Patterns of Historical and Contemporary Distribution and Occurrence of Imperiled Fish Populations in East Texas Streams

<p>East Texas supports a very diverse freshwater fish fauna, yet many of these species are listed as Species of Greatest Conservation Need (SGCN). In this study, I investigated historical and contemporary distribution trends of ten fish species listed as SGCN within the Neches, Sabine, and Cypress River basins in East Texas. Specifically, I examined regional and local environmental variables influencing their distributions and occurrences at both time periods. At the regional scale, I developed ecological niche models (Maxent) using occurrence data from 1940–1999 (historical) and 2000–present (contemporary, including surveys from 2023–2025) to evaluate changes in habitat and identify key regional environmental variables influencing species distributions across both time periods. At the regional scale, stream flow and stream order were key predictors for most focal species across both time periods, with higher probabilities of occurrence generally associated with higher order streams (i.e., 4–6) and high flows. Additionally, higher percentages of forest and pasture/crop land cover were associated with lower probabilities of occurrence for most of the focal species. At the local scale, I used local environmental variables (abiotic) and species co-occurrence (biotic) data collected during the current surveys 2023–2025 to examine local factors that could be influencing the presence of the focal species across these river basins. Among abiotic variables, stream depth, water temperature, stream order, and substrate diversity dominated by coarse materials (e.g., woody debris) and fine soils (e.g., mud/silt/clay) were important predictors for six of the focal species collected during this sampling period. Species co-occurrence models indicated that most focal species were positively associated (aggregated) with other species in the community that share similar habitat preferences. Although, the Blackspot Shiner revealed negative associations with other focal species, including the Sabine Shiner and Suckermouth Minnow. These species share similar habitat requirements, therefore, observed patterns may result from either interspecific interactions (not evaluated in this study) or variation in microhabitat use. Findings from this study indicate that both hydrological and land cover factors operating at the basin scale, and local habitat characteristics of each stream have contributed to the persistence of imperiled fishes in east Texas. In this study, I was able to collect eight of the ten proposed focal species, with the exceptions being the Silverband Shiner and Orangebelly Darter. Changes in suitable habitats for the species between time periods as suggested by predictive habitat suitability maps may have contributed to not collecting these species from surveyed sites. Both species had relatively few occurrence records in both the historical and contemporary datasets, however, they continue to persist in other drainages not included in this study, such as the Red River for the Orangebelly Darter and the Lavaca River and Red River drainages for the Silverband Shiner. Collectively, my research findings help to fill key information gaps and highlight areas within east Texas with high probabilities of occurrence for these species that can be prioritized for conservation and management efforts.</p>

Name thesis:degree_name

Master of Science - Biology

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Biology

Year dc:date.available

2025

Author dc:creator

• Moses, Maggie F

Contributors dc:contributor

• Dr. Carmen Montaña

Repository record dc:identifier

https://scholarworks.sfasu.edu/etds/664

OAI identifier oai:identifier

oai:scholarworks.sfasu.edu:etds-1716