In many exploited marine fish species, older individuals within cohorts often have slower growth rates at age than their younger counterparts, a process generally attributed to fishing. However, environmental changes might also contribute to the selective disappearance of faster growing individuals because of the increasing constraints acting on growth in suboptimal environments. Using otoliths of anchovy and sardine collected each year in spring since 2000 in the Bay of Biscay, we measured individuals’ growth during age-0 and catch-up growth during age-1, and followed their changes in time from 2000 to 2018 to quantify the magnitude of selective mortality. We then determined whether the variations in growth and selective mortality were related to seasonal temperature, food quantity, stock biomass or stock harvest rate. In both species, there was a decline in growth during age 0 over time and a catch-up growth declined in anchovy. Density-dependence had a strong effect on growth in anchovy. In both species, there was a systematic selective disappearance of individuals with large growth at age-0 within each cohort and selection has changed over time to favour individuals with large catch-up growth in anchovy. Moreover, diversifying selection occurred for growth at age-0 in both species and catch-up growth in anchovy. In anchovy, years with high selective disappearance of large individuals, high catch-up growth and high diversifying selection were those in which the harvest rates were high (environmental variables having more limited effect). In sardine, the selective disappearance of large individuals was stronger in years with low food quantity and the magnitude of selection acting on growth was unrelated to this stock’s harvest rate. Though fishing exerted strong selection pressure in anchovy, selective mortality against large growth still occurred even at low harvest rates in both species, suggesting that this might be a natural process affecting these small pelagic forage fish species. Although anchovy and sardine have a similar trophic position, their selection regimes differed due to differences in their stock dynamics, environmental sensitivity, and fishing rate. It might therefore be hazardous to extrapolate the responses of single species to environmental and anthropogenic factors onto others.

The initial objective of the PELGAS integrated survey was to assess the biomass of small pelagic fish in the Bay of Biscay in spring. Sampling has been extended to study the spatial structure and dynamics of the pelagic ecosystem in springtime. The PELGAS survey has produced since 2000 long-term time-series of spatially-explicit data and indices, describing the main pelagic ecosystem components: hydrology, phytoplankton, mesozooplankton, fish and megafauna. In addition to small pelagic fish biomass estimates used for fish stock assessment, the survey now delivers two types of ecosystem products: standard gridded maps of ecosystem parameters, and a time series dataset of indicators of the Bay of Biscay pelagic ecosystem state. The evolution of the PELGAS survey and sampling sampling designs are presented and discussed, to highlight their impact on the survey ecosystem products. The potential of PELGAS survey products for ecosystem assessment is demonstrated with two case studies. Series of multivariate maps are first analysed to assess the pelagic ecosystem spatial structure. A map of consistent ecosystem seascapes boundaries and of their inter-annual variability in time is presented. Second, time series of potential ecosystem indices derived from the survey are jointly analysed to select the most continuous indicators within, and across, several ecosystem components. Trends in the selected time series are interpreted to derive information on marine ecosystem status and dynamics. Challenges and future directions are discussed, with a focus on the new big data flows that could be provided by the survey in a near future.

The Pelagiques Gascogne (PELGAS) integrated survey has been developed by a multidisciplinary team of Ifremer and La Rochelle University scientists since 2000, joined by commercial fishermen in 2007. Its initial focus was to assess the biomass and predict the recruitment success of anchovy in the Bay of Biscay in spring. Taking advantage of the space and versatility of R/V Thalassa II, sampling has been progressively extended to other ecosystem components. PELGAS therefore further developed the second objective of monitoring and studying the dynamic and diverse Biscay pelagic ecosystem in springtime. The PELGAS survey model has allowed for the establishment of a long-term time-series of spatially-explicit data of the Bay of Biscay pelagic ecosystem since the year 2000. Main sampled components of the targeted ecosystem are: hydrology, phytoplankton, mesozooplankton, fish and megafauna. The survey now provides two main ecosystem products: standard raster maps of ecosystem parameters, and a time series dataset of indicators of the Bay of Biscay pelagic ecosystem state. They are used to inform fish stock and ecosystem-based management, and support ecosystem research. The present paper introduces the PELGAS survey, as a practical example of an integrated, vessel-based, ecosystem survey. The evolution of the PELGAS scientific team and sampling protocols are presented and analysed, to outline factors crucial to the success of the survey. Data and results derived from PELGAS are reviewed, to exemplify scientific questions that can be tackled by integrated ecosystem survey data. Advantages and challenges of the survey are discussed and put into the context of marine ecosystem surveys in the European Marine Strategy Framework Directive and the Common Fisheries Policy.

There is a growing interest in monitoring body condition of marine organisms in the context of the ecosystem approach to fisheries and global change. Fish condition is under the influence of environmental variability on seasonal scale, but also on longer timescales. It represents a good indicator of habitat quality or individual fitness, and is also a relevant parameter to evaluate energy transfer through the trophic chain. However, the sources of variability in fish condition need to be accurately understood and the significance of existing indices has to be correctly assessed. Here, we measured the energy density, a precise and global indicator of fish bioenergetic condition, for anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) in the Bay of Biscay and the English Channel, based on an extensive sampling design in 2014. First, we investigated the well documented relationship between percent dry mass and energy density, and showed that such relationship is species specific. Second, we observed distinct patterns in bioenergetic condition between anchovy and sardine. Both species display similar minimum values at size or age but maximum are significantly higher for sardine, reflecting a higher energy storage capacity that scales more strongly with size. Third, we confirmed the large seasonal variability in energy density of both species. In the Bay of Biscay, energy density values for anchovy and sardine (age 1 +) are 5.7 and 5.9 kJ g(-1) (wet weight) in spring and 6.8 and 7.9 kJ g(-1) in autumn, respectively. Our results revealed that fish from the English Channel display significantly higher energy density values in autumn (9.8 kJ g(-1) for anchovy and 10.5 kJ g(-1) for sardine) than those from the Bay of Biscay. When combined with size and weight at age it appears clearly that, after age 1, fish from the northern region display larger growth and energy reserves. This likely results from a higher zooplankton productivity in the English Channel or/and a selection pressure towards faster growing and faster reserve building individuals, to be able to survive a longer winter than in the Bay of Biscay. Finally, we described a dome shaped evolution of energy density with body size in case of sardine. Increase with size has been well documented but not the decrease at largest sizes. Several mechanisms may explain such a pattern, i.e. increasing investment in spawning, shift in diet or a metabolic trade-off between temperature and food availability, with regard to maintenance requirements.

Diversity among individuals in a population is an important feature linking vital rates with behaviour and spatial occupation. We measured the growth increments in the otolith of individual fishes collected on the annual fisheries survey PELGAS from 2001 to 2015. Individuals who grew larger at juvenile stage occupied later in life more off-shore habitats. Further, we analysed the allozymes of 13 different loci from 2001 to 2006. Alleles of the enzyme IDH showed different frequencies in inshore and offshore habitats. The population spatially segregates along a coast to off-shore gradient with individuals showing different early growth and allele frequencies. Results show how individuals in a population segregate spatially in different habitats in relation with phenotypic diversity. This implies modelling the population with individual-based and physiological approaches to fully grasp its dynamics. It also implies developing management strategies to conserve infra-population diversity as a means to garantee the occupation of the full range of habitats.

The objective of the study is a better understanding of recruitment variability in anchovy population. An Individual Based Model (IBM) is being developed for the full life cycle of anchovy. The early life stages are presented on this poster. The model is tested in a 1D-vertical framework for validation of the vertical distribution of modelled eggs and larvae against in-situ data. The dynamic Energy Budget (DEB) theory is the biological baseline for individual growth. We test its ability to simulate the observed growth curves between years with contrasted temperatures.

Fish length frequency histograms from research surveys are of prime importance for identifying habitats of different life stages, as well as for stock assessment. However, no method has thus far been available for mapping these histograms as spatially varying curves. Here, a procedure is applied to map spatially connected curves, and detail is given on how it can be applied to map the length frequency histograms. At each sample location, a fish length frequency histogram is given as a vector of non-independent values. The histogram is first modelled as a polynomial expansion on the basis of orthogonal polynomials. Then, the polynomial coefficients are mapped by co-kriging, after fitting a model of co-regionalization. The length frequency map is finally derived by linearly combining maps of polynomial coefficients. An estimation variance associated with the map is also derived. Maps of anchovy length distributions are produced by applying the method to midwater trawl length data from the PELGAS acoustic surveys in the Bay of Biscay. This novel approach extends the application of kriging techniques to curves or functions, opening new perspectives for mapping more complex information than just the values of fish density.

This document presents all the techniques used in routine by Ifremer to estimate the age of fish from the calcified piece. The procedure for estimating age describes each technical stage from the taking of the calcified piece through to the supplying of key sizes/ages to the European work groups. This procedure is specific to each species and even each population of fish.

Fish recruitment is the result of the integration of small-scale processes affecting larval survival over a season and large oceanic areas. A hydrodynamic model was used to explore and model these physical-biological interaction mechanisms and then to perform the integration from individual to population scales in order to provide recruitment predictions for fisheries management. This method was applied to the case of anchovy (Engraulis encrasicolus) in the Bay of Biscay (NE Atlantic). The main data available to investigate survival mechanisms were past growth (otolith) records of larvae and juveniles sampled at sea. The drift history of these individuals was reconstructed by a backtracking procedure using hydrodynamic simulations. The relationships between (real) growth variation and variations in physical parameters (estimated by hydrodynamic simulations) were explored along the individual trajectories obtained. These relationships were then used to build and adjust individual-based growth and survival models. Thousands of virtual buoys were released in the hydrodynamic model in order to reproduce the space-time spawning dynamics. Along the buoy trajectories (representative of sub-cohorts), the biophysical model was run to simulate growth and survival as a function of the environment encountered. The survival rate after 3 months of drift was estimated for each sub-cohort. The sum of all these survival rates over the season constituted an annual recruitment index. This index was validated over a series of recruitment estimations. The modelling choices, model results and the potential use of the recruitment index for fisheries management are discussed.

The relation between growth and survival was investigated using the otolith growth data collected during repeated larval surveys ( May - July) and a juvenile survey ( September) undertaken in 1999 on anchovy spawning and nursery grounds in the Bay of Biscay ( NE Atlantic). The paper describes the methodology for reading the larval and juvenile otoliths, for reconstructing the correspondence in space and time between juveniles and larvae using Lagrangian simulations, and for comparing the otolith growth rates among the reconstructed sub-cohorts. Virtual buoys were released weekly on the grid of a three-dimensional hydrodynamic model and their trajectories were tracked. The origin of an individual was determined by selecting the trajectory beginning on its hatching week and ending at the minimum distance of its sampling location on the sampling date. Larvae and juveniles with the same spatio-temporal origin were selected and supposed to belong to the same sub-cohorts. The surviving juveniles showed faster growth rates during their larval period than the pool of larvae they were estimated to originate from, which supports the idea of growth-selective survival. Alternative interpretations ( transport and gear selectivity) are discussed. Variations in otolith growth pattern also suggest a higher juvenile growth over the shelf break than in oceanic waters.