Hybridization, agency discretion, and implementation of the U.S. Endangered Species Act

Abstract

The U.S. Endangered Species Act (ESA) requires that the "best available scientific and commercial data" be used to protect imperiled species from extinction and preserve biodiversity. However, it does not provide specific guidance on how to apply this mandate. Scientific data can be uncertain and controversial, particularly regarding species delineation and hybridization issues. The U.S. Fish and Wildlife Service (FWS) had an evolving hybrid policy to guide protection decisions for individuals of hybrid origin. Currently, this policy is in limbo because it resulted in several controversial conservation decisions in the past. Biologists from FWS must interpret and apply the best available science to their recommendations and likely use considerable discretion in making recommendations for what species to list, how to define those species, and how to recover them. We used semistructured interviews to collect data on FWS biologists' use of discretion to make recommendations for listed species with hybridization issues. These biologists had a large amount of discretion to determine the best available science and how to interpret it but generally deferred to the scientific consensus on the taxonomic status of an organism. Respondents viewed hybridization primarily as a problem in the context of the ESA, although biologists who had experience with hybridization issues were more likely to describe it in more nuanced terms. Many interviewees expressed a desire to continue the current case-by-case approach for handling hybridization issues, but some wanted more guidance on procedures (i.e., a "flexible" hybrid policy). Field-level information can provide critical insight into which policies are working (or not working) and why. The FWS biologists' we interviewed had a high level of discretion, which greatly influenced ESA implementation, particularly in the context of hybridization.

Variable hybridization outcomes in trout are predicted by historical fish stocking and environmental context

“…Variation in outcomes of hybridization also poses a significant challenge for conservation of native species threatened by hybridization (Allendorf et al, , Todesco et al, , Grabenstein & Taylor, ). Historically, understanding threats to native species by hybridization has been complicated by the uncertain conservation value of hybridized populations (Allendorf et al, ; Allendorf et al, ), as well as ambiguity in the legal status of hybrids with ancestry from threatened or endangered species, especially in the U.S. under the Endangered Species Act (Knudsen et al, ; Lind‐Riehl, Mayer, Wellstead, & Gailing, ). While we do not advocate specific conservation actions based on this work at present, especially for individuals with 1%–10% ancestry from rainbow trout, our work suggests that a broader view of hybridization as a conservation challenge might be warranted.…”

Redefining the Role of Admixture and Genomics in Species Conservation

“…Answers to these difficult questions are going to be situation-dependent (Table S1; Lind-Riehl et al 2016). Where introgression from alien or domesticated species clearly threatens the fitness of native populations, conservation should act to limit hybridization (Table S1).…”

Concern over hybridization risks should not preclude conservation interventions

“…Fish and Wildlife Service biologists revealed that negative perceptions of hybridization dominate in the agency, although those with direct experience with hybridization tended to take a more nuanced view. Overall, the interviewed biologists expressed a desire for a more “flexible” policy, as long as it entailed procedural guidance on how to approach hybridization issues (Lind‐Riehl, Mayer, Wellstead, & Gailing, 2016).…”