Since its construction in 1966, the Glen Canyon Dam has altered habitat conditions in the Colorado River, affecting the survival of endangered native fish. The river is now characterized by reduced temperature and flow variation and the introduction of nonnative fish species, both of which could contribute to higher risks of infection and injury for native populations. This study's goal was to examine the health of humpback chub (HBC, Gila cypha) and flannelmouth sucker (FMS, Catostomus latipinnis), to examine differences in overall physical condition and visible injury patterns between the two species.
In the field, data was collected via capture of fish at sites along 280 river miles of the Colorado River in the Grand Canyon. FMS were the most commonly caught fish, with 116 fish captured, while 56 HBC were captured. FMS were caught at nearly all sites along the river, while 56 HBC were primarily caught at miles 61.5 and above 220. Fish had weight and length recorded and were visually scanned for gross pathology on the skin, eyes, caudal, dorsal, and pectoral fins, and the operculum. Using the collected data, we analyzed condition factors and injury frequencies across the two target species.
Length–weight regressions indicated strong positive relationships between length and weight for both species (R² = 0.980 for FMS, R² = 0.971 for HBC), providing a basis for assessing spatial condition trends and identifying individuals with outlier condition factors. While most individuals of both species exhibited no visible injuries, almost all observed injuries were classified as mild. HBC showed higher injury frequencies in the caudal fins and eyes and included occasional moderate to severe injuries, whereas FMS more often had mild injuries on the operculum. Additional analyses expand upon this work by comparing injury severity across river-mile locations, and assessing relationships between injury presence, injury severity, and injury type with condition factor to evaluate how physical condition relates to injury patterns within and between species. Establishing these species-specific baselines will enable the assessment of future environmental changes and their impacts.