Reproductive and Recruitment Success of Walleye in the Muskegon River

Primary Investigator:

Carl Ruetz* - Grand Valley State University

Co-Investigators:

Edward Rutherford - NOAA/GLERL
Jordan Allison - Grand Valley State University*
Joe Nohner, Jeff Elliot - Universtiy of Michigan*

NOAA Research Area:

Forecasting ecosystem events.

Performance Objective:

Increase number of fish stocks managed at sustainable levels.

Research Milestones:

Define the primary forcing factors and time and space scales that affect fish recruitment and fisheries production for selected coastal and Great Lakes regions.

Executive Summary of Rationale

Walleye (Sander vitreus) is an ecologically and economically important piscivore species in the Great Lakes. The Muskegon River is the second largest tributary to Lake Michigan and historically supported a large population of walleye, with estimates in the mid-1950s as high as 140,100 adult spawners (O’Neal 1997). However, by the 1960s walleye populations dropped to roughly 6,000 adults in the Muskegon River. Overfishing, alewife (Alosa pseudoharengus) predation on larvae, sea lamprey (Petromyzon marinus) predation on adults, and alterations in spawning and nursery habitat and water quality all may have contributed to this decline. Recent studies indicate the walleye population in the Muskegon River still don’t reproduce successfully due to factors occurring sometime during the first year of life. This project will provide information to evaluate multiple hypotheses related to the recruitment bottleneck during the egg and larval stages for the walleye population in the Muskegon River.

Our proposed study focuses on recruitment bottlenecks for walleye during the egg and larval stages in the Muskegon River. Results from this study will provide information to better evaluate egg production and viability in the Muskegon River, relative magnitude of egg predation, and larval walleye drift. Information gathered from this project will guide efforts to restore and manage walleye populations in the Muskegon River and other Great Lakes tributaries.

Proposed Work

Current/Ongoing

The purpose of this project is to investigate reproductive and recruitment success of walleye in the Muskegon River. We propose to conduct field sampling (see below) during two successive years. In each year, we will

a) Estimate egg deposition, survival, and hatching success in specific areas of the Muskegon River.
b) Relate effects of egg predation to egg survival and hatching success
c) Quantify emergence of larvae from natural substrates in specific areas of the Muskegon River
c) Estimate the drift of larvae from specific areas of the Muskegon River to Muskegon Lake.

Egg deposition. We will estimate egg deposition using egg mats deployed in the Muskegon River. Six egg mats will be deployed at each of three sites (i.e., known walleye spawning sites between the Pine and Thornapple boat launches downstream of Croton Dam). Egg mats will consist of furnace filter attached to a weighted frame, which have been successfully used in the Muskegon River (Ivan and Rutherford, in prep) and other rivers (Manny et al. 2007). Egg mats will be randomly assigned to locations with rocky substrate at each site. Egg mats will be retrieved every 4 days over 6 weeks during the walleye spawning season (i.e., totaling 10 collections). A total of 180 mats (3 sites × 6 replicates × 10 collection dates) will be collected to estimate egg deposition. A sub-sample of eggs collected will be hatched out at a Michigan DNR aquaculture facility to verify the eggs are viable and from walleye.

Egg survival and hatching success. We will estimate egg survival and hatching success using Plexiglas incubators deployed in the Muskegon River. Six egg incubators will be deployed at each of three sites (same sites used to estimate egg deposition). Incubators will be assigned to random locations with rocky substrate at each site. Plexiglas egg incubators will follow the design of Manny et al. (1989) and hold 50 fertilized eggs each. Fertilized walleye eggs will be obtained from the Muskegon River spawning run by Michigan DNR personnel. Fine-mesh nitex screening will be used to retain and protect eggs from invertebrate and fish predators and will provide an estimate of egg hatching success in the absence of predation. Incubators will be checked regularly, and hatching success (% hatch) will be determined after 14 and 21 days (hatching should peak after about 17 days given typical water temperatures). Thus, we will deploy 36 incubators (3 sites × 6 replicates × 2 collection dates) to estimate hatching success in the absence of egg predators. Additionally, replicate controls will be monitored at the hatchery under ambient river temperatures to compare fertilization and hatching success under controlled conditions.

Egg predation experiment. We will conduct a manipulative field experiment to estimate the relative effects of predation on walleye eggs in the Muskegon River. Mesh baskets (15 cm × 15 cm) lined with fine-mesh nitex screening (open on the top) will be filled with natural gravel substrate (scrubbed clean of debris) and inoculated with 20 fertilized eggs (median densities from Croton to Thornapple 20 eggs/m2). Once inoculated, egg baskets will be assigned to an exclosure or open-control cage constructed of 6-mm wire mesh. This mesh size will exclude fish › 45 mm TL (Ruetz et al. 2002) and similarly sized crayfish. Exclosure cages will have mesh on all sides, whereas open-control cages will lack mesh on the downstream side to allow predator access (e.g., Ruetz et al. 2002). Cages will be deployed at three sites (same sites used to estimate egg deposition), and cages and egg baskets will be retrieved after 1 week to determine the number of eggs remaining. A total of 36 cages (3 sites × 2 treatments × 6 replicates) will be used to examine the relative effects of predation on egg mortality. If eggs are available after the completion of the first experiment, then we will repeat this experiment a second time. We also will conduct a smaller-scale experiment using furnace filters inoculated with fertilized eggs to estimate the potential effects of predation on estimates of egg deposition. Finally, we will estimate the relative density (i.e., catch per unit effort) of potential predators via backpack electrofishing at each site.

Larval emergence. We will estimate the emergence of walleye larvae from the substrate using emergence traps. Emergence traps will consist of fine-mesh nitex screening over a metal frame (37 cm × 37 cm × 13 cm) with a collection bottle on the downstream side (see Dumas and Marty [2006] for a similarly-designed trap). Each trap will have a 15-cm skirt around the edge to be buried in the substrate. Four emergence traps will be deployed 24 hours at randomly assigned locations with rocky substrate at each of three sites (same sites used to estimate egg deposition). Sampling will be conducted 3 times/week for 3 weeks when emergence is thought to peak. The contents of each sample will be preserved in ethanol for inspection in the laboratory. A total of 108 samples will be collected to estimate the larval emergence (3 sites × 4 replicates × 9 collection dates).

Larval drift. We will conduct larval drift sampling immediately downstream of three walleye spawning sites (same sites used to estimate egg deposition) for 4 weeks encompassing the peak of walleye spawning and larval emergence. Sampling frequency will be 2 nights/week during the first and fourth weeks of sampling and 4 nights/week during the second and third weeks of sampling (i.e., 12 collection dates). Sampling will be similar to the approach used by Day (1991). The drift net will be deployed from the front of a boat (fished like a push net). Two replicate samples will be collected near the river’s surface and bottom. Each drift sample will be deployed for 10 min, and a flow meter will be placed in the mouth of the net to estimate the volume of water sampled. A total of 144 samples (2 water-column positions × 2 replicates × 3 sites × 12 collection dates) will be collected to estimate the density (#/m3) of larval walleye drifting in the water column in the Muskegon River. The contents of each sample will be preserved in ethanol for inspection in the laboratory. Concurrently with each sampling event at each site we will measure depth, velocity, temperature, turbidity, dissolved oxygen, and conductivity.

Scientific Rationale

Existing physical models of walleye recruitment success (Mion et al. 2006; Jones et al. 2006) are inadequate to explain walleye recruitment failure in the Muskegon River. Information gained from this study will quantify and partition sources of mortality that affect egg and larvae survival, and suggest ways to improve recruitment success.

Governmental/Societal Relevance

Environmental Objectives for Lake Michigan recognize tributaries as critical habitats for wild, self sustaining piscivore populations and fisheries. The available evidence suggests that establishing a self-sustaining walleye population in the Muskegon River is limited by survival of fish in the first year of life. This population was self-sustaining prior to 1960, but recruitment of juvenile fish has been very low for the past 48 years. This project will provide information to evaluate multiple hypotheses related to the recruitment bottleneck during the egg and larval stages for the walleye population in the Muskegon River.

Relevance to Ecosystem Forecasting

This study will improve existing forecasts of walleye recruitment in Great Lakes tributaries by combining physical and biological factors that influence survival and dispersal of walleye eggs and fry.

*Link leads off GLERL's website