Use of Fixed-Location, Split-Beam Sonar to Describe Temporal and Spatial Patterns of Adult Fall Chum Salmon Migration in the Chandalar River, Alaska

Abstract

Fixed-location, split-beam hydroacoustics was used to describe temporal and spatial patterns of upstream-swimming fall chum salmon Oncorhynchus keta in the Chandalar River, a tributary of the Yukon River, Alaska. Split-beam techniques allow for three-dimensional tracking of fish targets as they pass through the sonar beam. Elliptical-beam transducers were deployed from opposite river banks to optimize acoustic coverage and were aimed perpendicular to the current. Sonar systems were operated continuously from August 8 through September 22, 1996. Acoustic data on positional information of 204,153 upstream-traveling chum salmon were collected. Diel patterns in hourly passage rates differed between banks. On the left bank, chum salmon passage was highest during nighttime hours. On the right bank, fish did not show any consistent trend in diel passage rates. Chum salmon were generally shore oriented and swam near the river bottom. During daylight hours, fish were further offshore and closer to the bottom than during night. Besides providing accurate counts of fish passage, riverine split-beam hydroacoustics proved a nonintrusive method for studying the migratory behavior of fish.