Temperate eel populations have been in severe decline due to anthropogenic influences. In Europe, acts of regulation are in place for the sustainable management of the European eel (A. anguilla) population, through annual assessment of commercial landings and recruitment trends. Recruitment of juvenile eels into estuaries and subsequent rivers is thought to occur through usage of the flood, ebb and slack tides (Selective Tidal Stream Transport, STST) and other environmental variables. However, instalment of estuarine barriers is known to affect upstream migration with adverse consequences for the population.
To evaluate anthropogenic impact (e.g. estuarine barriers) on recruitment and aid in the improvement of population assessment, we present an Agent-Based Model (ABM) for the upstream migration of glass eels/ elvers through estuaries. A systematic review of the impacts of environmental factors based on a meta-analysis of the literature provided the behavioural parameters of the agents. The ABM is coupled to a hydrodynamic model of the Thames Estuary (UK) and simulations are validated with catchment data from different sampling sites along this waterway.
Results from the meta-analysis show that the predominant mechanisms for upstream migration include drifting with the flood tide and remaining in the substratum during ebb tide, whereas exploitation of the slack tide is debatable. Water temperature, the salinity gradient, and the moon phase are the most reported environmental variables affecting STST/ migration. Based on this, the ABM proved to be successful in predicting upstream migration along the Thames while explaining the efficiency of STST. Finally, the ABM is applied The Milford Haven Waterway (UK), which is heavily exploited by human activities, to provide information on possible recruitment success here and illustrate its functionality in the context of estuarine barrier management.