1. Keo Chan Advisor: Rebecca Asch
Detecting thresholds in relationships between climate and marine fishes in the California Current System
Keo Chan
Advisor: Rebecca Asch

2. Overview
Q: What can past relationships between fish distribution and environmental variables tell us about what will happen in unprecedented warming conditions?
Using presence/absence data collected by CalCOFI, which covers >60 years of fish larvae data
Tracking 6 environmental variables - month, temperature, salinity, O2, distance from shore, and abundance of zooplankton (food)

3. PDO - Pacific Decadal Oscillation
Adjusted to filter out the effect of global warming
Significant interannual-to-decadal variation
Cool → Warm, as well as other changes
Focusing at data
<-Source: NOAA

4. Methods Four species of fish chosen with contrasting attributes
Geographic spawner/Variable abundance: Anchovy
Geographic spawner/Stable abundance: California lanternfish
Environmental spawner/Variable abundance: Sardine
Environmental spawner/Stable abundance: Hake
GAM - Generalized additive model
Combine smoothing (spline) techniques with regressions
Relationships are often nonlinear
Stepwise procedure to refine model fit

5. Sardine (env spawner-variable abundance)
Top is earlier, cool period →
Cool period, only month and zoop are significant
Bottom is later, warm period
Month
Zoop abundance
Sardine presence/absence
Someone may ask you why the presence/absence data aren’t just ones and zeros in these graphs. Here is the answer in case you get this question. These graphs are showing the probability of presence of sardine after a logit transformation. The logit transformation is needed so that you can confirm to model assumptions (i.e., data have a normal distribution). If the inverse transformation were applied, the data would go between 0 and 1 again.
Temperature (°C)
Salinity O2
Dist to shore
Month
Zoop abundance

6. Sardine analysis Results suggest abundance might play a large role
Basin model of distribution
Very sensitive to food availability at low abundance (cool regime), shows selectiveness for other variables in warm period
Sardine larvae are mainly found in area with temperatures between 12-16° C
At high abundance, sardine exploit their niche and can afford to show preference for more variables
Source: CalCOFI Atlas 34

7. Conclusions
Suggests relationship between fish and the environment may change with climate change, perhaps even flipping
Even traditional geographic spawners are susceptible to changes in distribution
Changes in abundance have large effects on what kind of environment fish prefer
Some species will likely benefit while others will suffer
For those suffering, they may become more reliant on the distribution of their sources of food
Fish are consistent in which month they spawn, with slightly variability in the degree to which they prefer that month

8. Next steps Other fish species besides these 4
Analyze more recent PDO phases
Threshold gams
More research on zooplankton vs climate relationships

9. Skills learned Coding in Matlab and R
Biological statistics and modelling
Linking geoscience to the real world human ecosystem effects

10. Thanks to R Asch, J Sobolewska and Dr. Sarmiento
Questions?
Thanks to R Asch, J Sobolewska and Dr. Sarmiento