Pre-release processes influencing short-term mortality of glass eels in the French eel (Anguilla anguilla, Linnaeus 1758) stocking programme

The decline in the European eel has led the European Union to require that its Member States establish an Eel Management Plan, which includes a set of measures to help preserve and restore the wild eel populations. Stocking has been conducted in France since 2011 as part of this Management Plan. This stocking programme is based on a protocol designed by the French National Museum of Natural History and includes an assessment of the short-term (15 d after release) mortality and three recapture surveys at 6, 12, and 36 months after release. The present study aims to assess the different processes influencing the short-term mortality to provide recommendations to reduce mortality and increase the efficiency of the releases. A linear model was built to examine the different variables selected modelling. The resulting model explained 56.4% of the total deviance; the main factor in terms of explained deviance was the operation (31.2%), which actually includes a number of handling parameters. The other factors influencing the short-term mortality were the release year, the fishmonger that provided the glass eels, the duration of stalling (period of captivity) before release, the body condition, the marking, and the type of mortality test. It appears that some of these variables could be adjusted to reduce the short-term mortality. For instance, selecting the most suitable release sites to stock or selecting glass eels with good body condition, adjusting the duration of stalling, or limiting the marking should help reduce short-term mortality.