Fluctuations in European eel (Anguilla anguilla) recruitment resulting from environmental changes in the Sargasso Sea

Abstract

European eel decline is now widely observed and involves a large number of factors such as overfishing, pollution, habitat loss, dam construction, river obstruction, parasitism and environmental changes. In the present study, we analyzed the influence of environmental conditions in the Sargasso Sea and Atlantic ocean circulation on European glass eel recruitment success. Over a recent 11-yr period, we showed a strong positive correlation between an original index of glass eel recruitment and primary production (PP) in eel spawning area. Moreover, PP was negatively correlated with temperature in the Sargasso Sea. Therefore, we used sea temperature as an inverse proxy of marine production. A close negative relationship has been found over the last four decades between long-term fluctuations in recruitment and in sea temperature. These findings were reinforced by the detection of a regime shift in sea temperature that preceded the start of the decline in glass eel recruitment in the early 1980s. By contrast, variations in integrative indices measuring ocean circulation, i.e. latitude and strength of the Gulf Stream, did not seem to explain variations in glass eel recruitment. Our results support the hypothesis of a strong bottom-up control of leptocephali survival and growth by PP in the Sargasso Sea on short and long time scales. We argue that sea warming in the eel spawning area since the early 1980s has modified marine production and eventually affected the survival rate of European eels at early life stages.

Feeding on protists and particulates by the leptocephali of the worm eels <i>Myrophis</i> spp. (Teleostei: Anguilliformes: Ophichthidae), and the potential energy contribution of large aloricate protozoa

“…Ciliate abundance and availability might change owing to global climate change and its impact on the world's oceans (Miller et al, 2009). A shift in the complexity of primary producers driven by increased temperatures from large diatoms to small dinoflagellates, and consequent shifts in the abundance of heterotrophs and mixotrophs, could change food webs (Friedland et al, 2006;Bonhommeau et al, 2008) in ways that could compromise the availability of large protozoa as food for leptocephali. This would influence negatively the survival of eels through their early life history (Desaunay and Guerault, 1997).…”

Assessing the freshwater distribution of yellow eel

“…However, today it is declining sharply throughout its distribution area (Moriarty and Dekker, 1997;Dekker, 2003b). Although we do not understand the exact causes of this decline, it is speculated that the main factors involved are probably changes in oceanographic conditions that are assumed to be linked to climate changes (Desaunay and Guérault, 1997;Knights, 2003;Bonhommeau et al, 2008), habitat changes and the obstruction of migration by dams and other physical obstacles (Feunteun, 2002;Laffaille et al, 2004Laffaille et al, , 2007, and the impact of parasites and chemicals (Robinet and Feunteun, 2002;Kirk, 2003). In this context, Russel and Potter (2003) suggested that the precautionary approach is the most appropriate way to consider European eel stock management.…”

Genetic patchiness in European eel adults evidenced by molecular genetics and population dynamics modelling

“…Large-scale environmental fluctuations such as the North Atlantic Oscillation (NAO) have been linked to significant changes in the physical and biological structure of the North Atlantic Ocean, affecting thermal, wind and mixing parameters in areas of the Sargasso Sea that correspond spatially to the spawning grounds of the European eel (Knights, 2003;Miller, 2009;Miller et al, 2009). Environmental changes within the spawning and early larval development areas of eels in the Sargasso Sea might reduce the number of successful breeders and surviving larvae (Friedland et al, 2007;Bonhommeau et al, 2008). In a recent study using otolith microchemistry, Martin et al (2010) found significant differences in trace element signatures between glass eels/ elvers collected in European locations and leptocephali caught in the Sargasso Sea, suggesting that the former were born in a spawn- ing site linked to favourable transport and/or feeding conditions, while the latter may have been sampled in a less favourable region in the Sargasso Sea, with a low probability of reaching continental growth areas.…”

“…On the one hand, there are several anthropogenic factors mainly affecting eels on their continental phase, such as overfishing, migration barriers (dams and hydroelectric power plants), habitat loss, pollution (PCBs and heavy metals) and human-introduced diseases (EVEX virus) and parasites (the swimbladder nematode Anguillicoloides crassus) (Van den Thillart et al, 2009). On the other hand, climatic and oceanic events might contribute to the decline as they influence silver eel migration, mating and spawning success of adults in the Sargasso Sea, egg and larvae development, and larval survival during migration to the continental feeding grounds (Knights, 2003;Friedland et al, 2007;Bonhommeau et al, 2008;Miller, 2009;Miller et al, 2009;Martin et al, 2010).…”