Walleye, a popular freshwater fish, engage in a distinct reproductive process known as spawning. This annual event involves the release and fertilization of eggs, directly influencing the health and abundance of walleye populations.
Optimal Spawning Conditions
Walleye begin spawning in early spring, often after ice melt. Water temperature is the primary environmental cue, with spawning commencing between 40 to 50 degrees Fahrenheit (4 to 10 degrees Celsius) and peaking at 44 to 48 degrees Fahrenheit (6.7 to 8.9 degrees Celsius). Increasing daylight hours (photoperiod) also signals their migration to spawning grounds.
They prefer shallow areas, from 1 to 10 feet deep, with clean, hard bottoms of rocky cobble, gravel, or rubble. These locations are found in river rapids, tributary mouths, or windswept lake shoals, where water flow or wave action aerates and keeps eggs free of fine sediment. Some populations also use flooded wetland vegetation with sufficient water flow.
The Spawning Process
Before spawning, walleye migrate from deeper wintering areas to shallow spawning grounds. Males arrive earlier than females. During spawning, which often occurs at night, females release eggs into the water. Multiple males then release milt (sperm) to fertilize the eggs externally.
Walleye eggs are adhesive, sticking to rocky or gravelly substrate, preventing them from being swept away. A single female can deposit tens of thousands to over 100,000 eggs. After eggs are laid and fertilized, walleye do not exhibit parental care. An individual female can complete egg deposition in a single night, though the population’s spawning season may last a few weeks.
From Egg to Fry
Once laid, walleye eggs undergo an incubation period dependent on water temperature. At 40 degrees Fahrenheit (4.4°C), eggs may take approximately 26 days to hatch, while at 57 degrees Fahrenheit (13.9°C), hatching can occur in as little as 7 days. Newly hatched walleye, called fry, are very small, averaging about 0.3 inches (7.6 mm) in length.
Initially, fry rely on a yolk sac for nourishment. As the yolk sac is absorbed (within a few days to a week post-hatch), fry transition to feeding on small aquatic organisms. Their first food sources include zooplankton such as rotifers, copepods, and small cladocerans. This early life stage is highly vulnerable, and a significant portion of eggs and fry may not survive due to predation and environmental challenges.
Factors Affecting Spawning Success
Several factors can impact walleye reproduction. Habitat degradation, such as pollution, increased sedimentation, or physical alteration of shorelines, can damage or reduce suitable spawning grounds. Poor water quality, including contaminants or unusual pH levels, can negatively affect egg viability and fry survival.
Climate change, leading to fluctuating temperatures or extreme weather events, can disrupt spawning cues, potentially causing walleye to spawn too early or too late. This can result in eggs being laid in suboptimal conditions. Artificial water level fluctuations from dam operations can strand eggs, expose them to air, or wash them away, impacting reproductive success.
Natural predation on walleye eggs and fry by other fish, invertebrates, and birds contributes to mortality. Human activities, particularly fishing pressure, are managed through regulations like closed seasons during spawning to protect vulnerable walleye. These measures aim to ensure successful reproduction, supporting healthy populations.