Differential effects of behaviour, propensity to migrate and recruitment season on glass eels and elvers’ growing performance

Abstract

– Social interactions impact growth rate of animals in different ways such as direct or indirect competition for food and/or territories. In this study, behaviour of glass eels and elvers was described throughout three trials of 9 days spread out over 3 months. The impact of recruitment season (spring and autumn runs) and glass eels’ propensity to migrate (assessed thanks to an experimental sorting) on individual growth was studied. Overall, spring elvers were more aggressive and active than autumn elvers while autumn fish were more gregarious and reached a higher specific growth rate than spring fish. At the individual level, gregariousness and swimming, respectively, promote and impair growth rate. In addition, skinny individuals and individuals with high motivation to get food achieved better growth rate suggesting catch‐up growth processes. These findings may help in clarifying the complex relations between behaviour, growth, river basin colonisation and future sex (which is environmentally determined in eel) and then contribute to the urgent need of scientific knowledge to guide the stocking programme of this endangered species.

EvEel (evolutionary ecology-based model for eel): a model to explore the role of phenotypic plasticity as an adaptive response of three temperate eels to spatially structured environments

“…Their large distribution with spatially structured environments, panmixia, and passive larval drift limits the possibility of local adaptation and favours phenotypic plasticity as an adaptive response. Phenotypic plasticity in terms of sexual determination and subsequent sex ratio (Davey and Jellyman 2005), length-atsilvering (Vollestad 1992), growth rate (Geffroy and Bardonnet 2012), and natural mortality rate and migration behaviour (Edeline 2007;Cairns et al 2009) have actually been documented and analysed for a long time. However, they have generally been considered separately, or two by two, without considering the entire continental life cycle of eels.…”

“…5, scenario S2). Density dependence is known to play a major role in eel dynamics (De Leo and Gatto 1996), especially in migratory behaviour (Geffroy and Bardonnet 2012). Our assumption of distinct density-dependent sensitivity between males and females, i.e., females suffering a higher density-dependent natural mortality rate than males, is plausible for two main reasons: First, Holmgren et al (1997) observed that males at younger stages have a faster growth in mass, with higher condition indices, and so they may become dominant with respect to females.…”

Freshwater eels: A symbol of the effects of global change

“…Glass eels with high feeding rate and fast weight gain have a higher propensity to migrate (Bureau du Colombier, Lambert, & Bardonnet, ). These glass eels also display a more gregarious and less aggressive behaviour (Geffroy & Bardonnet, ). Habitat selection could be a trade‐off between growth (generally higher in downstream habitats), survival (generally higher in upstream habitats), competition avoidance (higher competition in downstream habitats) and energetic cost of migration (Drouineau et al., ; Edeline, ; Mateo, Lambert, Tétard, Castonguay, et al., ).…”

Réponses adaptatives des anguilles des régions tempérées à l’hétérogénéité environnementale et effets des pressions anthropiques

“…Les mâles sont concentrés dans la partie aval de la rivière où la densité d'individus est supérieure (Helfman et al, 1987 ;Tesch, 2003 ;Davey & Jellyman, 2005). Les individus à croissance rapide s'installent préférentiellement dans les habitats aval, alors que les individus à croissance plus lente ont tendance à s'installer à l'amont pour éviter la compétition (De Leo & Gatto, 1995 ;Daverat et al, 2006Daverat et al, , 2012Edeline, 2007 ;Geffroy & Bardonnet, 2012). Concernant la longueur à l'argenture (des mâles et des femelles), une plus petite taille à maturité est simulée dans la partie aval de la rivière, alors que des longueurs plus importantes sont retrouvées au fur et à mesure de la progression vers l'amont (Vøllestad, 1992 ;Oliveira, 1999).…”

“…I) (Vladykov, 1966 ;Helfman et al, 1987 ;Vøllestad, 1992 ;Oliveira et al, 2001 ;Davey & Jellyman, 2005 ;Kettle et al, 2011 ;Koops et al, 2014). Une hypothèse est que, malgré l'impossibilité d'adaptation locale, ces patrons soient liés pour partie à de la plasticité phénotypique qui pourrait être une réponse 2 adaptative à l'hétérogénéité environnementale (Vøllestad, 1992 ;Daverat et al, 2006 ;Edeline, 2007 ;Geffroy & Bardonnet, 2012 ;Drouineau et al, 2014), et à des polymorphismes génétiques soumis à de la sélection spatialement variable et à de la sélection d'habitat sous influence génétique (Côté et al, 2009(Côté et al, , 2014(Côté et al, , 2015Pujolar et al, 2011 ;Gagnaire et al, 2012;Boivin et al, 2015 ;Pavey et al, 2015) (Fig. 1).…”