Turning the screws for fish in the upper Middle Fork Salmon River

Another season of screw trapping has begun near Stanley. The rotary screw trap on Marsh Creek, a tributary to the Middle Fork Salmon River, is on the border of the Frank Church River of No Return Wilderness. In the winter and spring, it is only accessible via snowmobile or ATV with tracks. There is usually at least 6 feet of snow at the site when the trap is being installed in mid-March. 

There are rotary screw traps operated throughout the state, but the trap on Marsh Creek is unique for its remoteness and key spawning area for Chinook salmon. The upper Middle Fork Salmon River drainage near Stanley is one of the furthest inland wild steelhead and Chinook salmon spawning migration in the Columbia River basin. 

The juvenile fish travel over 800 miles down the Salmon, Snake and Columbia rivers before reaching the ocean. Wild spring Chinook salmon (one of our target species) generally spend 2-3 years in the ocean and return as adults in the fall to lay their eggs in streams where they hatched.

The screw trap is in place to capture juvenile fish migrating downstream to the ocean. Several tributaries to Marsh Creek have important spawning and rearing so the trap is situated downstream of these areas to capture juvenile fish leaving most of the basin area.

The trap is checked every day from mid-March through November and all fish in the trap are processed. A portion of wild Chinook and steelhead of a certain size are tagged with a passive integrated transponder (PIT) tag. 

This microchip-like tag is injected into the body cavity of the fish and allows biologists to track individual fish through their journey to and from the ocean. Throughout their migration, there are locations where they can get detected such as at PIT-tag arrays that are embedded in streams. PIT tagging juvenile fish allows biologists to make population estimates and gather a variety of information on survival. 

For more information and to see rotary screw traps in action throughout the state, follow these links:

What biologists learn as the screw trap turns and captures fish | Idaho Fish and Game

A day at a rotary screw trap | Idaho Fish and Game