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Radio Telemetry

Learning from the Fish

Surgical implantation of radio transmitterSurgical implantation of radio
transmitter in a fish

In the first phase of this project, we're hoping to learn about how fish use the Sun River between Gibson and Diversion dams. The best way to do this is to study some individual fish over a long period of time-to regularly follow them through different seasons to see how they respond to changing conditions in the river. But, how are we going to do this?

The best tool biologists have for monitoring movements of individual fish is called "telemetry", which is just a fancy word for attaching a transmitter to a critter and monitoring its travels. On larger animals, these transmitters can actually be carried somewhere on their body. For instance, elk and bears typically carry transmitters in special collars around their necks. On larger fish, like paddlefish and sturgeon, transmitters are often attached to the fins on top of their backs. However, it is difficult to attach transmitters to smaller fish without affecting their natural behavior. Thus, the best place for smaller fish to carry transmitters is actually inside their bodies! How did we go about doing this?

Streamside Surgery

Radio tag surgery on Rainbow TroutRadio tag surgery on
Rainbow Trout

The fish that get transmitter implants are usually captured by electrofishing or angling in the river. Then, surgically implanting the radio transmitters is a rather quick and simple procedure done streamside near where the fish are captured. Prior to surgery, the fish are anesthetized to keep them from moving. Once they are sound asleep, they are placed upside down on a small V-shaped surgery table and water is constantly squirted on their gills to allow them to breathe. A small (about ¾ inches) incision is made in their belly, and a small exit hole is created behind the pelvic fins to accommodate the antenna. The antenna is fed back through this hole as the transmitter is gently slipped through the incision and situated just above the pelvic girdle on the fish. Just like real doctors, we use stainless steel surgical staples to close the incision back up. This procedure takes only four to five minutes to complete. Once the fish regain consciousness, we attach a numbered plastic tag at the base of their dorsal fin for identification purposes, and we release them back into the river.

Transmitter Tidbits

Rainbow Trout radio transmitters
Rainbow Trout radio transmitters

Because the fish in the upper river near Gibson Dam are relatively small (largest in fall 2004 was 15 inches), we need to use small transmitters. The two different sized transmitters we used weighed just 7.7- and 8.9 grams, or about 0.3 ounces each, yet they send out a radio signal that can be detected with a special receiver up to a mile away! It is amazing what can be packaged in these tiny transmitters. For example, the transmitters implanted in fall 2004 have a delayed start, so they will not turn on until spring 2005. Then, once started, they will only emit a radio signal for 12 hours of each day, then turn off at nighttime. And finally, they are programmed to shut off during the winter months. The purpose of these on/off features is to greatly extend the battery life of the transmitter, which dictates how long we can follow our fish. The smaller transmitters should last about 500 days, while the larger ones are rated to last about 700 days, or nearly two years! Another great feature of these transmitters is that each emits a unique code that allows us to track individual fish. Thus, when we locate a signal we will know exactly which fish it is. There is a lot of technology packed into a very tiny waterproof transmitter!