How many off-channel habitats are needed to sustain genetic diversity in ‘big-river’ fishes?

Authors: Thomas Turner, Megan Osborne, Thomas Dowling

Year: 2019

Abstract

Fishes of the Colorado River Basin have suffered declines in abundance and genetic diversity attributable to large-scale river flow regulation that began in the early 1900s. Subsequent proliferation of non-native predators led to system-wide recruitment failures of Razorback Sucker, Xyrauchen texanus, and Bonytail, Gila elegans. A conservation plan to rear fishes in predator-free backwater habitats was proposed to facilitate recruitment. Genetic factors were considered, but uncertainties remained regarding sources of variance in reproductive success (VRS) that spoke to generality and efficacy of the backwater rearing strategy. In this study we used parent-offspring genotyping to evaluate VRS in Razorback Sucker and Bonytail. Individual VRS was higher in Razorback Sucker than Bonytail in a manner consistent with species-specific differences in life history, but neither species exhibited VRS in excess of Poisson expectation when parental contribution was greater than 50% in a given backwater. However, we observed ‘all or nothing’ recruitment events across backwaters that were presumably tied to local differences in water quality and predator regimes. Thus, as mean quality and stability of selected backwaters increases and variance in quality among backwaters decreases, fewer backwaters will be required to implement the conservation plan at proscribed levels of genetic diversity.