Estimating Esox lucius (Esocidae, Esociformes) Density and Population Structure in a Large European Alluvial River:

We developed a sampling protocol for pike (Esox lucius L., 1758) in large alluvial rivers in order to estimate adult population density and structure. This species is known as an indicator of lowland river biotic integrity in Europe evidencing the interest to determine population densities to a reliable degree of accuracy. A two occasion mark-recapture experiment based on a combination of net fishing and boat electro-fishing was specifically designed for monitoring of backwaters and channel sectors during the annual high flow level of an alluvial river, the Allier (France). Estimated densities calculated by using Chapman-Petersen and Log- linear models were weak, ranging from 0.68 (±0.16) fish.ha -1 to 0.71 (±0.20) fish.ha -1 . However, when the densities are divided by the area of potential riverine habitats, pike abundance was calculated as being 15.3 (±3.7) fish.ha -1 to 15.9 (±3.8) fish.ha -1 . Pike growth was high and 8 to 9 yearold females were captured. Age and sex distribution emerged as unbalanced, highlighting the precarious status of pike in the studied stretch of the river due to very limited recruitment. Pike were mainly captured in parapotamic side arms which underlines the importance of lateral habitats in semi regulated large alluvial rivers with wide riffle-pool-run sequences dominating geomorphological units.