What environmental factors reduce predation vulnerability for native fishes?

Authors: Ben Vaage, David L. Ward, Rylan Morton-Starner

Year: 2014 (xlvi)

Abstract

The incompatibility of native Colorado River fishes and nonnative warm water 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 are able to survive and recruit despite the presence of nonnative warm water fishes, indicating that specific environmental conditions may help reduce predation vulnerability. We experimented with turbidity, artificial water colorants, woody debris, aquatic vegetation, and rock substrates in a laboratory setting to determine if any of these types of cover could reduce predation vulnerability and confer survival advantages for juvenile bonytail, Gila elegans, (mean = 70 mm TL), roundtail chub, Gila robusta, (mean = 35 mm TL) and juvenile razorback sucker, Xyrauchen texanus (mean = 74 mm TL). Bonytail and razorback suckers were exposed to predation by adult largemouth bass, Micropterus salmoides, green sunfish, Lepomis cyanellus, and flathead catfish, Pylodictis olivaris, in overnight trials. Turbidity above 500 nephlometric turbidity units (NTU) reduced predation vulnerability by up to 50%, for the sight-feeding predators, but increased predation vulnerability to flathead catfish. No other treatment significantly reduced predation mortality. These results may help to explain patterns of wild juvenile razorback sucker recruitment at the turbid inflow of the Colorado River into Lake Mead, an area where flathead catfish are not currently present but other nonnative fishes are.

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