Dataset on European diadromous species distributions from 1750 to present time in Europe, North Africa and the Middle East.

EuroDiad version 4.0 is a set of data tables that store information about the presences/absences and population functionality of diadromous species (lampreys and fish) populations in selected catchments in Europe, the Middle East, and North Africa from 1750 to present time. This database contains distribution and life-history trait information for twenty-eight European diadromous species and geomorphological data for each of the selected catchments, though not every species has data for every catchment and time period. EuroDiad was originally created in 2005-2006 (EuroDiad 1.0 and 2.0), and contained data for 196 catchments and two time periods (1851-1950 and 1951-2010). It underwent a major update in 2009-2010 (EuroDiad 3.2) through a validation process by European fisheries experts. Version 3.2 included the addition of 63 small-sized catchments (< 10,000 km2) and an additional time period (1751-1850) for select species and catchments. This database underwent a second validation process in 2019-2020 and was updated to v 4.0, with the primary goal of providing information for a new generation of species distribution models, referred to as hybrid models, which incorporate both habitat suitability and population dynamics within their framework. Secondary objectives of this update were to: (a) incorporate new catchments for which information was provided by additional experts, (b) validate existing information about the presences or absences of diadromous species and categorize their population functionality within a catchment, and (c) perform data hygiene to prepare the database for broad dissemination. Information on the life history, morphology, and phenology of four emblematic species (i.e. eel, salmon, lamprey and shad) were added in this occasion. Data for this update were validated by DiadES project partners (www.diades.eu) and local experts. This update was focused on catchments located in the Atlantic Area for use in the DiadES project. Data were divided by country, and validation was performed for catchments in Ireland, the U.K., Spain, Portugal, and France under the supervision of national organisations in fisheries and environmental management. DiadES project partners were asked to validate geomorphological information for the catchment (location of the outlet, surface area of the drainage basin, length of the main watercourse, elevation at the headwaters), as well as the presences/absences information and population functionality categories for all species already present in EuroDiad for their country. If possible, verification was done for each of the three time periods. Partners were also asked to provide data for any other catchments for which they had access to information on fish population status. EuroDiad 4.0 now stores data for 350 catchments (of which 292 have population functionality records) and three time periods, though the precision of information varies and not every species has information for each time period. This validation process strengthened the usefulness of EuroDiad, which is now updated and available for use by the research community.

An innovative bivariate approach to detect joint temporal trends in environmental conditions: Application to large French rivers and diadromous fish.

Most key life-events of organisms are synchronized by complex interactions of several environmental cues to ensure optimal survival and growth of individuals and their offspring. However, global change is known to affect multiple components of ecosystems and cues at the same time. Therefore, detecting joint trends in covariate time series is a crucial challenge in global change ecology that has rarely been addressed so far. In this context, we designed an innovative combination of kernel density estimations and Mann-Kendall trend tests to detect joint temporal trends in a pair of environmental variables. This methodological framework was tested on >30 years (1976-2019) of water temperature and discharge data for 6 large French rivers (the Garonne, Dordogne, Rhône, Rhine, Loire and Vienne rivers). The implications of such trends in both temperature and discharge for diadromous species key life-cycle processes were then explored by checking if significant bivariate environmental changes occurred during seasons of upstream and downstream migration, and reproductive activities. Results were contrasted between rivers and seasons: many rivers displayed an increase in the number of days with high water temperature and low river discharge, but local discharge regulation measures could have mitigated the trend in discharge. Our findings showed that species migrating or spawning in spring were likely to be strongly impacted by the new environmental conditions in the Garonne, Loire and Rhône rivers, given the marked changes in water temperature and discharge associations detected by our new method. Conditions experienced by fall-running and spawning species have been strongly affected in all the rivers studied. This innovative methodology was implemented in a new R package, ChocR, for application to other environments and ecosystems.

The Combined Use of Correlative and Mechanistic Species Distribution Models Benefits Low Conservation Status Species.

Species can respond to climate change by tracking appropriate environmental conditions in space, resulting in a range shift. Species Distribution Models (SDMs) can help forecast such range shift responses. For few species, both correlative and mechanistic SDMs were built, but allis shad (Alosa alosa), an endangered anadromous fish species, is one of them. The main purpose of this study was to provide a framework for joint analyses of correlative and mechanistic SDMs projections in order to strengthen conservation measures for species of conservation concern. Guidelines for joint representation and subsequent interpretation of models outputs were defined and applied. The present joint analysis was based on the novel mechanistic model GR3D (Global Repositioning Dynamics of Diadromous fish Distribution) which was parameterized on allis shad and then used to predict its future distribution along the European Atlantic coast under different climate change scenarios (RCP 4.5 and RCP 8.5). We then used a correlative SDM for this species to forecast its distribution across the same geographic area and under the same climate change scenarios. First, projections from correlative and mechanistic models provided congruent trends in probability of habitat suitability and population dynamics. This agreement was preferentially interpreted as referring to the species vulnerability to climate change. Climate change could not be accordingly listed as a major threat for allis shad. The congruence in predicted range limits between SDMs projections was the next point of interest. The difference, when noticed, required to deepen our understanding of the niche modelled by each approach. In this respect, the relative position of the northern range limit between the two methods strongly suggested here that a key biological process related to intraspecific variability was potentially lacking in the mechanistic SDM. Based on our knowledge, we hypothesized that local adaptations to cold temperatures deserved more attention in terms of modelling, but further in conservation planning as well.