Deltistes luxatus

This species previously was included in the genera Chasmistes and Catostomus. Chasmistes and Deltistes are closely related to the older, more diverse, widespread genus Catostomus; Deltistes has unique triangular gill rakers and a ventral mouth with papillose lips and a terminal mouth (Scoppettone and Vinyard 1991).

Deltistes luxatus has hybridized with Chasmistes brevirostris and Catostomus snyderi (Lee et al. 1980).

Harris and Mayden (2001) used molecular data to examine phylogenetic relationships of major clades of Catostomidae. In all trees, Scartomyzon was paraphyletic and embedded in Moxostoma, and Catostomus was never recovered as monophyletic (Xyrauchen was embedded within Catostomus). They concluded that the phylogenetic relationships and taxonomic composition of taxa presently included in Moxostoma and Scartomyzon are in need of further study, as are the relationships and composition of the genera Catostomus, Chasmistes, Deltistes, and Xyrauchen, and the phylogenetic affinites of Erimyzon and Minytrema.

See also Smith (1992) for a study of the phylogeny and biogeography of the Catostomidae.

This species population size and area of occupancy have been substantially reduced when compared to historical levels. The legacy effects of habitat modification and continued poor water quality combined with the effects of climate change (e.g., more pronounced droughts) continue to depress populations. Recent conservation measures have improved habitat conditions, but further improvements are needed.

Endemic to the lakes of the upper Klamath Basin in southern Oregon and northern California, USA. Now limited to spawning populations in Upper Klamath and Clear Lakes, lake margin seeps, and spawning in most major tributaries to these lakes (USFWS 2019b). Based on expert opinion models for California (Santos 2015) and information in USFWS (2019) for Oregon, and using the methods described in Masters et al (2012) for fish species and other taxa using rivers and streams (HUC 12 watersheds), the range of this species is about 6500 km2.

This species is represented by two populations that are sustaining themselves without the input of larvae or older suckers from other areas (USFWS 2007). However, USFWS (2019) recognizes three distinct populations and points to genetic analysis by Dowling et al (2016) as a basis for defining conservation of populations.

Historical threats include: sucker mortality and habitat changes that resulted from the draining of the Tule Lake and Lower Klamath "basins" in the 1920s; adverse water quality, deriving in part from excessive nutrient inputs from agricultural sources, and causing algal blooms that in turn have resulted in massive sucker mortality; low water levels in Upper Klamath Lake caused by water removal for irrigation, hydroelectric generation, wildlife refuges, and instream flows for downstream fish populations (Kann and Walker 1999); diking and draining of wetlands bordering lakes (wetlands served as fish nursery habitat and probably buffered lakes from agricultural pollutants); and loss of spawning habitat due to damming of rivers (e.g., Chiloquin Dam constructed in 1928 on the Sprague River, Oregon, cut off access to 95% of historical spawning habitat for the Upper Klamath Lake population and precluded accumulation of suitable spawning gravels below the dam) (USFWS 1988, 1993, 2007; Scoppettone and Vinyard 1991; Perkins et al. 2000; Moyle 2002). Exotic fishes such as fathead minnow are abundant in some areas, but their effects on Lost River suckers are poorly known. The sport fishery in the 1960s and 1970s may have contributed to the decline (fishing for this species is now prohibited).

USFWS (2007) assessed threats as follows (abbreviated):

The rate of habitat change has slowed markedly, but only a small fraction of the original habitat remains, and much of the remaining habitat is in a degraded condition. Restoration efforts are beginning to reverse the trend, but will probably require many years to produce a substantially increased and stable habitat base for the Lost River sucker.

Adverse water quality is the most critical threat, and substantial improvement is not expected in the near future. Within the foreseeable future, there is a high probability of multiple mortality events that would greatly reduce population sizes. It is possible that infrequent recruitment would be unable to offset declines from such die-offs. However, though previous mortality events in Upper Klamath Lake resulted in substantial population losses, the sucker population was not extirpated and now again shows evidence of improvement. Thus, recruitment, although low, has enabled the Upper Klamath Lake population to survive, despite the impact of multiple mortality events.

Drought is a threat because of its potential to cut off spawning habitat, reduce rearing habitat, and increase disease, parasitism, and predation. Historically the species has persisted through periods of prolonged drought, but recent extended droughts are unprecedented.

Fish entrainment in water diversions and restricted passages are threats. Entrainment at Link River Dam and associated hydropower diversions likely poses a risk to the sucker. The threat there could be reduced if the hydropower diversions were screened or eliminated, and if discharges at the dam could be modified to reduce entrainment. Passage to spawning habitat in the Sprague River is still impeded by Chiloquin Dam, but that structure is planned for removal in the near future. Elsewhere in the upper basin, some entrainment of suckers is occurring, but mostly larvae are entrained, and USFWS does do not consider this a substantial threat at the population level.

Overutilization for commercial, recreational, scientific, or educational purposes is not regarded as a threat.

Disease, parasites, and predation/competition by exotic fishes pose some risk, although the degree to which they affect the species is not quantified. Disease and parasites alone may not pose a significant risk, but paired with the impacts of adverse water quality, they can substantially affect sucker survival.

Application of existing Endangered Species Act authorities, especially section 7, is probably maintaining existing sucker habitats and leading to reductions in mortality and improvements in habitat. However, given the continued vulnerability of the species to existing seasonal habitat conditions, these regulations have not been sufficient to substantially reduce the primary threat to the species.

Hybridization occurs among sucker species in the Klamath Basin, but it is not regarded as a significant threat.