Rotary screw traps on the Merced River. (photo: USFWS)

Heather Webb and Ken Behen, DJFMP-Stockton

In spring 2008, the Stockton Fish and Wildlife Office's Delta Juvenile Fish Monitoring Program assisted Cramer Fish Sciences of Oakdale, Calif. with monitoring and maintenance of two rotary screw traps on the Merced River.   The rotary screw traps were positioned side-by-side at River Mile 2, in Hilmar, Calif., and were used to capture smolt-sized salmon during peak outmigration. In addition to estimating fish abundance, the study incorporated qualitative observations on the health of captured individuals. Trap efficiencies were developed to accurately estimate fish abundance.  Predictive models will be developed to help managers make more informed decisions regarding future restoration efforts on tributaries of the Sacramento-San Joaquin Delta.