Integrating ecological and genetic insights to guide Gambusia nobilis translocations in Bitter Lake National Wildlife Refuge, New Mexico.

Authors: Casey Ernest, Brad Johnson, Peter Scott, Michi Tobler

Year: 2025

Abstract

Pecos gambusia, Gambusia nobilis, occurs in four localities along the Pecos River in New Mexico and Texas. At Bitter Lake National Wildlife Refuge, one of the two New Mexico localities, populations are restricted to isolated springs and spring-fed sinkholes. Habitat loss, together with geographic isolation, small population sizes, and the introduction of invasive Gambusia affinis, have contributed to the species’ designation as endangered since 1975. Translocation is a particularly compelling conservation strategy for G. nobilis in this system, given the replicative nature of its sinkhole habitats. Slowing population decline in current G. nobilis populations and establishing new populations in unoccupied sinkholes through translocations will be important for delisting this species all within their natural range. However, such management action requires investigation into the environmental and genetic predictors of successful colonization. To understand environmental conditions suitable for G. nobilis, we measured temperature, salinity, dissolved oxygen, and pH in each season across two years and assessed fish community compositions in all occupied and unoccupied habitats. Despite the small spatial scale at which these habitats occur, the environmental conditions as well as species representation and abundance are highly variable. We also collected tissue samples for population genomic analyses, quantifying patterns of genetic variation, population differentiation, and potential introgression with invasive G. affinis, which will allow us to identify potential source populations suitable for translocations. By integrating ecological and genetic data, this study will provide a foundation for evidence-based translocation planning that informs practical strategies for the recovery of G. nobilis within its natural range.