U

Undulating To move in waves. Referring to the movement of a female fish's tail in a waving motion used to move gravel for the construction of a redd.

Unhooking mat
A thick, soft, often inflatable, plastic mat, to lay large fish on when unhooking them, so protecting them from damage.

Up-trace
A wire trace which sits in a rig above the bait trace. It prevents a pike biting through the main line when it takes the bait in a float paternoster rig.

Upriver Bright stock (URB)
A stock of fall chinook destined for the Columbia River and several tributaries upstream from The Dalles Dam. These fish enter the Columbia from early August with the peak of the run at Bonneville Dam in early September.

Upwelling
The movement of nutrient rich waters from the bottom of the ocean to the surface.

Usable Stock
The number or weight of all fish in a stock that lie within the range of sizes customarily considered usable (or designated so by law). Also called; *standing crop.