Use of Cover for Concealment Behavior by Rainbow Trout: Influences of Cover Structure and Area

Abstract

Concealment behavior by stream salmonids can benefit individuals and populations, but the availability of concealment habitat may be limited in many streams. Quantification of concealment habitat is likely to be a valuable process in the management of stream salmonids; it is a necessary step in the application of spatially explicit, individual-based models that incorporate concealment behavior. We conducted a series of laboratory experiments with Rainbow Trout Oncorhynchus mykiss to aid in the identification and quantification of concealment habitat. Overall, individual Rainbow Trout about 12 cm FL readily used low-ceiling spaces with one, two, or four openings for concealment. Structures analogous to weakly undercut banks were used less. Mean use of different cover types was less variable in an experiment in which groups of three fish were tested. Individuals in groups rarely shared cover spaces, even though in another experiment individual fish readily occupied spaces less than 25% of the area of the spaces they rarely shared. One cover structure that was not preferred in a simple choice experiment was used as much as the preferred structure when the former was the only cover available, indicating that habitat preference experiments provide limited information when the issue is whether fish are willing to use specific habitats.

Received February 16, 2016; accepted June 18, 2016 Published online October 14, 2016

ACKNOWLEDGMENTS

Rod Nakamoto assisted with fish collection, PIT tag antennas, and the maintenance of fish in the laboratory. Kate Harvey assisted with analysis of photographs. Kathleen Matthews reviewed a previous version of the paper.