Winter Fish Studies on the Susitna River, South-Central Alaska

Northern rivers can be ice-covered for most of the year; consequently, fish populations are poorly documented due to logistical challenges from sampling under ice, shortened day length, transportation, and safety. Winter can also be a challenging period for fish due to ice formation and low streamflows, water temperatures, light levels, and productivity.  In the Susitna River, the ice-covered portion of the year includes critical periods for spawning, egg incubation, fry emergence, and rearing. During the winters of 2012/13 and 2013/14, a suite of techniques including: imaging sonar, underwater video, PIT and radio telemetry, minnow trapping, trot lining, Fyke netting, and electrofishing in open-water leads documented fish presence, habitat use, movement, diel behavior, and growth. Sampling at 59 sites resulted in >6,000 observations of 14 fish species. Juvenile salmon were most abundant in off-channel habitats where site fidelity was high. Paired day/night electrofishing, PIT antenna, and sonar indicated that juvenile salmon were most active during night and crepuscular periods. Salmon alevin emerged in February and fry were collected in March. Growth rates of juvenile salmon were low, but increased in April as days lengthened despite cold temperatures and low streamflows before ice breakup in May.