Modelling the recruitment of European eel (Anguilla anguilla) throughout its European range

Abstract

European eel (Anguilla anguilla) recruitment has been declining at least since the early 1980s at the scale of its distribution area. Since the population is panmictic, its stock assessment should be carried out on a range-wide basis. However, assessing the overall stock during the continental phase remains difficult given its widespread distribution among heterogeneous and separate river catchments. Hence, it is currently considered by the International Council for the Exploration of the Sea (ICES) more feasible to use glass eel recruitment data to assess the status of the overall population. In this study, we used Glass Eel Recruitment Estimation Model (GEREM) to estimate annual recruitment (i) at the river catchment level, a scale for which data are available, (ii) at an intermediate scale (6 European regions), and (iii) at a larger scale (Europe). This study provides an estimate of the glass eel recruitment trend through a single index, which gathers all recruitment time-series available at the European scale. Results confirmed an overall recruitment decline to dramatically low levels in 2009 (3.5% of the 1960–1979 recruitment average) and highlighted a more pronounced decline in the North Sea area compared to elsewhere in Europe.

Freshwater eels: A symbol of the effects of global change

“…However, the improvement in data quality and the recent development of a generic model that can be used at a larger geographic scale is a first step. For example, the GEREM model provides estimates of glass eel recruitment that can be used to assess glass eel fishery exploitation rates (Bornarel et al., ; Drouineau, Beaulaton, et al., ). The models EDA (Briand, Beaulaton, Chapon, Drouineau, & Lambert, ) or SMEP (Aprahamian, Walker, Williams, Bark, & Knights, ) can be used to assess the abundance of yellow eels in river catchments.…”

First examination of the Lough Neagh European eel (Anguilla anguilla) population for eel virus European, eel virus European X and Anguillid Herpesvirus‐1 infection by employing novel molecular techniques

“…The Lough Neagh European eel population has been intensively studied (Allen, Rosell, & Evans, ; Bornarel et al., ; Rosell, Evans, & Allen, ) during which no eels have been observed as displaying either acute or chronic viral signs. However, viral infections have been suggested to play a contributory role in the decline of the worldwide eel stock (Esteve & Alcaide, ; ICES, ; Van Ginneken et al., ) and husbandry practices associated with eel farming including stress induced by high stocking densities, water quality and unfavourable water temperatures have been identified as key factors influencing viral disease outbreaks (AHAW Scientific Panel, ; Hangalapura, Zwart, Engelma, & Haenen, ).…”

On the actual recruitment of European eel (Anguilla anguilla) in the River Ems, Germany

“…For example, historical sources occasionally reflected on glass eel catches not only below the (old) tidal weir but also at the sluice (e.g., Meyer, ; Meyer‐Waarden, ). Consequently, data for the historical recruitment series from the River Ems were grouped to a dataset defined as “relative time‐series with no information on the scaling factor” by a study modelling eel recruitment at the European range (Bornarel et al., ). Hence, the current data cannot be directly compared with historical data and therefore are by no means a continuation of the historical recruitment series from the River Ems.…”

“…Since the early 2000s, the European eel stock has been considered outside of safe biological limits (ICES/EIFAAC, 2016a) with recruitment estimated to have fallen to a few percent of historical levels (e.g., Jacoby & Gollock, ). The lowest recruitment levels were estimated for 2009 (altogether <5% of the 1960–1979 average, ICES/EIFAAC, ; Bornarel et al., ). The recruitment of glass eel to European waters in 2016 was estimated at 10.7% of the 1960–1979 level for the Atlantic with the Mediterranean and 2.7% for the North Sea (ICES/EIFAAC, 2016a).…”

“…In Germany, historical data exist from commercial glass eel fisheries in the River Ems. Recruitment time series as used by ICES in its yearly stock advice, that is, in the absence of a robust stock recruitment relationship (Walmsley, Bremner, Walker, Barry & Maxwell, ), also consider the historical glass eel catches from the River Ems (e.g., Bornarel et al., ; ICES/EIFAAC, 2016b; Moriarty, ).…”