A Quantitative Assessment of Spawning Habitat for Smallmouth Bass (Micropterus dolomieu dolomieu) in Northern Wisconsin Lakes

Abstract

Anthropogenic disturbances in near-shore littoral zones of lakes may affect spawning habitat and recruitment of smallmouth bass. However, the degree to which habitat models describe the critical spawning habitat that influences smallmouth bass populations is yet unclear. To better understand how littoral zone habitats regulate fish populations, the quality and quantity of smallmouth bass spawning habitat in two northern Wisconsin lakes were quantified. In general, nest sites in both lakes were located in water depths of 0.5 - 3.0 meters and in areas having more than forty percent gravel substrates that were not highly embedded. However, habitat selection differed between lakes. Resource selection functions that best described nest site selection in Big Crooked Lake contained as many as six significant habitat variables: percent sand, percent gravel, percent cobble, substrate embeddedness, wood cover, and rock cover. Correct classification rates were as high as eighty-four percent. In contrast, resource selection functions in Sanford Lake were more general containing four variables: percent sand, percent gravel, substrate embeddedness, and rock cover and having an overall classification rate of ninety-two percent. Transferability of these models differed substantially when validated across lakes. The more general model developed in Sanford Lake correctly classified one hundred percent of the nest sites in Big Crooked Lake, while the model developed in Big Crooked Lake correctly classified only eight percent of the nests in Sanford Lake. Thus, the less complex model was more transferable across lake systems. Overall survival from egg to post swim-up fry and then to age 0+ were similar across both lakes. However, survival rates of eggs to fry at the nest site were significantly different (p < 0.05) between lakes and was a function of a combination of biological and habitat variables. In Big Crooked Lake, where nest sites were located on coarser substrates, survival was high and the distance from nest to nest increased survival of eggs and fry on nest sites. However, in Sanford Lake where less coarse substrates occur, increasing cobble substrate, the diameter of cover, the water depth of the nest, and the length of the male bass on the nest were positively related to survival. Differences in habitat between lakes affected both habitat selection and survival. These analyses provide information to protect smallmouth bass spawning habitat, and provide quantitative models for habitat enhancement and mitigation in lakes.