Conservation Biogeography of Headwater Catfish (Ictalurus lupus) in the United States

Abstract

The aim of this study was to review the conservation status of Headwater catfish (Ictalurus lupus) in the United States with emphasis on Texas populations. This status assessment included evaluating the change in geographic distribution and measuring introgression and hybridization with Channel catfish (Ictalurus punctatus) to inform conservation prioritization in the United States with emphasis in Texas. I used machine learning methods (i.e., random forest and boosted regression tree) to construct species distribution models (SDMs) based on historical and contemporary presence-absence data using 23 environmental predictors based on remotely sensed stream network data. I measured introgression and hybridization with the widely introduced Channel catfish using external morphology and molecular markers. The sub-basin (8-digit hydrologic unit code) from which collections were made was the most important predictor of Headwater catfish occurrence across all models. Species distribution models illustrated temporal changes in Headwater catfish occurrence. Historically, Headwater catfish occurrence was higher among streams with higher slopes, closer distances from spring outflows, broader ranges of annual precipitation, and with higher portions of the network catchment classified as water. These shifts are likely related to both range contraction of the species and temporal variation in sampling locations. Morphological and molecular data revealed four non-introgressed and isolated locations where conservation of Headwater catfish are likely to be most successful. Species distribution models provide critical assessments of where a species might persist, but they require careful validation and cannot account for introgression. Pairing targeted sampling efforts with locations highlighted by SDMs can be used to promote systematic conservation planning for rare and threatened species.