Recent recruitment trends of juvenile eels in tributaries of the River Thames

Abstract

Over the past 25 years it has become apparent that European eel recruitment has declined despite increased awareness and the development of protective legislation at local, national and European levels. A number of factors in both the freshwater and marine environment have been identified as potentially causing the decline, but there is little evidence how they specifically affect eel populations. There has been very little monitoring of European eel populations and therefore few robust data sets to allow long-term analysis. Eels were monitored at three sites in the Thames catchment between 2005 and 2009. At one site (River Roding) the catch per unit effort declined significantly after 2007, whilst at the other sites (River Thames and River Darent) catches were low throughout the period of the survey. Comparison of eel abundances at the River Darent caught in the present study with those caught in the mid 1980s would indicate that recruitment has declined by over 99%. The study highlights the lack of data relating to eel recruitment in the River Thames, and the UK as a whole, and supports both improved monitoring and the adoption of a precautionary approach in their management, irrespective of the causal factors for the decline.