Long-Term Patterns of Fish Community Structure in Lake Mohave, Arizona-Nevada

Authors: Aaron Burgad, Brian Kesner, Paul Marsh

Year: 2018

Abstract

The Colorado River has undergone significant anthropogenic modifications, consequently native fish communities are severely imperiled. We examined temporal patterns in fish community structure over 37 years in Lake Mohave using bi-annual trammel net surveys (spring and autumn) that were initiated by W. L. Minckley in 1974. Specifically, we examined 1) historical changes in fish community structure to determine stability and persistence and 2) long-term abundance trends. Non-native fishes were established prior to surveys, precluding the ability to determine a “normal bounds” of historical fish community structure. The two remaining native fishes, Razorback Sucker, Xyrauchen texanus and Bonytail, Gila elegans, declined precipitously in abundance through time. However, a repatriation program initiated in 1991 prevented Razorback Sucker from extirpation, while reintroduction efforts for Bonytail have failed; wild populations of both species are gone. Total catch per unit effort (CPUE) averaged across seasons (range = 1.77 to 39.57) and species richness (x? = 8.08, SD = 1.38) showed a negative relationship with time. Long-term abundance trends indicated three non-native taxa (i.e., Gizzard Shad, Dorosoma cepedianum, Yellow Bullhead, Ameiurus natalis, and Smallmouth Bass, Micropterus dolomieu) increased, eight decreased, and six showed no relationship. Fish community composition shifted directionally through time in multivariate space, with the formation of four significant clusters indicating alternative states and low stability. The native fish community vanished shortly after the introduction of a suite of non-native taxa and Razorback Sucker persists in Lake Mohave only because of continued stocking. The contemporary population of Razorback Sucker is stable albeit less abundant than historically, thus continued adaptive management will be required to preserve the most genetically diverse population in the Colorado River system.