1. Investigating the Effects of Protected Slot Limits on Walleye Populations & Angler Harvest

2. MN Large Lakes Large Lake Data: Many Types of Data
Varying Amounts of Data
Large Lake Regulations:
Different Regulation Types
Different Implementation Dates
Combined Data from All Large Lakes
- Improved Power to Detect Common Effects
- Identify Lake-Specific Differences

3. I like to focus on question first, and at this stage very important to have input from biologists and managers. After have specific hypotheses about effects, we then determine what analysis is appropriate for the available data.
What does PSL do to the population?
Creates protected group of spawners, harvest smaller & bigger fish
Biological Effects:
- Recruitment effects?
- Growth rate effects?
Fishery Effects:
- size-specific catch rates?
- harvested biomass?

4. Creel Data
Many Zeroes
Zero is Lower Limit
High Variation

5. Zero-Inflated Generalized Poisson Regression
Discrete Response Variable
Response ≥ 0
Combines Three Models:
Overdispersion
Regression
Zero-Inflation
For Poisson-distributed variable:
E(X) = Var(X)
→ Model the extra variance as a function of covariates

6. Mille Lacs Example Analysis
Regression Model:
Number of Fish per Party ~ Time Fished + Year
ZIP:
P(Zero Catch) = f(DayType)
GP:
Number of Fish per Party ~ Time Fished
Overdispersion = f(DayType)
ZIGP:

7. Mille Lacs Example Analysis
Regression Model:
Number of Fish per Party ~ Time Fished + Year
ZIP:
P(Zero Catch) = f(DayType)
GP:
Number of Fish per Party ~ Time Fished
Overdispersion = f(DayType)
ZIGP:

8. More Analyses Available for different data & questions
LM – LMM
GLM – GLMM
Multivariate (PCA, CCA, MANCOVA)
with LL staff, Need to develop Ho’s about PSL Effects & how to test them with available data