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Impacts that cause highest mortality temperate eels do not necessarily have the greatest impact on species

Abstract : The worldwide decline of temperate eels is due to a synergistic combination of several anthropogenic pressures. However, eels display very specific life-cycles and amazing adaptation capacities that impair our ability to assess the relative effects of each pressure. Temperate eels are three panmictic catadromous species with an oceanic passive larval drift and large distribution areas with contrasted environments. Spatial patterns of life-history traits are observed and correlated with environmental gradients at both river catchment and distribution area scales. This raises the question of the effect of spatially heterogeneous anthropogenic pressures on these populations. GenEveel, an individual-based optimization model was able to mimic observed spatial patterns in length-at-silvering, sex-ratio and distribution of ecotypes, by assuming genetic-dependent habitat selection and phenotypic plasticity as adaptive responses to environmental heterogeneity. Depending on these mechanisms, the heterogeneity of anthropogenic pressures can have a wide range of effects in terms of life-history traits and demographic rates. In this context, different anthropogenic pressures (glass eel fishery, obstacle to upstream migration, turbine mortality and silver eel fishery) were included in the model to explore their impacts on the number of escapees, but also on other indicators accounting for sex-ratio in escapees, repartition between genotypes, mean length-at-silvering, and overall egg production. Our results demonstrate that phenotypic plasticity can act as a compensatory mechanism that mitigates the effect of some pressures (glass eel fishery and obstacle to upstream migration) and therefore be a source of resilience for the population. Moreover, it shows that the pressure inducing the highest direct mortality has not necessarily the greatest influence on the spawning biomass and does not necessarily exert the strongest selective pressure on ecotypes. Our results also suggest that management should not only focus on numbers and direct mortality but on the preservation of diversity within populations.
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https://hal.inrae.fr/hal-02607546
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Submitted on : Saturday, May 16, 2020 - 2:25:16 PM
Last modification on : Tuesday, September 7, 2021 - 3:54:10 PM

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  • HAL Id : hal-02607546, version 1
  • IRSTEA : PUB00057763

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M. Mateo, Patrick Lambert, S. Tétard, Hilaire Drouineau. Impacts that cause highest mortality temperate eels do not necessarily have the greatest impact on species. VII Congress of the Iberian Society for Ichtyology, Jun 2018, Faro, Portugal. pp.14. ⟨hal-02607546⟩

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