Federal legislation (Water Infrastructure Improvements for the Nation Act, 2016) requires the Oakdale and South San Joaquin Irrigation Districts and NOAA Fisheries to jointly establish a multi-year research program in the Stanislaus River to investigate whether predator removals are an effective strategy to improve the survival of juvenile salmonids. Initial project goals included efforts to: (1) gather data on the abundance, composition, and distribution of both native and nonnative fish predators in the Stanislaus River; (2) gather age composition and diet information from fish predators; and, (3) implement and assess removals of piscivorous fishes using a Before-After-Control-Impact study design. The sampling design allows for information to be gathered on both temporal and spatial aspects of predation in the Stanislaus River with randomly selected sampling locations revisited multiple times. Data will be analyzed using a robust design framework to account for the ability of tagged predators to move into and out of the sampled locations (i.e., an open population). Data from the study can provide insight on how predation risk (e.g., the number of Chinook salmon consumed by predators) may change through time and space as well as how predator populations may change throughout the study period.

1. Nonnative Predator Research and
Management on the Stanislaus River
2019 Field Activity Summary and Data Analyses
AFS & TWS Joint Annual
Conference, Reno, NV
Sept. 29 – Oct. 3, 2019
Presenter: Matt Peterson
Co-Authors: Jason Guignard,
Andrea Fuller, and Doug Demko

2. Overview
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• Background
• 2019 Research
Questions
• Methods
• Results
• Looking Forward

3. Study Area Map
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Reno

4. Low Survival of
Native Fish
• Fall-run Chinook
• Anadromous
• Juveniles outmigrate
to ocean in
winter/spring
• Many CA CV
populations
experience low
survival during this
life stage
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5. High mortality due to predation?
• Growing concern among fisheries managers
• Need for understanding ecology and management
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6. Establishment of Program
Key Requirements of Predator Research
Program:
• Evaluation of how predator populations are
affecting juvenile Chinook salmon survival
• Establish removals of predatory fish
• Assess how removals affect juvenile Chinook
salmon
• Develop research questions jointly with NOAA
Fisheries
• Conduct research from 2017 to 2021
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7. Research Questions or Objectives
• What is the abundance and composition of fish
predators in the Stanislaus River between Oakdale
and the confluence with the San Joaquin River?
• What are their diets made up of and what
proportion of predators consume juvenile Chinook
salmon?
• Conduct predatory fish removals and assess
responses to removals
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8. Study Area
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Reaches
Sample Sites
Reach 5
Reach 4
Reach 3
Reach 2
Reach 1
Ripon USGS Gauge

9. Methods
Boat Electrofishing
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10. Methods
Diet Collection, PIT tagging, and Scale
Collection
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11. Sampling Conditions
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Discharge
(cfs)
Water
Temperature
(ºC)
Date
Removal + PERs
Abundance

12. Catch Summary
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Species March April May June Total %
Black Bass 38 29 106 476 649 50.9%
Striped Bass 10 33 37 92 172 13.5%
Sunfish 12 4 63 89 168 13.2%
Hardhead (N) 10 29 47 62 148 11.6%
Sacramento
Pikeminnow (N) 24 9 9 48 90 7.1%
Catfish 2 0 9 38 49 3.8%
N = Native 1,276

13. How Many Predators?
• Used mark-recapture and hierarchical models
to develop estimates of abundance
• Robust Design MR and N-Mixture for open
populations
• Repeated visits at each site
• Accounts for imperfect detection
• Detection model = binomial
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14. www.FISHBIO.com
Binomial Detection Model
Detection modeled with:
Daily discharge,
temperature, turbidity,
conductivity, and rkm

15. Diet Composition
• Nearly 1,000 samples collected
• Visual + Genetic ID
• Wide range of diet items
• Insects, crayfish, mollusks, worms
• Frogs, voles, and birds!
• Fish (primarily native fishes)
• Lamprey, suckers, juvenile Chinook salmon
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16. Chinook Observations in Diet
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Species Catch n, diet
n, with
Chinook %
Black Bass 649 475 44 9.3%
Striped Bass 172 166 40 24.1%
Sunfish 168 65 0 0.0%
Hardhead (N) 148 82 0 0.0%
Sacramento
Pikeminnow (N) 90 45 1 2.2%
Catfish 49 49 0 0.0%
N = Native

17. Experimental Removals and
Assessment
• One pilot level removal conducted in 2019
• BACI Study Design
• 4.8 km study reach
• Assessed using Predation Event Recorders
(PERs)
• Tethered live juvenile Chinook salmon
• GPS-, video-enabled unit, with timer
• Pinpoint locations of predation at fine scale
• Index of survival used to assess removal effect
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18. Experimental Removals and
Assessment
• 240 Individual PERs Deployments
• 18 Predation Events (7.5%)
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19. 2020 Study Plan
• Continue abundance estimates and diet
assessment
• Expand removals and improve PERs
experiments
• Spatial replication
• Increased power to detect effect
• 2020 Hydrograph?
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20. Conclusions
• Stronger understanding of the predation
ecology in the system in 2019
• Expanded removals and assessments will
provide information on how to improve
management
• Collaboration with stakeholders and
participating agencies key to continued
success
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21. Acknowledgements
Key Collaborators: NOAA Fisheries (California Central Valley Office and Southwest Fisheries
Science Center), California Department of Fish and Wildlife (Region 4 and Fisheries Branch)
Funding provided by: Oakdale and South San Joaquin Irrigation Districts
We thank the following people for their efforts, support, and advice:
NMFS – Barbara Byrne, Amanda Cranford, Cyril Michel, Monica Gutierrez, Andrew Hein,
Maria Rea, Charlotte Ambrose, Steve Lindley, GarwinYip, Eric Danner, and Erin Strange
CDFW – RobTitus, Steve Tsao, Ryan Kok, Ryon Kurth, Jonathon Nelson, and Leslie Alber
FISHBIO – Shaara Ainsley, Tyler Pilger, Michael Hellmair, Patrick Cuthbert, Jeremy Pombo,
John Montgomery, Jim Inman, Chrissy Sonke, Mike Kersten, Tara Lamb, Garth Jaehnig, Rob
Fuller, Earl Fuller, Logan Douglas, Scott Stocker, Rick Biedenweg, Graham Buggs, Ian
Herzberger, Ben Griffith, Steve Clark, DeeThao, Erin Loury, Bryce Neal, Dana Lee, and
Garret Muniain
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22. FISHBIO
Oakdale, California
Chico, California
Santa Cruz, California
FISHBIO Laos
Vientiane Capital, Lao PDR
FISHBIO CR
Boca del Rio Sierpe
Costa Rica
Questions?
Matt Peterson
mattpeterson@fishbio.com
530.892.9686
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