Wednesday January 18, 2012
The new year marks a time when people vow to make big changes and start anew, and for fall-run salmon that change occurs when the fry begin emerging from their gravely nests (redds) to begin their journey to the sea. As in past years, we are using rotary screw traps to monitor and enumerate the outmigrating salmon. Early in the spring migration we predominantly catch salmon in the “fry” life-stage, when they are capable of swimming freely and capturing food. Occasionally we catch alevin, or sac-fry, with the yolk sac still present. On this particular occasion, we captured a Chinook alevin that was prematurely washed from its redd. With gills and fins yet to develop, this fish has little chance of survival, but it does demonstrate how vertebrate eyes are one of the first organs to form during embryologic development. Salmon, like most teleost fish, can see in color and have well-developed near-field vision.