French diadromous fish facing climate change : evolution of numbers and modification of migratory phenology
Diadromous fish are in decline in France and in the world. Living alternately in fresh and saltwater, they are faced with many pressures to which is added the ongoing climate change that leads mainly to three major modifications : (I) change in the area of distribution of species, (ii) modification...
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Other Authors: | , , , , , , , , |
Format: | Doctoral or Postdoctoral Thesis |
Language: | French |
Published: |
HAL CCSD
2021
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Subjects: | |
Online Access: | https://theses.hal.science/tel-04170626 https://theses.hal.science/tel-04170626/document https://theses.hal.science/tel-04170626/file/Hoffmann-Legrand_Marion.pdf |
Summary: | Diadromous fish are in decline in France and in the world. Living alternately in fresh and saltwater, they are faced with many pressures to which is added the ongoing climate change that leads mainly to three major modifications : (I) change in the area of distribution of species, (ii) modification of the timing of key moments in life cycles (e.g. migration, reproduction), and (iii) modification of the spatial synchrony of populations. Emblematic species of our rivers with high economic value, diadromous fish are the subject of management plans throughout France, mainly at the basin scale, with few perspectives on the state of these populations at the national scale. The objective of this work is to help to fill this gap by analysing data in all French river basins. These data were never pooled to date, nor valued at this spatial scale. We collected the data of 46 counting stations with a history of at least 10 years and about 5 diadromous taxa: Alosa spp. (gathering A. fallax and A. alosa), Anguilla anguilla, Petromyzon marinus, Salmo salar and Salmo trutta. Based on this dataset, we asked 3 questions : (i) how the counts of diadromous fish have evolved in France over the last 30 years, (ii) have these taxa modified their timing of migration during this period of study, and what are the explanatory parameters, and finally (iii) is there a spatial synchrony in the dynamics and timing of migration of these populations, and what are the explanatory parameters. We show that the evolution of counts is contrasted between species and basins, with taxa decreasing at the French scale (Alosa spp. and Petromyzon marinus) while others are increasing slightly or in stagnation. Alosa spp. is both the taxon showing the greatest decrease in its counts at the French scale and the least contrast between the basins, attesting to a fairly general decline in France. Analysis of the timing of migration has shown an overall advance in median migration dates for all taxa (except for glass eels), on average -2.3 days per decade (min= ... |
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