Gulo gulo: Warranted

In a 134-page decision that meticulously reviews available science and incorporates direct input from wolverine researchers, the US Fish and Wildlife Service announced on Monday that the wolverine is warranted but precluded for protection under the Endangered Species Act. The designation recognizes that wolverines face substantial threats, but deems other species of higher priority, placing the wolverine in limbo until the agency decides the species should be listed, or that it is not warranted.

Monday’s announcement represents an important step forward for those of us who work on wolverine research and conservation. The science encapsulates an extraordinary effort on the part of North American wolverine biologists, who were struggling to answer even the most basic questions when the wolverine was first proposed for listing in 1993. The fact that this decision was issued at all represents the persistence of the advocacy community in the face of very legitimate concerns about the basis of the 2008 decision. And the fact that climate change is cited as the primary threat represents, at the least, good science and a certain integrity on the part of decision makers willing to acknowledge that climate change is an issue – even if the ESA is powerless to force changes in regulations of carbon emissions.

The document is worth reading, especially for anyone interested in a thorough review of current wolverine science. For those who don’t have the time, here’s how the decision was reasoned, starting with the “warranted” designation.

Jeff Copeland’s 2010 paper linking wolverines to persistent spring snow and cool summer temperatures, and an unpublished climate model paper by Kevin McKelvey of the Rocky Mountain Research Station, underpinned the recognition of climate change as a substantial threat. The McKelvey paper modeled local-scale climate change in Rocky Mountain wolverine habitat over the next century, predicting a 23% loss of habitat by 2035, and a 63% loss by 2099. Acknowledging the natural rarity of wolverines, and their distribution at the southern edge of their range in an archipelago of high elevation habitat islands, the decision cited increasing difficulty in maintaining genetic connectivity among populations, and a decrease in breeding habitat, as the outcomes of warming. The loss of genetic diversity and the decrease in available habitat will lead directly to a decrease in wolverine numbers. Hence wolverines are threatened by loss of population, driven by climate change.

Trapping, disturbance due to recreation or industry, and development along dispersal routes constituted secondary threats. The decision states, probably accurately, that some disturbance and some mortality from a managed trapping season are not substantial threats to a healthy wolverine population. But synergy is a tricky thing, and in a world where population nodes are growing more separated and habitat is decreasing, every individual counts. Activities that wouldn’t normally pose a problem will potentially become overwhelming if climate change effects are fully felt.

Some more sobering numbers cited in the decision: the total population of wolverines in the Rockies is no more than 300, scattered in a meta-population across three states. The official effective population throughout the contiguous US – in other words, the number of wolverines contributing genes to the population – is 35. Of 13 haplotypes identified in wolverines throughout North America, only 3 are present in Rocky Mountain wolverines. Scientists estimate that an individual population of wolverines would need 400 breeding pairs to maintain genetic viability in isolation over the long term. Take note; that means that each node in the contiguous US would require 400 breeding pairs in the absence of reliable exchange among nodes. The Tetons, the population node next door to my office, host approximately five adult wolverines, and the range is saturated, all territories occupied. Five. That’s it.

Six states – Montana, Idaho, Wyoming, Washington, Colorado, and California – are included in current wolverine territory, as defined by this decision. California and Colorado’s inclusion is notable, despite having only a single confirmed male each. These regions were historically occupied by wolverines, and the decision acknowledges that the species was likely extirpated from its entire range in the Lower 48 during the first half of the 20th century, by predator control programs. In this scenario – we don’t have any proof, but it’s likely true – wolverines have only returned to the northern Rockies over the past few decades. The decision acknowledges that recolonization is still occurring and that wolverines may not have yet made it back to the further reaches of their range.

As for the 2008 decision’s assertion that US wolverines are not a distinct population segment (DPS) and are indistinguishable from Canada’s wolverines, the current decision cites both genetic evidence and management differences to draw a clear line between the two.

Of the five reasons that a species may be listed under the ESA, the decision found the wolverine warranted for four: loss of habitat (the primary threat, due to climate change), overutilization (trapping, a secondary threat exacerbated by climate change), inadequacy of existing regulatory mechanisms (development, a secondary threat likewise exacerbated by climate change) and other natural or manmade factors affecting its continued existence (loss of genetic diversity, again a secondary threat driven by climate change.)

This is how we arrived, finally, at a recognition of the threats facing wolverines. How wolverines ended up precluded, and what that means, is a topic for tomorrow.

In the meantime, although I don’t usually go in for gimmicks, I’m making it snow on my blog. I thought it was appropriate, in both a straightforward – wolverines like snow!- and an awful way – we all think it’s so cute when our computers snow, but we can’t muster the will to make sure it keeps doing so in reality.


2 thoughts on “Gulo gulo: Warranted

  1. Pingback: Potential Change to Polar Bear ESA Rule « The Wolverine Blog

  2. Pingback: How to Help Wolverines « The Wolverine Blog

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