Saturday, March 12, 2011

Additivity in wolf harvest

Scott Creel and Jay Rotella conclude:
Examined across populations, human killing of wolves is generally not compensatory, as has been widely argued. Management policies should not assume that an increase in human-caused mortality will be offset by a decline in natural mortality.
Seems pretty cut and dried, and looking at the way they analysed their data, I can't find any reason to disagree with them. Given their result, this is a very balanced and fair statement; they also say that some level of wolf harvest probably is sustainable. However that sustainable harvest is probably lower than proposed in current Montana and Idaho management plans.

Dr. The Bird Man wondered if Adaptive Management could be used to resolve the Additive/Compensatory controversy, along the lines of the North American Waterfowl Harvest Management Plan. I don't think it would help in this instance. The wolf harvest is marked by sharp distinctions in how wolves are valued among various stakeholders. In addition, the institutions tasked with managing wolves are new at the game - for the past 30 years that job has been handled by the USFWS. This means that everyone - for or against harvest of wolves - is learning a new set of skills, interacting with new people, and old people in new ways. In contrast, when the AM plan for waterfowl harvest was adopted in 1995, the institutions managing the harvest had been doing so for decades, using the same types of data, and the value diversity was (and still is) much lower than in the wolf case. It's worth noting that even after 12 years of analyzing data, the waterfowl AM process still couldn't distinguish between compensatory and additive harvest (Nichols et al 2007). I wonder if a meta-analytic approach similar to what Creel and Rotella used wouldn't be more helpful.

This does not mean that careful analysis and thinking about wolf populations won't be useful. The risk is that parties on both sides of the debate substitute arguments about the quality of the science for the real debate about how many wolves we want, or are prepared to live with. That's a value based question, and until the debate turns away from the science and focuses on the emotional, subjective, icky stuff, it'll be hard to resolve anything.


  1. So, you think that when there is too much controversy, AM is not a good approach? Where there is too much, let's say, value uncertainty, or at least value disagreement, AM is likely ineffective. That's interesting and I'd suggest that the current work in the Delaware Bay on horseshoe crab harvests, might be one test of that idea. We'll see how that one that turns out. I think some folks associated w/ Patuxent just did a giant SDM effort on wolf management. I have no idea how that went though.

  2. Agreed about the diversity of opinions regarding wolf hunting, but--as you point out--the state agency needs to have some objectives (for the harvest of wolves) that officially represent the diversity of opinion. The current harvest is based on some set of objectives that may/may not represent everyone's, someone needs to write a paper about what happens in an ARM (or more broadly, SDM) process when the objectives are ill-defined. We know it's bad, but how far off-track can you get? Are poor objectives worse than no/little data, or poorly constructed models?

    In the case of the NAWMP's modeling, there is some usefulness, I think, to the fact that the model can't distinguish between the two forms of harvest mortality: the resulting regulations take that fact into account. So, the regulations are more conservative that simply assuming compensatory mortality.