Résumé: Measuring individual feed intake of fish in farms is complex and precludes direct selective breeding for feed conversion ratio (FCR). Here, we estimated the individual FCR of 588 sea bass using individual rearing under restricted feeding. These fish were also phenotyped for their weight loss at fasting and muscle fat content as possible indirect indicators of FCR. The 588 fish were from a full factorial mating between parental lines divergently selected for high (F+) or low (F-) weight loss at fasting. The pedigree was known back to the great grandparents. A subset of 400 offspring and their ancestors were genotyped for 1,110 SNPs, which allowed estimating the genomic heritability of traits. Individual FCR and growth rate in aquarium were both heritable (genomic h² = 0.47 and 0.76, respectively) and strongly genetically correlated (-0.98), meaning that under restricted feeding, faster growing fish were more efficient. FCR in aquariums was significantly better for fish with two F- parents (1.38), worse for fish with two F+ parents (1.51) and intermediate (1.46) for crossbred fish (F+/F- or F-/F+). Muscle fat content was positively genetically correlated to growth rate in aquarium and during fasting. Thus, higher growth rate in aquariums, lower weight loss at fasting and fat content are all traits that could improve FCR in aquarium. Improving these traits would also improve FCR of fish in normal group rearing conditions, as we showed that groups composed of fish with good individual FCR were significantly more efficient in groups. The FCR of groups was also better when the fish composing the groups had, on average, lower estimated breeding values for growth rate during fasting (losing less weight). Thus, FCR in aquarium and weight loss at fasting are both promising to improve FCR of fish in groups. Finally, we showed that the reliability of estimated breeding values was higher (from +10% to +125%) with single-step genomic BLUP than with pedigree-based BLUP, showing that genomic data would enhance the accuracy of EBV prediction o in selection candidates from a limited number of sibs individually phenotyped for FCR in aquariums.

Résumé: Spatio-temporally stable prey distributions coupled with individual foraging site fidelity are predicted to favour individual resource specialisation. Conversely, predators coping with dynamic prey distributions should diversify their individual diet and/or shift foraging areas to increase net intake. We studied individual specialisation in Scopoli's shearwaters (Calonectris diomedea) from the highly dynamic Western Mediterranean, using daily prey distributions together with resource selection, site fidelity and trophic-level analyses. As hypothesised, we found dietary diversification, low foraging site fidelity and almost no individual specialisation in resource selection. Crucially, shearwaters switched daily foraging tactics, selecting areas with contrasting prey of varying trophic levels. Overall, information use and plastic resource selection of individuals with reduced short-term foraging site fidelity allow predators to overcome prey field lability. Our study is an essential step towards a better understanding of individual responses to enhanced environmental stochasticity driven by global changes, and of pathways favouring population persistence.

Résumé: Mid-latitude (similar to 30-60 degrees) seasonally stratifying shelf-seas support a high abundance and diversity of marine predators such as marine mammals and seabirds. However, anthropogenic activities and climate change impacts are driving changes in the distributions and population dynamics of these animals, with negative consequences for ecosystem functioning. Across mid-latitude shelf-seas marine mammals and seabirds are known to forage across a number of oceanographic habitats that structure the spatio-temporal distributions of prey fields. Knowledge of these and the bio-physical mechanisms driving such associations are needed to improve marine management and policy. Here, we provide a concise and easily accessible guide for both researchers and managers of marine systems on the predominant oceanographic habitats that are favoured for foraging by marine mammals and seabirds across mid-latitude shelf-seas. We (1) identify and describe key discrete physical features present across the continental shelf, working inshore from the shelf-edge to the shore line, (2) provide an overview of findings relating to associations between these habitats and marine mammals and seabirds, (3) identify areas for future research and (4) discuss the relevance of such information to conservation management. We show that oceanographic features preferentially foraged at by marine mammals and seabirds include shelf edge fronts, upwelling and tidal-mixing fronts, offshore banks and internal waves, regions of stratification, and topographically complex coastal areas subject to strong tidal flow. Whilst associations were variable across taxa and through space and time, in the majority of cases interactions between bathymetry and tidal currents appear to play a dominant role, alongside patterns in seasonal stratification and shelf-edge upwelling. We suggest that the ecological significance of these bio-physical structures stems from a capacity to alter the densities, distributions (both horizontally and vertically) and/or behaviours of prey in a persistent and/or predictable manner that increases accessibility for predators, and likely enhances foraging efficiency. Future conservation management should aim to preserve and protect these habitats. This will require adaptive and holistic strategies that are specifically tailored to the characteristics of an oceanographic feature, and where necessary, evolve through space and time in response to spatio-temporal variability. Improved monitoring of animal movements and biophysical conditions across shelf-seas would aid in this. Areas for future research include multi-disciplinary/ trophic studies of the mechanisms linking bio-physical processes, prey and marine mammals and seabirds (which may elucidate the importance of lesser studied features such as bottom fronts and Langmuir circulation cells), alongside a better understanding of how predators perceive their environment and develop foraging strategies during immature/juvenile stages. Estimates of the importance of oceanographic habitat features at a population level should also be obtained. Such information is vital to ensuring the future health of these complex ecosystems, and can be used to assess how anthropogenic activities and future environmental changes will impact the functioning and spatio-temporal dynamics of these bio-physical features and their use by marine predators.