Empirical evaluation of walleye thermal-optical habitat in northern Wisconsin lakes

Abstract

Walleye population productivity is influenced by water temperature and water clarity, and available evidence suggests that model-predicted thermal-optical habitat area (TOHA) considered optimal for walleye populations has declined in the upper Midwest. Despite apparent relationships between TOHA and walleye populations, estimation of TOHA relies on assumptions that have yet to be rigorously evaluated. Therefore, we employed acoustic and archival tagging to determine if: 1) walleye thermal-optical habitat varies among three northern Wisconsin lakes in relation to season and walleye total length; 2) the TOHA model employed in previous research accurately defines TOHA for walleye in the three study lakes; and 3) data resolution and cost-effectiveness differs between acoustic and archival tags used to monitor walleye habitat use. We selected three lakes with different basin morphologies and walleye recruitment histories that also provided high probabilities of recapturing tagged fish. We surgically implanted tags into walleye during May 2022 and recovered tags in May 2023. Light and temperature loggers were deployed within each lake along with acoustic receivers during this period. Preliminary results related to our first and second objectives will be presented. This research will help determine if walleye population status may be related to changing abiotic conditions and help inform future studies to describe habitat use of fishes in inland lakes.

Full text

Benjamin Vasquez, Daniel Dembkowski, Olaf Jensen, Stephanie Shaw, Greg Sass,
Quinn Smith, Holly Embke, Jake Vander Zanden, Zachary Feiner, Joseph Mrnak,
Gretchen Hansen, Daniel Isermann
Empirical Evaluation of Walleye Thermal-Optical
Habitat in Northern Wisconsin Lakes

Thermal and Optical Habitat Influence Walleye
Fishery Productivity
Hansen et al. 2019
Hansen et al. (2019). Water clarity and temperature
effects on walleye safe harvest: an empirical test of the
safe operating space concept. Ecosphere 10(5).
•Coolwater fish, prefer low water
clarity
•Lester et al. 2004: Thermal-optical
habitat area (TOHA)
•Model habitat ranges
•Optimal thermal: 11 – 25°C
•Optimal light: 8 – 68 lux

Review: Evidence that TOHA has Shifted in the
Upper Midwest
•Increased temperature
•Context-dependent
•Increased water clarity
•Decreased optical habitat
When water clarity increases:
Hansen et al. 2019
Optimal habitat
decreases

TOHA Model Assumptions Lacking Empirical
Support
• Walleye occur in “optimal” habitat ranges defined in
conceptual model
•TOHA is consistent across life stages
Question
•Is TOHA an accurate reflection of optimal walleye habitat?
•Can the TOHA model be improved?

Using Two Forms of Technology to Evaluate
TOHA
Archival tags
Acoustic telemetry

Objectives
Determine if:
1. Walleye TOHA use varies between two northern Wisconsin
lakes in relation to season and walleye total length
2. The TOHA model employed in previous research accurately
defines TOHA for walleye in two lakes

Walleye Sampling and Tagging

Study Lakes
Escanaba Sparkling
Lake type
Drainage Seepage
Area (ha)
123 64
Maximum depth (m)
8.8 20.0
Mean Secchi depth (m)
3.1 5.1
Recruitment status
Sustained Declining
WAE stocking?
No Yes

Tag Specifications and Configuration
Model Type n Est. tag life Frequency
DST
micro-
TD
Archival
100
355 days,
Memory full 8 mins, switches to
20 mins
V7TP-4X
Acoustic
40 365 days,
Battery dead Every 2.6 to
4.3 mins
Acoustic
Archival
1 inch
Both tags record
temperature and
pressure (depth)

Walleye Collection, Spring 2022
Fyke nets Night electrofishing

Tag Surgeries, Spring 2022
Post surgery
Length bins
Small 310-381 mm
Medium
381-456 mm
Large > 456 mm
Escanaba Lake, May 7th, 2022

Acoustic Receiver and Light – Temperature
Logger Deployments, Summer 2022
Escanaba Sparkling
HOBO Light-Temp Logger

Angler harvest, June 2022
Pelagic and Littoral Loggers, Summer 2023

Distribution of Walleye with “Recovered” Data
N = 36 N = 33

Objective 1: Determine if walleye TOHA use
varies between two northern Wisconsin lakes in
relation to season and walleye total length
Mixed effects linear model
•Model selection with AIC
•Individual random effect by fish
•Auto-regressive moving average
Data structure
•Mean temperature and depth values grouped by
individual fish, date, and time of day

Walleye Temperature Use Varies by Month
p < 0.01, t = 23.1,
df = 20,310
Temperature use was
similar among lakes
and sizes.

Walleye Depth Use Varies by Lake
zmax = 8.8 m
zmax = 20.0 m
p < 0.01, t = 4.0,
df = 20,278
Depth use was different
among lakes but not by
size.

Objective 2: Determine if the TOHA model
employed in previous research accurately
defines TOHA for walleye in two lakes
Zero-inflated mixed effects model (Tweedie)
•Model selection with AIC
•Individual random effect
Data structure
•Mean occupancy in thermal-optical ranges by
individual and date
•Includes proportion of available habitat

Are Walleye in Thermal Habitat?
Yes, occupancy is
influenced by the
availability of 11-25°C.
Escanaba Lake Sparkling Lake
p < 0.01, df = 20385,
Φ = 0.09

Are Walleye in Optical Habitat?
No, occupancy is not
influenced by the availability
of optical habitat.
p < 0.01, df = 20345,
Φ = 0.09
Escanaba Lake Sparkling Lake

Why Aren’t Walleye in Optical Habitat?
Escanaba in day
•Low DO in optical habitat
•Macrophytes?
Sparkling in day
•Available, but not
overlapping thermal habitat
•Walleye deeper on
average…compensation?
Night
•No 8-68 lux available
17%
3% 0%
18%
5% 0%
cr = dawn / dusk

Future Work with the TOHA Conceptual Model
•Thermal habitat
•Consistent among lakes and sizes
•Accurate
•Optical habitat
•Depth use different among lakes, consistent among sizes
•Light use appears arbitrary
•Needs revision
•Redefining TOHA
•Littoral habitat vs pelagic habitat (Summer 2023)
•Dissolved oxygen
•Water clarity in place of light-at-depth?