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Marine ecosystem models for fisheries management have been used to project interspecific biodiversity under several climate change and management scenarios considering ecological dynamics only. However, fish populations may also adapt to climatic and fishing pressures via evolutionary changes leading to modifications in their life history that could either mitigate or worsen pressures’ consequences. A multispecies eco-evolutionary model, Ev-Osmose, has been developed to account for evolutionary dynamics in marine fish biodiversity projections. In this model, life-history traits are mechanistically described by a bio-energetic model. Life-history traits are allowed to evolve as their values are transmitted through cohorts by gametic inheritance of parents’ genes. Under the selection pressures generated by climate change and fishing scenarios, energy fluxes and the resulting life-history traits may thus respond through phenotypic plasticity and microevolution. The Ev-Osmose model has been used to simulate the changes in biomasses, catches and species composition of North Sea exploited fish under climate change scenario (RCP8.5) for the period 2010-2100 with scenarios with and without evolution. The ecosystem's total biomass and catch stay steady in the absence of climate change whereas a great decline is projected under scenario RCP8.5. Total biomass is unaffected by evolution, while total catch drops even more with evolution than without. In an evolutionary setting, the species mean lengths exhibit changes at horizon 2100, mainly shrinkage. The species composition becomes more uniform, with a sharp rise in warm-water species and a fast decline in cold-water species, which is amplified by evolution. The fact that the biomass remains stable while the catch declines in scenarios with evolution compared to those without evolution shows that the adaptation of fish features primarily enables the avoidance of fishing pressure. Economic yield will likely be impacted by this direct impact on fishery yield will be further reduced by the decline in length and species variety. According to this first forecast study that considers evolutionary dynamics at the ecosystem level, the fishing industry appears to be the primary loser of fish evolutionary changes in response to climate change.

The otolith, found in both inner ears of bony fish, has mainly been used to estimate fish age. Another application that has been developing significantly in recent years, however, is the use of otolith shape as a tool for stock identification. Often, studies have directly used the shape asymmetry between the right and left otoliths. We tested the magnitude of directional asymmetry between the sagittal otoliths (left vs. right) of 2991 individuals according to their catch locations, and we selected species to evaluate whether directional asymmetry may itself be a tool to evaluate stock boundaries. Elliptical Fourier descriptors were used to describe the otolith shape. We used a flatfish, the common sole (Solea solea, n = 2431), from the eastern English Channel and the southern North Sea as well as a roundfish, the bogue (Boops boops, n = 560), from the Mediterranean Sea. Both species showed significant levels of directional asymmetry between the testing locations. The bogue otoliths showed significant asymmetry for only 5 out of 11 locations, with substantial separation between two large areas: the Algerian coast and the western part of the Italian coast. The sole otoliths showed significant asymmetry in the shape analysis (3.84–6.57%), suggesting a substantial separation between two large areas: the English and French parts of the English Channel and the southern North Sea. Consequently, directional bilateral asymmetry in otolith shape is a potential new method for stock identification., Biología de recursos vivos de Canarias, PACA-BIO, SI

International audience

In recent decades, marine reserves have been established to provide refuges for many exploited and non-exploited species to find habitats unaffected by fishing. They may also contribute to certain forms of fishing that benefit from the emigration of individuals to surrounding unprotected areas. The objective of this study is to estimate the effects of a no-fishing zone in front of the Flamanville nuclear power plant to protect a shellfish community. It is based on a particularly rich series of data that takes into account the spatio-temporal variability of natural origin, over 33 years and 16 sampling points. Eighteen years after the creation of the reserve, lobsters have colonised the entire ecological niche previously occupied by the crustacean community. The results suggest that the creation of the reserve has contributed significantly to the resilience of the lobster population through increases in abundance, size and proportion of ovigerous females. Increased abundance in the protected area has encouraged emigration of young individuals out of the reserve, and has probably supported the local fishery and increased its productivity over time. The results also suggest that other species have not benefited from the creation of the box, or in the case of edible crab, have suffered greatly from the increase in the lobster population. It is likely that the strong territoriality of this species has caused the competitive exclusion of edible crab and velvet crab, which have declined in abundance and size., Au cours des dernières décennies, des réserves marines ont été créées afin de fournir des refuges à de nombreuses espèces exploitées ou non qui peuvent y trouver des habitats non impactés par la pêche. Elles peuvent également contribuer à certaines formes de pêcheries qui bénéficient de l’émigration des individus vers les zones environnantes non protégées. Cette étude a pour objectif d'estimer les effets d’un cantonnement situé devant le CNPE de Flamanville visant à protéger une communauté de crustacés. Elle s’appuie sur une série de données particulièrement riche qui permet de prendre en compte la variabilité spatio-temporelle d’origine naturelle, sur 33 années et 16 points d’échantillonnage. Dix-huit années après la mise en place du cantonnement, le homard a colonisé l’ensemble de la niche écologique auparavant occupée par la communauté des crustacés. Les résultats suggèrent que la création de la réserve a largement contribué à accroître la résilience de la population de homard au travers de l’augmentation de l’abondance, de la taille, et de la proportion de femelles ovigères. L’augmentation de l’abondance dans le périmètre protégé a favorisé l’émigration de jeunes individus vers l’extérieur de la réserve, et a sans doute permis de soutenir la pêcherie locale et d’augmenter sa productivité au fil du temps. Les résultats suggèrent également que les autres espèces n’ont pas profité de la création de ce cantonnement, voire, dans le cas du tourteau, ont fortement pâti de l’augmentation de la population de homard. Il est probable que la forte territorialité de cette espèce ait provoqué l’exclusion compétitive du tourteau et de l’étrille dont l’abondance et la taille ont diminué.

Depth is one of the environmental variables influencing the structure of marine food webs by directly or indirectly influencing benthic-pelagic coupling and predator-prey relationships. In shallow waters, the high degree of connectivity between pelagic and benthic networks results in complex systems with multiple interactions. Digestive tract (DT) and stable isotope (SI) analyses were used to investigate depth-related changes in feeding patterns for 33 fish species (eastern English Channel [EEC]) collected between 5 m and 80 m depth. Fish species were first arranged into functional groups based upon trophic and habitat similarities. DTs were used to determine the general topology of the food web and SIs were used to estimate the contributions of different sources to fish diets. At the scale of the aggregated EEC food web, the main food sources for all groups were of benthic origin (> 50%). The aggregated food web was then used as a template to explore the influence of depth on resource use by predatory fish. Mixing models including depth as a continuous covariate successfully untangled and identified different feeding strategies among functional groups. In shallow waters, fish species benefited from both pelagic and benthic prey whereas, in deeper waters, they fed predominantly on either benthic or pelagic sources depending on their habitat preferences. Our results support the hypothesis of a stronger benthic-pelagic coupling in shallow waters, notably through fish diet, and highlight the importance of including environmental factors such as depth as proxies of habitat variation to fully understand resource use and food web structure in epicontinental seas.

38 pages; International audience

Industrial fishing has been identified as a cause for life history changes in many harvested stocks, mainly because of the intense fishing mortality and its size-selectivity. Because these changes are potentially evolutionary, we investigate evolutionarily stable life-histories and yield in an energy-allocation state-dependent model for Northeast Arctic cod Gadus morhua. We focus on the evolutionary effects of size-selective fishing because regulation of gear selectivity may be an efficient management tool. Trawling, which harvests fish above a certain size, leads to early maturation except when fishing is low and confined to mature fish. Gillnets, where small and large fish escape, lead to late maturation for low to moderate harvest rates, but when harvest rates increase maturation age suddenly drops. This is because bell-shaped selectivity has two size-refuges, for fish that are below and above the harvestable size-classes. Depending on the harvest rate it either pays to grow through the harvestable slot and mature above it, or mature small below it. Sustainable yield on the evolutionary time-scale is highest when fishing is done by trawling, but only for a small parameter region. Fishing with gillnets is better able to withstand life-history evolution, and maintains yield over a wider range of fishing intensities.