To solve any problem that impacts society, folks must agree on what the problem is and define it clearly. Unfortunately, the definition of an invasive species used by Minnesota’s (and most states’) government is neither precise nor the one accepted by many research scientists.
Examples of the problems resulting from lack of a precise definition abound, such as the passionate debate about whether or not to restrict stocking of muskellunge (muskies), Esox masquinongy, into Minnesota lakes. A favorite of some fishers, the muskellunge has been present in a relatively small number of lakes in the Upper Mississippi River watershed since the last glaciation ended about 12,000 years ago but now folks want to introduce them to more. But should introduced muskies be considered a native or an invasive species? There is a problem is with the legal definition and how it is followed. The Minnesota DNR (echoing a presidential executive order) defines invasive species as “species that are not native to Minnesota and cause economic or environmental harm or harm to human health.”
Although that may seem straightforward, there are two major issues. The first is that the relevance of “native” is unclear. In determining what makes a fish native, what really matters (from a scientific perspective) is not the state a species is found in (fish are apolitical), but rather what area of the watershed that that species of fish swam into on its own, is now naturally evolving in, and presumably in balance with. The issue should be ecological balance not politics. The second issue is related to the term “damage.” It is unclear what this means or how it should be evaluated. In particular, the term “environmental damage” lacks scientific relevance. Ecosystems simply are what they are; they cannot be damaged, although they can change (especially because of things folks add to them), often in ways that people dislike. Additionally, and perhaps most importantly, agencies and research organizations dealing with invasive species are not actually assessing economic damage. They aren’t routinely collecting data on the economic value of the resources they are managing and protecting or on how those values are being harmed or changed (or could be). Lacking objective metrics and data about ecosystem value, assessments of damage become largely a matter of conjecture. So administrators and managers decide what is native (and presumably “innocuous”) or invasive in our state, and what sort of effort is needed to address them, largely based on personal experience, which is by definition subjective and limited by who happens to be in the room. The end result? Unfocused, inefficient, scientifically indefensible, and unsatisfying policy.
Where does this leave us? We seem to have two options: we can either adopt a new definition or correct and then follow the present one. Most basic scientists, including me, use the definition coined by Professor Dan Simberloff (considered the father of the scientific discipline of invasion biology*): “species that arrive with human assistance, establish populations and spread.” Simberloff’s definition is objective, scientific, and quantifiable, focusing on the specific role of humans (vs. natural processes) in determining the presence a species. Using this more scientific definition, stocking muskies (or any species) into lakes and rivers where they were not naturally found is tantamount to introducing a non-native, invasive species if these species eventually breed and become established.
However, as appealing as Simberloff’s definition and its focus on natural processes is, it does not address “damage,” something many feel passionately about, especially if they are being asked to fund invasive species research and control. This is understandable and can easily be alleviated in a scientifically-rigorous manner simply by specifying that invasive species (as defined by scientific criteria) must by scored (or assessed) by how damaging they are (or are likely to be) in economic terms. For this, a rigorous socioeconomic evaluation of individual ecosystems would be conducted by applied economists to evaluate all aspects of ecosystems and roles of species in them and their combined economic values to all facets of society.
In this way, both the value of and damages to ecosystems could be assessed in quantitative and repeatable manners, and our efforts to target invasive species and systems could then be focused objectively and productively. Companies perform fact-based assessments of resource values all the time—why shouldn’t resource managers and scientists?
In summary, if politicians will not or cannot adopt the scientific definition of an invasive species, the present legal definition should be modified (its easy) and followed. The economic data that would be produced should then be used to determine exactly how damaging introduced (non-native) species actually are (or are likely to be) to all segments of society (i.e fishers, lake shore owners, resort owners, nature-lovers, canoeists, water-skiers, etc.) so reasonable decisions can be made at both the local (e.g. a biologically relevant scale) about whether and how particular species should be studied, regulated and / or controlled. Either way, it is high time that we used applied economics to inform invasive species research, management and control. I suggest that at least a third of our efforts be directed in this way, with another portion devoted to policy evaluation. Invasive species are as much a social problem as a biological one: we must recognize this if we want to succeed in managing and controlling them in ways that we can benefit from.
P.S. Whether introduced muskies should be considered invasive or not according to the legal definition, is in my opinion, presently unanswerable because there seemingly are no socioeconomic data on their overarching ecological effects. Perhaps we should get some?
*Simberloff, D. 2013. Invasive species: what everyone needs to know, Oxford University Press.