Density Dependence in Growth and Size Structure of NorthernPike Populations

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The density of northern pike Esox lucius was estimated using mark–recapture techniques and compared with measures of growth and population size structure among 12 north-central Minnesota lakes. The relationships between density and either proportional stock density (PSD, a length-frequency index) or mean back-calculated length were negative and nonlinear. Regression of loge density and PSD explained 63% of the variation in PSD, and regressions of loge density and mean back-calculated length by sex for ages 2–5 explained 47% to 67% of the variation in growth rates among lakes. The relationships remained consistent when data from 17 northern Wisconsin lakes were pooled with those from the 12 Minnesota lakes (although the R2 was reduced). The fastest growth rates and highest PSDs were observed at northern pike densities of less than 12–14 fish/ha. Inclusion of variables related to the productivity of the lakes only marginally improved the predictive capabilities of the relationship between loge density and growth in the Minnesota lakes. Lake productivity was more important, however, when data from Wisconsin and Minnesota lakes were pooled. In the pooled data, mean back-calculated length at age was negatively related to Secchi disk visibility and positively related to total alkalinity. Our results highlight the importance of density dependence in growth and population size structure for populations of northern pike within their native range.