Assessment of Eel Production in England and Wales in Light of the EU Recovery Plan

The European Eel Recovery Plan and ICES international stock assessment requires EU Member States to estimate their present-day silver eel escapement biomass and the potential in the absence of human impacts, their “best estimate of escapement that would have existed if no anthropogenic influences had impacted the stock”, and the lifetime mortality rate due to all anthropogenic impacts on eel in their waters. Here, we describe the development and application of a methodology to derive these stock indicators for the 11 River Basin Districts (RBD) of England and Wales. Without silver eel data, the method is based on yellow eel surveys conducted by the Environment Agency and its predecessors, and produces estimates for ‘today’ and before the recruitment crash in the early 1980s. Yellow eel biomass from the freshwater compartment in ‘eel index’ rivers is extrapolated to potential silver eel production using an individual-based life history model. Silver eel production per wetted hectare is applied to the RBD and losses due to fishing, abstractions, hydropower, barriers and pumping stations are subtracted to estimate silver eel escapement. This paper concludes with a discussion of the assumptions in this method and how these might be addressed in the future.