Fish movements can be tracked using hydroacoustic transducers. The transducers are placed near turbine intakes, or spillways, to detect the movement of fish through various downstream passage routes. Hydroacoustic transducers record echoes from objects passing through an acoustic beam. Mean target strengths of echo traces can be categorized into fish-equivalent length classes to interpret detected objects consistent with the fish species and life stages for a particular study area. The use of fish-equivalent length classes provides more information on the life-stages of fish entrained than pooled estimates for all length classes. Hydroacoustic estimates represent a relative index of entrainment rather than an absolute estimate because of false detections from debris, and the necessity of data filtering. The relative index allows many comparisons, including comparisons of various project operations, seasonal trends, daily trends, different life-stages, and various passage routes.

Although not discussed in detail here, the Pacific Northwest National Laboratory (PNNL) has been working with an alternative approach to hydroacoustics called an acoustic camera. Using Dual-frequency Identification Sonar (DIDSON), which was originally developed by the United States Navy's Space and Naval Warfare Systems Center, the acoustic camera promises to provide high resolution imaging of fish in turbid and low-light conditions. This technology is beginning to be experimentally deployed at some Columbia River projects.

4.3.2.1 Advantages and disadvantages of approach

Use of hydroacoustics to measure entrainment has advantages and disadvantages relative to the other approaches evaluated, as discussed below:

Advantages:

• Estimates of fish size are provided.
• Accuracy of detections are not light-sensitive.
• The equipment can be used in deep water locations.
• Estimates for individual passage routes can be provided, including seasonal and diel variation.
• Does not have to rely on a potentially biased sub-sample of fish, and instead evaluates any fish that passes detector.
• Has the ability to provide a continuous record at multiple passage routes simultaneously, so temporal and spatial patterns can be evaluated relative to project operations.

Disadvantages:

• The same fish may be detected more than once.
• Debris and bubbles in the water may be falsely counted as detections.
• Data filters used to eliminate false detections may eliminate actual detections.
• Reverberation noise and poor resolution near the substrate makes shallow water sampling difficult.
• Samples only a portion (typically 5–50%) of the intake, therefore extrapolation is necessary.
• Can only provide a relative index to fish passage unless calibrated by net sampling, and cannot directly provide species-specific estimates.

4.3.2.2 Site-specific considerations and applicability

Many of the advantages and disadvantages of this approach will depend on site-specific considerations, as discussed below:

• Will always provide more reliable results when detections are verified with direct captures or observations.
• May not be the best option for shallow water.
• Should not be used in a system that passes relatively high amounts of debris.
• Site-specific constraints on the placement of transducers include excessive turbulence, solid boundary layers, underwater obstructions, debris levels, and level fluctuations.
• Can be applied to facilities with numerous intakes.
• False detections can be recorded at units that frequently turn off and on if fish swim into units that are off-line. Records of project operations that indicate when routes are available are required for accurate evaluations.
• Has been applied at numerous large dams on the Columbia and Snake rivers, including at the Bonneville Hydroelectric Project (owned by the USACE, Portland District). Has also been applied at small dams, including at the Carmen-Smith Hydroelectric Project (FERC Project No. 2242), on the McKenzie River, Oregon.

4.3.2.3 Selected references

Ecology Group. n.d. Fisheries hydroacoustic technologies. Ecology Technical Group, Environmental Technology Division, Pacific Northwest National Laboratory, Richland, Washington.

EPRI (Electric Power Research Institute). 1992. Fish entrainment and turbine mortality review and guidelines. Final Report. Research Project 2694-01; EPRI TR-101231. Palo Alto, California.

Hedgepeth, J.B., D. F. Fuhriman, G. M. W. Cronkite, Y. Xie, and T. J. Mulligan. 2000. Atracking transducer for following fish movement in shallow water and at close range. Aquat.
Living Resour., Vol 13, 305-311.

Johnson, G. E., J. R. Skalski, and D. J. Degan. 1994. Statistical precision of hydroacoustic sampling of fish entrainment at hydroelectric facilities. North American Journal of Fisheries Management 14: 323-333.

Johnson, R. L., S. M. Anglea, S. L. Blanton, M. A. Simmons, R. A. Moursund, G. E. Johnson, E. A. Kudera, J. Thomas, and J. R. Skalski. 1999. Hydroacoustic evaluation of fish passage and behavior at Lower Granite Dam in spring 1998. Final report, PNWD-2448. Prepared by Battelle, Pacific Northwest Division, Richland, Washington for U. S. Army Corps of Engineers, Walla Walla District, Walla Walla, Washington.

Ploskey, G. R., C. R. Schilt, J. Kim, C. W. Escher, and J. R. Skalski. 2003. Hydroacoustic evaluation of fish passage through Bonneville Dam in 2002. Final report PNNL-14356. Prepared by Pacific Northwest National Laboratory, Richland, Washington for U. S. Army Corps of Engineers, Portland, Oregon.

4.3.1 Introduction

Page 64 of 134

4.3.3 Individual tagging