Hydroacoustic Technology, Inc.
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  Technology on the Horizon

HTI's research and development team offers a few insights to some of the fisheries technologies that are currently in being tested.

Marine Acoustic Tag Receiver System
Equipment Released Spring 2016

Based on a proven system designed for freshwater application, the architecture of the HTI Marine Acoustic Tag System retains the functionality of the existing system including processing techniques that allow simultaneous tracking of multiple targets (literally hundreds simultaneously) with high precision. HTI’s Marine Acoustic Tag System uses an acoustic frequency of 80 kHz to minimize the frequency dependent acoustic absorption in salt water. The 80 kHz frequency used for these tags is above the hearing range of most marine mammals including harbor seals thereby reducing the tagged fish detection by predators observed for tags operating at a lower acoustic frequency. The system can be used to discern fine-scale movement and resource selection by marine organisms. This system is currently in-field testing in the Salish Sea. The project which is being done jointly with Cornell University is designed to study the long term behavior of rockfish in a marine protected area.

The acoustic tagging systems currently available for the marine environment generally lack the precision positioning capabilities of those used in freshwater. The behavioral data provided thus far has been incomplete due to the large positional errors and limits on the number of targets that can be simultaneously detected. This lack of precision is a result of the tag signal design and processing technique which is susceptible to high rates of tag collisions and inaccuracy in the tag signal arrival time measurement which results in inaccurate positional data. With these currently used systems, it is difficult to achieve target position estimates more precise than approximately ±10 meters, even with sophisticated multiple hydrophone deployments. Commonly used single-hydrophone monitoring systems provide only confirmation of target presence within the detection range surrounding the acoustic tag receiver.

HTI systems are unique in that they utilize “pulse-rate encoding” which provides increased detection ranges, improved signal-to-noise ratios and pulse-arrival resolution, and decreased position variability when compared to other types of acoustic tags (Ehrenberg and Steig 2003). Pulse-rate encoding uses the interval between each transmission to detect and identify the tag. Each tag is programmed with a unique pulse-rate to track movements of individual tagged fish. The HTI Marine Acoustic Tag System uses the same processing software as our freshwater tagging systems which if used in groups of 3-4 receivers can monitor tagged aquatic life in 2D and 3D.

Researchers can add the HTI Marine Module to existing HTI Model 290-Series Acoustic Tag Systems or work with HTI’s Marine-Only Acoustic Tag System. Add the new HTI Marine Module to adapt existing HTI Acoustic Tag Receivers to detect both the 307 kHz freshwater frequency as well as the 80 kHz marine tag frequency. This will allow researchers to track marine predators and freshwater migrating species (e.g., juvenile salmonids) in 2D/3D fine-scale resolution simultaneously without any tag signal collisions.

The resulting system currently in testing would allow mapping of fish and other marine species attributes, such as site fidelity, migration routes, and habitat preference, over extended areas and time periods. In addition, this extended-range, high-precision, 3D acoustic tag-tracking system would improve basic scientific research of marine population dynamics. Currently available.

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