Rotary Screw Traps Frequently Asked Questions

Rotary screw trap (RST) are specially designed sampling devices to capture downstream migrating juvenile fish such as salmon and steelhead. They are large, cylindrical traps that float on pontoons and are used to trap fish. The traps consist of three main components: a 5-foot or 8-foot diameter cone, a trap box, and pontoons. Inside of the cone, wings are situated in a spiral shape so that as stream currents push against them the cone will rotate on its horizontal axis, much like windmills. As downstream-moving fish enter the mouth of the rotating cone, they are guided to a submerged trap box where the fish are held until they are sampled and then released. The pontoons provide floatation for the cone and trap box assembly. 

What is a Rotary Screw Trap used for? 

To monitor fish population – abundance, timing, size, survival, and behavior — often in order to develop restoration actions. 

Who is using Rotary Screw Traps? 

Anyone studying fish populations to see how many of a particular species is surviving in the river and what issues they may be facing. The data gathered by the traps is often used by scientists, environmentalists, engineers, and government agencies to inform fish population enhancement actions.   

What should I know about Rotary Screw Traps? 

Rotary Screw Traps can be dangerous to you and your loved ones—including your pets. You can easily enter the mouth of the rotating cone, become injured by the rotating wings, and even possibly get pinned underwater. Never swim or float near a Rotary Screw Trap and make sure your pets don’t go near them either. Do not climb on a Rotary Screw Trao, as this is dangerous and could possibly damage the trap. 

Why do I need to know about Rotary Screw Traps? 

Because one may be coming to a river near you soon! The Yuba Salmon Study is a collaborative workgroup with a focus on investigating the biological, technical, and funding feasibility of reintroducing spring-run Chinook salmon to historical habitat in the upper Yuba River Watershed, has a specific emphasis on assessing the reintroduction potential of the North Yuba River upstream of New Bullards Bar Reservoir. To better understand the feasibility of this reintroduction, there is a planned placement and operation of two traps in the North Yuba River. The Yuba Salmon Study will mitigate any potential hazards that these traps pose by selecting locations on the river with minimal beneficial uses such as recreation and avoiding high-use public access areas.