Incidence of spinal injuries in migratory Yellowstone cutthroat trout captured at electric and waterfall-velocity weirs

Abstract

The South Fork Snake River (Idaho, USA) supports a native Yellowstone cutthroat trout (YCT) population Oncorhynchus clarkii bouvieri (Richardson) threatened by non-native rainbow trout O. mykiss (Walbaum). Electric weirs prevent rainbow trout passage into YCT spawning tributaries but may cause spinal injuries. YCT captured at electric weirs on Palisades and Pine Creeks and a control waterfall-velocity weir on Burns Creek were X-rayed in 2012 and 2013 to estimate spinal injury rates. Electrical pulse frequency was increased from 2012 to 2013 at the Palisades (from 11.5 to 20 Hz) and Pine weirs (13–20 Hz), and spinal injury rates were found to increase from 11.3 to 21.3% at Palisades and from 6.5 to 14.7% at Pine, while Burns injury rates remained constant (4.5% in 2012 and 6.0% in 2013), suggesting the electric weirs caused spinal injuries in YCT. Lower pulse frequencies may minimise YCT spinal injury but still prevent rainbow trout from accessing YCT spawning tributaries.