We are Going to Need a Bigger Razorback: Flathead Age Structure and Predation Potential in the Lower Colorado River

Authors: Tiffany Love-Chezem, Chase Ehlo, Ethan Rasset, Aaron Meuhler

Year: 2024

Abstract

Flathead Catfish, Pylodictis olivaris, were introduced into the Lower Colorado River (LCR) near Yuma, AZ in the 1960’s, but have been increasing their range upstream and have been detected as high as Needles, CA. Not much is known about the age structure of this invasive species in the Colorado River, however the link between length and gape width is well understood. Their large gap width makes even large Razorback Sucker, Xyrauchen texanus, vulnerable to predation, and current stocking strategies that were developed to increase survival of Razorback Suckers may not work for Flathead Catfish. To explore the age structure and how it related to their predation potential, otoliths were removed from 24 Flathead Catfish of various sized captured throughout Lake Havasu. Otoliths were mounted in resin and cut using a high-speed isometric saw, aged independently by two biologist, and demographic modelling was completed via von Bertalanffy growth curves and catch curves. Ages ranged from 2 to 28 years old, with Flathead Catfish being able to eat most Razorback Sucker at stocking around four years of age, but not being able to eat all Razorback until around nine years of age. A better understanding the population structure of Flathead Catfish could lead to regulations or control programs that could reduce predation of Flathead Catfish on native species in the LCR.