by Scott Brown
MWA e-Newsletter Editor
The popular panfish known as bluegill (Scientific name: Lepomis macrochirus) and many other sunfish species that are often present in thousands of Michigan’s inland lakes begin their annual spawning season in response to mid-to-late spring water temperatures of 67° F. The annual spawning ritual begins as male bluegills create protective depressions of up to twelve inches in diameter in water depths of up to four feet by using their tails to scoop out sand and other organic materials while leaving gravel in place. Located in areas of flat or gradually sloping lake bottom not occupied by submerged aquatic plants, bluegill spawning beds often consist of up to 50 gravel lined depressions. The annual spawning ritual begins as a female bluegill approaches the nest prompting the male to begin circling and making grunting noises. The motion and sound of the males attracts females. If the female enters the nest, both the male and female will circle each other, with the male expressing aggressive behavior toward the female. If the female finds the male attractive and chooses to stay, the pair will enter the nest and come to rest in the middle. With the male in an upright posture, the pair will than touch bellies, quiver, and spawn. Successful spawning occurs when the male’s sperm combines with the female’s eggs that than fall gently into the protective interstitial spaces that exist between the gravel that lines the nest. A healthy large female bluegill can produce up to 100,000 eggs. Her role now complete, the female bluegill leaves the nest – leaving the male to protect the developing eggs. Male bluegills protect their nests by aggressively chasing away potential predators and by preventing sediment from smothering the eggs by fanning the nest with his tail (see photo above).
Lake associations and others interested in protecting the reproductive rituals of bluegill and other sunfish species can begin by identifying areas within a particular inland lake that support spawning beds and encourage boaters to stay out of these areas during the annual spawning period. The turbulence created by a single motorboat pass through an active spawning area occupying shallow water can cause tiny developing sunfish eggs to be flushed out of their nests that than become vulnerable to predation. Lake associations should also discourage fisherman from fishing in spawning areas – the loss of male bluegills who are actively defending their nests during the spring spawning period can result in the loss of tens of thousands of developing eggs as now unprotected nests become vulnerable to predators. It is also important to point out that male bluegills that are caught during the annual spawning period should be immediately returned to the lake so they can continue to pro-actively protect their nests. Lake stewards can also help ensure the success of bluegill annual reproductive cycles by preserving natural shorelines and native aquatic plant communities that each provide optimal habitat for the fry and juveniles of bluegills and other sunfish species.