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Climate change has non-linear impacts on species distributions and abundance that have cascading effects on ecosystem structure and function. Among them are shifts in trophic interactions within communities. Sites found at the interface between two or more biogeographical regions, where species with diverse thermal preferenda are assembled, are areas of strong interest to study the impact of climate change on communities' interactions. This study examined variation in trophic structure in the Celtic Sea, a temperate environment that hosts a mixture of cold-affiliated Boreal species and warm-affiliated Lusitanian species. Using carbon and nitrogen stable isotope ratios, trophic niche area, width, and position were investigated for 10 abundant and commercially important demersal fish species across space and time. In general, the niches of Boreal species appear to be contracting while those of Lusitanian species expand, although there are some fluctuations among species. These results provide evidence that trophic niches can undergo rapid modifications over short time periods (study duration: 2014–2021) and that this process may be conditioned by species thermal preferenda. Boreal species displayed spatial variation in trophic niche width and seem to be facing increased competition with Lusitanian species for food resources. These findings underscore the need to utilize indicators related to species trophic ecology to track the ecosystem alterations induced by climate change. Such indicators could reveal that the vulnerability of temperate ecosystems is currently being underestimated.

Fisheries can generate feeding opportunities for large marine predators in the form of discards or accessible catch. How the use of this anthropogenic food may spread as a new behaviour, across individuals within populations over time, is poorly understood. This study used a 16-year (2003–2018) monitoring of two killer whale Orcinus orca subantarctic populations (regular and Type-D at Crozet), and Bayesian multistate capture–mark–recapture models, to assess temporal changes in the number of individuals feeding on fish caught on hooks (‘depredation’ behaviour) of a fishery started in 1996. For both populations, the number of depredating individuals increased during the study period (34 to 94 for regular; 17 to 43 for Type-D). Increasing abundance is unlikely to account for this and, rather, the results suggest depredation was acquired by increasing numbers of existing individuals. For regular killer whales, a plateau reached from 2014 suggests that it took 18 years for the behaviour to spread across the whole population. A more recent plateau was apparent for Type-Ds but additional years are needed to confirm this. These findings show how changes in prey availability caused by human activities lead to rapid, yet progressive, innovations in killer whales, likely altering the ecological role of this top-predator.

Jolly-Seber capture-mark-recapture models to estimate Crozet regular and type-D Killer whales populations. All codes are available for the simulation, the real data and the trends analysis (1) Simulation code (codesimul.R) is running alone. (2) Real data code (code_vraidata_revfin.R) makes use of three matrices that change depending on the ecotype: - The Capture History (CH_2106_m.csv, CH_2106_d.csv), rows correspond to individuals and columns to years. For regular killer whales this matrix contains 3 possible observations (observed from the coast, observed depredating, non observed) and 2 observations for Type-D killer whales (observed depredating, non observed) - The Marking status (Mk_2106_m.csv, Mk_2106_d.csv), rows correspond to individuals and columns to years. For both ecotype they contain three possible marking status as described in the ESM. - The maturity status (St_2106_m.csv, St_2106_d.csv), rows correspond to individuals and columns to years. For both ecotype they contain four different states (non identify, new-born, juvenile and adult). Two other matrices are the same for both ecotypes - The standardized effort (Effort_stand_boat.csv) contains the yearly effort divided by the maximum number of photographs taken during the study period. - The state matrix (z_init_cro2705.csv) is used to initiate the state matrix from the models. (3) The trend_test.R file presents the extraction of model outputs (regular killer whales: CrozetFinrevfinfin.Rdata, Type-D killer-whales: DFinrevfinfin.Rdata) and their analysis trough different linear and non linear models.

Rajidae stocks (Raja clavata, Raja brachyura, Raja montagui, Raja microocellata, Leucoraja naevus and Raja undulata) in the English Channel and North Sea (ICES divisions 3a, 4 and 7d) are actually managed as a complex (“skates and rays”) and subject to a single TAC. TAC advices from the ICES are based on scientific survey indices trends from each species. Rajidae catches are mainly bycatch from flatfish fisheries such are sole (Solea solea) and plaice (Pleuronectes platessa) fisheries. Furthermore, because of their top predator position as well as their life history, Rajidae are species sensitive to overfishing. These different factors have led to a revision in stock assessment methods. ICES classified Rajidae as category 3 data limited stocks. The lack of available data does impact stock assessment model choice. As part of SUMARiS Interreg project a set of three data limited models have been tested: CMSY, SPicT and a state space bayesian production model. All of this model results support an increase in Rajidae stock biomass since the implementation of management measures in 2009. However, differences between stocks have been highlighted. The relative biomass of Thornback ray (Raja clavata), the prevailing species in the area, is up to three times more than other species biomass. This report presents the state of art in Rajidae stock data, as well as the different assessment models tested on 30 January 2020., Les stocks de Rajidae (Raja clavata, Raja brachyura, Raja montagui, Raja microocellata, Leucoraja naevus et Raja undulata) en Manche et Mer du Nord (divisions CIEM 3a, 4 et 7d) sont actuellement gérés en tant que complexe multispécifique (« raies ») sujet à un unique TAC. Les recommandations de TAC du CIEM s’appuient sur les tendances des indices d’abondance issus de campagnes scientifiques de chacune des espèces du complexe. Les captures de Rajidae sont principalement constituées de captures accessoires, liées à la pêche de poissons plats tels que la sole (Solea solea) et la plie (Pleuronectes platessa). De plus, du fait de leur position de prédateur supérieur et en raison de leur histoire de vie, les Rajidae constituent des espèces sensibles à la surpêche. Ces différents facteurs ont mené à la révision des méthodes d’évaluation de stock. Les Rajidae font partie des stocks à données limitées du CIEM de catégorie 3. La limitation des données disponibles impacte le choix des modèles d’évaluation de stocks. Dans le cadre du projet Interreg SUMARiS un set de trois modèles à données limitées a été testé : CMSY, SPicT et un modèle de production bayésien hiérarchique. L’ensemble des résultats de ces modèles supporte une augmentation de la biomasse des stocks de Rajidae depuis la mise en place de mesures de gestion en 2009. Cependant des disparités entre stocks ont été mises en évidence. La biomasse relative en 2018 de la raie bouclée (Raja clavata), espèce dominante de la zone, est jusqu’à trois fois plus importante que celle des autres espèces. Ce rapport présente l’état des lieux des données disponibles sur les stocks de Rajidae, ainsi que différent modèles d’évaluation testés au 30 janvier 2020.