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 If you want to fit fish with radio transmitters, you've got to catch them first -- it's that simple. But it's really not so simple how biologists catch them. For different fish species, biologists catch them in many different ways. For some fish, in some places, they use what they call electrofishing equipment. These are boats that have generators and electrodes on them that pump electricity into the water which stuns the fish so biologists can net them. Other times, in other places, fish are caught by fishermen who tag them and put them back. Still other times, biologists put fish traps out which catch fish for them. Over the years, biologists have used many different methods to capture fish and have learned that some methods work best with certain species, while other methods work best with other species.
Blue suckers and shovelnose sturgeon were captured in a special kind of nets called trammel nets. These nets were six feet deep and 150 feet long. These trammel nets were similar to a basic gill net -- a net that catches fish by their gills when they try to go through them -- except it has three panels of nets overlapping each other. The trammel nets had a one-inch-square mesh panel on the inside surrounded by a six-inch mesh panel on each side. These nets were put out with a boat across the river, and drifted downstream with the river's current along the bottom for up to 10 minutes. The nets were then pulled back into the boat. Fish that were captured in the nets were then immediately removed and put in a large tub filled with water. The blue suckers and shovelnose sturgeon that were implanted with radio transmitters during September and October of 2001 were captured at several locations on the Missouri River, including the mouth of the Milk River, near Wolf Point, Culbertson, and the confluence of Missouri and Yellowstone rivers. Hoop nets were another type of gear used to capture some of the blue suckers that were implanted in the fall of 2001. These nets are 3.6 feet in diameter and are a series of hoops covered with netting that form a fish trap. The hoop nets actually look like an oversized minnow trap and are anchored in areas of the river with moderate currents.
Not even biologists are sure why fish would want to swim into these contraptions -- maybe it's because they want to get out of the current -- but they do. Of all the places they were tried on the Missouri River, the hoop nets were especially effective in capturing blue suckers near Culbertson. Paddlefish were captured with a different style of net. Long floating gill nets -- six feet deep by 300 feet long with different panels of two-inch, three-inch and four-inch-square mesh -- were drifted downstream with the current in the same way the trammel nets were fished. Because paddlefish are usually suspended in waters up off the bottom (as opposed to blue suckers and shovelnose sturgeon that are usually found right on the bottom), these nets float on the surface and hang down into the water column. All of the paddlefish implanted with radio transmitters in the fall of 2001 were captured below the confluence of the Missouri and Yellowstone rivers near Erickson Island, which is actually in North Dakota. Biologists attempted to capture paddlefish at other sites further up the Missouri River in Montana, but were unsuccessful in those attempts. By the time the netting was done in the fall, biologists had captured enough fish to implant radio transmitters in 19 paddlefish, 17 blue suckers and 29 shovelnose sturgeon. The next step was implanting the radios.
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