Fisheries Application of Side Scan Sonar within the Yukon River, Alaska

Fisheries application of side scan sonar within the Yukon River, Alaska

Heather A. Leba¹ and Carl T. Pfisterer²

¹Alaska Department of Fish and Game, Commercial Fisheries Division, 333 Raspberry Road, Anchorage, AK 99518; phone: 907-267-2385; email: heather.leba@alaska.gov

²Alaska Department of Fish and Game, Commercial Fisheries Division, 1300 College Road, Fairbanks, AK 99701; phone: 907-459-7323; email: carl.pfisterer@alaska.gov

Side scan sonar is commonly used in search and recovery applications, yet there is a dearth of information about its utility for counting fish. Side scan sonar was deployed at Pilot Station, Alaska during the 2010 and 2011 Chinook salmon seasons to determine the efficacy in fisheries assessment within the Yukon River. The objective of this project was to augment the existing sonar types at Pilot Station, to observe fish beyond the split-beam and DIDSON sonar ranges on the left bank of the river, and to determine the success of fish detection during high water events or periods of high silt load. The sonar used was capable of operating at two frequencies (400 kHz and 900 kHz) depending on the range ensonified and the desired resolution. The side scan was deployed concurrently with normal left bank sonar operations to enable comparison of fish counts and distribution. Four different deployment strategies, incorporating both mobile and stationary deployments, were investigated to enumerate salmon.  Preliminary results during periods of relatively low turbidity indicate high correlation between the split-beam and side scan estimates suggesting the side scan will be a useful diagnostic tool for assessing the performance of the split-beam sonar during periods of high turbidity.   Echogram data was easy to interpret during calm river conditions but became problematic with high wind or wave activity. We aim to address this issue during future deployments.