Phd : Understanding and Modeling Fish Swimming and

**General areas of responsibility** The aim of the Halieutique Grand Ouest (HALGO) unit is to develop knowledge and methods for the ecosystem approach to fisheries, and in particular for the integrated assessment of ecosystems. The unit contributes to defining the conditions for sustainable exploitation of fisheries resources and ecosystems. Its research project has two main themes: Ecosystem dynamics, from source to ocean, and Integrated assessment and sustainability of ecosystems. The Technologies et Biologie Halieutiques (LTBH) laboratory is particularly involved in assessing and reducing the environmental impact of fishing gear. Summary Using a multidisciplinary approach combining fisheries technology, applied ethology, artificial intelligence, functional ecology and quantitative ecology, the ESCAPE project (in which this thesis is included) aims to understand, quantify and model the various stages in the capture and escape processes. The main aim is to understand the underlying behavioral laws linked to the morphological, functional and social determinism of species and individuals. The different hypotheses of escape strategies will be tested using numerical tools for coupled animal-fishing gear modeling. The results, based on a combination of in situ observations and modelling, will enable us to estimate the intra - and inter-selectivity properties of fishing gear, with a view to contributing to the design of innovative fishing gear for more sustainable exploitation of marine resources. Chapter 1: Understanding behavior and its determinants The data extracted from the underwater videos collected will be used to characterize the use of space by the different species, as well as its variability in terms of time (tow duration), space (codend/extension) and mesh type. Secondly, a fine-scale analysis of individual and group trajectories on a micro-scale (< 1 m) will test the extent to which swimming speed, frequency and angle of turns, and angle of contact with the mesh are related to the visual and swimming abilities of species and individuals (size), and determine the effect of crowding (spatial and/or social) on the triggering of escapes through the mesh, as well as on their probability of success. Chapter 2: Coupled fish-gear modeling The study of fishing net dynamics is carried out using a "multi-gear" fishing simulation platform, FineLab (an extension of DynamiT software). This platform allows individuals (IBM models, Individual Based Model) to interact with fishing gear. The power of IBM models lies in their flexibility in representing observed natural processes, such as fish swimming and escape behaviors, but also in their ability to study the link between individual behaviors and the resulting collective dynamics. This approach makes it possible to estimate the main parameters of gear selectivity, such as size at 50% of escapement or "selection range", depending on the environment, the species present and their specific behaviours. The second part of the thesis will focus on improving the existing IBM model, based on the results of Chapter 1, and optimizing parameter values until trajectory sets comparable to in situ observations are obtained. The graphical environment of the platform will allow the visualization of trajectories to facilitate the understanding of machine/individual interactions. Key words Behavioral ecology, social ecology, artificial intelligence, fishing gear selectivity, IBM model, numerical simulation **Required Knowledge, skills, and characteristics** - Skills in artificial intelligence (deep learning) and image analysis appreciated. - Interest in fisheries and marine ecosystem management. **Specific working conditions** Phd is a real opportunity to work on Ifremer's scientific and technological priority themes. It entitle the holder to a gross monthly salary of 2300 euros gross for a period of 3 years, which cannot be combined with other scholarships. - a curriculum vitae - a covering letter - a reference letter - an academic transcript (Bachelor + Master 1 and first semester Master 2) Qui sommes nous ? **The Institute and the recruiting departement** A pioneer in ocean science, IFREMER’s cutting-edge research is grounded in sustainable development and open science. Our vision is to advance science, expertise and innovation to: - Protect and restore the ocean - Sustainably use marine resources to benefit society - Create and share ocean data, information & knowledge. With more than 1,500 personnel spread along the French coastline in more than 20 sites, the Institute explores the 3 great oceans: the Indian, Atlantic and Pacific oceans. A leader in ocean science, IFREMER is managing the French Oceanographic Fleet and its dedicated scientists create ground-breaking technology to push the boundaries of ocean exploration and knowledge, from the abyss to the atmosphere-ocean interface. Well-established in the international scientific community, our scientists,