Colorado River Otter- EP

CRE AT-RISK SPECIES VIGNETTES – Larry Stevens

• Sonoran River Otter
• The Sonoran river otter [Lontra canadensis sonora (Rhoads, 1898)] was a large, dark subspecies that was endemic to the Colorado River basin in pre-dam time.
• It likely ranged widely and fed opportunistically on fish, terrestrial animals, and invertebrates.
• Known only from a few specimens, the otter appears to have been relatively rare in Grand Canyon prior to Glen Canyon Dam.
• A photograph of Nathaniel Galloway holding two trapped individuals in Utah is the only known photograph taken of Sonoran river otter.
• Documented in Grand Canyon in 1957, the last reliable otter sighting was reported by Terry Brian at the mouth of Awatubi Canyon (Mile 58R) in 1984.
• Natural rarity and susceptibility to in-breeding depression made the Sonoran river otter particularly sensitive to range restriction by dam construction, and it is now likely extinct.
• The Four Corners states have all released other river otter subspecies into their reaches of the Colorado River surrounding Grand Canyon, further guaranteeing the irrecoverability of the Sonoran river otter genotype. *Proposals to reintroduce otters into Grand Canyon emphasize the need to restore the ecological function of a top mammalian picsivore; however, many are concerned that introduced otter might feed on endangered humpback chub. *Therefore, otter reintroduction plans appear to have been shelved until the native fish assemblage in Grand Canyon has been recovered.