Gill netting during sonar operation verified that the target species, chum salmon, was the predominant fish species migrating past the sonar site. The average annual population was 230,000 fish from 1995 to 1997. In 1998 and 1999, the average run size dropped to 82,000 fish. The Fairbanks Fishery Resources Office uses resistance board weirs in several important drainages to gather accurate information about spawning salmon stocks. Weirs allow biologists to determine the escapement and run timing of salmon stocks, as well as determining their sex and size composition.
Weirs also help evaluate the effectiveness of aerial surveys as a method of estimating escapement.
A weir consists of interlinked floating panels that stretch across the whole river. The panels are anchored to the river bottom on the upstream side. This allows water to flow through, but stops the upstream passage of fish. The center of the weir has a chute with a gated holding pen. As salmon swim into the pen, biologists count the fish and identify the species, then release them to continue swimming upstream to spawn.