Eight conservation groups are petitioning the state of Montana to end the wolverine trapping season. As I understand it, the petition is not a lawsuit, it’s simply a request, with accompanying background information, that the state put an end to wolverine trapping before the beginning of the 2012 season in December. The state approved the trapping season on Thursday; they have 60 days to respond to the petition, but seem unlikely to change their position. Current regulations allow for take of five animals, with a female subquota of three, which means that if a female wolverine is trapped in any of the three regions where take is allowed, the season in that region ends.
Trapping is a major source of mortality for wolverines, and while the species can probably handle the pressure in a place like Alaska, where distribution is continuous across the landscape, it creates bigger problems for meta-populations inhabiting high-altitude habitat islands. These high altitude islands are predicted to shrink in coming years as climate change affects snowpack. In Montana, the smaller mountain ranges are likely to hold one or two reproductive females at most; trap one of these animals, and you knock the reproductive potential of that range back by 50-100%. Eventually, these ranges may be recolonized, but recolonization can take years, and those years represent lost time for wolverines to gain a stronger foothold, with greater levels of genetic diversity, across the region. Trapping creates mortality sinks on the landscape, and the loss of a single breeding female has a disproportionate effect on the overall population. The 2010 USFWS ruling that designated wolverines warranted for protection under the ESA suggested that a viable population of wolverines throughout the Rockies must include 400 breeding pairs, which means 800 animals¹ contributing to the population. We currently estimate that we have no more than 300 wolverines, total, in the Lower 48, and that only about 50 of these are contributing to the population. That means that the population is 750 breeding animals short of sustainability, and given the slow reproductive rate, we can’t afford to be taking reproductive wolverines out of the population.
The wolverines of the Rockies face added pressure as they disperse across vast swaths of lowland non-habitat in which growing human population and ever-increasing infrastructure create a potentially deadly obstacle course. These wolverines have to make it across hundreds of miles to find new territories, and the more young wolverines that set out, the greater the chances of one of them reaching and establishing a new territory and beginning to contribute to the population. Young wolverines have a high mortality rate even before dispersal, so the population needs as many young as possible to maintain viability over the long term. We can also speculate – although this is based on intuition, not data – that because wolverines do disperse so widely, wolverines in Wyoming, Idaho, and points further south do or will depend on infusions of DNA from dispersing Montanan wolverines. So there are compelling reasons to end the trapping season in Montana, and the most compelling is encapsulated in one phrase: In the Rockies, every wolverine counts.
Balanced against this, however, are a couple of points that deserve mention, because they were glossed over or else misrepresented in the petition and the news articles linked above. By the early 20th century, wolverines had been extirpated from the Lower 48 (and they were never “prolific across the West,” as the petition claims; “prolific” implies the production of numerous offspring. Humans are prolific. Wolverines, due to their breeding biology, are not and never have been.) They are currently recolonizing and expanding their range; they are not currently retracting, and they are not “on the brink of extinction,” as a representative of one environmental group claimed. They have continued to push into unoccupied habitat in spite of a Montana trapping season that, until several years ago, allowed unlimited take. Many of the statistics cited in the petition, on trapping as a percentage of recorded wolverine mortalities, come from this earlier period of unregulated trapping, and Montana has been commendably responsive to the concerns of conservationists; they’ve scaled back the trapping season twice in the past few years and closed two of the regions where trapping was previously allowed. Several wolverine biologists with whom I’ve spoken feel that trapping really isn’t a big problem for wolverines when weighed against the long-term threats of climate change. I don’t think any of us like wolverine trapping, because there’s always the risk that an animal that you know and respect will be caught, and I wake up each morning of trapping season with a worried heart, but as one biologist put it to me, “If you’re going to argue against trapping, just go ahead and admit that it’s an emotional stance you’re taking, not a scientific one.”
So, yes, I admit that it’s an emotional stance, although I’m not convinced that science contradicts emotion in this case, because we don’t know enough about how populations behave at the southern edges of their range. Maybe it’s a coincidence that wolverines have started popping up in Colorado and possibly Utah in the years since Montana scaled back its season. On the other hand, maybe, with human-created mortality sinks removed, the landscapes to the north are more fully saturated, and the entire population is more rapidly pushed south into unoccupied habitat. It’s not really a question of whether wolverines can make it in the short term with some additional offtake from trapping; it’s a question of how much faster they would recolonize new habitat without that offtake, and whether that additional speed provides them with an edge as snowpack shrinks over the longer term. It would be great if we had the funds to monitor this, but we don’t, so in the meantime we should err on the side of caution and do all that we can to keep every breeding wolverine alive and contributing to the population.
Whether this particular strategy – throwing a petition at the state of Montana when there’s already a rapidly-approaching deadline for a federal listing decision – is the best way to achieve this goal is, however, up for some pretty fierce debate. I’ll get into that later, but in the meantime, don’t take this post as an anti-trapping advocacy position statement. It’s not. It’s simply an attempt to clarify some of the ways in which trapping might, or might not, affect the population, and why we might think about being precautionary in this instance.
¹ The warranted-but-precluded decision doesn’t specify whether this refers to 400 unique pairs, or whether it refers to wolverine breeding habits observed in studies, in which a single male usually mates with two females whose territories overlap with his. So we may be discussing 800 individual breeding wolverines, or we may be discussing 600 – 200 males and 400 females. Either way, it will take decades to build the population to these levels.
A few additional resources:
George Wuerthner, the only individual to sign the petition, has a blog here.
The story has received widespread (not “prolific”) coverage across the West, in Montana, Wyoming, Idaho, California, Alaska, and Washington, to name a few. Almost all of these articles are the same AP piece, of which two versions seem to exist; a longer piece, and a shorter. An article also appeared in USA Today. Here’s another one from the Summit County Citizens Voice. And here’s an opinion piece from the Missoulian. I’m hoping to do a post analyzing some of the language in these articles, press releases, and blog posts, but if I don’t get around to it before I leave on my trek, I’d be interested in knowing what people think, not just about the issue of trapping, but about how the discussion is represented in the media.