DELTA LEAD SCIENTIST: Effects of stressors on native fish communities

At the January meeting of the Delta Stewardship Council, Delta Lead Scientist Dr. Laurel Larsen began a series of reports that, over the next few months, will highlight the science that the Council funded through the Delta Science Fellows in 2018.

The Delta Science Fellows Program, a partnership with California Sea Grant, provides two years of research funding and mentorship to master’s students, Ph.D. students, and postdoctoral scholars working on questions of management relevance in the Delta.  The research topics must be directly related to the Science Action Agenda.

I hope that the next few lead scientist reports will drive home just how impactful this funding program can be, both for the science and for building the next generation of science leaders in the Delta,” said Dr. Larsen.

The research highlights will be presented thematically; this month’s theme is the effects of physical environment characteristics, such as temperature and oxygen, on native fish species of special concern.  These three studies addressed Action 4AA of the 2017-21 Science Action Agenda, which called for improving the understanding of interactions between stressors and managed species and specifically the need to better understand salmonid temperature tolerances in streams.

Effects of temperature on longfin smelt larvae

The first study, by Delta Science Fellow Yuzo Yanagitsuru at UC Davis, studied the longfin smelt, a threatened species under the California Endangered Species Act that was recently recommended for protection under the federal Endangered Species Act.  

Longfin smelt underwent a near collapse of its population in 2015, and its abundance is currently less than 1% of what it was before the 1980s.  In response to that bottleneck, the Fish Conservation and Culture Laboratory at UC Davis initiated a captive culture program for longfin smelt.  However, that program,  modeled on the protocol for raising Delta smelt in captivity, was consistently unsuccessful in rearing longfin smelt from the larval stage.

Yuzo’s work investigated the root cause of the mortality seen in those culture attempts,” said Dr. Larsen.  “He hypothesized that the temperatures at which the larvae were being reared resulted in growth rates and swimming speeds too slow for successful feeding of those larvae once they had absorbed the yolk and oil from the egg.  Indeed, Yuzo’s laboratory experiments supported that hypothesis with higher hatch rates and larger sizes generally observed in the longfin smelt reared at the lower temperatures, although there was also a lot of variability.”

However, all of the test groups still experienced mortality before the yolk and oil had been absorbed, and so the team proposed that factors other than starvation might be inhibiting the success of the longfin smelt culture program.  So although that study didn’t reveal the smoking gun in their lack of success, studies such as this are an important step toward eventually building successful methods for raising longfin smelt in captivity, and that might be what ultimately helps prevent extinction or further endangerment.

Longfin Smelt: Effects of Temperature on Hatching and Growth Performance of Embryos and Yolk-sac Larvae of a Threatened Estuarine Fish: Longfin Smelt.  Yanagitsuru et al. 

Effects of environmental variability on Delta smelt

The second study focused on the endangered Delta Smelt by UC Davis Fellow Levi Lewis, now a principal investigator of a research lab at UC Davis.  Though many studies had focused on the cause of the Delta smelt’s precipitous decline since the 1980s, none of those previous studies had revealed a single dominant cause, and studies of how environmental factors impact fish are notoriously difficult.

Fish responses to manipulation in captivity might not be representative of how they respond in the wild.  In the wild, observational studies are complicated because fish move around, making it difficult to relate their characteristics to snapshots of the environment captured in sampling.

During his Ph.D., Levi Lewis worked to develop new technology that has addressed these challenges and really been transformative in our understanding of Delta smelt,” said Dr. Larsen. 

Levi’s work used fish otoliths, which are tiny bones in the inner ear of the fish that, similar to tree rings, grow continuously and produce ring-like structures that can be precisely measured to estimate fish growth rates over known time intervals.  He analyzed the otoliths of archived specimens of Delta smelt to quantify each fish’s growth rate over the two weeks before capture and related those growth rates to the environmental conditions sampled at the time of capture, assuming that those conditions were representative of what the fish actually experienced over that small two-week timescale.

Thus, he overcame the challenge of fish movement, obscuring the relationship between long-term average quantities such as size and the type of conditions that the fish actually experienced over those long periods of time,” said Dr. Larsen.

Through this study, Levi and team found that warm temperatures, those greater than 68 degrees Fahrenheit, drastically depress the growth rates of Delta smelt, as does a clear sediment-free water column,” she continued, noting that the invasive overbite clam has impacted sediment in the water column, which can have a negative impact on the Delta smelt.

They also found that high salinities depress growth rates, which supports the ongoing use of flow management actions to enhance the extent and quality of low salinity habitats in late summer into early fall.  Meanwhile, their findings on the effects of temperature highlight the ongoing challenge that we’re going to face in managing Delta smelt populations during hot droughts, as we’ve been experiencing.”

Delta Smelt: Otolith-based Approaches Indicate Strong Effects of Environmental Variation on Growth of a Critically Endangered Estuarine Fish.  Lewis Et Al., Marine Ecology Progress Series, 2021.  

Effects of temperature and low oxygen levels on chinook salmon

The third study, by Annelise Del Rio, a former fellow at UC Davis and now a scientist at the Puget Sound Partnership, worked to understand how temperature and low oxygen levels might impact chinook salmon, both individually and taken together.  

The study noted that while temperature management for Chinook salmon, such as the release of water from the cold water pool at Shasta Dam, is usually based on known lethal effects, sub-lethal effects could also contribute to the decline of Chinook salmon populations through reduced feeding success, increased predation or reproductive impacts,” said Dr. Larsen.  “However, there’s a research gap and understanding what those effects are.  Anneliese conducted laboratory experiments to explore the effects of common stressors on Chinook salmon embryos after hatching.  As a general marker of stress, she measured the embryos metabolic rates.  Those studies revealed that warm temperatures alone are a strong driver of adverse sub-lethal effects, but that when combined with low oxygen levels, those impacts were most severe.

Chinook Salmon: Differential Sensitivity to Warming and Hypoxia during Development and Long-Term Effects of Developmental Exposure in Early Life Stage Chinook Salmon.  Del Rio Et Al., Conservation Physiology, 2021. 

Activities of the Delta Science Program

2022-2026 Science Action Agenda

The public comment period for the 2022-2026 Science Action Agenda closed on January 21st.  In addition to sharing the draft via email lists, the Delta science program staff sought comment by carrying out targeted outreach with presentations to the Collaborative Adaptive Management Team and the Delta Independent Science Board.  Dr. Larsen said a lot of excellent feedback was received through discussions at other collaborative venues and the written comments received.  As a result, they are revising the document with a final release anticipated in late spring of 2022.

Delta Science Fellows

The request for applications for the Delta Science Fellows Program was released on January 25th.  In addition to the usual proposals on understanding the physical, biological, and chemical aspects of the Delta, they are also specifically soliciting social science proposals.  They will have a separate review panel of social science experts for those proposals.   

All prospective fellows must submit a Notice of Intent by February 28th.  The notice of intent is a simple online form that helps to ensure the right expertise on the review panels for the proposals.  The applications are due on April 20th.  Awards are anticipated to be announced in June, with work to begin in the fall of 2022.  Click here for more information and how to apply.

To help the prospective fellows prepare strong proposals, the Delta Science Program and California Sea Grant will host an informational webinar on February 7th between 10:30 and noon.

Delta Invasive Species Forum

The Delta Interagency Invasive Species Coordination Team symposium was held on December 15th and focused on early detection and rapid response to invasive species in the Delta.  The recording is available here and the agenda is here.

Delta Social Science Community of Practice

The steering committee for the Delta Social Science Community of Practice Steering Committee met on January 18th.  The community of practice includes social science researchers, agency scientists, and practitioners interested in building knowledge on the social, political, and cultural dynamics of the Delta.  The bulk of the January meeting consisted of a presentation from Randy Schuster of the USGS, who is working within the US Department of the Interior to build a social-behavioral economic science community of practice to connect social scientists across federal agencies within the Interior Department.  The steering committee also set their goals for 2022 and discussed new synthesis or research efforts that the members might initiate in the upcoming year.  For more information, click here to visit the webpage at the Council’s website.

Adapting Restoration for a Changing Climate Symposium

The Adapting Restoration For A Changing Climate Symposium will be held on February 2 and 3.  The symposium, organized by the Delta Science Program, explores how restoration projects are integrating immediate and long-term climate change considerations into their planning and implementation in the San Francisco Bay-Delta and beyond.  The talks, panels, and interactive discussions, many given by or facilitated by Council staff, will explore the planning, implementation, funding, permitting, collaboration, and communication strategies for climate-adaptive restoration and emphasize the importance of long-term resilience in the face of sea level rise.  The conference is virtual and free.  Click here to register.

Upcoming brown bag seminar series on Delta governance

The Delta Science Program is planning a three-part brown bag seminar series for the spring titled, What is Delta governance anyway?  The series will focus on the institutional structures that influence the environmental management of the Delta, with the premise that governance is something we’re all taking part in and that many people talk about.  Yet, we don’t necessarily have a shared or even particularly clear understanding of what it is.  The series is designed to help build that understanding and draw upon academic, social, and scientific research and practical insights.

Each seminar will feature a panel of speakers focused on a particular theme.  The theme of the first webinar on March 1st is environmental governance.  The second webinar on April 13th will have a theme of collaborative governance.  The third webinar on May 5th will focus on adaptive governance.  Registration is coming soon.

Delta Lead Scientist: Ask Me Anything

The December 20th session of the Delta Lead Scientist Ask Me Anything was co-hosted by the Senior Environmental Scientist Rachel Klopfenstein with the Delta Science Program and focused on the Science Action Agenda.  The archive of that session is available online at the Delta Stewardship Council Instagram site.

The January 31st session will highlight science synthesis activities in the Delta.  The Delta Science Program’s Dr. Sam Bishevken and Pascal Gertler will serve as co-hosts.  They will discuss what synthesis is, why it is important, and discuss the Delta Science Program’s latest partnership with the National Center for Ecological Analysis and Synthesis to analyze decades of monitoring data to identify how the food web responds to changes in different environmental variables.  The session takes place on January 31st at noon and will be archived at the Delta Stewardship Council’s Instagram site.

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