Of all the sensitive species at Warm Springs Natural Area, the Moapa dace is the most imperiled. This warm water fish only occurs in the warm springs, tributaries and upper main stem of the Muddy River – and nowhere else on earth. The current population of Moapa dace counted by snorkel surveys is 1,533 in August 2017.
Listed as an endangered species in 1967 under the federal Endangered Species Preservation Act, the preservation and population recovery of the Moapa dace has received the highest priority in the management of Warm Springs.
The recovery of the Moapa dace population is dependent upon restoring stream habitat quality and the removal of non-native, invasive and predatory fish, parasites and vegetation.
Recovery efforts at Warm Springs have resulted in fish that appear healthy and are reproducing. The population has grown from 459 in 2008 to more than 1,500 as of August 2017. The goal is an adult population of 6,000 adult Moapa dace.
The Moapa dace can be identified by the large black spot near the base of its tail fin.
The Moapa dace population is tracked by snorkelers who count the fish one by one.
Moapa dace have an average life span of at least four years, but can live up to eight years in the main stem of the Muddy River. During their early stages of life, Moapa dace require the warmth of the spring water. As adults, they can tolerate slightly cooler water. However, they return to the spring outflows to reproduce. Reproduction takes place year round, but peak reproduction occurs in the spring when the food sources, such as insects and algae, are most readily available.
Habitat preference varies with each life stage. As the Moapa dace grows and can tolerate cooler temperatures it will venture away from the spring-water source. Moapa dace live in three habitat types: thermal springs, thermal tributaries, and the mainstem river.
Young Moapa dace start out feeding on algae. As the fish grow older, they eat invertebrates in addition to algae.
Birds, including the Great Blue Heron, are the natural predator of the Moapa dace. However, the introduction of non-native fish, including tilapia, into the Muddy River system has created unnatural predators that have threatened the Moapa dace population. Fish barriers have been installed to help prevent these predatory fish from reaching the Moapa dace within the spring tributaries.