The survival, growth and diet of pike fry, Esox lucius L., stocked at different densities in experimental ponds

Abstract

Yolk‐sac pike fry were stocked at densities of 0.74 – 81.4 m−2 in two ponds, each divided into eight sectors (mean area 155.8 m2). Growth and survival were recorded from May to December 1985. The growth rates were variable within each sector. The size‐range of sampled fish increased throughout the year, but showed no significant correlation with density. Fry survival was initially density‐independent but switched by late June/July to density‐dependence, ranging from 0.5 to 43.6% of initial stocking numbers. The highest mean daily mortality rates occurred during May‐July. The final survival in December ranged between sectors from 0.059 to 11.25% of the starting stock densities. The final biomass per unit area of pike surviving in December was not related to initial stocking density. In Pond 1 the mean biomass produced was 2.21 gm−2 and in Pond 2 was 3.49gm−2.Pike fry < 30 mm fed only on invertebrates; those 30–100 mm took a wide range of invertebrates, cyprinids. sticklebacks and other pike. Cannibalism occurred at most densities between 5.45 and 81.4 fish m−2.Where attempts are made to increase pike production in managed populations by releasing small fry, an upper stock density of 5 fry m−2 is advised if large, density‐dependent mortalities are to be avoided.