Successful Collection and Captive Rearing of Wild-Spawned Larval Klamath Suckers

Shortnose Chasmistes brevirostris and Lost River Suckers Deltistes luxatus endemic to the Klamath River Basin on the California–Oregon border have experienced dramatic population declines in parallel with many other Catostomid species. Captive propagation has become a key element of many endangered fish recovery programs, although there is little evidence of their success in restoring or recovering fish populations. We initiated a novel rearing program for Klamath suckers in 2016 with the goal of developing a husbandry strategy that better balances the ecological, genetic, and demographic risks associated with captive propagation. We collected 4,306 wild-spawned Klamath sucker larvae from a major spawning tributary May–June 2016 and reared them at a geothermal facility established through a partnership with a local landowner and aquaculture expert. Mortality during collection was <1%. We reared larvae in glass aquaria for 17–78 d until they reached approximately 30 mm total length, upon which we moved them to round fiberglass tanks for 14–46 d or until reaching approximately 60 mm total length. Overall survival of larvae to ponding for final growout was 71%. Larval tank-rearing survival was 98% for 37 d until an isolated fish health incident affected three aquarium populations, reducing survival to transfer to 75%. Survival after transfer to round fiberglass tanks for 14–46 d was 94%. This study outlines the first successful collection and early life-history husbandry of wild-spawned endangered Klamath suckers that we are aware of.

What Environmental Conditions Reduce Predation Vulnerability for Juvenile Colorado River Native Fishes?

The incompatibility of native Colorado River fishes and nonnative warm-water sport fishes is well documented, with predation by nonnative species causing rapid declines and even extirpation of native species in most locations. In a few rare instances, native fishes can survive and recruit despite the presence of nonnative warm-water predators, indicating that specific environmental conditions may help reduce predation vulnerability. We experimented with turbidity, artificial blue water colorant (artificial turbidity pond treatment), woody debris, rocks, and aquatic vegetation in a laboratory setting to determine whether any of these types of cover could reduce predation vulnerability and confer survival advantages for juvenile Bonytail Gila elegans (mean = 70 mm total length), Roundtail Chub Gila robusta (mean = 35 mm total length), Humpback Chub Gila cypha (mean = 67 mm total length), and Razorback Sucker Xyrauchen texanus (mean = 74 mm total length). We exposed selected species of juvenile native fishes to predation by adult Largemouth Bass Micropterus salmoides, Smallmouth Bass Micropterus dolomieu, Green Sunfish Lepomis cyanellus, Flathead Catfish Pylodictis olivaris, and Black Bullhead Ameiurus melas in overnight trials. Razorback Suckers served as prey in trials conducted with Largemouth Bass and Black Bullhead. Bonytail served as prey in trials conducted with Largemouth Bass and Flathead Catfish. Roundtail Chub served as prey in trials conducted with Smallmouth Bass and Green Sunfish. We matched sizes of predator and prey so that the maximum body depth of the prey never exceeded 40% of the maximum anatomical gape of the predators. Turbidity of 500 nephlometric turbidity units reduced effectiveness of sight-feeding predators such as Largemouth Bass, Smallmouth Bass, and Green Sunfish by up to 50% but also increased predation vulnerability to non–sight-feeding predators (Flathead Catfish and Black Bullhead) by up to 55%. Turbidity was the only treatment that significantly altered predation mortality of native fish. These results may help explain recent patterns of wild juvenile native fish recruitment to adult life stages at the Colorado River inflow in to Lake Mead and at the inflow of the San Juan River into Lake Powell. Both areas possess abundant introduced predatory fishes but are also very turbid.

Considerations for the Propagation and Conservation of Endangered Lake Suckers of the Western United States

Decades of persistent natural and anthropogenic threats coupled with competing water needs have compromised numerous species of freshwater fishes, many of which are now artificially propagated in hatcheries. Low survival upon release is common, particularly in systems with substantial nonnative predator populations. Extensive sampling for Shortnose (Chasmistes brevirostris) and Lost River Suckers (Deltistes luxatus) in the Klamath River Basin on the California–Oregon border have failed to detect any new adult recruitment for at least two decades, prompting an investigation into artificial propagation as an extinction prevention measure. A comprehensive assessment of strategies and successes associated with propagation for conservation restocking has not been performed for any Catostomid. Here, we review available literature for all western lake sucker species to inform propagation and recovery efforts for Klamath suckers and summarize the relevance of these considerations to other endangered fishes.

Retention of Ancestral Genetic Variation Across Life-Stages of an Endangered, Long-Lived Iteroparous Fish

As with many endangered, long-lived iteroparous fishes, survival of razorback sucker depends on a management strategy that circumvents recruitment failure that results from predation by non-native fishes. In Lake Mohave, AZ-NV, management of razorback sucker centers on capture of larvae spawned in the lake, rearing them in off-channel habitats, and subsequent release ("repatriation") to the lake when adults are sufficiently large to resist predation. The effects of this strategy on genetic diversity, however, remained uncertain. After correction for differences in sample size among groups, metrics of mitochondrial DNA (mtDNA; number of haplotypes, N H , and haplotype diversity, H D ) and microsatellite (number of alleles, N A , and expected heterozygosity, H E ) diversity did not differ significantly between annual samples of repatriated adults and larval year-classes or among pooled samples of repatriated adults, larvae, and wild fish. These findings indicate that the current management program thus far maintained historical genetic variation of razorback sucker in the lake. Because effective population size, N e , is closely tied to the small census population size (N c = ~1500-3000) of razorback sucker in Lake Mohave, this population will remain at risk from genetic, as well as demographic risk of extinction unless N c is increased substantially.

Positive Phototaxis in Larval Bonytail

We conducted an experiment to determine phototaxis in bonytail Gila elegans, a Colorado River basin endemic fish. We tested groups of 50 protolarvae (6.1–8.9 mm total length) in darkness for 2 h or 4 h with illuminated (lighted) and nonilluminated (unlighted) traps suspended in aquaria in pairs (one lighted and one unlighted, two lighted, or two unlighted); we repeated each trial three times. Among all trials, lighted traps captured 60% (359 of 600) of available larvae, which was significantly more than the 0% (1 of 600) from unlighted traps. Results demonstrate positive phototaxis and suggest larval light-trapping could be used to detect the presence of larval bonytail or to monitor or collect individuals for management of this critically imperiled species.