Fisheries, Subsistence, and Habitat
Publications Searchable Database
Search Again| Division: | Commercial Fish |
| Title: | The feasibility of using a split-beam sonar to estimate salmon passage on the Nushagak River as a potential replacement for an echo-counting Bendix sonar |
| Author: | Maxwell, S. L., D. Degan, A. V. Smith, L. McKinley, and N. E. Gove |
| Year: | 2007 |
| Report ID: | Alaska Department of Fish and Game, Fishery Manuscript No. 07-11, Anchorage |
| Abstract: | A split-beam sonar was tested on the Nushagak River as a potential replacement for an existing Bendix sonar used to enumerate migrating adult salmon Oncorhynchus spp. The Bendix counter is an echo-counting sonar deployed at a fixed location nearshore with the beam directed perpendicular to current flow. In 2000, limited datasets were collected alternately off the right and left banks with 2 split-beam transducers, 1 nearshore and 1 offshore. From 2001–2003, we collected paired data along the right bank between the split-beam and the Bendix sonar. Hardware and software difficulties created numerous setbacks in data collection and processing. Calibration and aiming protocols were developed to help standardize procedures and make it easier for technicians to set up the split-beam system. Diagnostic plots displaying the river bottom and vertical and range position of fish targets showed that the 2-transducer, split-beam system was inadequate for detecting fish. Due to changing water levels, a wider transducer beam might ensonify more of the water column, but the range would be compromised. A program developed to autotrack the split-beam sonar data failed because the riverine data was extremely noisy, and the signal processing removed many of the echoes needed to track the fish. We looked at the cross-river salmon distribution by using a wave drag model coupled with flow data to predict where the salmon should be, and then tested the model with range information from 2 sonars and drift gillnetting catch data. We compared 5, 10, 15, and 30 min/h sampling periods from a continuous split-beam sonar dataset and selected a 10 min/h sampling strategy. Paired data comparisons from the sonar’s did not produce a relationship similar to 1. The difference between counts was most pronounced in 2001 and 2003, while 2002 was more similar. It was determined that the split-beam sonar was not the best replacement for the Bendix sonar. During the study period, we began testing a dual-frequency identification sonar (DIDSON). The DIDSON is proving to be a better choice for the Bendix sonar replacement because of its wider viewing angles, higher resolution of fish targets, and ease of operation. |
| Keywords: | Split-beam, Bendix, sonar, salmon, hydroacoustic, sonar transition, Bendix replacement, sockeye salmon, Chinook salmon, Oncorhynchus nerka, Oncorhynchus tshawytscha. |