West Fork has partnered with a client to implement a multi-year study to investigate the status and relative abundance of fall and spring Chinook in the Chehalis River basin. Small tissue samples were collected from Chinook fry every week over the course of the outmigration period and genotypes were tested as being homozygous fall, homozygous spring or heterozygous hybrids. Understanding the true status of these stocks in the basin is vital to the development of the Chehalis Basin Strategy and its Aquatic Species Restoration Plan (ASRP).
Small inclined plane screen traps designed in-house by West Fork were deployed at six sites downstream of known Chinook spawning areas. The natural flow of water through the trap deposits fish into a live box located immediately downstream of the perforated incline that sieves the water flowing over it. Loss of water through the inclined screen and perforated side panels means only a modest amount of water enters the live box. This reduction of water flow protects fish from turbulent conditions in the confined spaces of the live box. Fish are either unable to escape the box due to the water velocity coming over the lip of the inclined screen or are disinclined behaviorally to leave the confines of the box once they are in it. A drum screen powered by a rotating paddlewheel located at the rear of the live box works to remove debris. This allows the trap to fish effectively over a long period of time in organic-debris laden rivers.