Effects of Total Suspended Sediment (TSS) and Turbidity on fishes of the Rio Yaqui
USFWS, AZGFD, Cuenca los Ojos Foundation
September 2011 to December 2013
The effects of turbidity and total suspended sediment (TSS) on Rio Yaqui fishes are unknown, but have been studied on other fish species. Potential changes in TSS and turbidity are of special importance to the rare headwaters species of the Rio Yaqui assemblage in the USFWS San Bernardino National Wildlife Refuge (AZ) because of recent U.S. Department of Homeland Security activities and construction of new barriers along the U.S./Mexico border adjacent to fish habitat. Increased turbidity and TSS may change food supply, food acquisition by fish, and disrupt reproductive efforts. We are testing the effects of TSS and turbidity on Yaqui chub Gila purpurea, an endangered minnow restricted to the Rio Yaqui drainage of southern Arizona and northern Mexico. Yaqui chub consume small invertebrates and algae, thus increased sedimentation could negatively impact their diet. Additionally, Yaqui chub breed throughout the summer so increased sediment draining into the Rio Yaqui during summer storms could negatively impact their reproduction. Yaqui chub eggs, larvae, and adults will be exposed to different concentrations of suspended sediment in aquaria, based on levels of TSS and turbidity found in the Rio Yaqui during storm events. Each treatment will last for 11 days, the duration of the longest flood event in 2011. At the end of the treatment period, the hatch rates for egg and survival rates for larval and adult fish will be quantified. Additionally, the feeding rate for adult fish will be quantified. To assess change in food supply we will collect invertebrate samples before, during, and after the summer monsoon season and will analyze changes in abundance and diversity of invertebrates throughout monsoon season. To date, aquaria have been set up to begin Yaqui chub propagation. Automatic water samplers are in place in Rio Yaqui to collect first flush samples of storm water and samples are being analyzed for TSS concentration and turbidity.