OPPORTUNITE DE THESE 2026 Etude du comportement et de la dispersion d'espèces d'écrevisses invasives en fonction des caractéristiques d’écoulements

Thesis topic and scientific objectives This thesis addresses the need for a mechanistic understanding of the processes controlling the dispersal of invasive crayfish in watercourses. The central question is to determine how flow regimes, and in particular velocity, turbulence, bottom substrate and the local flow structure around individuals, influence the dispersal of crayfish, and to what extent the differences observed between species can be explained by interactions between morphology, posture and local hydrodynamics. The first step will be to experimentally characterise the dispersive behaviour of several invasive crayfish species as a function of flow velocity, turbulence and bottom substrate in a controlled hydrodynamic channel. The second objective will be to identify critical hydraulic thresholds that limit or promote active dispersal and to compare these thresholds between different species. The thesis will also analyse the three-dimensional structure of the flow around crayfish in order to link velocity and turbulence fields to the behavioural strategies observed and to test the hypotheses formulated in the literature concerning the role of morphology, posture and contact with the substrate. Finally, the experimental results will be compared with field data from individual PIT tag tracking at a control site, then synthesised in the form of habitat-hydraulic relationships that can be integrated into modelling tools, such as the HABBY software developed by INRAE and OFB. Methodology The experimental work will be conducted in a hydrodynamic channel with controlled flow, allowing the characteristics of the flow and the bottom substrate to be systematically varied. The movements and dispersion of crayfish will be quantified from individual tracking using AI-based software. The flow will be characterized at high spatial and temporal resolution, particularly at the individual level, in order to identify local hydrodynamic structures that may influence dispersion properties. At the same time, field measurements will be carried out on the La Rhune River (Vienne, 86) using PIT-tag devices to document the movements of crayfish in their natural environment and establish a link between these movements and local hydraulic conditions and substrate characteristics. Local modifications to the site will complement these observations, allowing for a comparison of results before and after intervention, and a comparison of laboratory results with those observed in the field. Finally, the results will be incorporated into an applied assessment process, aimed at setting specific hydraulic preference parameters for crayfish and integrating them into HABBY-type software, in order to produce spatial maps of areas favorable or unfavorable to dispersal and to assess the potential effect of hydraulic developments Required profile/areas of competence: Master's degree in Fluid Mechanics, Environment, Biology, Engineering Sciences. Writing skills in English would be appreciated Duration : 36 months (from October 1, 2026, to October 1, 2029)