Chemical Application Techniques Used to Eradicate Blue Tilapia from Thermal Warm Springs, Muddy River, Nevada

Blue Tilapia Oreochromis aureus invaded the Muddy River in the early 1990s and began to harm native fishes. Gut content analysis showed that Blue Tilapia ate fish, including endemic Moapa White River Springfish Crenichthys baileyi moapae and endangered Moapa Dace Moapa coriacea.  By 2008, only 459 Moapa Dace were observed throughout their entire range above a barrier that maintained a tilapia-free zone.  Chemical removal of Blue Tilapia began in the South Fork Muddy River in 2009, and again in 2011.  South Fork is a low gradient, low velocity flow supplied entirely by warm springs. Thermal water conditions and habitat complexity increased the risk that rotenone did not reach lethal concentrations in all locations.  Blue Tilapia also utilized small mammal burrows for refuge. Intensive vegetation removal, motorized application techniques, and four sequential rotenone treatments over two months in 2011 altered physical conditions increasing tilapia exposure. Timing treatments allowed Blue Tilapia eggs to hatch and expose larval tilapia to subsequent treatments.  Monthly snorkel surveys show that the South Fork of the Muddy River is currently free of Blue Tilapia since 2011.  Major efforts including additional fish barriers and rotenone treatments are currently underway to further remove this threat throughout the Muddy River.