Climate change is expected to drive species ranges towards the poles and to have a strong influence on species distributions. In this study, we focused on diadromous species that are of economical and ecological importance in the whole of Europe. We investigated the potential distribution of all diadromous fish regularly encountered in Europe, North Africa and the Middle East (28 species) under conditions predicted for twenty-first century climate change. To do so, we investigated the 1900 distribution of each species in 196 basins spread across all of Europe, North Africa and the Middle East. Four levels were used to semiquantitatively describe the abundance of species, that is missing, rare, common and abundant. We then selected five variables describing the prevailing climate in the basins, the physical nature of the basins and reflecting historical events known to have affected freshwater fish distribution. Logistic regressions with a four-level ordinal response variable were used to develop species-specific models. These predictive models related the observed distribution of these species in 1900 to the most explanatory combination of variables. Finally, we selected the A2 SRES scenario and the HadCM3 (Hadley Centre Coupled Model version 3) global climate model (GCM) to obtain climate variables (temperature and precipitation) at the end of this century. We used these 2100 variables in our models and obtained maps of climatically suitable and unsuitable basins, percentages of contraction or expansion for each species. Twenty-two models were successfully built, that is there were five species for which no model could be established because their distribution range was too narrow and the Acipenser sturio model failed during calibration. All the models selected temperature or/and precipitation as explanatory variables. Responses to climate change were species-specific but could be classified into three categories: little or no change in the distribution (five species), expansion of the distribution range (three species gaining suitable basins mainly northward) and contraction of the distribution (14 species losing suitable basins). Shifting ranges were in accordance with those found in other studies and underlined the high sensitivity of diadromous fish to modifications in their environment.

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Temperate eels Anguilla anguilla (European eel), A. rostrata (American eel) and A. japonica (Japanese eel) are three catadromous species which have been declining since the 1970s/1980s despite their remarkable adaptive capacity. Because of their specific life cycles, which share distant oceanic spawning grounds and continental growth stage, eels are affected by five components of the global change: (a) climate change affecting larval survival and drift, (b) an increase in pollution leading to high levels of contamination exacerbated by their high lipid levels, (c) increasing fragmentation and habitat loss that reduce dramatically the amount of available habitats and induce increased spawner mortality, (d) the appearance of Anguillicola crassus a parasitic alien nematode that impairs spawning success, and (e) the impact of commercial and recreational fisheries for all life stages of eel. In this context, the rapid increases of pressures during the “Great Acceleration” have surpassed the adaptive capacity of eels. This illustrates that cumulative effects of global change can lead to the collapse of species, even in species that have amazingly high adaptive capacities.

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Rougier, T., Lambert, P., Drouineau, H., Girardin, M., Castelnaud, G., Carry, L., Aprahamian, M., Rivot, E., and Rochard, E. 2012. Collapse of allis shad, Alosa alosa, in the Gironde system (southwest France): environmental change, fishing mortality, or Allee effect? – ICES Journal of Marine Science, 69: 1802–1811. At the end of the 20th century the allis shad population in the Gironde was the largest in Europe. During the first decade of the 21st century, catches declined dramatically by two orders of magnitude, and a fishery moratorium was implemented in 2008. This deterioration in the status of the stock was confirmed by three independent assessments (abundance of juveniles and of potential and effective spawners). Three hypotheses on the cause of the collapse were examined: (i) an environmental change in freshwater and/or in the estuary; (ii) an increase in marine and/or estuarine mortality; and (iii) the presence of an Allee effect. Changes in flow, temperature, and water quality over the period were inconclusive, but remain a possible causative factor. The instantaneous rate of marine (mean: 0.7 year−1, s.e. 0.1 year−1) and estuarine (mean: 2.6 year−1, s.e. 0.1 year−1) mortalities showed no trend between 1991 and 2003. Nevertheless, the past high estuarine (fishing) mortalities combined with a demographic Allee effect in the reproduction dynamics could explain the population collapse and hamper the stock recovery under the moratorium. This conclusion is, however, tentative as it was not possible to prove the presence of the density-dependent mechanism associated with the demographic Allee effect.

Because of their threatened status, sturgeons (Acipenseridae) can no longer be sacrificed for stomach content analysis. We tested a nonlethal method of gastric lavage on Siberian sturgeon Acipenser baeri. The efficiency and harmlessness of the method were tested with four different volumes of food (10, 20, 30, and 40 cm3), each composed of brown shrimp Crangon crangon, Chironomidae, earthworm Lumbriscus terrestris, and sand goby Pomatoschistus minutus. The Siberian sturgeons were force‐fed before the gastric lavage was performed. Some prey were recovered from all the sturgeons, and the average food item recovery rate from stomach contents was 67.5%; recovery of brown shrimp and sand goby (78.2%) was greater than that of vermiform items (51.4%). The volume of food had no significant influence on the prey recovery rate. No mortality resulted from the gastric lavage. However, the method is not totally benign because the fish that had undergone gastric lavage averaged significantly greater weight loss than the control fish during the 60‐d follow‐up period.

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