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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.

SEAwise deliverable 6.7 is the first of two deliverables in task 6.4. It investigates the consistency of existing targets and limits from the Common Fisheries Policy (CFP) and the Marine Strategy Framework Directive (MSFD). Trade-offs between different objectives (ecological, economic, social), targets and limits are highlighted. A wide range of model types (from bio-economic to full ecosystem models) has been applied to various case study areas across the North East Atlantic and Mediterranean. Although model predictions are by nature uncertain, this study provides important information on likely inconsistencies between existing targets and limits and trade-offs expected under ecosystem- based fisheries management (EBFM). The scenarios investigated include the current range of management applied in terms of the Maximum Sustainable Yield (MSY) concept (i.e. strict MSY approach vs. Pretty Good Yield (PGY) approach allowing sustainable deviations from single species FMSY point estimates). The landing obligation is a key aspect of current fisheries management and was fully considered, in particular for mixed demersal fisheries. Maintaining current fishing effort without further management measures was the least sustainable option in nearly all cases studies. This approach led to increased risk of stocks falling below critical biomass limits. Although the fishing effort adaptions needed is highly case specific, this indicates that further management measures are likely to be needed to ensure a sustainable exploitation of all stocks. Scenarios applying a strict MSY approach in combination with the landing obligation (i.e. FMSY as upper limit with fisheries ending when the first stock reaches FMSY) in most case studies led to the lowest fishing effort. This had positive effects on MSFD related indicators such as bycatch of Protected, Endangered and Threatened (PET) species, benthic impact and the Large Fish Indicator as well as global indicators such as CO2 emission or eco

Understanding the dynamics of species interactions for food (prey-predator, competition for resources) and the functioning of trophic networks (dependence on trophic pathways, food chain flows, etc.) has become a thriving ecological research field in recent decades. This empirical knowledge is then used to develop population and ecosystem modeling approaches to support ecosystem-based management. The TrophicCS data set offers spatialized trophic information on a large spatial scale (the entire Celtic Sea continental shelf and upper slope) for a wide range of species. It combines ingested prey (gut content analysis) and a more integrated indicator of food sources (stable isotope analysis). A total of 1337 samples of large epifaunal invertebrates (bivalve mollusks and decapod crustaceans), zooplankton, fish, and cephalopods, corresponding to 111 taxa (94% determined at the species level), were collected and analyzed for stable isotope analysis of their carbon and nitrogen content. Samples were collected between 2014 and 2016, mostly during the month of November and between 57 and 516 m depth. Sample size varied between taxa (from 1 to 52), with 98 taxa having at least three samples. The gut contents of 1027 fish belonging to 10 commercially important species: black anglerfish (Lophius budegassa), white anglerfish (Lophius piscatorius), blue whiting (Micromesistius poutassou), cod (Gadus morhua), haddock (Melanogrammus aeglefinus), hake (Merluccius merluccius), megrim (Lepidorhombus whiffiagonis), plaice (Pleuronectes platessa), sole (Solea solea), and whiting (Merlangius merlangus) were analyzed. Sampling occurred in November 2014 and 2015. The gut content data set contains the occurrence of prey in gut, identified to the lowest taxonomic level possible. No prey were assigned for 274 empty gut contents. To consider potential ontogenetic diet changes, a large size range was sampled for each species. The TrophicCS data set was used to improve understanding of trophic re

Predictive selectivity modelling is used to study fishing gear selectivity. These models rely on fish morphology parameters and fall-through experiments. Here, we developed a model of the mechanical interaction between a fish and a netting mesh during an escape attempt. In this model, the fish is described with three parameters: the first parameter measures its mechanical ability to penetrate a mesh and the others are body stiffness coefficients accounting for fish body deformation under mesh twine pressure. These parameters were identified from the results of a bench test simulating a fall-through experiment through a single 60-mm Polyethylene (PE) mesh. A rigid circular cone, a rigid elliptical cone and a small number of horse mackerel and haddock, offering a limited length range, were tested. Results were generalised and compared with those obtained on a piece of netting. Within the model's assumptions, it is possible to predict the success of an escape attempt if one knows the three fish parameters and the mesh load in normal and transverse directions. The study showed that escape potential is greater through an actual deformable mesh than through a non-deformable mesh. The potential size of this difference depends on the mesh load and orientation.

While, quantifying trophic interactions is a critical path to understanding and forecasting ecosystem functioning, fitting trophic models to field data remains challenging. It requires flexible statistical tools to combine different sources of information from the literature and fieldwork samples. We present EcoDiet, a hierarchical Bayesian modeling framework to simultaneously estimate food-web topology and diet composition of all consumers in the food web, by combining (i) a priori knowledge from the literature on both food-web topology and diet proportions; (ii) stomach content analyses, with frequencies of prey occurrence used as the primary source of data to update the prior knowledge on the topological food-web structure; (iii) and biotracers data through a mixing model (MM). Inferences are derived in a Bayesian probabilistic rationale that provides a formal way to incorporate prior information and quantifies uncertainty around both the topological structure of the food web and the dietary proportions. EcoDiet was implemented as an open-source R package, providing a user-friendly interface to execute the model as well as examples and guidelines to familiarize with its use. We used simulated data to demonstrate the benefits of EcoDiet and how the framework can improve inferences on diet matrix by comparison with classical network MM. We applied EcoDiet to the Celtic Sea ecosystem, and showed how combining multiple data types within an integrated approach provides a more robust and holistic picture of the food-web topology and diet matrices than the literature or classical MM approach alone. EcoDiet has the potential to become a reference method for building diet matrices as a preliminary step of ecosystem modeling and to improve our understanding of prey-predator interactions.

Management targets for biodiversity preservation are shifting from individual species to an ecosystem-wide focus. Indeed, the perturbation analysis of interaction networks, such as food webs, better captures the response of biodiversity to environmental pressures than single-species considerations. Here we propose a framework that examines food web robustness to a given perturbation based on life history traits and the topology of the food web, at different scales: local (species), intermediate (species directly linked together by a trophic interaction), and global (food web). Applying this framework to the Celtic Sea, a historically exploited fishing ground, we showed that the species sensitive to fishing were not the most central (i.e. with many interaction links, estimated based on eigenvector centrality) and that there is no both highly sensitive and exposed species to fishing. We then investigated how the loss of central, sensitive and exposed species to fishing could impact the robustness of the food web. We showed that the food web was the least robust to the simulated loss of species with many predators (i.e. forage species) and most exposed to fishing pressure, indicating that conservation priority could be focused on these species. Estimating species’ sensitivity to fishing was insufficient to predict food web robustness since the simulated removal of the most sensitive species led to a robustness level similar to that of a random removal sequence. Unlike what is often documented, the network appeared relatively robust to the simulated loss of the most central species, due notably to their implication in redundant trophic interactions and the fact that their disappearance increases modularity. This suggests that species-level metrics such as centrality should be completed by analysis at the scale of the whole food web to prioritize species conservation.

Both trophic structure and biomass flow within marine food webs are influenced by the abiotic environment and anthropogenic stressors such as fishing. The abiotic environment has a large effect on species spatial distribution patterns and productivity and, consequently, spatial co-occurrence between predators and prey, while fishing alters species abundances and food-web structure. In order to disentangle the impacts of the abiotic environment and fishing in the Celtic Sea ecosystem, we developed a spatio-temporal trophic model, specifically an Ecopath with Ecosim with Ecospace model, for the period 1985–2016. In this model, particular attention was paid to the parameterization of the responses of all trophic levels to abiotic environmental changes. Satellite remote sensing data were employed to determine the spatial distribution and annual fluctuations of primary production (PP). Spatial and temporal changes in the habitat favorable for zooplankton were predicted with a novel ecological-niche approach using daily detection of productivity fronts from satellite ocean color. Finally, functional responses characterizing the effect of several abiotic environmental variables (including, among others, temperature, salinity and dissolved oxygen concentration, both at the surface and at the bottom) on fish species groups’ habitat suitability were produced from the predictions of statistical habitat models fitted to presence-absence data collected by multiple fisheries-independent surveys. The dynamic component of our model (Ecosim) was driven by time-series of fishing effort, PP, zooplankton habitat suitability and abiotic environmental variables, and was fitted to abundance and fisheries catch data. The spatial component of our model (Ecospace) was constructed, for specific years of the period 1985–2016 with contrasted abiotic environmental conditions, to predict the variable distribution of the biomass of all functional groups. We found that fishing was the main driver o

Knowledge about fish behavior is crucial to be able to influence the capture process and catch species composition. The rapid expansion of the use of underwater cameras has facilitated unprecedented opportunities for studying the behavior of species interacting with fishing gears in their natural environment. This technological advance would greatly benefit from the parallel development of dedicated methodologies accounting for right-censored observations and variable observation periods between individuals related to instrumental, environmental and behavioral events. In this paper we proposed a methodological framework, based on a parametric Weibull mixture model, to describe the process of escapement attempts through time, test effects of covariates and estimate the probability that a fish will attempt to escape. We additionally proposed to better examine the escapement process at the individual level with regard to the temporal dynamics of escapement over time. Our approach was used to analyze gadoids swimming and escapement behaviors collected using a video set up in front of a selective device known to improve selectivity on gadoids in the extension of a bottom trawl. Comparison of the fit of models indicates that i) the instantaneous rate of escape attempts is constant over time and that the escapement process can be modelled using an exponential law; ii) the mean time before attempting to escape increases with the increasing number of attempts; iii) more than 80% of the gadoids attempted to escape through the selective device; and iv) the estimated probability of success was around 15%. Effects of covariates on the probability of success were investigated using binomial regression but none of them were significant. The data set collected is insufficient to make general statements, and further observations are required to properly investigate the effect of intrinsic and extrinsic factors governing gadoids behavior in trawls. This methodology could be used to b

Most European fishing fleets will need to drastically reduce their unwanted catches to comply with new rules of the common fisheries policy. A more practical way to avoid increasing on-board sorting time and issues linked to storage capacity is to prevent unwanted catches in the first place. We assessed the selectivity properties of an experimental fishing gear that combined a 100 mm T90 cylinder with 130 meshes in the extension and a 100 mm T90 codend of 33 meshes (experimental gear) compared to a 100 mm diamond mesh extension and codend (control gear) during commercial trips using twin trawls. Analysis of the relative size composition of catches indicated a significantly higher escapement of small fish of several target species (e.g. Lepidorhombus whiffiagonis, Melanogrammus aeglefinus, Raja spp, and Lophius spp) and non-target species (e.g. Capros aper and Gurnards spp) from the T90 experimental trawl compared to the control trawl (n = 49 hauls), resulting in a significant reduction of unwanted catches of Gadidae, Triglidae, and Caproidae. In contrast, nonnegligible commercial losses of small grade target gadoid species were observed. Mixed general linear models showed that the proportion of ray, haddock and anglerfish retained per length class decreased with increased tow duration. The T90 experimental gear will perform at a commercial level when targeting monkfish, megrim, rays and large haddock, however fishers are not likely to use this gear when targeting smaller-bodied species such as cephalopods, small haddock, whiting (Merlangius merlangus) and hake (Merluccius merluccius), because the gear is likely to allow large numbers to escape. Selectivity studies often focus on a short list of target species; however, catches of non-target species under quota can be problematic for some fisheries. For example, under the implementation of the Landing Obligation catches of boarfish could choke the French whitefish demersal fisheries in the Celtic sea, as France has n

Global climate change has already caused bottom temperatures of coastal marine ecosystems to increase worldwide. These ecosystems face many pressures, of which fishing is one of the most important. While consequences of global warming on commercial species are studied extensively, the importance of the increase in bottom temperature and of variation in fishing effort is more rarely considered together in these exploited ecosystems. Using a 17‐year time series from an international bottom‐trawl survey, we investigated co‐variations of an entire demersal ecosystem (101 taxa) with the environment in the Celtic Sea. Our results showed that over the past two decades, biotic communities in the Celtic Sea were likely controlled more by environmental variables than fisheries, probably due to its long history of exploitation. At the scale of the entire zone, relations between taxa and the environment remained stable over the years, but at a local scale, in the center of the Celtic Sea, dynamics were driven by inter‐annual variation in temperature. Fishing was an important factor structuring species assemblages at the beginning of the time series (2000) but decreased in importance after 2009. This was most likely caused by a change in spatial distribution of fishing effort, following a change in targeted taxa from nephrops to deeper water anglerfish that did not co‐vary with fishing effort. Increasing bottom temperatures could induce additional changes in the coming years, notably in the cold‐water commercial species cod, hake, nephrops and American plaice. We showed that analyzing co‐variation is an effective way to screen a large number of taxa and highlight those that may be most susceptible to future simultaneous increases in temperature and changes in exploitation pattern by fisheries. This information can be particularly relevant for ecosystem assessments.

La règlementation « zéro rejet » de PCP vise à éliminer progressivement les rejets de pêche en mer. Pour y parvenir, des mesures techniques de sélectivité, option abordée par ce projet, doivent permettre de réduire la capture des individus non valorisés. On cherche dans la partie initialement nommée SCOTCH du projet FUSION à accompagner ces évolutions techniques par une prise en compte des comportements des individus en lien avec le fonctionnement de l’engin de pêche. Les travaux effectués dans le cadre du projet FUSION concernent les chaluts mais pourraient être transposés à tout engin constitué de filet.

The ICES Working Group on Mixed Fisheries Advice (WGMIXFISH-ADVICE) chaired by Claire Moore, Ireland, met at ICES headquarters in Copenhagen, Denmark, 28 October–1 November 2019 to produce mixed fisheries forecasts for the North Sea, Celtic Sea, and Iberian waters Mixed fisheries advice highlights the potential implications of single-stock (total allowable catch and effort) management on the catches of multiple stocks caught together in mixed fisheries. It takes into account past fishing patterns and catchability of the different fleets, and the TAC advice produced by the single-stock advice groups for 2019 to provide quantitative forecast of over- and under-exploitation of the different stocks given mixed fishery interactions. Forecasts were based on the “FCube” (Fleet and Fishery Forecasts) methodology for the Celtic Sea and North Sea, and on the “FLBEIA” (Fisheries Library Bio-Economic Impact Assessment) methodology for the Iberian Waters—with a range of potential management scenarios relevant for the specific regional fisheries. The North Sea demersal mixed fisheries projections consider the single-species advice for cod (cod.27.47d20), haddock (had.27.46a20), whiting (whg.27.47d), saithe (pok.27.3a46), plaice (ple.27.420 and ple.27.7d), sole (sol.27.4), turbot (tur 27.4), and Norway lobster Nephrops norvegicus (functional units [FUs] 5–10, 32, 33, 34, and 4 outFU). The most limiting TAC in 2020 will be the TAC for cod for particular fleets (“cod-ns” scenario). The “min” scenario gives a 14% higher catch of cod compared to the “cod-ns” scenario, due to the relaxing of the constraint on a stock where the country is not assumed to be limited for that stock, but the model does not take into account quota reallocation between fleets. Substantial overshoot of TACs can occur under other scenarios (e.g. “max” scenario). This “range” scenario suggests that the potential for mixed fisheries mismatch would be lowered with a 2020 TAC in the lower p

Under the Landing Obligation (LO) fishers will need to reduce or land fish that were previously discarded. In this chapter we look at how they might be able to do that by summarising a number of studies conducted in various European regions. We start by describing a series of “challenge” trials where fishers tried to reduce their discards by whatever (legal) means they thought best. In some cases, they were able to reduce unwanted catches, in others they were less successful. We also interviewed fishers not involved in the trials to ask them what they thought they could do. We explore their approaches which generally fell into three categories: more selective gear; tactical and strategic changes; and management changes. Scientific data (surveys, landings, and observers data) can also be valuable to help fishers to decide where and when to fish to best avoid unwanted catches and maximise opportunities to catch their quotas. We provide some examples of this type of approach, and also how these can be adapted for use as interactive online apps that fishers can use in planning or whilst at sea