Should One Age a Warmwater Fish in a Coldwater System?

Authors: Pilar Wolters, Dave Rogowski

Year: 2018

Abstract

Accurate estimation of age and growth rates of fish provide vital information for fishery management. The construction of Glen Canyon Dam and subsequent release of cold hypolimnetic water from Lake Powell drastically lowered the water temperature of the Colorado River, negatively affecting the growth of warmwater native and nonnative fishes. In 2013, we began collecting Common Carp dorsal spines for aging and determining growth rates in fish captured from two locations 1) a seasonally warmed backwater upstream of Lees Ferry and 2) the mainstem Colorado River. Two biologists aged digital images of 212 Common Carp spine sections. No identifying information was included in the images. Exact agreement between the readers was poor, with only 8.1% and 27.3% agreement for Common Carp from the Lees Ferry backwater and mainstem Colorado River, respectively. Reader inconsistencies as well as recapture data from tagged fish suggests that aging warmwater fish species in a cold, relatively stable temperature regime is neither precise nor accurate. The results of our study could provide insight on the accuracy and practicality of aging warmwater native fishes of the Colorado River such as Flannelmouth Sucker, Bluehead Sucker and the endangered Razorback Sucker and Humpback Chub.