Density and biomass of native northern pike populations in relation to basin-scale characteristics of north-central Minnesota lakes

Habitat and ecological constraints that influence populations of northern pike Esox lucius at the scale of the lake basin were determined for 16 north-central Minnesota lakes that varied in size, depth, and chemical productivity. The density and biomass of northern pike greater than 350 mm total length were highly variable among takes (3.2-59.0 fish/ha, 3.6-33.6 kg/ha). Densities of large northern pike were very low; fish longer than 600 mm averaged only 1.6 fish/ ha. Northern pike populations were more closely linked to lake morphometry than to differences in other ecological factors, such as water productivity, exploitation, or the relative abundance of prey fish. For northern pike exceeding 350 mm, numbers and mass were most strongly related to littoral and optimum thermal habitat; percent littoral area was the most important variable explaining the density differences. Literature values from other geographic areas tended to support the importance of littoral habitat except when recruitment was limited by winterkill. For large northern pike (> 500 mm), the total area of the Minnesota lakes and shoreline length became more important than littoral area for predicting numbers and mass. Our results point to fundamental relationships between northern pike populations and the morphometry of the lake basins they inhabit. The suitability of a lake's habitat to support northern pike (as influenced by basin morphometry) has strong effects on their density, which in turn has important effects on growth rates, production, and population size structure.