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 and the antenna hanging down for the radio transmitter. To find out where fish go, you need to mark them somehow. For years, fisheries biologists relied on a variety of tags to learn where fish travel. Fish would be captured and then fitted with metal or plastic tags which had a number on them. Then they'd let the fish go and hope that either they netted the fish again someday or a fisherman would catch the fish and mail the tag back to them. Using tags like this, they would know where the fish was first caught and tagged. They'd know where the fish was caught again sometime later. They could also tell how much the fish grew in the time in between. It was good information for a biologist to have, but it didn't really tell the whole story of where the fish went and what it did.
But first you've got to somehow fit the fish with a transmitter. Think of it as fish surgery, right on the banks of the Missouri River. Transmitters were implanted into selected fish near where they were caught. The fish were placed belly-up on a foam trough and water was continuously flushed into their gills with a small pump Fish breathe through their gills, taking oxygen from the water, so that's why a continuous water supply to the gills was important. Because these fish are so docile, biologists didn't need to use anesthesia to perform the surgery. An incision was made into the belly of the fish and the transmitter was inserted. A small hole was made through the skin on the belly behind the incision to accommodate the trailing antenna. Sutures (sometimes called stitches) were used to close up the incision. Most fish required six to 12 sutures depending on the size of the transmitter. The transmitters that were used have both radio and acoustic components, meaning they can be located by two different means -- either by radio or sonic waves. Radio waves are detected by using an antenna, much like an AM/FM radio. Sonic waves are detected below the water's surface using a small plastic cone-shaped gizmo called a hydrophone. Each transmitter has its own unique code, so biologists are able to distinguish between individual fish. That way they can keep track of each fish, identifying them by their own unique radio wave or sonic wave. The transmitters placed in shovelnose sturgeon and blue suckers are about one-half-inch by three-inches and weigh about an ounce (out of the water). Those used in the paddlefish are considerably larger, measuring about one-inch by four-inches and weigh four ounces (out of water). Life of the smaller transmitters used in the blue suckers and shovelnose sturgeon is estimated to be about three years, while the larger transmitters used in paddlefish could last nearly 13 years. Transmitter life is limited by the size of battery, which is limited by the size and weight of the transmitter the fish can reasonably carry. As a general rule of thumb, it is suggested that transmitter weight not exceed more than two percent of the total weight of the fish. Once the radio transmitters were implanted in the blue suckers, shovelnose sturgeon and paddlefish, the next step was to follow the radioed fish .
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