UC Davis Research Project 4

Fisheries evaluation of floodplain rearing and migration in the Yolo Bypass floodplain

The Yolo Bypass is a 59,000-acre flood bypass structure that diverts floodwaters from the Sacramento River, Cache Creek and Putah Creek around the city of Sacramento and surrounding metropolitan areas.  Given substantial evidence over nearly fifteen years for its benefits to native fishes during flooded periods, the Bypass has become the focus of interest in managing seasonally flooded habitat in the Delta.
We will examine the survival and movement patterns of adult white sturgeon (A. transmontanus), steelhead trout (O. mykiss) smolts, and Chinook salmon (O. tshawytscha) in the Yolo Bypass floodplain through the use of ultrasonic telemetry. This study can be viewed as a classic mark-recapture experiment with multiple recapture locations and complete capture histories.  From the data collected we will be able to reconstruct each fish’s migratory pathway, and examine the role of the Yolo Bypass floodplain in the behavioral ecology and life history of native California fishes.

The project aims to inform floodplain restoration efforts that will optimize salmon rearing and sturgeon spawning and rearing functions.  Our research objectives are:

  1. Describe rates of survival and movement of juvenile salmonids in the Yolo Bypass.
  2. Describe residence times and movement patterns of white sturgeon in the Yolo Bypass.
  3. Determine whether variation in rates and patterns can be correlated with water level (flood year vs. dry year), velocity, water temperature, habitat structure, etc
  4. Determine whether there are specific areas, regions, or depth ranges of the floodplain where there is evidence of increased mortality or holding behavior.

For two years we will surgically implant Vemco V5 tags into the peritoneal cavity of 50 steelhead smolts and 50 chinook smolts raised at the Coleman National Fish Hatchery (CNFH). These new ultrasonic tags are small enough (under 5% of fish body weight) that they do not affect swimming performance, predation rates, or growth rates of the juvenile salmonids.

Smolts will be released into the upper reach of the perennial channel (called the Toe Drain) of the Yolo Bypass.  Adult white sturgeon will be sampled from the fyke net in the Toe Drain, maintained by the Department of Water Resources.  We will implant the sturgeon with Vemco V16 tags (tag life: 10 years) and release them back into the Toe Drain.  Adult spawning Chinook salmon will be sampled from the fyke net or gill netted – these fish will be tagged with Vemco V9 tags using a “backpack” method so as not to perform invasive surgery on spawning fish.  All tags will be detected with an array of Vemco VR2W monitors placed throughout the Toe Drain in dry years and throughout the Yolo Bypass as a whole in flood years.

We have completed almost all of the fish tagging for our first season, a dry year.  Twenty-five steelhead smolts and 25 Chinook smolts were tagged and released into the Toe Drain in late March.  A total of 68 white sturgeon were tagged in the spring.  We will be tagging 25 adult migrating Chinook salmon in the fall to monitor how spawning fish use the Yolo Bypass habitat.  We have been retrieving and downloading monitors from the spring tagging season, and should have all of the tag detection files in hand within the next few months. We will be using Hydra to store all of our detection data.  Feel free to contact us with questions or with requests for outside tag detections on our monitors.