Alaska’s predator control programs — aimed at boosting moose, caribou and deer populations for hunters — do not work, according to research by two retired state Fish and Game biologists and a University of Alaska Fairbanks professor.
The study they’re presenting at the International Mammalogical Congress in Anchorage on Thursday, published in the scientific journal Diversity, says an analysis of one Southcentral Alaska game unit, Game Management Unit 13, found no increase in moose harvests in the years following predator control work there.
The state Division of Wildlife Conservation disputes that, saying not enough time had passed between the predator control work and the analysis of moose harvests to expect higher numbers of moose.
But the study’s lead author, Sterling Miller, spent two decades at the Division of Wildlife Conservation and says the state’s predator control programs are driven by politics, not science.
The following transcript has been lightly edited for clarity.
Sterling Miller: I think the Fish and Game Department, and the Division of Wildlife Conservation, has not done adequate analysis, and in some cases even misled the Alaska public about whether or not these programs are accomplishing their objectives. So we decided to look at one study area, which is an area where I worked for 20 years, where predator management on bears has been going on, effectively, since 1980, and it’s been increasing throughout that time. And wolf management has been also very aggressive and really accelerated in 2005. So we decided to look and see whether or not harvest of moose has increased in this area. So that’s called a case history analysis.
Casey Grove: It seems like a lot of number crunching. How do you do the work of doing an analysis like that?
SM: Well, one of the problems with the way intensive management has been conducted in Alaska is that they don’t set it up with an experimental design where it can be readily analyzed. They just kind of back into these things. The Board of Game just decides that they would like to be able to harvest more moose in some area, or caribou, and then so they just start liberalizing regulations and sometimes going to active predator control, which involves shooting predators from aircraft. So what we had to do was try to patch it together from existing data, which is basically just the harvest data, is all we had. We looked at various time lags between predator harvests in a year, you know, one (year), two, three, four, five, six, seven, eight, nine, ten, up to the end of the data time series, to see whether or not there were correlations between the number of predators killed for each of the three predator species and numbers of moose subsequently harvested. And we were unable to see any correlation with any time lag.
CG: I’m no, you know, biologists myself, but I feel like it’s fairly well understood that predators like wolves and bears definitely prey on moose calves. I think it’s even maybe noted in that paper. So how is it possible that killing those predators in a predator control program would not result in more moose?
SM: That is an excellent question, Casey and in fact, there are a lot of people that are very confused on exactly that point. And, you know, I actually, in 1979, a colleague and I in Unit 13, did an experiment in which we moved 49 grizzly bears out of the headwaters of the Susitna River just south of the Alaska range. And then we looked to see whether or not there was any response in moose calf survivorship. And in fact, there was a response. You know, the calves are born in the spring, and that very fall, there was an increase in calf-cow ratios. But the real question is, do those calves survive into subsequent years and become adults? Or are they subject to what’s called compensatory mortality, which means that they die of something else? And in fact, in very many cases, particularly when a population of moose, for example, is near carrying capacity, the mortality to the calves is not additive. That means if you can kill, you kill all the predators and the calves would still die of something else, because predation is not the limiting factor.
CG: Well, I have to ask, I mean, this has been a controversial program, predator control in Alaska, for a long time. And I wonder, how do you think that the state is going to receive this research that says that it’s not working?
SM: Well, the state is pushing back. You know, there are some good biologists in the state. And there are some analyses that have been done, which I believe are being done in the wrong way, because they compare between areas, rather than doing within an area. But there are a lot of things that affect calf survivorship and densities of moose other than predation. And so it’s very difficult to compare between areas. The thing that most likely is a big difference between areas is habitat conditions, and habitat conditions can vary dramatically. For moose, for example, the big variable that affects habitat conditions are fires. And if you have fires, it sets back the vegetation so that there’s an earlier successional stage, you know, more willows and less spruce trees. And that’s good for moose. But it’s very difficult to do a controlled burn in Unit 13. It’s very hard to get permission from the federal agencies, particularly the BLM. And there’s a lot of pushback from people who have cabins and things in the area. The Fish and Game Department has to manage anytime where there is more demand for ungulates than than is supply. They have to do intensive management, and really, the only kind of intensive management that can be done or has been done is predator control, because the other strings on what’s limiting, like habitat conditions, are really not strings you can pull very effectively or inexpensively.
Editor’s note: In response, the acting director of the Division of Wildlife Conservation, Ryan Scott, says the division “respectively disagrees” with Miller and his colleagues. Scott says the study’s time period was too short and that, while there are factors other than predators to consider, predator control is a tool the division uses to turn around declining prey populations. “People have very strong feelings about intensive management and the negative aspect,” Scott said. “There’s a lot of Alaskans that feel positively about it, and it impacts Alaskans.”