Diets of Larval Walleyes in Northern Wisconsin Lakes

Nathan Jaksha1, Daniel Isermann2, & Daniel Dembkowski1

University of Wisconsin-Stevens Point1, USGS-Wisconsin Cooperative Fishery Research Unit2

Introduction

  • Walleye are an important species in Wisconsin that support both recreational hook-and-line and tribal spear fisheries.
  • Walleye recruitment has declined in some lakes that previously supported natural recruitment yet has remained stable in other lakes.
  • Recent studies suggest that a recruitment bottleneck may be occurring at or before the larval stage in lakes exhibiting declines in natural recruitment.
  • Reasons for the contrasting trends in recruitment among populations are unclear, as are mechanisms underlying the recruitment bottleneck in lakes with declining recruitment.
  • Differences in prey availability among lakes with different recruitment histories could contribute to the observed trends in recruitment.
  • Assessment of larval walleye diets from lakes with different recruitment histories could provide important insight to the role of prey resources in explaining trends in walleye recruitment in Wisconsin lakes.
Photo of an adult walleye sampled by the Wisconsin DNR

Objective

Describe diet composition of larval walleyes in northern Wisconsin lakes displaying two different recruitment histories: sustained natural recruitment (S-NR) and declining natural recruitment (D-NR).

Methods – Sampling

  • Larval  walleye sampling occurred during 2016 & 2017 on 13 lakes
    • Five of these lakes were resampled in 2018
  • Sampling started mid-May each year
    • Continued at 7-10 d intervals until early June
    • Surface temps = 11-16˚C
  • Larval walleyes were collected using a 1,000-µm mesh conical ichthyoplankton net.
    • Towed at surface (5 min) at both nearshore (within 100-m) & offshore locations (≥100-m) at night
  • Percid larvae identified to species using dichotomous keys
    • Random subset selected for genetic verification of visual species identification using PCR techniques

Methods – Diets

  • Gut contents of each fish were removed and diets were quantified using mean percent composition by number of individual diet items.
  • Zooplankton items classified to order for adult copepods and genus for cladocerans
  • Larval fish encountered in diets identified genetically using qPCR techniques
Magnified image of a zooplankton (Daphnia spp.) diet item
Magnified image of a larval Walleye

Results – All Lakes

  • Larval walleye collected from 6 S-NR lakes and 4 D-NR lakes (diets summarized in Table 1).
  • Guts were removed from 115 larval walleyes (mean TL = 11.4 mm; range = 6.4 –22.0 mm).
  • 27% of diets (31 of 115) were empty
  • 37% of diets (42 of 115) contained larval yellow perch
  • 16% of diets (18 of 115) contained zooplankton
Table 1. Mean percent composition by number and counts of prey items observed in larval walleye diets from all lakes combined.
Diet Item% CompositionCount
Daphnia spp.15.041
Calanoid Copepods1.83
Cyclopoid Copepods5.816
Bosmina spp.0.53
Larval Fish63.349
Unidentifiable13.510

Results – S-NR vs. D-NR Lakes

  • S-NR Lakes = 86 larval walleye (diets summarized in Table 2)
    • Larval walleye mean length = 11.3 mm (range = 6.5 -22.0 mm)
    • 38 % of diets (33 of 86) were empty
    • 31% of diets (27 of 86) contained larval yellow perch
    • 20% of diets (17 of 86) contained zooplankton
  • D-NR Lakes = 29 larval walleye (diets summarized in Table 2)
    • Larval walleye mean length = 12.4 mm (range = 7.8 -21.0 mm)
    • 28% of diets (8 of 29) were empty
    • 52% of diets (15 of 29) contained larval yellow perch
    • 3% of diets (1of 29) contained zooplankton
Table 2. Mean percent composition by number and counts of prey items observed in larval walleye diets from S-NR and D-NR lakes.
Recruitment History:S-NR LakesD-NR Lakes
Diet Item% CompositionCount% CompositionCount
Daphnia spp.19.1404.81
Calanoid Copepods2.530.00
Cyclopoid Copepods8.1160.00
Bosmina spp.0.730.00
Larval Fish60.13471.415
Unidentifiable9.4523.85

Discussion

  • Larval yellow perch were the dominant prey item for larval walleyes in lakes exhibiting both sustained and declining natural recruitment.
    • Extent of piscivorymuch greater than previously assumed
  • In general, larval walleyes in S-NR lakes consumed a greater diversity of prey items and more zooplankton than larval walleyes in D-NR lakes.
  • Further statistical analyses required to determine if diets and prey availability differed between S-NR & D-NR lakes.

Acknowledgements

  • This study was funded by the Wisconsin Department of Natural Resources through the Fisheries Analysis Center at the University of Wisconsin-Stevens Point.
  • Jason Gostiaux
  • Walleyes for Tomorrow: Research Fellowship

U.S. Fish and Wildlife Service Seeks Public Input to Increase Access to Refuge System Lands

As part of its ongoing effort to increase public access on federal lands, the U.S. Fish and Wildlife Service today announced (news release attached) it is seeking the public’s assistance to develop a list of its managed lands that would benefit from new or increased access routes. 

On March 12, 2019, President Donald Trump signed into law the John D. Dingell Jr. Conservation, Management, and Recreation Act (S.47, the Dingell Act), which directs the Service and other federal land management agencies to develop a priority list of lands that have significantly restricted or no public access where that access could be improved. The public is encouraged to identify national wildlife refuges, fish hatcheries and other lands managed by the Service that meet the complete criteria. 

Comments will be accepted over a 30-day comment period from February 10-March 11, 2020. 

Some of the criteria for nominated lands include: public lands must be managed by the Service and 640 contiguous acres; have significantly restricted or no public access; and be open under federal or state law to hunting, fishing, or use of the land for other public recreational purposes. 

For additional information and a full list of required criteria for consideration as specified by the Dingell Act, visit: https://www.fws.gov/refuges/realty/Public-Access-Nominations.html

Commenters are encouraged to review the required criteria and include additional information as to why the parcel should be on the Service’s priority list. Once the comment period closes the Service will evaluate the nominations to determine which lands meet the requirements and considerations specified by the Dingell Act.

Flexible Classification of Wisconsin Lakes for Improved Fisheries Conservation and Management

Successful fisheries management practices developed for one ecosystem can often be used in similar ecosystems. We developed a flexible lake classification framework in collaboration with ~100 fisheries biologists for improved fisheries conservation management in Wisconsin, USA. In total, 5,950 lakes were classified into 15 lake classes using a two tiered approach. In tier-one, lakes were clustered into “simple” and “complex” sportfish assemblages. In tier-two, lakes were further clustered using accumulated degree days, water clarity, and special cases. We focus on temperature and clarity because these factors often drive fisheries change over time — thus a lake’s class can change over time. Lake class assignments were refined through a vetting process where fisheries biologists with expert knowledge provided feedback. Relative abundance, size-structure, and growth rates of fishes varied significantly across classes. Biologists are encouraged to utilize class interquartile ranges in fisheries metrics to make
improved fisheries assessments. We highlight hard-won lessons from our effort including: (1) the importance of co-developing classification frameworks alongside fisheries biologists; and (2) encouraging frameworks where lakes can shift classes and fisheries expectations over time due to factors like climate change and eutrophication.

Expanded Assessment of Recruitment Bottlenecks for Age-0 Walleye Sander Vitreus in Northern Wisconsin – Thesis

A Thesis Submitted in partial fulfillment of the requirements of the degree
MASTER OF SCIENCE IN NATURAL RESOURCES (FISHERIES)
College of Natural Resources UNIVERSITY OF WISCONSIN
Stevens Point, Wisconsin

Many northern Wisconsin lakes that historically supported naturally-recruiting walleye Sander vitreus populations have shown declines in recruitment over the last 10-15 years. Previous research conducted on four northern Wisconsin lakes suggested a recruitment bottleneck was occurring before mid-July in lakes with declining walleye natural recruitment. Effective management of walleye populations involves understanding these recruitment bottlenecks, as potential management solutions may vary in relation to when and why this recruitment failure is occurring. To further assess these recruitment bottlenecks, I expanded on the previous assessment to determine if: 1) timing of a recruitment bottleneck for age-0 walleyes was consistent among lakes with declining
recruitment; 2) abiotic and biotic metrics differed between lakes with declining (D-NR) and sustained (S-NR) walleye recruitment, with a specific focus on the abundance of edible zooplankton and 3) catch-per-effort (CPE) of larval and post-larval walleyes can be used to predict the presence, absence, and relative strength of walleye year-classes indexed by standard fall electrofishing conducted by the Wisconsin Department of Natural Resources and the Great Lakes Indian Fish and Wildlife Commission.

Changes To The Fox River Locks?

Here is an article ran in today’s Milwaukee Journal Sentinel on concerns over potential changes to the Fox River locks and the formation of the Winnebago System Fisheries Preservation Alliance.

2017-18 Winnebago System Walleye Report

Attached is the 2017 Winnebago Walleye Report. The report covers a variety of topics including 2017 spring water level and walleye hatch results, 2017 spring adult spawning stock results, walleye exploitation and reward tag study results, a walleye population outlook, and a regulation change discussion update.

Walleye anglers have enjoyed some productive walleye fishing on the Winnebago System over the last few months, particularly in May and June. Many anglers have also been wondering how the 2018 walleye hatch will stack up after the historical spring weather events that swept through the area (you may remember the 30 inch snow event in April). DNR staff and a host of local volunteers completed the first round of the Annual Lake Winnebago Bottom Trawl Assessment last week.

Preliminary results indicated a measurable 2018 walleye hatch (5.7 young of year/trawl), but we will have to wait until the September and October trawling rounds are completed for official results. The survey is also vital for evaluating the year class strength of other sport and forage fish species in Lake Winnebago. Stay tuned for the annual trawling report once the survey concludes in fall. I hope you enjoy the walleye report and good luck with your summer fishing adventures. We are committed to service excellence.

Visit our survey at http://dnr.wi.gov/customersurvey to evaluate how I did. Adam D. Nickel Phone: (920) 424-3059 adam.nickel@wisconsin.gov

Click here for 2017-18 Winnebago System Walleye Report

The Sauger Project – WFT

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