Cooperative Fish and Wildlife Research Units Program: Texas
Education, Research and Technical Assistance for Managing Our Natural Resources

Blue Sucker Cycleptus elongatus is a state-listed threatened species in Texas and is considered vulnerable throughout its range. Once considered a single, wide-ranging species, blue suckers are now recognized as a complex of closely related, but genetically and morphologically distinct species within the genus Cycleptus, including an undescribed species within the Rio Grande Basin. Blue suckers are long-lived (≥22 years) and late-maturing (5-6 years) though it is not yet clear if there is geographical variation in these traits. These fishes are associated with big river ecosystems and are highly potadromous, potentially making spawning migrations of 500 km or more. Blue suckers, like most imperiled catostomids, face threats at multiple life history stages. Spawning seems to be restricted to riffle complexes with large cobble substrat5, but it is unclear if habitat quality or availability is a limiting factor to populations in Texas. The early life history of blue suckers also is poorly understood, but has been hypothesized as being vulnerable to flow alteration. It is unclear what the specific factors are that are driving the decline of Blue Suckers in Texas (e.g., flow alteration, water quality, habitat fragmentation, and changing land use) and how they interact to influence abundance and distribution.

The Rio Grande Blue Sucker population is identified as a species of greatest conservation need in the Texas Conservation Action Plan (TCAP). Water quality deterioration and habitat degradation and fragmentation associated with reservoir construction and the resulting alterations to flow regime are probably responsible for declines of Blue Sucker in the Rio Grande basin, but similar to other populations in Texas, little is known of the population size, age structure, spawning habits, and habitat use of Rio Grande Blue Sucker. It is likely still locally abundant within the Big Bend region of Texas and Mexico despite comprising < 1.0% of the fish assemblage in recent surveys. However young-of-year Blue Sucker seem to be relatively common in the Big Bend region compared to other river systems in Texas, indicating that the population may not be experiencing the same factors suspected of limiting recruitment elsewhere despite reductions in the magnitude of flow fluctuations and geomorphological changes to the river system, e.g., channel narrowing and floodplain accretion.

In contrast to the Rio Grande, Blue Sucker in the lower Sabine River seems to be less abundant. Recent surveys indicated that Blue Sucker comprised approximately 0.2% of the fish assemblage in the lower Sabine River, though adult individuals were encountered in all expected habitats and may have been locally abundant. The Sabine River Blue Sucker population has experienced many of the same anthropogenic habitat alterations as other populations in Texas. However, the lower Sabine River is unique in being one of the few rivers in Texas impacted by hydropower generation. In particular, the lower Sabine River experiences rapid, daily fluctuations in flow, i.e., hydropeaking,) that have the potential to negatively impact Blue Sucker growth and recruitment. While juvenile Blue Suckers occasionally have been encountered captured from the lower Sabine in recent surveys, there are indications that both larger and smaller individuals are less common in the lower Sabine River than in the lower Colorado River. Furthermore based on preliminary data, individuals in the lower Sabine River may be smaller than those of the same age from the lower Colorado River. While recent surveys suggest that Blue Suckers are consistently undertaking spawning migrations and accessing spawning habitats in the lower Sabine River, there has not been a successful attempt to characterize recruitment in this population.

This study will provide data on current demographic characteristics, habitat use patterns, and recruitment dynamics of the Rio Grande Blue Sucker, an endemic species which has declined across much of its range, and Blue Sucker in the lower Sabine River.