Climate change and passive transport of European eel larvae

Abstract

One hypothesis to explain the large decline in the recruitment of the European eel (Anguilla anguilla) from the 1980s onwards is that a change in ocean circulation has influenced the drift of eel larvae, resulting in lower recruitment. To test this hypothesis, a simple Lagrangian model was constructed to simulate a passive drift from the spawning area in the Sargasso Sea to the European shelf. The simulation utilised the velocity data from a reanalysis of ocean climate, the Simple Ocean Data Assimilation (SODA 2.1.6), for the period 1958-2008 covering the time of regime shift in eel recruitment. The average drift time and latitudinal distribution of the arrival of eel larvae were explored for a range of constant depth levels and instantaneous mortalities. The model showed that the proportion of eel larvae carried by the North-East Atlantic Current to northern latitudes of arrival was greater before 1970, whereas there was an increase in amount of larvae being entrained into the southbound current branches after this time. The overall success of drift from the spawning area to the East Atlantic was not affected and clearly contradicts that this could explain the observed recruitment decline.

Freshwater eels: A symbol of the effects of global change

“…Three main mechanisms have been proposed: a limitation in trophic conditions (Bonhommeau, Chassot, & Rivot, ; Bonhommeau et al., ; Desaunay & Guerault, ; Friedland, Miller, & Knights, ; ICES, ; Kettle & Haines, ; Knights, ; Munk et al., ), changes in oceanic currents modifying larval transport (Castonguay, Hodson, Moriarty, et al., ; Friedland et al., ; ICES, ; Knights, ; Zenimoto et al., ), and/or spatial oscillations of a salinity front used by adult eels to detect the spawning grounds which then lead to oscillations in the success of larval transport (Kimura, Inoue, & Sugimoto, ; Kimura & Tsukamoto, ). In addition to statistical correlations, Lagrangian simulations of larval drift have also been carried out to explore some mechanisms (Bonhommeau, Castonguay, Rivot, Sabatié, & Le Pape, ; Bonhommeau et al., ; Kettle & Haines, ; Kim et al., ; Melià et al., ; Pacariz, Westerberg, & Björk, ; Zenimoto et al., ). These simulations suggested that, while for European eel the correlation between NAO and recruitment more likely reflects an indirect effect of trophic conditions in the Sargasso Sea (Bonhommeau et al., ; Pacariz et al., ), changes in oceanic currents directly affect Japanese eel larval drift (Kim et al., ; Zenimoto et al., ).…”

The ecology of oceanic dispersal and survival of anguillid leptocephali

“…There presently is little or no data available about the levels of mortality from starvation or predation experienced by leptocephali in the ocean and only general mortality values have been used for modelling purposes (Bonhommeau et al 2009b;Melià et al 2013;Pacariz et al 2014). The unusual biology and behavior of this type of larvae probably make it inappropriate to make assumptions about mortality based on knowledge of juvenile or adult eels or from other types of fish larvae that have different food sources, shorter larval durations, and smaller maximum sizes.…”

Synergistic patterns of threat and the challenges facing global anguillid eel conservation

“…The role these processes play in influencing eel populations is debated (Kimura et al, 2001;Bonhommeau et al, 2008;Miller et al, 2009;Pacariz et al, 2014), not least because so little is known about the marine component of anguillid life histories. Highly pertinent however, is that climate change is most likely to impact individuals during their most critical life stages; the oceanic migration of the larva from the spawning site to their coastal and freshwater growth habitat (i.e.…”

“…For example, two large hydropower facilities in the St. Lawrence River, Canada were estimated to cause cumulative annual downstream silver eel mortality of ∼40% (Verreault and Dumont, 2003) and across the waterways of Europe over 24,000 hydropower plants are now installed (van der Meer, 2012). The role of changing oceanic conditions as a result of climate change is increasingly being discussed in relation to eel larval migration and the subsequent recruitment of glass eels to continental waters (Castonguay et al, 1994;Dekker, 2004;Bonhommeau et al, 2008;Miller et al, 2009;Baltazar-Soares et al, 2014;Pacariz et al, 2014) although decoupling the impact of climate change from historic, natural variability in recruitment is difficult (Kim et al, 2004). Other factors that are implicated in affecting anguillid abundance include disease and parasites, predation, and pollutants (Robinet and Feunteun, 2002;Fazio et al, 2012;Wahlberg et al, 2014).…”