Mitigation banking is a tool now widely used in wetland conservation programs but is only beginning to be used in endangered species conservation programs. In the wetland programs, mitigation banking has long been promoted as a way to conserve wetlands at a lower cost than by traditional forms of mitigation. It also creates an incentive for at least some landowners to create, restore, enhance, or preserve wetlands, in order to be able to sell “credits” to others who need to mitigate projects that damage wetlands. Because the laws protecting wetlands and endangered species permit otherwise prohibited activities if they are properly mitigated, the interest in endangered species mitigation banking may well grow, just as wetland mitigation banking did.
In addition to the inherent differences between wetlands and other endangered species habitats, there also are differences in the purposes of the federal programs that seek to conserve them that, too, can give rise to different mitigation strategies. For example, the goal that has guided wetland policy during the past decade has been “no net loss” of wetland acreage and function. Whereas measuring wetland function is difficult, measuring wetland acreage is easy. That is, if there are x million acres of wetlands in the United States today and will be x million acres ten years from now, the goal of no net loss (at least with respect to acreage) will have been achieved. The goal of the ESA, however, cannot be achieved simply by freezing the status quo. Rather, one must reduce the likelihood of extinction–or, conversely, increase the probability of survival–to a safe level. When a species is no longer in danger of extinction in the foreseeable future and is not likely to become so, it is considered to have recovered. This, in turn, allows it to be removed from the endangered species list.
Recovery requires that the threats to a species’ survival be reduced. It does not necessarily mean an increase in the numbers or distribution of a species (though it usually does). Indeed, it may be possible for a species to decline in total numbers even as its likelihood of survival increases. This could happen, for example, if none of the habitat of a declining species were initially under the sort of ownership that ensured the active management needed to perpetuate it. If, through public acquisition or otherwise, one could be assured that some of its habitat would be appropriately managed, that fact might improve its prospects of survival enough for recovery.
For many endangered and threatened species, recovery objectives are often expressed as a number of populations of a given size occupying a secure habitat. To meet these objectives, it is not necessary for every occurrence of a species to be maintained where it now is. Instead, if occurrences of the appropriate size and distribution can be secured, the recovery goals can be achieved regardless of what happens to the smaller, more isolated populations.