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What is Radio Telemetry?
Tracking Fish Tracking fish

In its broadest sense, telemetry can be defined as the art and science of conveying information from one location to another.With radio telemetry, radio signals are utilized to convey that information.

The tracking method of choice for most freshwater research is radio telemetry. Biologists can equip trout with amazingly small radio transmitters and track their movements and behavior with the aid of receivers. Radio telemetry system designs commonly utilize aerial antennas to establish "listening" zones to detect signals.

How Do They Do It?

Milltown Radial Gate Milltown Radial Gate

Milltown Dam is equipped with a radial gate (or screw gate) that can be opened up to allow water to bypass the hydroelectric facility and flow directly downstream. Dam managers use the radial gate as a management tool to release excess water and to clean debris from the dam. Fisheries biologists use this same site to capture upstream migrating fish trapped in the small concrete depression below the radial gate. Bull trout and westslope cutthroat trout are attracted to this site, and once the radial gate is closed, the fish become stranded and are netted by the biologists.

Captured Fish are then Anesthetized

Fish Belly Fish Belly

Captured fish are anesthetized (60 mg/L tricaine methanesulfonate [Finquel™]), and placed on their dorsum in a V-shaped operating table. During surgery their gills are irrigated with dilute Finquel™ to maintain unconsciousness. Incisions are made along the linea alba immediately anterior to the pelvic girdle and a transmitter is inserted into the body cavity. An external antenna is passed through the body wall posterior to the pelvic fins. Radio transmitters do not exceed 2% of fish weight and range in size from 6.0 to 8.9 g in air. All bull trout are implanted with 8.9 g transmitters to minimize stress despite that larger transmitters could be used. For this size radio transmitters, transmitter life ranges from 237-344 days, and transmitters emit a signal 5 seconds at 150 MHz. Incisions are closed with surgical skin staples.

Surgical tools (including staple gun and staple remover) are sterilized in dilute Betadine™ and rinsed with 0.9% saline solution prior to each surgery. New surgical blades, latex gloves and sutures (silk or steel) are used for each surgery. After surgery, fish are placed in a live car in the river to regain consciousness and equilibrium, and then released.

In summary, biologists put the captured fish to sleep using a prescribed drug. A small cut is made on the fish's belly, and a small radio transmitter is placed inside. This small radio has an wire antenna attached to it which is located outside of the fish's body. The biologist then uses stitches to close the opening which prevents the radio transmitter from falling out of the fish. After surgery, the fish are kept in a holding pond until they fully recover from the surgery and are then released back in the river above the dam.

Using Radio Telemetry

Antenna Antenna

Fish are located at least three times per week during migrations and more frequently (up to seven times per week) during spawning to determine what tributaries are used for spawning and other migration information. Locations of radio-tagged fish are made from the ground using a truck mounted omni-directional whip antenna, by hand with a three-element antenna, or from a small fixed wing aircraft with a three element antennae mounted on a wing strut.

Why Do Biologists Track Fish?

Pointing at a Redd Pointing at a Redd

Biologists are using radio telemetry as part of a study to assess the effects of Milltown Dam on native fluvial bull trout and westslope cutthroat trout populations in the Upper Clark Fork River. The goals of this study are to restore connectivity (access) to the Upper Clark Fork River and Blackfoot River from below Milltown Dam; to determine the effectiveness of trapping and hauling fish over the dam to restore connectivity; to restore spawning fish to upriver populations; to better understand the impacts of Milltown Dam on upriver fish populations; to better understand fish movements; to gain a better understanding on habitat requirements; to help locate critical spawning streams; and to help us identify human impacts to native fish such as undersized culverts and unscreened irrigation ditches.

In the photo, Ron Pierce, a fisheries biologist, is pointing to a bull trout redd in Monture Creek. Radio telemetry projects help biologists find critical spawning sites in tributaries such as Monture Creek. Trout redds (or spawning beds) are areas where female fish lay on their sides and flap their caudal fins or tails making a depressional bed in the gravel. After spawning, the pair then covers their eggs with gravel from immediately upstream the same way they made the nest. This process turns the gravel upside down exposing the reddish gravel from underneath. Within a few weeks of spawning, the red gravel begins to turn green from algae growth and the redd blends in with the surrounding gravel.