Located at the eastern end of the Montezuma Slough in the Sacramento-San Joaquin Delta near Collinsville, the Suisun Marsh Salinity Control Gates maintain proper salinity levels in the Suisun Marsh during periods of low Delta outflow. These levels affect the growth of food plants for waterfowl using the marsh as a wintering area. Photo taken September 19, 2014. Florence Low / California Department of Water Resources

DELTA STEWARDSHIP COUNCIL: Some good news for Delta smelt

Located at the eastern end of the Montezuma Slough in the Sacramento-San Joaquin Delta near Collinsville, the Suisun Marsh Salinity Control Gates maintain proper salinity levels in the Suisun Marsh during periods of low Delta outflow. Photo by DWR.
Operation of Suisun Marsh salinity gates to benefit Delta smelt is successful; First experiments with captive-bred Delta smelt show promise

At the February meeting of the Delta Stewardship Council, some council members had questions about actions the state was taking to address the ever-declining population of Delta smelt, and particularly about the use of captive-bred Delta smelt.  At the March council meeting, Dr. John Callaway, Delta Lead Scientist, and Dr. Louise Conrad, Executive Officer of Science, updated the council members on the latest activities to help the smelt.

Dr. Callaway began by addressing the question about the use of captive Delta smelt, noting that it was one of 13 priority actions identified in the Delta Smelt Resiliency Plan.  The specific action of the captively-reared Delta smelt population is part of the action around the development of the Rio Vista Research Station and Fish Technology Center; a key part of developing that as a fish technology center is providing for a better facility for developing and culturing Delta smelt, he said.

At the previous meeting, the council members had questions about the urgency and what the effort is towards addressing the challenges around Delta smelt.  “I think there is certainly an urgency,” Dr. Callaway said.  “The recent surveys that have been done with Delta smelt – there’s hardly any fish that are being captured.  The current population estimate is based on the current sampling is about 5000 fish, down from hundreds of thousands of fish in previous decades, so there’s an enormous decline in the population and definitely enormous awareness that the resiliency strategy and all of the work towards implementing really does highlight that .

Beyond the resiliency strategy, Dr. Callaway said that through the science plan, they are working to promote the development of topic-specific science implementation efforts, or science plans around specific issues.  A science plan has recently been completed around the Delta smelt that is specifically focused on addressing flow issues that affect Delta smelt, as well as using cultured fish as a way to evaluate flow experiments.  There are also structured decision making efforts that are ongoing with the Bureau, and also the Collaborative Adaptive Management Team’s effort on Delta smelt.

Dr. Louise Conrad then discussed two of the 13 actions in the Delta Smelt Resiliency Plan which have had encouraging results.

Suisun Marsh Salinity Gates

The Suisun Marsh Salinity Gates are located in Montezuma Slough on the upstream side of Suisun Marsh.  Normally, the salinity gates are operated in mid-fall to help create fresh food for migrating waterfowl.  However, this action in the Delta Smelt Resiliency Plan examined whether expanded operations could improve conditions for Delta smelt and other fish.

Delta smelt avoid excessively salty waters, so when the salinities increase in the summer, the smelt shift upstream away from Suisun Marsh.  In an effort to create a more hospitable habitat for Delta smelt in the marsh, the Department of Water Resources operated the gate throughout the month of August to direct more fresh water flows for fish into the Suisun Marsh.

The idea with this action within the resiliency strategy is to operate them in the summer to reduce salinity in Suisun Marsh,” said Dr. Conrad.  “That’s important because in the summertime is when Delta smelts have a lot of habitat constriction; there isn’t a lot of habitat that’s available, especially that’s in the proper salinity range.  These gates were operated at a time of year when Delta smelt would need more low salinity habitat.  Suisun Marsh also has high quality food sources and more favorable water temperatures, and this provided access to some habitat that they otherwise wouldn’t have had because it would be too salty.

During the action, there was quite a bit of monitoring done to look at the results, and it was successful in that the salinity was reduced and fisheries monitoring did find Delta smelt in the marsh, so that was a positive result.  All the other monitoring suggested that maybe they wouldn’t have been there give what had been observed in previous years, said Dr. Conrad.

There are plans to continue this action in future years, as it is a success story for providing space for Delta smelt at a tough time of year.

Using captive-bred Delta smelt

There has been increasing conversation and dialog about the possibility for using captive-bred Delta smelt to supplement wild populations.  One of the concerns is that Delta smelt are so fragile, they wouldn’t survive the transportation and release.  So in January of 2019, the Department of Water Resources along with other agencies devised a system of cages that are deployed in the Deep Water Ship Channel from a boat using a buoy system to keep them linked together.

It turned out much better than anyone expected,” Dr. Conrad said.  “The fish survived quite well.  The average survival across the cages was over 95%, so this told us that we can transport, put Delta smelt into a cage and in the wild, and they will survive at the life stage they tried it, which was near adults.”

“This is a great success story because it gives not only some hope that captive supplementation program might be worth considering,” continued Dr. Conrad.  “Now that we have this tool where you can successfully keep Delta smelt in natural habitat and see what happens to them, what conditions are appropriate and what conditions might not be, and also look at life stages that are appropriate for release.

Delta Smelt facility with tanks for genetically diverse smelt populations. Photo by DWR.

Dr. Callaway also noted there were questions regarding regulatory constraints for the use of captive fish.  The experiments with captive smelt were accommodated through existing permits, so probably what’s limiting it is the number of fish that are available, but now that people see this is possible, there probably will be many more requests and opportunities to use the smelt to test a wide range of other questions, he said.

In terms of using captive reared fish for supplementation of the existing population, there are still a number of questions around that such as at what life stage might they be able to survive, where would you release them, and other questions, so the idea is to do additional caged experiments over the coming year or years and really fine tune our understanding so that we can make use of them for supplementation, assuming that things continue to go forward,” said Dr. Callaway.


Vice-Chair Randy Fiorini referenced the discussion at previous meeting and said, “I got the sense that there were some that didn’t think there was enough happening and that there was a lack of a sense of urgency about trying to save the smelt.  I appreciate you coming back to us and providing us factual information that would suggest that there is a sense of urgency and that there is a lot going on in terms of how to identify improve conditions for smelt.”

Councilmember Ken Weinberg acknowledged that there are more things going on perhaps they realized.  “This idea of taking lessons learned this year and implementing next year, but there’s a process to that.  Is it the peer review that slows it down?

Most of that is going on within Collaborative Adaptive Management Team (CAMT) and the Collaborative Science and Adaptive Management Program (CSAMP),” said Dr. Callaway.  “I think the current plan is to do some actions this year based on last year’s results.  There’s likely to be a flow experiment if needed, and the salinity gates will be evaluated again if needed, so it’s not like we are waiting a long time.  We are taking what was learned last year and improving the actions for this coming year and the moving forward.”

Thanks to the leadership of the folks who created this guiding document called the Delta Science Plan, it’s framed up that we need to coordinate our efforts and take a more conscious holistic approach rather than a single species approach,” Chair Susan Tatayon said.  “I’m really excited that we are on the frontier of these tools.  I think the science plan and the leadership of our science program and DPIIC and the funding initiative are moving us more and more toward that more holistic approach.”

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