A comparison of habitat suitability criteria for Apache trout and the non-native virile crayfish

Authors: Sally Petre, Scott A. Bonar

Year: 2012 (xliv)

Abstract

Over the past century, fishes endemic to the southwestern United States have declined in abundance and range, resulting in the listing of the majority of these species (70%) under the U.S. Endangered Species Act (ESA). Apache trout, Oncorhynchus giliae apache, a salmonid endemic to the White Mountains of east-central Arizona, is listed as threatened under the ESA. Major reasons for the decline and listed status of Apache trout include overfishing, drought, habitat degradation and negative species interactions. A recently introduced invasive species thought to affect Apache trout recovery is Orconectes virilis, or virile crayfish. To date, no mechanical or chemical removal methods have been found to be effective or efficient for suppressing crayfish populations. However, altering certain habitat parameters to disfavor crayfish, while maintaining Apache trout habitat parameters, may be effective. Therefore we developed habitat suitability criteria for Apache trout and virile crayfish to assess overlap in criteria and to identify if habitat could be manipulated to favor Apache trout but suppress virile crayfish. We sampled the West Fork of the Black River by snorkel survey to identify where Apache trout were located (occupied vs. unoccupied) and measured environmental parameters (water velocity, depth, substrate, instream cover, overhead cover and temperature) at occupied and unoccupied locations. We used a 1m² quadrat sampler to sample for crayfish at random locations throughout the same stream. We performed a habitat suitability analysis to develop habitat suitability criteria for both species. Apache trout and virile crayfish occupy similar depths; however, virile crayfish occupy areas with significantly lower mean water column velocity than Apache trout (p=0.03). Overall, virile crayfish are found in slower, warmer water compared to Apache trout and in areas where they can hide under cobbles or instream cover. We hope to use this assessment of habitat suitability criteria as a tool to better understand virile crayfish and Apache trout interactions as well as manage Apache trout recovery streams.