Rotary screw traps
Young salmon and steelhead heading to the ocean are called smolts, others are called parr. In many places, Fish and Game uses a rotary screw trap, which is basically a big cone that sits on pontoons floating on the river. When the cone is lowered into the water, the trap can collect some of the smolts as they swim downstream. The young salmon and steelhead scooped up in the cone are passed into a tank at the back of the trap.
Biologists then remove the captured fish to study them. Fish caught are counted, measured and tagged with a PIT tag before being released back to the river to continue their journey. Screw traps are an important tool