Effects of Climate-Driven Water Level Loss on Fish Habitat Availability, Predator-Prey Interactions, Population Dynamics, and Behavior in Two North Temperate Lake Basins

Global climate change is expected to influence freshwater ecosystems. Fishes may be particularly vulnerable to climate change, as altered thermal and dissolved oxygen regimes may effect fish species diversity, distributions, and potentially result in local extirpations. Climate change may also influence fishes through alternative mechanisms, such as drought. Natural littoral structure (e.g., coarse woody habitat, CWH) can serve as critical fish habitat for prey production, refuge, and spawning sites. Yet, available littoral structures may be lost to lake level declines induced by drought. A prolonged drought in northern Wisconsin, USA allowed us observe conditions similar to those expected to occur in many north temperate lakes. We used two isolated basins of Little Rock Lake to test for the effects of drought on littoral habitat loss and fish predator-prey interactions, population dynamics, and behavior. During our study (2001-2009), the lake level of Little Rock Lake declined over 1.1 m and more than 75% of the previously submerged CWH was lost from the littoral zone. The loss of CWH was associated with prey fish (yellow perch, Perca flavescens) populations falling below detection, altered piscivore (largemouth bass, Micropterus salmoides) densities, shifts in bass foraging behavior, and reduced bass growth rates. Our results suggest that CWH loss associated with reduced lake level can severely alter fish populations. Our study highlights the importance of considering alternative mechanisms by which climate change may influence fish and fisheries, such as drought-induced lake level reductions, as scientists and lake managers look toward the future of aquatic ecosystems in a changing climate.