A fair scale for mitigation

Compensatory mitigation projects that fully offset development-incurred losses are, unfortunately, far and few.  When it comes to biodiversity, species decline continue.  ‘Restoration at multiple trophic levels’ (2003), by Deborah French McCay and Jill J. Rowe, laid out a novel approach to compensatory mitigation, based on the North Cape oil spill, presenting a new framework for estimating the appropriate scale of restoration: primary production, across multiple trophic levels.

Aerial view of the January 19, 1996 North Cape oil spill, with the tug boat Scandia in the upper portion of the photo, and the tank barge North Cape in the lower portion. An estimated 828,000 gallons were spilled, resulting in hundreds oiled birds and large numbers of lobsters, surf clams and sea stars found dead on the beach. The North Cape oil spill is considered to be an important legal precedent since it was the first major oil spill to occur after the 1990 Oil Pollution Act, passed in the wake of the devastating Exxon Valdez spill in Alaska. Photography by E.R. Gundlach.

Having concluded that species impacted by the North Cape spill would benefit especially from habitat restoration, McCay and Rowe’s model “builds upon food chain energetic and habitat equivalency analysis, […] convert[ing] losses of production of multiple species to an energetically equivalent single trophic level so that the scale of necessary compensatory restoration can be computed.”  So, food webs and trophic energy efficiencies can be used to pinpoint the level at which restoration appropriately compensates for the total spill-related injury; trophic level dynamics would then ensure that the system would return to a normal balance.  Additionally, McCay and Rowe correct for the delay between injury and restoration by considering the biomass directly lost plus that not produced at a 3% annual discount rate, as recommended by NOAA.  Thus, they came to the conclusion that restoration of around 20 acres of highly productive eelgrass beds, combined with ongoing recovery activities, would sufficiently compensate for spill injuries with no net loss.

McCay and Rowe are the first to admit that their model presents shortcomings linked to the uncertainty that lies in estimate-driven modeling, and the use of primary production as a proxy for multiple ecosystem processes.  Nonetheless, they argue that “[u]sing production as the scaling metric also allows for differences in body size and growth rate between the individuals killed and the ones added by restoration while still achieving equivalence and thus compensatory replacement.”  While conceding their model has room for improvement, they assert that they have opened up new paths for research – a different ecosystem function may be a more suitable vector for evaluating restoration benefits, and needs only to be discovered.

Example of trophic pyramid, from National Park Service. In McCay and Rowe's model, development incurred-loss of consumers (herbivores and carnivores) can be appropriately offset through primary production.

While this approach, as interpreted for an oil spill, lacks the advantage of species specificity, it presents an exciting venue for compensatory mitigation and endangered species incidental take permits (ITPs).  Rooted in sound understanding of species and habitat interactions, mitigation could compensate for take of listed species to a standard that sustains ecosystem processes and adequately offsets the loss caused, without being arbitrary or punitive to the developer.  The current incidental take calculation process is far from perfect, and the adoption of objective and appropriate mitigation scaling could bring ITPs one step closer to their intended purpose: to strike a balance between development interests and species recovery efforts.

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Katherine Eshel is the Endangered Species Policy Intern for Defenders of Wildlife. Katherine works on research and writing projects for various endangered species policy issues, including current regulatory reform.

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