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Fisheries discards have become a source of concern for the perennation of marine resources. To reduce discards, the European Union adopted a Landing Obligation under the reform of its Common Fisheries Policy. However, food web consequences of reducing discards remain uncertain since their degree and pathway of reintegration are understudied. We used multi-marker DNA metabarcoding of gut contents and an ecological network approach to quantify marine fauna reliance on discarded fish and functional importance of discard consumers in coastal fishing grounds. We show that potential discard consumption is widespread across fish and invertebrates, but particularly important for decapods, which were also pinpointed as functionally important. Potential discard consumption may represent up to 66% of all interactions involving fish prey in the reconstructed network. We highlight that discard reliance may be more important than previously assessed in some fishing areas and support functionally important taxa. While reducing discarding remains a conservation priority, it is crucial to understand discards reintegration in marine food webs to anticipate changes in the context of an ecosystem approach to fisheries management.

Coastal marine ecosystems are under many pressures, including bottom trawling, which is the most widespread human activity that directly affects seabed habitats. Therefore, it is of great importance to characterize the impacts of bottom trawling on bentho-demersal communities, which can be done through the study of indicators sensitive to trawling pressure. Using a functional indicator applied to 54 underwater video transects, we mapped the sensitivity to trawling of epibenthic invertebrates and fish communities in the Celtic Sea. We determined the relative influence of environmental and fishing variables on sensitivity and traits distribution. Our results suggest that community sensitivity to trawling is mainly driven by a spatial gradient of depth and primary productivity that separates the area into two main regions: a shallow, productive area, with low sensitivity and a higher abundance of swimming and crawling organisms, and a deeper, less productive area, with higher sensitivity due to a higher abundance of fixed, filter-feeding organisms. Fishing intensity also drives the sensitivity of communities confirming that they have already been shaped by a long history of mixed fisheries. The methodology used here provides a valuable monitoring tool and could be used to predict communities’ response to changes in fishing intensity and climate change.

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 relationships and ecosystem functioning in the Celtic Sea. Data are released under a CC-BY-NC-SA license, and please cite this paper when reusing the data.

International audience; Due to its selective removal, fishing pressure has long influenced the dynamics of species based on their life history traits. Sensitivity to fishing increases along a "fast-to-slow" gradient of life history strategies, and the "slow" species (large, long-lived, late-maturing, giving birth to few large offspring) require the most time to recover from fishing. In the North East Atlantic, after having reached extreme levels, fishing pressure has decreased since the 1980's due to management measures such as total allowable catch (TAC) or area closure. An effect on the distribution of species as well as a potential recovery could be expected. However, temporal patterns of life history strategies are rarely linked to management measures. In addition, a larger emphasis is often put on exploited or emblematic sensitive species but rarely on assembly processes at the ecosystem scale (both commercial and non-commercial species). Based on a 17-year time series of 101 taxa (fishes, elasmobranchs, bivalves, cephalopods and crustaceans), we observed a negative relationship between the biomass of taxa sensitive to fishing and bottom trawling pressure, as well as an increase in their total biomass in the Celtic Sea. Over the whole area, stochasticity appeared as the dominant assembly process. Deterministic assembly processes were at play in the centre of the area where significant overdispersion (caused by the presence of both slow and fast taxa) were observed. The absence of sensitive taxa from the rest of the Celtic Sea appeared to be caused mainly by a historical effect of environmental filtering when fishing was high. At the local scale, we related the decrease in fishing pressure to the increase in biomass of five of the most sensitive taxa. This local decrease in fishing pressure, resulting from the implementation of an area closure, highlights the positive effect of such management measures in less than two decades.

The analysis of the dynamics of interaction networks (i.e. trophic webs) better capture the state of ecosystem facing a perturbation than individual species dynamics could. We propose a framework that examines network robustness to a given perturbation at the local (species), mesoscale (species directly linked together) and global (network) level, based on traits and the topology of the network. Using the Celtic Sea as an example, we showed that the network was the least robust to the simulated loss of forage taxa and the most exposed taxa to fishing pressure, indicating conservation priority could be focused on these taxa. However estimating the sensitivity to fishing at the taxa ‘level was insufficient to predict the robustness of the network. The network appeared relatively robust to the simulated loss of the most central taxa, suggesting that mesoscale metrics such as centrality, although widely used, are not always adapted to prioritize species conservation.

Quantification of the escapement rate of unwanted fish through a selective device is usually based on catch comparison. This study proposes a new, time efficient method to automatically compare two selective devices by automated counting of fish escapements through each selective device based on video sequences. First, sea trials were conducted to record video sequences of fish escaping a white and black square mesh panel. Then, all of the underwater sequences were automatically analysed by a computer vision software for automated object detection and tracking. Finally, the algorithm was assessed using 150 min of video sequences analysed by humans. We observed that the variability in escapements rate between all the observers on reference video sequences could reach 5%. As the difference in escapements rate between the algorithm and the observers was lower than the variability between observers, the automated approach was validated. The software detected a significant difference in fish escapement rate according to the net colour in the camera field of view: 60% of all fish escaped through the white panel. Our results suggest that net colour influences the escape rates of fish. The colour of the selective device should therefore be investigated further with the aim of increasing their efficiency. Further development of the software could be done to identify species and size of the fish and assess the effectiveness of a selective device by species and size.

In the Bay of Biscay, the selective properties of otter trawls have mainly been studied with regard to single species. However, for bottom trawl multispecific fisheries targeting fish, it remains challenging to find a selective device capable of limiting catches of small individuals of several species without commercial losses. The present study focuses on an innovative technical solution to reduce catches of undersized individuals in a multispecies bottom trawl fishery in the Bay of Biscay. We tested a cylinder made of 100-mm diamond meshes turned at 90°, namely T90 inserted in the extension piece. We present the selectivity results obtained for six commercial species. This device allows the escape of small Solea solea, Trachurus trachurus and Spondyliosoma cantharus individuals. No commercial losses of Sepia officinalis were recorded. Patterns for Dicentrarchus labrax and Mullus surmuletus require further investigation due to limited fish size ranges in the dataset.

The characterization and quantification of diets of nine commercially important Celtic Sea fish species (black-bellied angler Lophius budegassa, blue whiting Micromesistius poutassou, Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus, European hake Merluccius merluccius, megrim Lepidorhombus whiffiagonis, European plaice Pleuronectes platessa, common sole Solea solea and whiting Merlangius merlangus) was undertaken November 2014 and November 2015 to gain a better understanding of fish feeding strategies, prey preferences, competition for resources and, more generally, increases knowledge of marine ecosystem functioning. Prey were classified into 39 taxonomic groups. A feeding overlap index and multivariate analyses were used to classify the fishes into four main trophic groups where interspecific competition for resources may be important: piscivorous species, omnivorous species, planktivorous species and invertebrate benthic feeders. Ontogenetic changes in diet were also considered for L. budegassa, G. morhua, M. aeglefinus, M. merluccius and M. merlangus through partitioning into size classes. This revealed an important shift in the diet of M. merluccius from omnivory to piscivory, whereas M. aeglefinus exhibited no significant ontogenetic change in diet, remaining an invertebrate benthic feeder. Feeding strategies of these species were also investigated using the Shannon niche-breadth index and other descriptors, such as the total number of taxonomic groups of prey and the mean number of prey in gut contents.

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.

By 2019, the Common Fisheries Policy will prohibit discarding in all European fisheries of any pelagic, demersal or shellfish species for which removals are managed by TACs and quotas or minimum sizes. However, the regulation allows for exemptions from the prohibition for species for which scientific evidence demonstrates high survival rates associated with discarding. Producing reliable evidence of high survival typically requires long and costly studies involving tagging or captivity. This paper proposes to use the capacity to resist air exposure, a key stressor for discarded animals, as a proxy for survival that can be used to prioritize candidate species for more in-depth discard survival studies. The time required to induce mortality (TM) in air-exposed fish was estimated for ten discarded species under commercial fishing conditions for two artisanal French otter trawlers in the Bay of Biscay and in the English Channel. European seabass, plaice, sole and skates had extended TM values on average, suggesting that these species are good candidates. The three species observed in both regions (plaice, sole and skates) had larger TM values in the English Channel experiment compared to the Bay of Biscay experiment. Among the four measured external conditions that could influence TM (air temperature, fish length, tow depth and tow duration), the air temperature was the most important and the factor that most distinguished the two experiments.

International audience; 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 covariations 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 probably driven by interannual 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 covary 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 covariation 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.

Two vitality index approaches have been demonstrated to be good proxies of discard survival in similar fishing and environmental conditions: Reflex Action Mortality Predictors combined with injuries (RI) scores that measure the proportion of impaired reflexes and injuries, and a simpler, quicker, but less precise approach based on ordinal categories related to fish body movements and injuries (semi-quantitative assessment, SQA). This study assessed and compared these two approaches for five species (two flatfishes, skates, a seabass and a catshark) discarded in a coastal otter trawl fishery in the Bay of Biscay. All species displayed good vitality status according to both indices and were not very sensitive to the fishing nor their biological conditions. Still, flatfishes were more sensitive to discarding while the catshark was very resistant. Furthermore, depending on species, the impairment of some reflexes and injuries were associated to stressing factors, highlighting the potential of the approach but also the complexity involved in building a relevant score. The SQA index was highly correlated with the RI score and was sensitive to more sources of stressing factors for similar predictive performance. While the relevance of these two approaches should be ultimately determined by the strength and consistency of their association with discard survival, these results suggest that the RI approach was not more effective than SQA despite the extra labour and time involved in collecting the data.

On January 1st, 2016, the French mixed Nephrops and hake fishery of the Grande Vasière, an area located in the Bay of Biscay, fell under the discard ban implemented as part of the new European Common Fisheries Policy. The fleet records historically high levels of discard despite numerous gear selectivity studies. Together with high discards survival, new technological solutions to minimize catches of undersized individuals could justify local exemptions from the discard ban. Our study focuses on the effects of two selective devices, a square mesh cylinder (SMC) and a grid, on the escapement of undersized individuals and discard reduction. Relative catch probability of the modified gear compared with the traditional gear was modelled using the catch comparison method. Potential losses from the commercial fraction of the catch were taken into account to assess their influence on the economic viability of fishing with the modified gears. The two devices had similar effects on undersized Nephrops escapement and on discard reduction, with median values of 26.5% and 23.6% for the SMC and of 30.4% and 21.4% for the grid, respectively. Only the grid was efficient for undersized hake, recording median values of escapement and discard reduction equal to 25.0% and 20.6%, respectively. Some loss from the commercial fraction of the catch was to be expected with both devices, which could be compensated for in the long term by the contribution of undersized individuals to the stock biomass. Our results support the use of selective gears technology as part of an integrated framework including control and management measures to mitigate the effect of the discard ban both for fishers and for the ecosystem. Further work is needed to quantify the effect of additional escapement from the gear on stock dynamics.

The impacts of bottom trawling in coastal ecosystems are significant, not only for targeted species but also for non-commercial ones. However, the critical gaps in scientific knowledge associated with these impacts on untargeted but functionally important species remain to be filled. This is notably the case for a great proportion of discarded invertebrates, for which only a handful of studies have investigated their survival. In this study, 600 individuals from six different benthic invertebrate species were collected in commercial conditions in the Bay of Biscay for short-term survival experiments. Overall, the observed survival after 100–130 h and the predicted survival via mixture models were very high (>93%) for Asterias rubens, Aphrodita aculeata, Buccinum undatum and Pagurus sp. Survival of Maja brachydactyla was lower though still high (>80% overall) and Atelecyclus undecimdentatus was more vulnerable to trawling and handling, with ∼ 50% of survival. Both showed 100% mortality when presenting carapace cracks and survival of M. brachydactyla was lower when missing appendages. No biotic nor abiotic parameters were correlated to survival, except injury class for M. brachydactyla and A. undecimdentatus. This study shows an overall high survival but highlights the fact that otter trawl fisheries may differentially affect discarded benthic invertebrates, therefore bringing light for future studies on longer-term impacts on benthic communities and coastal ecosystems. Furthermore, we recommend incorporating survival rates of discarded invertebrates in ecosystem-level modelling studies and encourage the use of detailed information and biomass reports of benthic invertebrates for a better management of natural populations and fisheries resources.

The landing obligation implemented under the European Union Common Fisheries Policy prompted the development of selective devices for fishing gear to reduce unwanted catches. In the Bay of Biscay, a collaborative project between scientists and fishermen evaluated catch rates and length frequencies of caught species from two innovative trawl devices, which were compared to the gear that is currently used in the fishery. The experimental designs were: (1) a 90 mm square mesh bycatch reduction device inserted in the tapered section (SMBRD) and (2) a 70 mm T90 mesh codend and extension (T90). Each selective device was tested separately using the twin trawl method for catch comparison on board commercial vessels: SMBRD was tested on board vessels targeting Nephrops and T90 on board vessels targeting demersal fish. This study focused on hake (Merluccius merluccius), which is an important bycatch species, red mullet (Mullus surmuletus) and common sole (Solea solea), which have high commercial value, and horse mackerel (Trachurus trachurus), which is nearly never discarded. Horse mackerel and hake escaped through the two devices tested, resulting in fewer unwanted catches in the selective trawls without commercial loss. For sole, more individuals were caught with the SMBRD than with the standard gear. The T90 resulted in the escapement of most red mullet across its entire length range observed, resulting in significantly lower Catch Per Unit Effort of landings and unwanted catch, probably due to unsuitable mesh size and shape for that species. These results have direct application for multispecies fisheries in which fishermen have to appropriately select devices according to the specific characteristics and species composition of their fisheries.

International audience; Human activities affect continental shelves, especially due to the harvest of living marine resources. Understanding their functioning and dynamics has become a growing concern in recent decades, especially through use of trophic modelling approaches. Studying the feeding ecology of key component species also improves this understanding by providing accurate information on trophic processes, particularly the dependence on trophic pathways. This study focuses on the trophic ecology of four large gadiforms (cod, haddock, whiting and hake) found on the continental shelf of the Celtic Sea. The study combines information on recently ingested prey (gut content analysis) and a more integrated indicator of food sources (stable isotope analysis). Two size classes of each species were considered (small and large – split around 20 cm for haddock, whiting and hake and 60 cm for cod), as were shallow and deep zones. The four gadiforms show distinct feeding niches and strategies, which limit interspecific competition. Cod and haddock relied mainly on the benthic trophic pathway but differed in favouring piscivory and invertivory, respectively. Hake fed mainly on the pelagic trophic pathway, while whiting seemed to feed on both pathways. Ontogenetic shifts from invertivory to piscivory were observed for whiting in both zones and for hake and cod in the deep zone. An unexpected shift from the pelagic to the benthic trophic pathway was observed from small to large haddock in the deep zone. Taking into account the descriptions of diets made in adjacent ecosystems throughout the year, the four species show trophic plasticity towards one of the trophic pathways or the other. Differences between the shallow and deep zones were related to benthic and pelagic prey characteristics, which themselves are driven by the sedimentary and hydrological context, especially thermal stratification.

Improving the selectivity of a fishing gear is one technical management measure to significantly reduce by-catch of non-commercial species or undersized individuals. The efficiency of selective device is mainly estimated by comparing species composition, the biomass and length spectrum of caught individuals and escapees while the functional traits of species are rarely accounted for. Using an innovative technical device to reduce catches of undersized individuals in a multispecific bottom trawl fishery in the Bay of Biscay, namely a T90 mesh cylinder, we measured functional traits on both caught and escaped individuals of 18 species. Using a Principal Component Analysis and K-means partitioning, we clustered species into 6 groups illustrating 6 different locomotion strategies. We identified functional traits related to body size, visual ability and locomotion, differing between caught individuals and escapees using Linear Mixed-effects Models. As expected, escapees were smaller on average but also tended to be more streamlined, with a high position of the eyes and fin features characteristic of manoeuvrability and propulsion. Here, we present how a trait-based approach can shed light on the biological characteristics influencing the efficiency of selective devices.

Summary Based on towed underwater videos, diversity patterns and their main environmental and anthropogenic drivers were assessed in the “Grande Vasiere” (northeast Bay of Biscay), one of the main French fishing grounds. The density of bentho-demersal megafauna was recorded along 152 transects in this area in 2014. The highest number of taxa and densities were observed on the external margin of the Grande Vasiere, in deep areas with low fishing intensity. The highest levels of taxa evenness were located on the central and coastal parts that are shallower and exposed to medium to high trawling intensity. Multivariate analysis identified four different communities driven by fishing intensity, depth, sediment type and bottom current speed. We distinguished three communities in the centre of the Grande Vasiere covered by medium to highly trawled soft sediments and characterized by Hydrozoa, Crustacea such as Munida rugosa, Nephrops norvegicus and Goneplax rhomboides and Actinopterygii unidentified. A fourth community was identified on the external margin, deeper, undergoing lower trawling intensity than the other communities and dominated by sessile filter feeders. The fragile taxa observed in this study had almost always been unobserved by from previous studies using scientific trawl sampling. Underwater video thus allowed collecting unprecedented data by direct visualization of the seabed and the observation of fragile taxa that cannot be effectively sampled by traditional scientific sampling methods used in previous studies.

SUMMARYTrawling activities are considered to be one of the main sources of disturbance to the seabed worldwide. We aimed to disentangle the dominance of environmental variations and trawling intensity in order to explain the distribution of diversity patterns over 152 sampling sites in the French trawl fishing-ground, the Grande Vasière. Using a towed underwater video device, we identified 39 taxa to the finest taxonomic level possible, which were clustered according to their vulnerability to trawling disturbance based on functional traits. Using generalized linear models, we investigated whether the density distribution of each vulnerability group was sensitive to trawling intensity and habitat characteristics. Our analyses revealed a structuring effect of depth and substratum on community structure. The distribution of the more vulnerable group was a negative function of trawling intensity, while the distributions of the less vulnerable groups were independent of trawling intensity. Video monitoring coupled with trait-based vulnerability assessment of macro-epibenthic communities might be more relevant than the traditional taxonomic approach to identifying the areas that are most vulnerable to fishing activities in conservation planning.

Summary In marine ecosystems, the study of trophic relationships has extensively benefited from the development of stable isotope analyses (SIA) as dietary tracers. SIA are particularly useful in elucidating the structure of deep sea food webs given the constraints involved in obtaining gut-content data from deep trawling. We used carbon and nitrogen stable isotope analyses and Stable Isotope Bayesian Ellipses in R (SIBER) and Stable Isotope Analysis in R (SIAR) routines, to determine the trophic ecology of five deep-sea fishes from the upper continental slope of the Celtic Sea. SIA made it possible to deduce some general tendencies in food-web structure and species trophic interactions and confirmed diet determined by gut-content analysis for the same species, in other ecoregions. More specifically, mixing models revealed that the deep sea species considered are omnivorous and are able to feed on all the sampled taxa. Based on isotopic ratio, no clear differences in fish diet could be detected from one species to another except for rabbit fish, which has benthic affinities. Three species, blackbelly rosefish, greater forkbeard and softhead grenadier showed overlapping isotopic niches. This study is the first attempt to describe the trophic ecology of deep sea species on the Celtic Sea upper continental slope. In the context of the development of ecosystem integrated modeling approaches for managing fisheries in the Celtic sea, and considering the vulnerability of deep-water species, improving the knowledge on the trophic ecology of these local species is of importance in order to allow their sustainable exploitation.

The development of the vessel monitoring system (VMS) in the recent years has offered high-resolution data to map the distribution and intensity of fishing activities and contributed to enhancing the potential identification of fishing impacts. However, impacts could vary at very small scale and the resolution of VMS data might not be fine enough. Other proxy could be used, such as trawl marks visible on the seabed observed by underwater video or side-scan sonar to evaluate small-scale trawling effort. In the Bay of Biscay, an underwater video survey of the Nephrops norvegicus fishing ground was conducted and provided environmental characteristics such as depth and number of trawl marks at 152 transects. The relevance of observed trawl marks as a small-scale proxy of trawling effort was tested depending on the sediment type. The model showed a significant positive relation between density of marks and trawling effort for all sediments together but a different relation for each sediment type. Considering each sediment type separately, the unexpected high number of marks observed on sands could be linked with cohesive interactions between calcium carbonates particles while the low number of marks on fine lithoclastic muds could be due to sediment reworking and bioturbation. We conclude that the impact of trawling on the seabed varies with the type of sediments, hydrodynamic parameters, bioturbation and trawling intensity, leading to a very complex relationship. Trawl marks observed on video footage thus could be used as a proxy of trawling effort among the same type of sediment and not for fine lithoclastic muds.

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches., This research was conducted as part of C.S.B.’s Ph.D dissertation, which was funded by the University of Southampton and NERC (NE/L50161X/1), and through a NERC Grant-in-Kind from the Life Sciences Mass Spectrometry Facility (LSMSF; EK267-03/16). We thank A. Bates, D. Sims, F. Neat, R. McGill and J. Newton for their analytical contributions and comments on the manuscripts.

International audience; Recent theoretical considerations have highlighted the importance of the pelagic-benthic coupling in marine food webs. In continental shelf seas, it was hypothesized that the trophic network structure may change along an inshore-offshore gradient due to weakening of the pelagic-benthic coupling from coastal to offshore areas. We tested this assumption empirically using the eastern English Channel (EEC) as a case study. We sampled organisms from particulate organic matter to predatory fishes and used baseline-corrected carbon and nitrogen stable isotope ratios (δ13C and δ15N) to determine their trophic position. First, hierarchical clustering on δ13C and δ15N coupled to bootstrapping and estimates of the relative contribution of pelagic and benthic carbon sources to consumers' diet showed that, at mesoscale, the EEC food web forms a continuum of four trophic levels with trophic groups spread across a pelagic and a benthic trophic pathway. Second, based on the same methods, a discrete approach examined changes in the local food web structure across three depth strata in order to investigate the inshore-offshore gradient. It showed stronger pelagic-benthic coupling in shallow coastal areas mostly due to a reorganization of the upper consumers relative to the two trophic pathways, benthic carbon sources being available to pelagic consumers and, reciprocally, pelagic sources becoming accessible to benthic species. Third a continuous approach examined changes in the mean and variance of upper consumers' δ13C and δ15N with depth. It detected a significant decrease in δ13C variance and a significant increase in δ15N variance as depth increases. A theoretical two-source mixing model showed that an inshore-offshore decrease in the pelagic-benthic coupling was a sufficient condition to produce the δ13C variance pattern, thus supporting the conclusions of the discrete approach. These results suggest that environmental gradients such as the inshore-offshore one should be accounted for to better understand marine food webs dynamics.

In the English Channel and Southern Bight, French demersal trawlers target a mix of demersal species including whiting (Merlangius merlangus). The discard ban to be implemented in January 2016 motivated fishermen to look for technical measures to reduce unwanted catches of undersized individuals (

Species that have a high likelihood of surviving the discarding process have become great concern since the European Union reformed the Common Fisheries Policy and enacted a landing obligation prohibiting the discarding any individuals of species under quota. Among species presenting an elevated survival potential, plaice ( Pleuronectes platessa ) is one of the most discarded in the coastal otter trawl fishery in the English Channel. The objective of this study is to provide the most reliable estimates of plaice survival after release in commercial conditions, and to identify the factors that influence survival rates. A captivity experiment was conducted in January–February in the English fishery to assess the survival of discarded plaice as a function of a semi-quantitative index of fish vitality, which has been demonstrated to be a good proxy of fish survival in comparable fishing and environmental conditions. This study examined the potential of this index to estimate discard survival in three trials from the English and French fisheries and at three different seasons. The vitality index was then used to analyse the influence of several factors (fishing practices, environmental conditions and fish biological characteristics) on the discard survival. The survival rates for plaice were accurately estimated at 62.8% in January–February, 66.6% in November and 45.2% in July. While these rates remained substantial whatever the fishing, environmental or fish biological conditions, the time fish spent on the deck, the bottom and air temperatures, the tow depth and the fish length had a significant influence on plaice survival. In practice, plaice survival could be enhanced by releasing the fish early during catch sorting and avoiding exposure to extreme air temperatures.

The new Common Fisheries Policy may exempt some species from the landing obligation if a high survival rate can be demonstrated among discards. This study focuses on the survival capacity of Nephrops norvegicus discarded from trawlers of the Bay of Biscay (France). Three sea trials were conducted on board 3 commercial trawlers and 15 fishing operations were sampled. The vitality of Nephrops was classed into three categories (healthy, moribund or dead) before release at sea and samples of healthy and moribund individuals were kept in captivity on Nephrops grounds for three days. A Generalised Linear Model was used to examine the variability in the proportion of healthy Nephrops discarded, which was significantly influenced by tow duration, duration of air exposure and temperature, as well as individual length. By combining the results on vitality before release at sea with those on survival in captivity following re-immersion, resampled by bootstrapping, it was calculated that 51% [42–60%] of discarded Nephrops would survive after three days of re-immersion. We discuss the sources of variability in survival rate, as well as the implications of a potential exemption from the landing obligation for this species.

For the ecosystem approach to fisheries management, understanding population dynamics and ecosystem resilience in response to the landing obligation acted by the reform of the European Common Fishery Policy (CFP) is currently an important avenue of research. This study attempts to assess the impact of the new CFP on marine food webs. Total carbon and nitrogen loss induced by a discard ban were estimated for the ecosystem of the Bay of Biscay based on French At-Sea Observer data and carbon and nitrogen content of discarded fish. Changes in predator diets were estimated by comparing two Bayesian mixing models, one mimicking the current situation and the second the application of the new CFP (removing the discarded species that would be landed from the model). Results illustrate a substantial shift in predation effort toward remaining available prey. The impact of changes in diet on individual and population health and on ecosystem functioning are important issues that remain to be assessed. A sister study could be carry out in another ecoregion, at a finer spatial scale in order to compare impacts and ecosystem responses. European monitoring programs such as DC-MAP and the Marine Strategy Framework Directive (MSFD) would help us to gain an understanding of how the food web would reorganize itself.

The present work analyses the spatial and temporal variations of the herbivorous fish assemblage on 10 coral reef sites in the Caribbean island of Guadeloupe (French West Indies). The herbivorous fish assemblage was assessed by visual census along band transects; environmental data were collected to determine the relationship between environmental conditions and temporal and spatial variations in herbivorous fish abundance and distribution. Spatial variation in species abundance was related to variation of the benthic cover (e.g., coral and algae), depth, and protection status among sites. Short-term fluctuations of herbivorous fishes on the reef flats were linked to tide, swell, and wind, whereas long-term variations were seasonal and highly correlated to annual water temperature oscillations.

Seagrass beds, mangroves, and coral reefs are often located adjacent to one another, but few studies have focused on the influence that their proximity may have on their fish assemblages. Juvenile fish assemblages of seagrass beds, differing according to their adjacent habitats, were investigated in the Caribbean island of Guadeloupe. We tested whether adjacent habitats influence (i) the structure and composition of juvenile fish assemblages and (ii) the size class distribution of fishes using analysis of variance (ANOVA) and multivariate permutation tests. Significant differences in species richness, abundance, and size were identified between the two types of seagrass beds. Close to the reef, daytime fish assemblages were constituted of seagrass beds resident species, while at night, indicator species of seagrass beds belong to reef families. Near coastal mangroves, the shift between day and night is less evident. Fish size class distributions confirm the sequential use of the two types of seag...

1. The development of macroalgae to the detriment of corals is now one of the major threats to coral reefs. Herbivorous fishes are partly responsible for algal regulation on coral reefs and their overexploitation favours the shift from scleractinian coral-dominated systems towards macroalgae-dominated systems. 2. Marine protected areas (MPAs) that have been established worldwide may benefit coral reefs through the maintenance of high densities of herbivorous fishes which regulate algal growth. 3. The paper assesses whether small MPAs in the Caribbean are able to enhance herbivorous fish stock and by controlling macroalgae help to maintain reef ecosystems. A visual census using band-transects was undertaken around Guadeloupe island where marine reserves have been in place since 1979. The effects of MPAs on both benthic communities and herbivorous fishes are examined. 4. Inside MPAs, herbivorous fish biomass was almost twice as high as outside MPAs and macroalgal cover was significantly lower. Fish size class distributions revealed that large individuals occurred mainly inside MPAs and that few male individuals were found outside MPAs. Copyright (C) 2010 John Wiley & Sons, Ltd.

The fish fauna of Thalassia testudinum (Konig) seagrass beds was studied at two sites in the Grand Cul-de-Sac Marin Bay (Guadeloupe, French West Indies). The first seagrass bed was located near a coral reef and the second was near coastal mangroves. Both habitats were sampled during day and night, using a purse-seine and a trap net. A total of 98 species belonging to 36 families were observed. Distance-based redundancy analyses revealed two site-specific assemblages of fishes. Diel assemblage shifts were more pronounced in the seagrass beds near coral reefs than in those near mangroves, due to the existence of nocturnal trophic incursions of coral reef fishes into seagrass beds. First-order carnivores dominated the trophic structure of the fish assemblages during both day and night. At night, Haemulidae, Holocentridae and Apogonidae took the place of Labridae, Chaetodontidae and Mullidae present by day near the reef. This switch did not occur near the coast where the exchanges between seagrass beds and mangrove appear to be less important than with the reef ecosystem. Thus, it appears that the adjacent seascape habitat setting affects the intensity in diel variability of the seagrass bed fish community.

International audience; Coastal and estuarine systems provide nursery grounds for many marine fish species. Their productivity has been correlated with terrigeneous inputs entering the coastal-estuarine benthic food web, thereby favouring the establishment of fish juveniles. Studies in these ecosystems often describe the nursery as a single large habitat without verifying nor considering the presence of contiguous habitats. Our study aimed at identifying different habitats based on macrozoobenthic communities and morpho-sedimentary characteristics and assessing the trophic interactions between fish juveniles and their benthic preys within these habitats. It included 43 sampling sites covering 5 habitats in which we described taxonomically and quantitatively the invertebrates and fish communities with stable isotopes and gut contents. It suggested that the benthic common sole Solea solea displayed feeding plasticity at the population level, separating the juveniles (G0) from the older fish (G1) into different "feeding sub-populations". Size-based feeding plasticity was also observable in the spatial occupancy of that species in the studied bay. The demersal pouting, Trisopterus luscus, equally used the different habitats but displayed low feeding plasticity across and inside each habitat. Stable isotopes proved to be powerful tools to study the spatial distribution of trophic interactions in complex ecosystems like the bay of Vilaine and to define optimal habitats for fish that use the coastal-estuarine ecosystem as nursery grounds

International audience; A major challenge in ocean and coastal management is to find simple ways to evaluate the health of such complex ecosystems. This task may prove complicated as selection criteria needs to be established for choosing appropriate indicators and evaluation tools which do not mask or leave out inherent ecosystem properties and dynamics. Here, we review some empirical analyses and modelling techniques which can be used to derive environmental health indicators. With a series of case studies ranging from the combined use of structural and functional attributes of the system, to modelling outputs that integrate the biological and physical environments, we illustrate the usefulness and complementarities of these methods to assess ecosystem health. The choice of relevant indicators will depend on the ecological questions raised as well as the biological and habitat components considered which can range from a single level (individual or population) to multiple levels (community or ecosystem-based indicators) in the ecosystem. Each method has its own capabilities and limitations that may render it useful or insufficient in some cases. We suggest, however, that, whenever possible, the combination of ecological attributes and tools should be used to improve our knowledge and assessment of marine ecosystems for better management and conservation in the future.

Distribution patterns of many native and exotic fish species are well documented, yet little is known about the temporal dynamics of native and exotic diversity in relation to changes in land use. We hypothesised that colonisation rates would be higher for exotic fish species and that extinction rates would be higher for native species in large stream systems. We also predicted that cold-water species would be more impacted than thermally tolerant species. To test these hypotheses, we used generalised linear mixed models to compare changes in native and exotic fish species richness over 10 years in a French drainage basin subjected to landscape alterations. Exotic fish were more susceptible to local extinction than the native ones. Extinction was greater among cold-tolerant species and at higher elevations. Colonisation by exotic species was higher at lower elevations. Although a decade of expanding urbanisation affected fish colonisation, agricultural lands experienced higher extinction rates. In the context of global changes in land use and population pressure, our study suggests that the temporal dynamics of fish diversity are driven by landscape alterations as well as by the thermal tolerance of species

We tested the impacts of most common sample preservation methods used for aquatic sample materials on the stable isotope ratios of carbon and nitrogen in clams, a typical baseline indicator organism for many aquatic food web studies utilising stable isotope analysis (SIA). In addition to common chemical preservatives ethanol and formalin, we also assessed the potential impacts of freezing on delta C-13 and delta N-15 values and compared the preserved samples against freshly dried and analysed samples. All preservation methods, including freezing, had significant impacts on delta C-13 and delta N-15 values and the effects in general were greater on the carbon isotope values (1.3-2.2aEuro degrees difference) than on the nitrogen isotope values (0.9-1.0aEuro degrees difference). However, the impacts produced by the preservation were rather consistent within each method during the whole 1 year experiment allowing these to be accounted for, if clams are intended for use in retrospective stable isotope studies.

SUMMARYAbility to demonstrate statistical patterns of distribution by threatened species and by their potential competitors will determine success in forecasting locations at greatest risk, and ability to target management efforts. A self-organizing map algorithm (SOM) was used to derive probabilities of presence of native (Austropotamobius pallipes) and exotic (Orconectes limosus, Pacifastacus leniusculus and Procambarus clarkii) crayfish species with respect to physical and land-cover variables in a large stream system, using a simple presence-absence dataset of species. Crayfish were sampled at 128 sites representing 86 rivers. The probability of occurrence of the native species increased at higher elevations above sea level and lower temperatures; populations appeared to be mostly confined to headwater streams where exotic competitors were unable to withstand the colder conditions. The distribution of exotic species was correlated with anthropogenic factors, such as the degree of urbanization and agricultural land area. Complementary modelling tools, such as GIS and SOMs, can help to maximize the information extracted from available data in the context of biological conservation.

International audience; Although being a widely introduced and successfully established species, the European catfish Silurus glanis L. (the world's third largest freshwater fish) remains poorly studied in its introduced areas. Here we studied the trophic ecology of non-native European catfish in a large river system in south-western France using stomach content and stable isotope analyses (SIA). We used fin samples for SIA of catfish and hence tested the validity of using fin tissue as a proxy for muscle in SIA. The mean δ15N and δ13C values analysed from fin tissues did not differ from those analysed from muscle tissue and reflected strong and consistent relationships (r2 = 0.95 for carbon and r2 = 0.98 for nitrogen). The δ15N values varied almost 5‰ among the analysed catfish individuals, while δ13C values varied >5‰. Total length of these catfish ranged from 200 to 2240 mm and was correlated with δ15N and especially with δ13C values. Although catfish length and δ15N values were positively correlated, the mean trophic positions of catfish increased only slightly from smaller individuals to larger ones (4.3 to 4.7). However, larger catfish were considerably 13C-enriched in their δ13C values compared to smaller individuals and had up to 4‰ higher δ13C values than their expected aquatic prey. This might indicate frequent consumption of mammals and/or non-aquatic birds by the larger sized individuals, which were found in the catfish stomachs.