Date of Award
Master of Science (MS)
Dr. Robert J. Edward
Dr. Robert I. Lonard
Dr. Frank W. Judd
This study investigated the small aquatic ecosystems of Santa Ana National Wildlife Refuge, located in a predominantly agricultural area of the Lower Rio Grande Valley, Texas. Fishes and water quality data were collected for 13 months to determine the status of fish populations and the factors which influence their distributions on the refuge.
Sixteen fish species were collected during the study, however, more than 20 species are known to inhabit the Rio Grande in the vicinity of the refuge. Water source played a major role in influencing fish species richness in these aquatic ecosystems. Diverted river water offered the best source of fish species immigrants.
Gambusia affinis, Cyprinodon variegatus, Menidia beryllina and Poecilia latipinna maintained relatively high abundances throughout the study. Gambusia affinis was the most abundant species collected from the refuge while C. variegatus contributed the greatest biomass. Fish abundance patterns were closely related to changes in water temperature.
Organochlorine pesticide and trace element analysis were performed on samples of Dorosoma cepedianum collected from the refuge. Organochlorine residues including DDD and DDE were lower than values previously reported from the Rio Grande and surrounding areas. Trace element residues including selenium, arsenic and lead exceeded the National Academy of Sciences criteria for the safety of fish. Furthermore, mercury residues exceeded the Environmental Protection Agency criteria for the protection of aquatic life. The occurrence of these residues in fish samples from the refuge could not be linked to any one contaminant source.
Pan American University