Telemetry is now being used to study wildlife, and has been particularly useful for monitoring threatened species at the individual level. Animals under study may be fitted with instrumentation ranging from simple tags to cameras, GPS packages and transceivers to provide position and other basic information to scientists and stewards.
Telemetry is used in hydroacoustic assessments for fish which have traditionally employed mobile surveys from boats to evaluate fish biomass and spatial distributions. Conversely, fixed-location techniques use stationary transducers to monitor passing fish. While the first serious attempts to quantify fish biomass were conducted in the 1960's, major advances in equipment and techniques took place at hydropower dams in the 1980’s. Some evaluations monitored fish passage 24 hours a day for over a year, producing estimates of fish entrainment rates, fish sizes, and spatial and temporal distributions.
In the 1970’s, the dual-beam technique was invented, permitting direct estimation of fish size in-situ via its target strength. The first portable split-beam hydroacoustic system was developed by HTI in 1991, and provided more accurate and less variable estimates of fish target strength than the dual-beam method. It also permitted tracking of fish in 3D, giving each fish’s swimming path and absolute direction of movement. This feature proved important for evaluations of entrained fish in water diversions as well as for studies of migratory fish in rivers. In the last 35 years, tens of thousands of mobile and fixed-location hydroacoustic evaluations have been conducted worldwide.
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