Figure 6. Testing tag detection. After hydrophones were deployed, a Ping-Around™ was performed to verify hydrophone positions and hydrophone detectability. During this test, the hydrophones are changed from a receiving only state to an active “pinging” state whereby they transmit the same codes as fish tags. Next, an active acoustic tag (the same size and output that were subsequently implanted in fish) was towed behind a boat throughout the tailrace to test array coverage and tracking performance. Tags were programmed to transmit two separate “coded” signals (3 ms, and 5 ms) and three separate non-coded signals (1 ms, 3 ms, 5 ms). Through preliminary test, we determined that the 5 ms coded pulse had the greatest range and detectability, which was then selected for the fish. The initial test also showed that all hydrophones were functional at setup and that hydrophones had sufficient detection range to locate tagged fish present in the high noise conditions in the tailrace.

1

Tag Tracking Results in the Tailrace Acoustic tagging studies routinely provide information about fish presence and absence. This detection information is combined into a chronology of time-stamped tag detections to measure fish survival and fish passage estimates, among others. Beyond this simple tag detection data, if tag detections are uniformly spaced to a high level of precision then the detection time series can be used to assess fish behavior even in acoustically noisy environments, such as the tailrace of a hydroelectric dam. In Brazil’s São Francisco River, the Federal University of Lavras Department of Biology (UFLA), and one of Brazil’s largest electrical power producers and distributors, the Companhia Energética de Minas Gerais (Cemig) began an unprecedented study. In order to improve fisheries management downstream of the Três Marias Dam, they set out to monitor fine-scale fish behavior. Acoustically tagged fish were simultaneously detected and identified in real-time at a distance up to 100 m (328 ft) in the turbulent water of the dam’s tailrace. An active part of Cemig’s conservation initiative, Peixe Vivo Program, the results will be used to increase the understanding of how fish move and behave near power generating units during various stages of operation. In this poster, we document equipment (Figure 1), implementation, methodology and additional considerations (Figures 3-4) for acoustic tag tracking in acoustically loud environments. Additionally, we will discuss the procedures for testing tag tracking results in the tailrace (Figure 6). This work was also documented for a PhD thesis for UFLA researcher and Oregon State University exchange-student, Fabio Suzuki.

Abstract

Solutions

We determined that detecting and tracking the behavior of acoustically tagged fish in noisy tailrace environments is feasible. The methods that we used for our feasibility study were sufficient to address research objectives and provided two-dimensional tracking information from tagged fish. Spatial resolution of fish position was significantly improved by using encoded pulses and appropriately spaced hydrophones within the study area. When multiple hydrophones are deployed to provide fine-scale 2D or 3D fish track data, then sudden behavioral changes and quantifiable patterns of swimming behavior can be measured. High-resolution fish track data provides valuable information that can aid in characterizing tailrace swimming behavior under different plant operational regimes. The conclusion of this project will provide the group with vital fisheries data and correlated tag visualizations (via HTI’s AcousticTag Software) to accurately illustrate how fish approach one of the plant’s noisiest and most turbulent areas, the powerhouse tailrace.

Conclusion

Tracey Steig, Colleen Sullivan & Sam Johnston HTI Hydroacoustic Technology, Inc. (206) 633-3383 tsteig@HTIsonar.com

Evaluating Fish Passage in Noisy Environments Using Acoustic Telemetry Fish Passage 2013

June 25-27 2013

Figure 4. Proper hydrophone deployment. With an adequately spaced hydrophone array, tagged fish can still be detected and tracked in hydropower dam tailraces. Adequate spacing may account for the reduction in tag ranges due to higher levels of noise and air entrainment in the tailrace environment. Detection ranges among HTI’s acoustic tags and hydrophones average up to 1 kilo-meter (33,280 ft), however, to compensate for the amount of noise and entrained air present, they were placed and tested in closer proximity (50 m / 164 ft). The geo-referenced image above illustrates shallow and deep hydrophone placement.

Figure 2. Feasibility testing in-situ. Detection feasibility tests were conducted near Brazil’s Três Marias Dam located on the São Francisco River. The image above left and top right was taken when the dam was non-operational (no high noise conditions) so that the hydrophones could be deployed and tested. The lower right image illustrates a hydropower dam turbine that can create highly turbulent waters in the dam’s tailrace.

Downstream at Hydropower Dams

Data courtesy of the Federal University of Lavras' Dept. of Biology (UFLA), the Companhia Energética de Minas Gerais (Cemig), one of Brazil's largest power generators & distributors, & Peixe Vivo Program, a Cemig conservation initiative.

Acknowledgments

Double pulse tag in noisy environment without subcode filter.

Tag Tag

Double pulse tag in noisy environment with subcode filter.

Figure 5. Tag parameters and filters for overcoming noise. To overcome noise challenges, combined filters can be used (e.g., filters for subcodes, period, threshold, noise band). The example above shows a double pulse tag with and without a subcode filter in a noisy environment. Also vital to effectively tracking in noisy environments is the ability to control (increase) the energy of the tag’s pulse. Increasing the width of the pulse (or burst), increases the energy in the pulse, allowing it to travel farther through entrained air and noisy environments. Pulse encoding and digital signal processing techniques compress the output pulse, allowing increasing resolution and maximum detection range (Ehrenberg and Steig 2003).

Figure 3. Sources of Noise. Challenges often found in hydropower dam tailraces include the environmental factors noted above. Alone or together, they can significantly reduce the range of signal detection for acoustic tags, making it difficult to detect and acquire fine-scale behavioral data.

Challenges, Methodology & Considerations

Entrained Air (Scattering)

Density Differences (Turbulence, Sound

Speed Changes)

Debris (Scattering, Blocking)

Acoustic Noise (Constructive & Destructive

Phase Interference)

Figure 1. Acoustic Telemetry System. The acoustic telemetry system includes HTI’s Model 290 Acoustic Tag Receiver, hydrophones, Model 795 Acoustic Tags, and a computer with AcousticTag Software to receive and process tagged fish positioning data.

Equipment for Detecting Fish Passage

Acoustic Tags