by Jacob Montgomery
Central Valley Project Manager

Field Note: Fish Food on the Floodplain

CalTrout’s Central Valley 2021 field season (Oct 1, 2020 – April 1, 2021) marked the much-awaited second year study of large-scale Fish Food export. For some brief background, the Fish Food export program is CalTrout’s novel management practice for transferring benefits of winter-flooded habitat that juvenile salmon can not get to, back to fish wedged between the river levee system. The Fish Food program is the compliment to the Nigiri Project. With Nigiri, we bring fish onto the floodplain, and with Fish Food, we bring the floodplain back to the fish. In 2019, we ran the pilot year for Fish Food and got some very positive results.  

For a in-depth review of the data, please check out this “on-demand” presentation I gave to the Delta Science Conference this past April.

Now, the second year of implementing the Fish Food program posed several questions:

• How far downstream does a food-web subsidy continue to benefit fish?
• How would this practice work in an average or dry water year (relative to the very wet year 2019)?
• Could we implement the practice at new locations with different sets of infrastructure?
• Could we get added benefit from draining fields mid-winter, re-flooding, and then draining again in spring?
• How do we work with existing waterfowl and shorebird conservation programs to ensure we’re not competing for flooded acreage, but rather manage the resource to the benefit of birds and fish?
• How do we navigate implementing the practice with a limited water supply?
• And how do we continue to collect quality data during this large-scale experiment while operating safely within COVID protocols? 

Before getting into the results, I have to acknowledge both my crew and our partners in this work. The Central Valley region employs four full time technicians to help me conduct all the field work, collect samples, manage fish, process laboratory samples and analyze data. They are incredible! In addition to the greatest conservation program demands we’ve ever had, the crew dealt with weekly COVID testing, less direct supervision, and more independence as we maintained isolated teams of two so that the project would be insulated from any potential illness threat and/or quarantine. Our farmer, water contractor, and bird conservation partners were also amazing this year. Until about the turn of the new year, there were significant water restrictions in place and there was less water supply than what anybody had expected, let alone not enough for us to achieve all our management goals for the flood season. But we all stayed in very close with open communication throughout the winter, and everybody found ways to compromise and contribute to mutual flooding and draining goals for birds and for fish. 

We learned a lot in this second year of Fish Food. In addition to working at our Pilot Year location (RD 108’s Rough and Ready Pumping Station, northern Yolo County), we tested Fish Food management practices at three new locations in Sutter County and documented similar benefits to the food-web in the Sacramento River and Sutter Bypass. We were able to achieve multiple flood/drain cycles from the same fields on about 3,000 acres. Not only did the food-webs rebound in their second flood cycle to the levels achieved in the first cycle, but the mid-winter drain provided lots of extra habitat for shorebirds that typically is not available that time of year and had no negative impact on waterfowl hunting. Caged fish at the floodplain outlet grew 8.3X faster than baseline, upstream control fish. Caged fish six miles downstream of the floodplain outlet still grew 4.5X faster than baseline, upstream control fish.

The food-web subsidy likely continued to benefit river fish further down, but six miles was as far as we looked. These results are even better than the Pilot Year, when caged fish at the floodplain outlet grew 5X faster than baseline, upstream control fish. Most of this difference is because the upstream control fish grew 30% slower this year than they did in 2019. And this makes total sense given what we know about fish habitat in wet and dry years. In wet years, the lower Sacramento River is a pretty good place to be a juvenile salmon. Despite the channelization and leveed banks making a relatively homogenous environment, there are shelfs and gravel bars and side channels, etc. still within the levees that activate at high water and create some habitat diversity. Additionally, flood waters create a visual screen of turbidity and activate the bypass system, and the largest network of off-channel habitat becomes available for juvenile fish rearing and an outmigration corridor relatively protected from predators. But in dry years, the lower Sacramento is a very difficult place to be a juvenile salmon. The channel is barren and sterile of foodweb production, and the water is clear and full of visual predators.

It is exactly in these dry years when the Fish Food program can have a massive impact on the Central Valley’s salmon populations. Management actions like Fish Food can provide wet year benefits in dry years with a very small volume of water. A recent summary report we produced for the Bureau of Reclamation (funders of Fish Food) estimates that with just 13,000-acre feet of water we could have doubled the size of one million 1-gram juvenile salmon! Just imagine what benefits could be conveyed to the salmon population by implementing Fish Food across the entire Valley floor… 

This coming year we will be hoping for rain and continuing to develop the Fish Food program. 

And in personal news, my wife and I have our own fry developing! She’s been on the yolk for about six months already and we expect her to be free swimming somewhere around November 1, 2021 (just in time for floodplain season!). I’m so excited to start grooming the next generation of field biologists, conservationists, and anglers. ?