Rhinichthys nevadensis caldera, Moyle & Buckmaster & Su, 2023

Moyle, Peter B., Buckmaster, Nicholas & Su, Yingxin, 2023, Taxonomy of the Speckled Dace Species Complex (Cypriniformes: Leuciscidae, Rhinichthys) in California, USA, Zootaxa 5249 (5), pp. 501-539 : 523-524

Rhinichthys nevadensis caldera , new subspecies, Long Valley Speckled Dace

Table 3 , Fig. 4 .

Synonymy: Rhinichthys osculus subsp. Sada et al. 1995:356; Moyle 2002:161.

Otherwise see synonyms for Desert Speckled Dace, Rhinichthys nevadensis .

Holotype: WFB 5000 ( Fig. 4 ). Standard length 60 mm, fork length 70 mm; White Mountain Research Center , Northeast Pond 37.360618°N 118.329370°W. Inyo County, California, July 29, 2021. Nicolas Buckmaster , Rosa Cox , California Department of Fish and Wildlife

Paratypes: WFB 5001-5009 (n=9). Same as holotype.

Meristic s: holotype (paratypes)

Lateral line scales: 64 (59–80). Lateral line incomplete.

Scales above lateral line: 10 (9–12), scales difficult to discern.

Scales below lateral line: 9 (6–10), scales hard to discern

Dorsal-fin rays: 8(7–8), counts include single unbranched ray.

Anal-fin rays: 7 (6–7), counts include single unbranched ray.

Pectoral-fin rays 13 (11–12), counts include anterior and posterior single unbranched rays.

Pelvic 7 (6–8), counts include single unbranched ray.

Caudal-fin rays 19 (19).

Diagnosis. The Long Valley Speckled Dace is a cryptic taxon, very similar in its meristics to the Amargosa Speckled Dace ( Table 3 ). They are distinguished from other Speckled Dace by their being endemic to the Long Valley region and having a distinct evolutionary lineage, as revealed by genomics ( Su et al. 2022). Adults are small (rarely more than 75 mm SL) and recognizable as Speckled Dace by their thick caudal peduncle, sub-cylindrical body, small fins, small eyes (relative to head), and blunt, pointed snout. In life, they are a bronzy color with light speckling ( Fig. 6 ). Striping is largely absent. Maxillary barbels and a frenum are usually absent. They can be distinguished statistically from similar Amargosa Speckled Dace by slightly higher average numbers of pectoral and pelvic, higher lateral line scale count, lower lateral line pore scale count, and absence of maxillary barbels ( Sada et al. 1989, 1995). The following mean counts (standard error) are from Long Valley Speckled Dace collected in Whitmore Hot Springs and at an unnamed spring at Little Alkali Lake ( Sada 1989, Table 3 ): lateral line scales 61.7 (1.4); lateral line scales with pores 19.0 (5.0); dorsal-fin rays 8.0 (0.0); anal-fin rays 7.0 (0.0); pectoral-fin rays 13.0 (0.4); pelvic 7.4 (0.2).

Description. Long Valley Speckled Dace are small, active fish with the typical Speckled Dace morphology, as described for the species.

Genetics/Genomics. Sada et al. (1989, 1995), using isozymes and morphometrics, were the first to recognize Long Valley Speckled Dace as different from other dace populations in the region. Oakey et al. (2004), Mussmann et al (2020) and Su et al (2022) all found genetic differences that separated Long Valley Speckled Dace from Amargosa and Lahontan Speckled Dace.

Distribution. The historic range of this dace 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. It quite likely had its origins when Speckled Dace colonized the upper Owens Valley region from the Mono Lake Basin via Adobe Valley, during a late Pleistocene pluvial period. During this time, Mono Lake levels were high enough so that it periodically spilled into Adobe Valley, which drained into the Owens River, from which fish presumably moved upstream into Long Valley. Subsequent down-faulting of the Owens River and formation of steep waterfalls in the Owens River gorge likely isolated Long Valley from the Owens Valley around 100,000 years ago ( Hildreth and Fierstein 2016).

Note. Long Valley Speckled Dace were considered to be one of the scattered populations of Owens Valley Speckled Dace until Sada et al. (1993, 1995) showed it was genetically and morphometrically distinct and that it was closely related to dace populations in Ash Meadows, Amargosa River, and elsewhere in Owens Valley and Death Valley. Moyle (2002) and Moyle et al. (2015) recognized it as an undescribed subspecies. Our analysis shows that the Long Valley Speckled Dace is a distinct lineage confined to a small part of the Owens Valley region. It merits subspecies designation based on the following lines of evidence.

Taxonomy. Multiple analyses indicate that Long Valley dace is a distinct lineage (subspecies) within Desert Speckled Dace, R. nevadensis ( Oakey et al 2004, Mussmann et al. 2020, Sada et al. 1995, Moyle 2002, Moyle et al. 2015 and Su et al., 2022).

Geography/geology. During pluvial periods of the Pleistocene, the Death Valley region was a series of interconnected large lakes, with abundant fishes (Hubbs and Miller 1948). When the climate changed and heavy precipitation stopped falling, the lakes and rivers dried up or became small remnants of what they once were. This process resulted in numerous isolated Speckled Dace populations with little, or at least very infrequent, opportunity for genetic exchange. See Desert Speckled Dace account for more details.

Long Valley is part of the Death Valley regional endemism hotspot with numerous endemic plants and animals, including fishes ( Sada et al. 1995). Long Valley Speckled Dace can be regarded as another organism endemic to the isolated Owens Valley region.

Genetics/genomics. Sada et al. (1993, 1995) were first to recognize that Long Valley Speckled Dace were genetically distinct from other dace, a finding confirmed by other studies ( Mussmann et al. 2020, Su et al. 2022). See Amargosa Speckled Dace ( R. nevadensis nevadensis ) description for more details.

Etymology. The Long Valley Speckled Dace was historically known only from small streams flowing into the Long Valley Caldera, the remnants of a gigantic volcano that last erupted 0.7 million years ago ( Hildreth and Fierstein 2016). They colonized the remnants of the caldera during the late Pleistocene, hence caldera.

Conservation Status. Long Valley Speckled Dace have been extirpated from all but one of their historic collection sites, including Hot Creek. The only population left in its native range (as of 2021) is in Whitmore Marsh and its inlet stream in Long Valley ( Moyle et al. 2015). Unfortunately, this marsh is now maintained by the outflows of a hot spring system that has been developed as a public swimming pool by the Town of Mammoth Lakes. Discharge is approximately 2 cfs and is lightly chlorinated. The outlet stream feeds an alkaline marsh of roughly 1 acre. In 1989, dace occupied 250 meters of stream and two large shallow ponds less than a half meter deep ( Moyle et al 2015). Surveys in 2002 and 2009 by CDFW found this population to be relatively stable (S. Parmenter, CDFW, pers. comm. 2009). In 2018, 2019, and 2020, they were not found in these habitats (S. Parmenter, CDFW, in Center for Biological Diversity, 2020). However, in 2021 and 2022, trapping produced a few fish (R. Black, CDFW, pers. comm, 2021). The only other population is in a single artificial pond into which they were introduced at the White Mountain Research Center, outside their native range; the status of this dace population is checked by CDFW on a routine basis (R. Black, CDFW, pers. comm.).

The multiple causes of decline are discussed in Moyle et al. (2015) and Center for Biological Diversity (2020). The CBD (2020) has petitioned to have this dace listed as endangered under the federal ESA or else have all Speckled Dace in the Death Valley region included under the 1984 listing of Ash Meadows Speckled Dace as endangered. It is listed as a Species of Special Concern (critical concern) by CDFW.

Figures

FIGURE 4. Holotypes of new taxa of Rhinichthys described in this paper, A. Santa Ana Speckled Dace (R. gabrieleno WFB 3498. B. Long Valley Speckled Dace (R. nevadensis caldera) WFB 5000, C. Warner Speckled Dace (R. klamathensis goyatoka) WFB 122-10-44, D. Sacramento Speckled Dace (R. klamathensis achomawi) WFB 3171.

FIGURE 6. Top. Holotype, Lahontan Speckled Dace, from Rutter (1903). Middle, Long Valley Speckled Dace from Whitmore Marsh, 2014, showing life colors. Photo by Jacob Katz. Bottom: Western Speckled Dace, type specimen, from Evermann and Meek (1898).