Yolo Bypass Fish Monitoring Program

The fyke trap sampling is designed to examine adult fish species composition and the timing and duration of fish migration through the Yolo Bypass. Sampling began in 1999 and occurs Monday-Friday from October through June, the period over which most adult fish species migrate. The fyke trap used is 10’ in diameter and 24’ in length. 

Rotary screw trap sampling examines the species composition, relative abundance, and emigration timing of fish moving out of the Yolo Bypass floodplain. The 8’ diameter trap tends to sample smaller species, juvenile salmonids and juveniles of other species. Sampling began in 1998 and occurs Monday-Friday from January through June, the period over which most juvenile fishes move out of the floodplain.

Rotary Screw Trap deployed in the Yolo Bypass Toe Drain. CDWR image.

Beach seine sampling is conducted in perennial ponds, shallow shoals, and seasonally flooded areas to examine stranding patterns, species abundance, and species composition across different water year types, in different regions, and at different points during the flood cycle. Sampling began in 1998 and currently takes place biweekly year-round and weekly during flooding periods. The seine used is 25’ x 4’ with a 4’ bag with 1/8” mesh. 

Zooplankton sampling evaluates and compares the seasonal composition and abundance of zooplankton in the Yolo Bypass floodplain with the mainstem Sacramento River. This monitoring also provides data on food availability for fishes since zooplankton are an important diet component for many species and life-stages. Sampling began in 1999 and currently occurs biweekly, year-round. This sampling utilizes a 50-micron mesh conical plankton net and a 150-micron mesh, 0.5m in diameter and 2m long, conical plankton net. 

This monitoring targets aquatic and terrestrial insects and other surface-oriented invertebrates to examine and compare composition and abundance between the Yolo Bypass and Sacramento River. Aquatic and terrestrial insects are an important component in the diet of juvenile and adult fishes, including two important natives: juvenile Chinook Salmon and Sacramento Splittail. Sampling has occurred since 1998 and currently runs biweekly, year-round. This sampling utilizes a 500-micron mesh, 0.46m (mouth width) x 0.3m (mouth height) x 0.91m (net length), drift net. 

The collection of fish larvae and eggs measures seasonal variation in densities and species assemblages within the Yolo Bypass. Sampling began in 1999 and occurs biweekly from January through July currently, and used to occur year-round. The net used consists of 500-micron mesh and is 0.65m in diameter and 2m long.

Chlorophyll sampling compares seasonal and annual variation in primary production within the Sacramento River and the Yolo Bypass. Sampling began in 2001 and has occurred biweekly, year-round, since 2011.