Ecological Characterization of the Rio Grande Fish Assemblages in Big Bend and Lower Canyon Areas
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Proposed objectives of this study were to quantify the current fish assemblage, to assess historical changes in the fish assemblage, to determine spatial and seasonal trends in the fish assemblage, to assess patterns in spatial and temporal habitat associations of the fish assemblage, and to quantify reproduction and food habits for obligate riverine fishes within the Big Bend reach of the Rio Grande.
Section I of this report satisfies the proposed objectives of the study. Spatial and temporal trends in fish occurrence, abundance, and habitat associations are provided for fishes in the Big Bend reach of the Rio Grande. Reproduction and food habits are described for only one obligate riverine fish (Tamaulipas shiner Notropis braytoni), which is sufficiently abundant in the Big Bend reach to allow a thorough assessment. Notes on the diet and population structure are provided for another obligate river fish (blue sucker Cycleptus elongatus).
Section II provides additional information on the distribution and diets of larval fishes in the Big Bend reach of the Rio Grande. Maintenance of viable riverine fish populations usually depends on the amount and availability of nursery areas for fish larvae. In addition, success of the repatriation efforts of Rio Grande silvery minnows depends on adequate nursery habitats. This study quantifies occurrences and abundances of larval and juvenile fishes within known Rio Grande nursery habitats and documents food items consumed by the larval and juvenile fishes.
Section III describes the spatial and temporal distributions and habitat associations of macroinvertebrates in the Big Bend reach of the Rio Grande. Macroinvertebrate communities generally are more susceptible to certain anthropogenic modifications (water pollution) than fishes. Collectively, assessment of fish and macroinvertebrates provide a much broader perspective on how anthropogenic modifications (water pollution for macroinvertebrates; reduced instream flow for fishes) impact the biotic integrity of arid systems.
Appendix I contains a published article that was generated during this project. During early stages of field collections, an exotic tapeworm (Bothriocephalus acheilognathi; Cestoda: Pseudophyllidea) was observed in larval fishes. Morphological and genetic analyses confirmed the first record of the exotic tapeworm in the Rio Grande drainage. Occurrence of Bothriocephalus is problematic for fishes in the Rio Grande, especially those of conservation concern.