Plasticity of European flounder life history patterns discloses alternatives to catadromy

Abstract

European flounder Platichthys flesus life history patterns were investigated in 3 basins along a latitudinal gradient (Minho, N Portugal; Gironde, SW France; Seine, N France). We used coupled Sr:Ca and Ba:Ca otolith signatures and microstructure to retrospectively determine habitats occupied by flounder during their life, including early larval ontogeny. Flounder exhibited high life history plasticity among and even within basins, apparent by the diversity of habitats used during larval ontogeny and throughout their lives, and by the age at which flounder migrated to freshwater. Egg signatures probably had a strong maternal influence, and our interpretation suggests that flounder spawned and/or hatched predominantly in brackish waters in the Minho, while in the Gironde and Seine, flounder spawned and/or hatched either in coastal, brackish or freshwater environments. The freshwater egg signature was most frequent in the Seine. These interpretations contradict the current general assumption that flounder spawn exclusively in coastal waters. During pre-metamorphosis and metamorphosis, flounder were predominantly in brackish waters in the Minho, while in the Gironde and Seine, they were mainly in coastal and freshwater environments, respectively. The diversity of flounder life histories (LH) (i.e. sequence of habitat residence: freshwater, brackish or coastal) after metamorphosis was similar between the Minho (LH = 13), Gironde (LH = 13) and Seine (LH = 14) basins. The age at which flounder migrated to freshwater also varied among sites, at an earlier age in the Minho and Gironde (<0.5 yr old) than in the Seine, where flounder migrating from the coast into freshwater reached maximum frequencies at age 1.3 yr old. Thus, catadromy in European flounder may be facultative, and the factors influencing flounder high LH plasticity deserve thorough research. © 2012 Inter-Research and Fisheries and Oceans Canada.