Workshop on the temporal migration patterns of European eel (WKEELMIGRATION)

Abstract

1. The Workshop on the temporal migration patterns of European eel (WKEELMIGRATION) was formed to answer the questions posed by the EC on the temporal migration patterns of European eel in EU areas 2. In this report the group explored data supplied from EU Member States and Norway on time-series of fishery landings and eel monitoring, and reviewed the scientific literature to describe the period and the peak time of abundance of glass, yellow and silver eel stages in the different EU regions and through narrow straits and whether these have changed substantially since the implementation of Eel Management Plans, and whether fishery closures in 2018 and 2019 appeared to follow the relevant EC/GFCM temporal closure periods. 3. There are seasonal and geographic patterns of migration of immigrating recruits (glass eel plus older stages) and emigrating silver eel. Typically, recruits arrive later further north along the Atlantic coasts and much later in the Baltic, whereas arrival patterns in the Mediterranean are more complex. Silver eel emigrations follow the reverse pattern, typically starting earlier at the furthest distances from the oceanic spawning grounds, although there appears to be a spring emigration in the Baltic region. The yellow eel situation is more complex and difficult to examine as they do not typically follow discrete migrations. There may be seasonal redistributions of yellow eel in some waters but there was an absence of obvious latitudinal patterns and seasonalities. There were very few differences in seasonality suggested by comparisons of before and after the EMP implementation, there were only very limited data from which to make these comparisons, but the WK did not identify any biological reasons why substantial differences might have happened. There were limited data to examine the seasonality of glass and silver eel passage through the narrow water areas of the Baltic and Mediterranean, and the English Channel, but patterns suggested by tracking studies were consistent with migration patterns of nearby areas. Most of the fishery closures implemented in 2018 followed the requirements of the EC closures for that time. Many more appeared not to follow the requirements during the 2019/2020 period but these warrant further investigation before drawing strong conclusions. 4. In general, uncertainties remain because data were very limited from which to make comparisons across the desired continental geographic scale, across 20 years, and for multiple eel life stages. The WK is confident that it had access to the best available data from fishery landings and monitoring studies, albeit that the complexities of aquatic habitats, their definition and delineation, and life stages complicated analyses. However, the description of fishery closures was more complicated than envisaged, for example because closures are rarely complete across the whole EMU but instead may target certain eel stages, fishing gears or waterbodies within an EMU, and consequently further work is recommended to fully document and analyse these. 5. The WK has addressed the ToR with the available data and information, but highlighted gaps in the knowledge that limited its ability to provide complete answers.