Hydroacoustic Repeatability in High Savery Reservoir

Travis Neebling , Wyoming Game and Fish Department, Casper, WY
The repeatability of, or ability to get consistent population estimates from, hydroacoustics is dependent on a number of factors.  The chief concern is ensuring adequate “coverage”, or sufficient transect distance relative to surface area to account for variability in fish density.  A number of small studies have been conducted on High Savery Reservoir, south-central Wyoming, to evaluate seasonal and daily variability (or repeatability) of fish population estimates from hydroacoustics.  The reservoir was sampled in the spring, summer, and fall of 2011 using standardized hydroacoustic transects and mid-water curtain netting locations.  Sport fish population estimates were fairly stable throughout the year (+/– 18% of average); however, the estimate of non-native, non-game individuals increased throughout the year, as the reservoir became anoxic from the bottom up.  Spring sampling yielded the population estimate closest to the average and also reduced the number of non-native fish in the gill nets.  In the spring of 2012, the reservoir was sampled for four consecutive days using the standardized methods.  Daily population estimates were repeatable within +/– 10% of the average.  Population estimates were highly correlated (R2 = 0.9) with wind speed which is likely due to increased acoustic noise and thus false targets.