Population Assessment and Microhabitat Associations of Repatriated Guadalupe Bass in an Urbanized Texas Stream
The Guadalupe Bass, Micropterus treculii, is a Species of Greatest Conservation Need found only in streams draining the Edwards Plateau in Central Texas. In 2015-16, the Texas Parks and Wildlife Department introduced M. treculii to the Mission Reach, a 16.9 km segment of the upper San Antonio River that had been restored from homogenous artificial channel to pool-riffle habitat complexes in 2013 by the San Antonio River Authority. Informal surveys suggested a self-recruiting population; however, no formal assessments were conducted after the introduction and prior to this study. My objectives were to (1) characterize population densities of M. treculii and largemouth bass, Micropterus salmoides, and (2) quantify seasonal variation in microhabitat use in the restored reach. Eight uniformly distributed sites were selected for this study, five of which were wadeable pool-riffle units and three of which were non-wadeable pools. A capture-mark-recapture study was used to estimate population densities of both species in March of 2022. During the capture-mark-recapture study, a total 278 M. treculii and 365 M. salmoides were captured via boat and backpack electrofishing. Population densities based on the Schnabel Method were 39 fish/ha for M. treculii and 33 fish/ha for M. salmoides. To quantify microhabitat associations, fish were also sampled in July and October of 2021 and in January and April of 2022, and microhabitat variables of depth, velocity, substrate, and habitat cover were recorded at each location a fish was sampled. During the four microhabitat association sampling events, a total of 527 M. treculii and 732 M. salmoides were captured. Smaller M. treculii were associated with shallow water of higher velocities and with larger substrate than M. salmoides. Larger M. treculii and M. salmoides occurred in deeper pools, representative of the ontogenetic habitat shift from riffle to pool habitats for M. treculii. Segregation of M. treculii and M. salmoides along a lotic-lentic gradient in the restored stream matches patterns observed in non-urbanized watersheds. These findings demonstrate a successful repatriation of a M. treculii population that is self-recruiting and utilizing the engineered riffle habitats in this restored urban stream.