Regulation of Biomasses of Small (<41 cm) Northern Pike (Esox Indus L.), with Special Reference to the Contribution of Individuals Stocked as Fingerlings (4–6cm)

The composition and abundance of four northern pike (Esox lucius L.) populations were monitored in the period 1974–82. The biomasses of 0+ pike, pike <35 cm and pike <41 cm were negatively correlated with those of larger individuals following an exponential relationship. It is argued that this density-dependent relation is the result of a regulation in which intraspecific predation may play a major role. The standing stock of pike <54 cm, if related to pike habitat available, was very similar both among sites within years and among years within sites. This stock is tied to a maximum per unit of vegetated area. Within this maximum the biomass of pike <41 cm is determined by the biomass of larger individuals. Therefore stocked pike did not contribute extra biomass to the population.