French Research Institute for Exploitation of the Sea
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Avis de l'lfremer sur le renouvellement de la dérogation DGAL à l'utilisation de la moule comme espèce sentinelle dans le secteur du Traict du Croisic pour le suivi des toxines lipophiles
No full textThe El Niño Southern Oscillation (ENSO) recharge oscillator conceptual model : achievements and future prospects
No full textThe recharge oscillator (RO) is a simple mathematical model of the El Niño Southern Oscillation (ENSO). In its original form, it is based on two ordinary differential equations that describe the evolution of equatorial Pacific sea surface temperature and oceanic heat content. These equations make use of physical principles that operate in nature: (a) the air-sea interaction loop known as the Bjerknes feedback, (b) a delayed oceanic feedback arising from the slow oceanic response to winds within the equatorial band, (c) state-dependent stochastic forcing from fast wind variations known as westerly wind bursts (WWBs), and (d) nonlinearities such as those related to deep atmospheric convection and oceanic advection. These elements can be combined at different levels of RO complexity. The RO reproduces ENSO key properties in observations and climate models: its amplitude, dominant timescale, seasonality, and warm/cold phases amplitude asymmetry. We discuss the RO in the context of timely research questions. First, the RO can be extended to account for ENSO pattern diversity (with events that either peak in the central or eastern Pacific). Second, the core RO hypothesis that ENSO is governed by tropical Pacific dynamics is discussed from the perspective of influences from other basins. Finally, we discuss the RO relevance for studying ENSO response to climate change, and underline that accounting for ENSO diversity, nonlinearities, and better links of RO parameters to the long term mean state are important research avenues. We end by proposing important RO-based research problems.
Key Points
The recharge oscillator (RO) simple mathematical model explains most of El Niño Southern Oscillation (ENSO) key properties
The RO can be extended to account for ENSO pattern diversity (some events peak in the central, others in the eastern equatorial Pacific)
We propose research avenues for using the RO to address the influence of climate change and other climate modes on ENSO
Plain Language Summary
The El Niño Southern Oscillation (ENSO) is the main driver of Earth's year-to-year climate variations. ENSO arises from air-sea interactions in the tropical Pacific, but influences climate and societies globally. In recent decades, progress in the observing system and in numerical modeling yielded a better understanding of the physical processes that govern ENSO. Such understanding can be encapsulated in the recharge oscillator (RO) conceptual model, a simple mathematical representation of ENSO fundamental mechanisms, which accounts for ENSO's essential properties: its amplitude, dominant period, tendency to peak at the end of the year, and tendency for larger warm (El Niño) than cold (La Niña) events. We discuss this framework and propose how to adapt it to explore pressing research topics. First, recent research indicates that the RO can be extended to account for the ENSO diverse spatial patterns of ENSO variability, with anomaly centers in either the central or eastern Pacific. Second, we discuss RO applications for studying influences of regions outside the tropical Pacific on ENSO. Finally, we discuss the RO as a tool to understand the ENSO response to climate change. We conclude by compiling important problems related to these challenging topics
Environmental and geographical drivers of reef fish beta diversity across the depth gradient
No full textThe swift decline of coral reefs stands out as a significant biodiversity challenge confronting our generation, and mesophotic coral ecosystems (MCEs; reefs between 30 and 150 m) have been proposed as refuge habitats that may be less affected by climate change and human impacts compared to their shallow counterparts. However, MCEs are often distinct from shallow reefs, and studies assessing how marine biodiversity changes along the depth gradient and what factors can influence marine communities in MCEs are still scarce. Here, we conducted underwater visual censuses to evaluate how fish assemblages change among islands and environmental characteristics across the shallow to mesophotic depth gradient within the Cabo Verde Archipelago. Our results show that the beta diversity of reef fish assemblages was mainly driven by depth and environmental factors such as temperature and benthic variables. A consistent trend of increasing beta diversity from the shallow to the lower mesophotic zone was observed among the islands, with the lowest variation in species composition observed between the shallow (5-30 m) and upper (31-60 m) mesophotic depths. Lower species richness and higher turnover was observed within lower MCEs (61-85 m), suggesting saturation in fish richness at small scales, possibly a result of changes in microhabitat heterogeneity. Furthermore, the effect of geography was negligible, and local-scale environment characteristics were the main drivers of differences in species assemblages. Evidence suggests that increased fishing pressure on the most populated island may reduce the biogeographic influence on fish assemblages across the archipelago
Campagne dédiée à l’évaluation des effets biologiques induits par la contamination chimique en baie de Seine et de Somme. SELIMANCHE 2021
No full textLe dispositif « SELI » est mis en place depuis 2017 pour acquérir des données sur les effets biologiques intégrateurs de la contamination chimique chez des organismes marins (poissons et bivalves). Il permet de renseigner la base de données du Conseil International pour l'Exploration de la Mer (CIEM (ICES en anglais)), et ainsi d’alimenter le groupe de travail ICES/BEC (Biological Effect of Contaminants) et de renseigner le descripteur 8 de la Directive Cadre Stratégie pour le Milieu Marin (DCSMM) qui définit le Bon Etat Ecologique comme un état où le niveau de concentration des contaminants ne provoque pas d’effets dus à la pollution. Le présent rapport concerne le volet SELIMANCHE 2021, c’est-à-dire la mise en oeuvre du dispositif SELI en Manche en 2021. Des poissons plats (n=108 soles et 40 flets) ont été collectés sur le Navire Océanographique (N/O) Côtes De La Manche du 30/08/2021 au 08/09/2021 (https://doi.org/10.17600/18001614). De plus, des bivalves (n= 120 moules, 15 moules/station) ont été prélevés en février 2022 à 8 stations du suivi du Réseau d’Observation de la Contamination Chimique du littoral dans la Matière Vivante (ROCCH MV). Les biomarqueurs suivis sont ceux listés dans l’arrêté national BEE 2019 et couvrent plusieurs états et modes d’action des contaminants : biomarqueurs de la santé générale de l'organisme (indices somatiques (e.g. RGS, RHS), stabilité de la membrane lysosomale), biomarqueurs de génotoxicité (cassures de brins de l’ADN (test des comètes) et micronoyaux), biomarqueur de neurotoxicité (AChE), biomarqueur d’exposition aux HAP (métabolites de HAP chez les poissons) ainsi que des analyses histopathologiques des gonades et du foie. Les contaminants suivis sont des contaminants organiques hydrophobes (historiques et d’intérêt émergent : PCB, PBDE, HBCDD, PFAS et pesticides organochlorés (OCP)) et des éléments traces métalliques susceptibles de s’accumuler dans les organismes et/ou de s’amplifier dans les réseaux trophiques. L’ensemble de ces analyses permet d’évaluer : 1) les réponses biologiques observées chez les organismes marins (poissons plats, bivalves) 2) le niveau d’imprégnation des organismes marins (poissons plats, bivalves) par les contaminants chimiques, et à moyen-terme : 3) si les réponses biologiques observées peuvent être associées à l’exposition à un stress chimique dans des zones de pressions anthropiques variées ? Le présent rapport est organisé selon un niveau d’intégration croissant : il commence par décrire chaque biomarqueur et chaque famille de contaminants individuellement, puis des représentations intégrées sont proposées pour avoir une vision de plus en plus globale de la contamination chimique et de ses effets en baies de Seine et Somme en 2021
Benchmark on selected sea bass stocks (WKBSEABASS)
No full textThe benchmark workshop on sea bass (Dicentrarchus labrax) (WKBSEABASS) was conducted over an extended period, spanning from 2023 to 2024, to agree on the stock identities, stock struc-ture, and assessment methodologies in future assessments of sea bass in the North Sea, Northeast Atlantic, and down to the Bay of Biscay. The benchmark had a strong focus on the investigation of spatial boundaries of the population within the area and the migratory behaviour and mixing between units. As part of the current benchmarking process, the evidence on stock identity for sea bass in North-ern and Biscay stocks was reviewed, and plausible stock structure scenarios for the ICES sea bass benchmark were proposed (ICES, 2023). This generated several potential stock identities that included: a single stock covering the whole area; the current Northern (ICES divisions 4.b–c, 7.a, and 7.d–h) and Biscay (ICES divisions 8.a–b) stocks with mixing; and three equally plausible scenarios with three subpopulations and mixing (ICES, 2023). At the data workshop, it was iden-tified that there was insufficient data to model the Irish Sea (7.a) separately, and catch was low in this area, so it was merged with the Celtic Sea for modelling. In addition, there was insufficient resource to test all scenarios, so two were chosen: the current Northern and Biscay stocks with exchange of catches; and a single meta-population model containing North Sea (4.b–c, 7.d), Celtic and Irish Seas (7.a, 7.e–h), and Biscay (8.a–b) subpopulations with mixing (Figure 1). At the mod-elling workshop, it was decided to start with the simpler of the two scenarios (i.e. Northern and Biscay stocks with exchange of catches; Figure 1A) due to the complexity of the full mixing model (Figure 1B). As a result, only scenario A, Northern and Biscay stocks with exchange of catches (Figure 1A), was taken forward to the benchmark. The data workshop was conducted from 29 January to 2 February 2024 in Copenhagen, followed by intersessional work in groups to address and produce the missing data identified at the work-shop. Catch numbers at length, natural mortality-at-age, recreational catches and survey indices were recalculated based on the latest insights and tools provided and additional data becoming available. Key to this process was also the advanced understanding and estimation processes of the recreational fishery data, while tagging data provided a quantity for the mixing of the stocks. For both regions, new SS3 models were created, with a proportion of the catches, according to data from tagging studies, being reallocated from the Northern to the Southern stock. Baseline models for both areas were created, which had to pass a set of diagnostics, including diagnostics on catch and survey residuals, parameter uncertainty estimates, trends in spawning-stock bio-mass (SSB), Fishing mortality (F), Recruitment (R) and retrospective analyses, set out at the be-ginning of the benchmark workshop. Setting out a set of diagnostics before the benchmark will considerably improve the transparency and comparability of such a process and improve the flow of the workshop. Discussion focused on some poor fits to specific fleets, which is outlined under the individual headings of the stocks. Once the base models had been finalized, each of them was assigned several sensitivity tests and alternative scenarios to find the best model to describe the state of the stock: Northern stock • Different time-series of recreational fisheries catches. • Turn off the extra standard deviation for juvenile surveys. • Discard as retention function for OTB and SEINE as catch fleet. • Mirror OTB discard fleet to OTB landings fleet and remove discard length information. • Recreational fleet as landed and discarded fraction. • Use of Lorenzen M. • M profiling. • Steepness profiling. • Associate ALK to a different fleet than OTB. • Estimate all growth parameters. • Assume no movement of fish from the Southern to the Northern stock. • Leave one out (surveys). Southern stock • Use of Lorenzen M. • M profiling. • Steepness profiling. • Estimate all growth parameters setting A for L2 at 16 years old. • Assume no movement of fish from the Southern to the Northern stock. • Leave one out (surveys). • Random walk for GTR and LL instead than blocks. • Switch off extra standard deviation for LPUE. • Switch off the random walk for GNS and substitute with blocks. • Decrease CV of the last 2 years of the OTB discards. • Associate ALK to a different fleet than OTB. All scenarios were then tested with a script comparing the previously created diagnostics to find the models with the best fit. Some of the scenarios were purely done for the sensitivity of the model (such as the scenario not to transfer the catches from the northern model to the southern model to account for mixing). In contrast, others focused on the selectivities of the various time-series, the setting of natural mortality, etc. It was agreed to treat some of the dataseries the same way in both models, such as the re-calculation of the recreational data back in time; both models were successfully completed, and the reference points were estimate
Shift in demersal marine communities at the edge of two biogeographic areas between 1996 and 2021
No full textMarine ecosystems are facing pressures from climate change and anthropogenic activities. While the induced impacts are widely observed, studied and modelled to define projections and management advice, the evolution of marine biodiversity still needs to be described and understood at local scales. The northern part of the Bay of Biscay is particularly concerned since at the edge of two marine provinces that discriminate Lusitanian and Boreal species, and with intense fishing pressure due to the presence of many commercial species. In the late nineties, a scientific survey characterized the demersal biodiversity of this area using underwater video transects and 25 years later, the same transects were revisited using a ROV. The taxonomic richness and densities from these two periods were compared to detect and describe changes in community composition and highlight potential shifts between Lusitanian and Boreal species. Taxonomic richness remains stable over time with 38 taxa in the 1990s, 39 in the 2020s, among which 37 were common to both periods. Yet, global abundance decreases significantly with disparities among taxa. Some Lusitanian species have significantly increased in density while some Boreal ones decreased. Two variables were identified to drive the change in community structure: fishing effort and seawater temperature. These findings echo other works in the area based on yearly, extensive bottom trawl surveys, while we highlighted the same structural community changes with one-off video sampling, bringing to the fore the robustness of videos sampling for monitoring diversity shifts in response to climate change
