Quantification of Walleye Spawning Substrate in a Northern Minnesota River using Side-Scan Sonar

Evaluating aquatic habitats is an important component of many ecological studies and natural resource assessments, but traditional habitat evaluations are time and labor intensive and do not provide continuous data. Side-scan sonar (SSS) can provide a low-cost method that collects continuous aquatic habitat data. We used SSS mapping to quantify suitable spawning substrate available toWalleye Sander vitreus during the 2015 spring spawningmigration in a 10.8-km reach of the Tamarac River, Minnesota. The SSS map had 78.0% agreement with reference points classified in the field, and the proportion of reference points predicted as suitable using the SSS map was not significantly different than the proportion of reference points observed to be suitable. Suitable substrate forWalleye spawning comprised 8.4%(26,392 m(2)) of the total area mapped. The estimated number of females that suitable substrate could support was lower than the number that likely migrate up the Tamarac River and suggests that access to spawning substrate may sometimes limit reproductive success. This study demonstrates that a relatively inexpensive SSS unit can be used to efficiently map aquatic habitat while acquiring quantitative and qualitative data.