the day before the bear-hunting season started. She said 9,000 of them were in the U.P. and 2,000 were in the Lower Peninsula.

“Based on the data, the bear population in the U.P. has been stable for about the last 20 years,” Mayhew said. “Those figures only include bears that are at least a year old before bear season begins. They do not include cubs.

“Since females with cubs are protected during hunting season, there has been a gradual increase in the number of reproductive females in the population, and there has also been a gradual increase in the average number of cubs per female,” she said. “Females of reproductive age only have cubs every other year. If you average out the number of cubs produced per year for all females, it is 1.2. If you only consider reproductive females, meaning those that had cubs that year, the number of cubs per female is about 2.5.”

Productive females can have as many as five cubs, but three or four cubs are more common. Some females, such as first-time mothers, only give birth to one cub, however. Mayhew did not have an estimate of the number of reproductive females that there would be in the state per year.

If one-third, or 3,630 members of the bear population, were reproductive females, however, they would produce 9,075 cubs. That would put the state bear population at about 20,000. Not all cubs survive their first year of life, though. Cub mortality varies by region, being the highest in portions of the U.P. where wolves prey on cubs.

Mayhew said that by using this new method of estimating the bear population, the DNR can produce an annual estimate after the new data gathered each year is plugged into the equation. That’s cheaper and less labor-intensive than previous methods. In the past, tetracycline baits have been used to estimate bear numbers in the U.P., and DNA analysis of bear hair collected from baited snares has been used in the northern Lower Peninsula. Both of these methods are labor-intensive and costly.

In the U.P., tetracycline capsules are wrapped in bacon for bait and are hung from trees to increase the chances that bears will eat them. The tetracycline stains the teeth of bears, and those that have been marked in this fashion can be detected when the teeth of harvested bears are examined. Hundreds of these baits are put out across the U.P. each time this type of marking effort is done.

Then biologists have to revisit the baits to determine which ones have been eaten by bears. For accuracy, it’s important for researchers to be able to differentiate between baits eaten by bears and non-target animals such as fishers and raccoons. To aid in determining what animal ate baits during 2014, game cameras were placed to monitor 97 baits.

Setting up baited hair snares at a number of locations in the Lower Peninsula and collecting hair samples from them also takes time. Then DNA information has to be extracted from those samples and analyzed.

Bear-population estimates for the U.P. based on tetracycline baits conducted previously were what led wildlife biologists to think bear numbers were declining there, which led to a 32-percent reduction in the number of bear licenses issued for the U.P. from 2012 through 2014. Those estimates, according to the DNR, were inaccurate based on the more recent statistical reconstruction method.

“All methods used to estimate populations are subject to errors,” DNR wildlife researcher Dwayne Etter said. “That was the best available information at the time. We now recognize we have problems with the tetracycline capsules used in baits. The capsules are now thinner than they used to be. When we wrapped them in bacon this year, the moisture from the bacon dissolved the capsules, making the baits less appealing to bears. That might be responsible for fewer baits taken by bears than fewer bears being present.”

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