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ERMS


(The transition from salmon parr to smolt usually occurs during the spring of the year in which the fish migrates to sea. In some rivers, however, the transition begins during the previous autumn. These fish, known as “presmolts”, assume some of the silver smolt coloration and begin moving downstream.  Scientists believe they remain in fresh water and only move to the ocean the following spring, after over-wintering in the river.)

(Male salmon parr sometimes mature while still in freshwater. Known as precocious parr, they streak into redds of large female salmon just after they have deposited their eggs in an effort to fertilize as many as possible before the large males that courted these females can. Researchers are trying to determine whether these parr become autumn presmolts or if they smoltify the following spring.)

(The smolt stage marks the Atlantic salmon’s transition between fresh and salt water. Changes occur in their physiology, colour and behaviour. Smolts are believed to have a narrow time frame in which to leave the river and enter the most favorable conditions at sea. If they miss these conditions, they may undergo a temperature shock and/or arrive at sea when food resources are low. Both conditions can increase mortality.)

(A smolt wheel is designed to safely capture fish for live return to the river.  At 1.5 meters in diameter, almost 5 meters in length, and weighing approximately 500 kg, this device floats between a catamaran's pontoons, tethered to a cable strung above the water, which allows the wheel to float at varying water levels. The drum's wide end faces upstream into the current.  As water hits the drum, it causes the wheel to rotate.  Captured fish are forced into water pockets within the drum and are then lifted and deposited into a live well, where they are safe until researchers can process them.  The part of the drum in the water is generally submerged to a maximum depth of one meter, the depth at which smolts travel during downstream migration.)