Rhinichthys nevadensis caldera

Rhinichthys nevadensis caldera was formerly described in 2023 (Moyle et al. (2023). Numerous have studies confirmed that this taxon is genetically distinct from other dace (Sada et al. 1993, 1995; Mussmann et al. 2020, Su et al. 2022, Moyle et al. 2023). It was previously called Rhinichthys osculus ssp. 12 in this database.

Exceedingly small remaining population with on-going threats.

The Long Valley speckled dace is a California endemic taxon limited in distribution to a single population occupying two small pools and about 0.30 meters of associated stream as part of Whitmore Hot Springs, Mono County, California (Moyle et al 2015). The historic range of this species was in the outlets of hot springs and associated marshes in the remains of the Long Valley volcanic caldera, just east of Mammoth Lakes, Mono County, as well as in Hot Creek (Moyle et al. 2023).

The California Natural Diversity Database hosts two occurrences of the Long Valley speckled dace; one identified as possibly extirpated and the other as presumed extant however these data were last updated in 2012. Based on descriptions in Moyle et al (2015) and Miller (2020), for purposes of this assessment, the Long Valley speckled dace is represented by a single occurrence.

The primary threat to wild Long Valley speckled dace populations is intensive recreational use associated with use of the hot springs for bathing and swimming (Miller 2020; Moyle et al. 2015). The remaining Whitmore Hot Springs location was converted to a swimming pool by Mono County and chlorinated substantially reducing habitat suitability. Outflows form the pool is the sloe remaining water source for the sole remaining population. In general, recreational uses introduce pollutants and often result in small impoundments used for swimming and fishing that reduce or eliminate down stream flows. Grazing is prevalent along the entire remaining stream segment occupied by Long Valley speckled dace (Moyle et al 2015). Grazing has resulted in increased nutrient loading through introduction of fecal material, degradation of stream banks and subsequent sediment deposition and structural changes to hydrology, and reduction or elimination of riparian vegetation and is identified as a serious threat to the remaining population. The Long Valley speckled dace is highly vulnerable to chance environmental or demographic events, to which small populations are particularly vulnerable. The combination of few remaining known populations, small range, and restricted habitat makes the subspecies highly susceptible to extinction or extirpation from a significant portion of its range due to random events such as drought, disease, or other events.