Population Estimates and Water Quality Summary for Native Fish Backwater Habitats (2009-2010)

Authors: Robert Randall, Mitch Thorson

Year: 2010 (xlii)

Abstract

Off-channel, protected habitats are an important management tool for the recovery and conservation of threatened and endangered fishes. Habitats managed by the U.S. Fish and Wildlife Service’s Arizona Fish and Wildlife Conservation Office (AZFWCO) follow the strategies outlined by the Lower Colorado River Management Plan (LCRMP). These strategies include 1.) use of hatcheries to produce larger fish for reintroduction, 2.) use of natural or constructed habitats to develop self-sustaining populations and to produce larger fish for release into the mainstem, and 3.) use of exploited habitat made available by reservoir drawdown or drying to establish populations of large adults. We provide a brief summary of the stocking history, population estimates for razorback sucker, Xyrauchen texanus, and bonytail, Gila elegans, as well as water quality monitoring for selected backwaters from 2009-2010. Since 2005, over 9,000 razorback sucker and bonytail, have been stocked in seven backwater habitats along the lower Colorado River. These habitats have the ability to produce large (>400mm) fish in less than one year with an average growth rate of 10mm per month. Maintaining acceptable water quality throughout the summer months continues to be a challenge, as dissolved oxygen levels (mg/L) in some habitats can decrease below 2mg/L. Information gained from this study will be used to modify management actions and rearing techniques to grow fish of larger size before release into the lower Colorado River. In addition to evaluating survival of the fish once they are in the mainstem, we recommend that success or failure will be measured on the numbers and sizes of fish harvested rather than just initial stocking numbers.