Vegetative Substrates Used By Larval Northern Pike in Rainy and Kabetogama Lakes, Minnesota

Our objective was to identify characteristics of aquatic vegetation communities used as larval northern pike nursery habitat in Rainy and Kabetogama lakes, glacial shield reservoirs in northern Minnesota.  Larval northern pike were most commonly sampled using quatrefoil light traps among floating-leaf burreed Sparganium fluctuans, common burreed Sparganium eurycarpum, sedges Carex spp., hybrid cattail Typha x glauca, and wild rice Zizania palustris.  A negative binomial model of light-trap catches for 2012 from eleven bays included water depth and the presence of cattail as significant variables.  Our results contradicted previous research that documented northern pike avoidance of cattail for spawning and decreased spawning success due to cattails blocking access to submerged aquatic vegetation (SAV).  In our study, cattail dominated the larval habitat but residues of SAV from the last summer were accessible for spawning.  Ultimately, the species of aquatic vegetation may not be as important as the physical form of the vegetation.  Water-level regulations may influence SAV form, density, and type in shallow-water habitats of reservoirs during nursery periods.  Future development of an SAV density and composition spatial distribution model will help managers to quantify suitable habitat for northern pike larvae throughout Rainy Lake and Namakan Reservoir for different water-level regulation scenarios.