Resident and migratory tactics in freshwater European eels are size‐dependent

Abstract

1. When entering freshwater, young European eels either become resident or disperse to settle upstream. While this process shapes the whole population structure, little is known about how the 'decision' is made. Here, we investigated the possible role of body size. 2. A 1-year capture-recapture programme was carried out on 1505 European eels (length-range 62-633 mm) at two freshwater sites on the Saucats River, France. Eels were separated into two groups based on body length and this determined the tagging method; 1350 smaller eels (<240 mm) were tagged with visible implant elastomer tags, and 155 larger eels (>239 mm) were tagged individually with a passive integrated transponder. 3. Migration was detected only in eels <240 mm and decreased with increasing body length within this group. The probability of migration was higher in the summer, suggesting an environmental window for upriver dispersal. During this period, the mean probability of migration was estimated at 0.79 for 62-mm-long eels, 0.5 for 121 mm-long eels and 0.05 for 223 mm-long eels. 4. This is the first study to demonstrate, using capture-recapture models, the existence of differing eel behavioural tactics (residence and migration) based on body size. Such models are useful tools for analysing site fidelity and dispersal. If we assume that a migration probability >0.05 means that such eels contribute substantially to upriver colonisation, this corresponds to eels <220 mm in the Saucats River, although the threshold body size may be highly dependent on the river system.

Freshwater eels: A symbol of the effects of global change

“…Diadromous fish, such as eels, undergo two long migrations (Tesch, ): The first migration, from the spawning grounds to their growth habitat, includes a phase of active upstream migration in river catchments during the early years of their continental life‐stage (Castonguay, Hodson, Couillard, et al., ; Fukuda, Aoyama, Yokouchi, & Tsukamoto, ; Imbert, Labonne, Rigaud, & Lambert, ). During the second migration, eels return to the oceanic spawning grounds from their growth habitats in rivers or coastal waters.…”

“…Diadromous fish, such as eels, undergo two long migrations (Tesch, 2003): The first migration, from the spawning grounds to their growth habitat, includes a phase of active upstream migration in river catchments during the early years of their continental life-stage Fukuda, Aoyama, Yokouchi, & Tsukamoto, 2016;Imbert, Labonne, Rigaud, & Lambert, 2010 Year Fertilizer consumption (million tonnes) or worse in the United States (Busch, Lary, Castilione, & McDonald, 1998), especially because most dams lack fishways (MacGregor et al, 2009). In Europe, 50%-90% of habitats were lost by the end of the twentieth century (Feunteun, 2002).…”

Sex differentiation and sex determination in eels: consequences for management

“…Once entirely pigmented, they are called yellow eels and their upstream migratory behaviour is deemed to disappear by the time they reach 25 cm (Imbert et al 2010). Then, some individuals progress into the estuary and colonize the river basin whilst continuing to grow.…”

Dispersal and behavior of Pacific halibut Hippoglossus stenolepis in the Bering Sea and Aleutian Islands region

“…data). Further investigation of the influence of size and age on dispersal patterns in the PIT tag data is warranted and ongoing, as size-dependent dispersal has been demonstrated in a variety of taxa, from fishes (Dorazio et al 1994, Imbert et al 2010) to arthropods (Etherington & Eggleston 2003, Okada et al 2007). In the meantime, the likely oc currence of ontogenetic redistribution indicated by conventional and PIT tag data does not preclude the establishment of spawning stock structure, indicated by PAT tag results, at scales relevant to fishery management.…”