The lower Trinity River and Trinity Bay in Texas represent the southern limit of the native range of striped bass (Morone saxatilis). Life-history traits of fishes in the northern hemisphere often vary with latitude, with southern populations exhibiting faster growth, earlier age at maturity, reduced longevity, and higher mortality than northern populations. At this southern limit, water temperatures in the Trinity River often exceed reported tolerances for striped bass. We evaluated the likelihood that this fringe striped bass population can persist by examining their life history characteristics, their movements, and the occurrence of thermal refuges in the lower Trinity River. Spawning adult striped bass were collected from 2006 to 2011 to describe life-history characteristics, and ultrasonic telemetry was used from 2008 to 2010 to evaluate movements, and identify thermal refuges. Striped bass in the Trinity River matured earlier, had higher mortality rates, and shorter longevity than striped bass populations near the center of the species range. High mortality and short lifespan limited female adult striped bass to only two or three spawning opportunities. While striped bass used the entire reach of river from Lake Livingston Dam to Trinity Bay, over half of the individuals known to survive through at least one summer spent the summer months near a known thermal refuge near Lake Livingston Dam. No other thermal refuges were discovered. Additional degradation of thermal conditions in the Trinity River would jeopardize persistence of striped bass in this system because it would likely further truncate age structure and reduce spawning opportunities.
