Since 2008, Mediterranean small pelagic fish populations, particularly sardines Sardina pilchardus, have shown shrinking and adult overmortality, likely driven by bottom-up processes. Although energy availability has declined, adults still invest heavily in reproduction, possibly at the expense of other traits such as maintenance, growth and survival. Such trade-offs may alter their immune status, making individuals more prone to diseases. Here, we experimentally investigated the effects of seasonal feeding conditions (winter vs. summer) on sardine immune status. We provided the first description of leucocyte populations in sardines, including both non-specific and adaptive immune cells. Feeding conditions did not highly affect proportions of immune cells. However, the oxidative status of leucocytes was modified over time, likely reflecting seasonal changes, including energy re-allocation mechanisms during reproduction. These findings suggest that poor feeding conditions do not necessarily affect negatively immune status, but this requires confirmation through immune challenges.

Anthropogenic activities have led to the persistent build-up of trace metals and organic pollutants in coastal ecosystems, threatening aquatic life. Gilthead seabream, a commercially valuable species, often inhabits Mediterranean lagoons that function as vital nursery grounds. In this study, we examined 93 juvenile seabreams from three Tunisian lagoons to evaluate contamination levels and their effects on otolith morphology. We measured inorganic and organic contaminants in fish muscle and investigated their potential effects on otolith shape and asymmetry. Clear fish muscle contamination signatures emerged across sites: Tunis Lagoon exhibited the highest levels of contamination, followed by Ghar El Melh, while El Biban Lagoon appeared relatively pristine. Relatively elevated levels of metals (e.g., Pb, Ni, Be) and persistent organic pollutants (e.g., PCBs, DDTs, PBDEs) were observed in the more impacted lagoons. Notably, we found that otolith shape and fluctuating asymmetry were significantly associated with contaminant exposure, even after accounting for natural variables like fish size and lipid content. Specific pollutants, especially Cu, Rb, Sr and DDT, were linked to altered otolith morphology, suggesting disrupted biomineralization. The stronger response of the left otolith suggests that sub-lethal stress impairs developmental stability. Although fish muscle contaminant levels generally fell below food safety thresholds, the observed effects on otolith development raise concerns about functional consequences and underlying physiological stress. Our results highlight otolith asymmetry as a sensitive bioindicator of environmental stress in wild fish. By integrating shape analysis with contaminant profiling, this study offers a powerful tool for assessing pollution impacts in vulnerable Mediterranean nursery habitats.

Identifying and monitoring the processes underlying changes in individual life-history traits and population size are essential to better predict natural populations' responses to environmental changes and sustainably manage natural resources. In marine ecosystems, the global decline in small pelagic fish (SPF) growth and survival capacities was linked to overfishing and climate change, but the underlying mechanisms remain elusive, although SPF play a central ecological role and sustain large fisheries. To address this issue, we combined a set of physiological markers (assessing digestive enzyme activity, oxidative, chronic, and nutritional stress) and environmental variables for sardine (Sardina pilchardus) in three environmentally contrasted areas surrounding the French coast. Overall, we found sardines with higher chronic stress, lower content in eicosapentaenoic acid (EPA), and lower digestive enzyme activity in the Gulf of Lions, an area marked by a 30% decline in sardine size-at-age and a strong adult overmortality. In contrast, sardines from the English Channel, where no such demographic decline is observed, exhibited better physiological conditions. Sardines appeared to be in poorer physiological health under warmer sea surface temperatures and lower phytoplankton concentrations. However, links between physiology and environmental variability were less clear in the Bay of Biscay, an area with similar growth and survival declines than in the Gulf of Lions. These findings highlight the critical impact of environmental factors on the physiological status and overall health of sardine populations but with global and local patterns of response, emphasizing the unique challenges faced by each population of this species.

The increase in trace element concentrations in the aquatic environment due to anthropogenic activities, urges the need for their monitoring and potential toxicity, persistence, bioaccumulation, and biomagnification at different trophic levels. Gilthead seabream is a species of commercial importance in the Mediterranean Sea, both for the aquaculture and fisheries sectors, however very little is known about their trace element contamination accumulation and the resulting effect on their health status. In the present study, 135 juveniles were collected from seven coastal lagoons known to be essential nursery areas for this species. We measured seventeen different inorganic contaminants at the individual level in fish muscle (namely Al, As, Be, Bi, Cd, Cr, Cu, Hg, Li, Ni, Pb, Rb, Sb, Sr, Ti, Tl and Zn). Our results revealed the accumulation of multiple trace elements in individuals and distinct contamination signatures between lagoons which might lead to contrasted quality as nurseries for juveniles of numerous ecologically and economically relevant fish species in addition to seabreams. We further evaluated the potential adverse effect of these complex contamination mixtures on the liver (the main organ implicated in the metabolism of xenobiotics) and red muscle (a highly metabolic organ) using a proteomic approach. Alterations in cellular organization pathways and protein transport were detected in both tissues (albeit they were not similarly regulated). Chromosome organization and telomere maintenance in the liver appeared to be affected by contaminant mixture which could increase mortality, age-related disease risk and shorter lifetime expectancy for these juveniles. Red muscle proteome also demonstrated an upregulation of pathways involved in metabolism in response to contamination which raises the issue of potential energy allocation trade-offs between the organisms' main functions such as reproduction and growth. This study provides new insights into the cellular and molecular responses of seabreams to environmental pollution and proposed biomarkers of health effects of trace elements that could serve as a starting point for larger-scale biomonitoring programs.

In marine ecosystems, the presence of trace elements resulting from anthropogenic activities has raised concerns regarding their potential effects on marine organisms. This study delves into the intricate relationship between trace element contamination and the physiological responses of a key marine species in the Mediterranean Sea: the European sardine. Since 2008, this species has been experiencing a significant crisis in the region, prompting numerous studies to investigate the potential factors behind the dramatic decline in sardines size, age, and body condition. However, thorough information on chemical contamination by trace elements and its physiological impact on this species was lacking. We found evidence for the accumulation of multiple elements in sardines, with a light East-West contamination gradient within the Gulf of Lions. While macro-physiological parameters (i.e. body condition) were not affected by contamination, pathways involved in cellular organization and response to stress were clearly upregulated, particularly in the liver, but also in muscle. In addition, a global upregulation in processes linked to the immune system, lipid homeostasis and oxidative stress was recorded in the liver. The associated energetic cost may add a substantial burden to sardines that already face multi-factorial constraints. This study also allows to pinpoint biomarkers of exposure and effects that may be important for monitoring Mediterranean sardine health. The results of this study and particularly the complex changes in protein expression demonstrate the need for future studies to test the concomitant effects of multiple stressors acting simultaneously, including large scale contamination.

Multifactorial studies assessing the cumulative effects of natural and anthropogenic stressors on individual stress response are crucial to understand how organisms and populations cope with environmental change. We tested direct and indirect causal pathways through which environmental stressors affect the stress response of wild gilthead seabream in Mediterranean costal lagoons using an integrative PLS-PM approach. We integrated information on 10 environmental variables and 36 physiological variables into seven latent variables reflecting lagoons features and fish health. These variables concerned fish lipid reserves, somatic structure, inorganic contaminant loads, and individual trophic and stress response levels. This modelling approach allowed explaining 30 % of the variance within these 46 variables considered. More importantly, 54 % of fish stress response was explained by the dependent lagoon features, fish age, fish diet, fish reserve, fish structure and fish contaminant load latent variables included in our model. This integrative study sheds light on how individuals deal with contrasting environments and multiple ecological pressures.

Aquatic ecosystems can exhibit seasonal variation in resource availability and animals have evolved to cope with the associated caloric restriction. During winter in the NW Mediterranean Sea, the European sardine Sardina pilchardus naturally experiences caloric restriction owing to a decrease in the diversity and quantity of plankton. However, ongoing global warming has had deleterious effects on plankton communities such that food shortages may occur throughout the year, especially under warm conditions in the summer. We investigated the interactive effects of temperature and food availability on sardine metabolism by continuously monitoring whole-animal respiration of groups of control (fed) and food-deprived sardines over a 60-day experiment in winter (12 degrees C) or summer (20 degrees C) conditions under natural photoperiod. In addition, we measured mitochondrial respiration of red muscle fibres, biometric variables and energy reserves of individuals sampled at 30 and 60days. This revealed that winter food deprivation elicits energy saving mechanisms at whole animal and cellular levels by maintaining a low metabolism to preserve energy reserves, allowing high levels of survival. By contrast, despite energy saving mechanisms at the mitochondrial level, whole animal metabolic rate was high during food deprivation in summer, causing increased consumption of energy reserves at the muscular level and high mortality after 60days. Furthermore, a 5-day re-feeding did not improve survival, and mortalities continued, suggesting that long-term food deprivation at high temperatures causes profound stress in sardines that potentially impairs nutrient absorption.

Since 2008, there has been a major decrease in the numbers of old and large sardines in the Gulf of Lions, which has had a major effect on regional fisheries. A bottom-up process involving a shift in diet towards smaller planktonic prey has been suggested as the main driver of this development. Yet, the reproductive capacities of the sardines have not changed, suggesting potential modifications in energy allocation trade-offs. Whether this could also affect maintenance, in particular at the end of the winter reproductive period, and explain the lower adult survival and the disappearance of older individuals remains unclear. We therefore experimentally investigated the consequences of seasonal food availability (summer vs. winter) on life-history traits and energy allocation trade-offs at the individual and population levels. Our results indicate that food resources during summer had a major effect on energy reserves and growth, limiting the maximum size and body condition reached at the end of reproduction. In addition, food restrictions during growth and/or reproduction periods led to physiological costs mediated by increased oxidative damage. Mediterranean sardines did not show any ability for compensatory growth and did not appear to be capital breeders. Instead, they displayed individual differences in coping with physiological constraints and displayed various life-history strategies regardless of food availability. We highlighted 3 main individual energy allocation strategies: (1) preferential allocation to body condition or (2) to growth, or (3) simultaneous allocation to reproduction and growth. These issues are key, as climate change is expected to favour smaller phytoplankton, which might amplify the deterioration in the condition of pelagic fish.

Studies of the diet, feeding habits and trophic activity of top marine predators are essential for understanding their trophodynamics. The main direct method used for such studies thus far has been morphological inventories of stomach contents. This approach presents limitations such as missing gelatinous prey, which are usually digested too quickly to be detectable. Here, we analysed the stomachs of 48 Atlantic bluefin tuna (Thunnus thynnus, approximately 15 to 60 kg, including juveniles and adult fishes) collected from the Mediterranean Sea through the metabarcoding of two gene regions (cytochrome c oxidase subunit I (COI) and the ribosomal 18S-V1V2 region). The identified prey taxa and their relative read abundances (RRAs) estimated using COI results were in line with the findings of morphologically based inventories simultaneously performed on the same set of tuna samples. In both cases (and with the same rankings), the prey taxa included anchovy (Engraulis encrasicolus, here detected in more than 80% of samples, RRA = 43%), sardine (Sardina pilchardus, also approximately 80%, RRA = 30%), sprat (Sprattus sprattus, approximately 66%, RRA = 8%), mackerel (Scomber colias, approximately 44%, RRA = 7%) and cephalopods (approximately 15%, RRA = 1.4%). Another striking result was the detection, based on 18S (with which vertebrates were detected as the most abundant group, RRA = 61.6%), of a high prevalence and diversity of gelatinous organisms (RRA = 27.1%), including cnidarians (6.7%), salps (11.7%), and ctenophores (8.7%), the latter increasing with the size of the predator. These results thus support the hypothesis of the role of gelatinous prey in the diet of Atlantic bluefin tuna, suggesting that this species is even more generalist and opportunistic than previously thought. This study further confirms that DNA metabarcoding can be a powerful tool for assessing the diet and trophodynamics of top marine predators.

Uncommon fish records may reflect local or global changes of fish composition resulting from environmental changes or anthropog,enic activities. Significant records of uncommon marine fishes, including migrant, non-native, cryptic, rare and threatened species, collected in French waters or by French vessels in European waters, observed by scuba divers or beachgoers, are reported for the year 2019. They include first, new, rare and unusual records for the following 33 species: Tetronarce nobiliana, Gymnothorax unicolor, Maulisia mauli, Salmo trutta, Grammonus aler, Photostomias guernei, Ifintaia loppei, Echiodon drummondii, Holocentrus adscensionis, Nerophis lumbriciformis, Scorpaena scrofa, Lepidoirigla dieuzeidei, Eutelichthys leptochirus, Liparis montag tti, Mycteroperca rubra, Serranus cabrilla, Remora remora, Caram: crysos, Naucrates doctor, Trachurus picturatus, Seriola rivoliana, Argyrosomus regius, Parablennius pilicornis, Pseudoscopelus astronesthidens, Deltentosteus collonianus, Didogobius schlieweni, Didogobius splechinai, Gobius couchi, Gobius f.;asteveni, Lebetus guilleti, Synapturichthys kleinii, Lagocephalus lagocephalus and 21.1ola mola, among which I. loppei, H. adscensionis and P. astronesthidens represent first records for the French waters and additions to the Checklist of the marine fishes from metropolitan France. Photostomias guernei is a first record for the Bay of Biscay, found close the French ETV,.

Ce guide presente les modes et regles de prelevement puis de stockage des otolithes de grands pelagiques (thons et espadons). Ils ont ete mis en place dans le cadre de projets de recherche comme « Germon » (http://wwz.ifremer.fr/lareunion/Les-projets/GERMON-en-cours), « IOSSS-Espadon » (http://wwz.ifremer.fr/lareunion/Les-projets/IOSSS-ESPADON) et «thon rouge (ICCAT-GBYP) » et dans le cadre de reseaux de surveillance coordonnes au niveau international, en particulier au sein du reglement europeen sur la collecte des donnees halieutiques (DCMAP, Data Collection Multi Annual Programme). Ce guide a pour but de standardiser les prelevements d’otolithes effectues a l'Ifremer sur ces grands pelagiques. Il reprend et complete la synthese francaise des procedures d'estimation d'âge (Mahe et al., 2009), le manuel d'utilisation du fichier : Parametres biologiques v7.xls (Mahe et al., 2007) et le guide de prelevement des pieces calcifiees (Mahe et al., 2013).

During the last decade, particular attention has been paid worldwide to the problem of by catch and discards in fisheries. Collaborative research between fishermen and scientists is important to fisheries management. Partnerships with commercial longline fishermen were developed to enable them to participate in two research projects in order to integrate their information, experience and expertise. These programmes, financed by the fishing industry and regional councils were designed to describe the activity of the fisheries, to assess the scale of fishery effects on the various taxa, to study ecology and explore spatial population genetic structure in the western part of the Mediterranean Sea of the blue shark (Prionace glauca) and stingray (Pteroplatytrygon violacea) and finally to propose mitigation measures to reduce impacts on elasmobranches, sea birds and sea turtles. Communication, education, post-implementation monitoring and long-standing collaboration are the key factors to success. This presentation shows the progress realized to date.

Uncommon records of fishes may evidence local or global changes in fish composition resulting from environmental change or anthropogenic activities. Significant records of uncommon marine fishes, including migrant, non-native, cryptic, rare and threatened species, collected in French waters or by French vessels in European waters, observed by scuba divers or beachgoers, are reported for the year 2018. They include first, new, rare and unusual records for the following 52 species: Hexanchus griseus, Squatina squatina, Gymnura altavela, Acipenser sturio, A. gueldenstaedtii, Dalophis imberbis, Nemichthys curvirostris, Eurypharynx pelecanoides, Maulisia mauli, M. microlepis, Sagamichthys schnakenbecki, Melanostomias bartonbeani, Astronesthes niger* , Leptostomias gladiator*, Chlorophthalmus agassizi, Magnisudis atlantica, Evermannella balbo, Regalecus glesne, Luvarus imperialis, Raniceps raninus, Fistularia cf. petimba* , Trigla lyra, Lepidotrigla dieuzeidei, Micrenophrys lilljeborgii, Howella atlantica*, Pomatomus saltatrix, Serranus cabrilla, Caranx crysos, Seriola rivoliana, Trachinotus ovatus, Lobotes surinamensis, Sarpa salpa, Chelon ramada, Pseudoscopelus altipinnis* , Trachinus draco, Parablennius pilicornis, P. ruber, Buenia affinis, B. jeffreysii, Chromogobius zebratus, Didogobius splechtnai, Gammogobius steinitzi, Gobius couchi, G. kolombatovici, Lebetus sp., Speleogobius trigloides , Thorogobius macrolepis, Vanneaugobius dollfusi, Siganus rivulatus* , Lepidocybiumflavobrunneum, Hyperoglyphe sp. et Pegusa cf. nasuta, among which six, marked with an asterisk (*), represent additions to the Checklist of the marine fishes from metropolitan France and one, N. curvirostris, is a first record for the Mediterranean.

Uncommon records of fishes may evidence local or global changes of fish composition resulting from environmental modifications or anthropic activities. Significant records of uncommon marine fishes, including threatened species, collected in French waters or by French vessels in European waters are reported for the year 2017. They include first, new, rare and unusual records for the following species: Sphyrna zygaena, Acipenser sturio, Muraena helena, Nessorhamphus ingolfianus, Evermannella balbo, Raniceps raninus, Cheilopogon heterurus, Scopelogadus beanii, Zenopsis conchifer, Eutelichthys leptochirus, Serranus cabrilla, Naucrates ductor, Seriola rivoliana, Gobius gasteveni, Gobius paganellus, Lepidocybium flavobrunneum, Ruvettus pretiosus, Hippoglossus hippoglossus, and Sphoeroides pachygaster.

During the last decade, particular attention has been paid worldwide to the problem of bycatch and discards in fisheries. Collaborative research between fishermen and scientists is important to fisheries management. Partnerships with commercial longline fishermen were developed to enable them to participate in two research projects in order to integrate their information, experience and expertise. These programmes, financed by the fishing industry and regional councils were designed to describe the activity of the fisheries, to assess the scale of fishery effects on the various taxa, to study the ecology and explore spatial population genetic structure in the western part of the Mediterranean Sea of the blue shark (Prionace glauca) and sting rays (Pteroplatytrygon violacea) and finally to propose mitigation measures to reduce impacts on elasmobranchs, sea birds and sea turtles. Communication, education, post-implementation monitoring and long-standing collaboration are the key factors to success. This presentation shows the progress realized to date.

Small pelagic fish are key components of marine ecosystems and fisheries worldwide. Despite the absence of recruitment failure and overfishing, pelagic fisheries have been in crisis for a decade in the Western Mediterranean Sea because of a marked decline in sardine size and condition. This situation most probably results from bottom-up control and changes in the plankton community towards smaller plankton. To understand such an unusual phenomenon, we developed an original and innovative experimental approach investigating the mechanisms induced by a reduction in the quantity and size of sardine prey. While experimentations offer the unique opportunity to integrate behavior and ecophysiology in understanding key demographic processes, they remain rarely used in fisheries science, even more so on small pelagics due to the notorious difficulty to handle them. The results revealed that food size (without any modification of its energy content) is as important as food quantity for body condition, growth and reserve lipids: sardines that fed on small particles had to consume twice as much as those feeding on large particles to achieve the same condition and growth. Such a strong impact of food size was unexpected and may reflect a different energy cost or gain of two feeding behaviors, filter-feeding versus particulate-feeding, which would have to be tested in further study. As increasing temperature favors planktonic chains of smaller size, climate change might actually accelerate and amplify such phenomenon and thus strongly affect fisheries.

In the Gulf of Guinea, bigeye tuna (Thunnus obesus; BET) and yellowfin tuna (Thunnus albacares; YFT) are an important part of commercial fisheries and play a prominent ecological role as top predators. Using fatty acid profiles and carbon and nitrogen stable isotopes, we examined their trophic niche partitioning in this understudied region. Trophic niche overlap was high (>70%), similar to percentages in other ocean basins. BET occupied a higher trophic position than YFT and fed on deeper prey (high δ15N values and high proportions of monounsaturated fatty acids). The trophic position of YFT decreased slightly in the last 15 years (δ15N values decreased by ∼0.5‰), suggesting a change in epipelagic communities, as observed in the eastern Pacific Ocean. Ontogenic changes were limited to BET. For both species, the dietary proportion of the diatom marker 20:5(n-3) increased in the seasonal upwelling area, highlighting the influence of seasonal habitat on the diet of tuna. The relatively lipid-rich muscle (∼6% dry mass) of Atlantic tropical tuna suggests a richer diet in this region than that of Indian Ocean tropical tuna and (or) differences in energy allocation strategies.

Various protocols are currently used to study marine lipids, but there is a growing interest in working on dry samples that are easier to transport. However, reference protocols are still lacking for dry samples. In order to make recommendations on this use, lipid classes and fatty acids (FA) obtained from six analytical protocols using two different tissue states (dry vs wet) and three extraction methods (automat vs manual potter vs leaving the solvent to work on tissue) were compared. Three dry storage modes of tissue (freezer vs gas nitrogen vs dry room) during one and three months were also compared. These comparisons were made on seven marine species with different lipid profiles, including fishes, crustaceans and mollusks. Lipid classes and FA obtained from wet and dry tissues were similar, but they were affected by the extraction methods. Regardless of tissue state, "Leave to work" methods obtained the highest lipid quantities, followed by manual potter and automat methods (ca. 90% and 80% of "Leave to work" methods, respectively). Linear relationships allowed correction for lipid classes and FA concentrations obtained from different protocols. The repeatability of all protocols still needs to be improved, especially for fish species. Increasing the replicate number for each sample might be an indirect way to improve lipid quantification. Our results show that storing dry tissues in the freezer for more than one month was associated with a decrease in lipids, which is also observed for other storage methods. For qualitative studies of FA (expressed in %), a three-month storage of dry tissue in freezer did not affect the relative composition of species/tissues with a lipid content below 20% of dry weight.

1 Ifremer, UMR MARBEC, Station Ifremer de Sète, Avenue Jean Monnet, CS 30171, 34203 Sète Cedex, France. (CM-D) (Corresponding author) E-mail: cmellon@ifremer.fr. ORCID iD: http://orcid.org/0000-0002-2811-1779 (LM) E-mail: Luisa.Metral@ifremer.fr. ORCID iD: http://orcid.org/0000-0002-8187-0053 (SM) E-mail: Serge.Mortreux@ifremer.fr. ORCID iD: http://orcid.org/0000-0002-446-2592 (JMF) E-mail: Jean.Marc.Fromentin@ifremer.fr. ORCID iD: http://orcid.org/0000-0002-1496-4332 2 Université d’Aix Marseille, Mediterranean Institute of Oceanography (MIO), UM 110, 13288 Marseille Cedex 09, France. (MH) E-mail: mireille.harmelin@mio.osupytheas.fr. ORCID iD: http://orcid.org/0000-0003-3085-2899 3 Ifremer, Laboratoire Biogéochimie des Contaminants Organiques, ZI de la Pointe du Diable, CS 10070, 29280 Plouzané, France. (VL) E-mail: Veronique.Loizeau@ifremer.fr. ORCID iD: http://orcid.org/0000-0001-8038-9981 4 Ifremer La Réunion, Rue Jean BERTHO BP 60 97822 Le Port Cedex, France. (DR) E-mail: David.Roos@ifremer.fr. ORCID iD: http://orcid.org/0000-0003-0273-3585

Recently, the abundance of young Atlantic bluefin tuna (Thunnus thynnus) tripled in the northwestern Mediterranean following effective management measures. We investigated whether its predation on sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) could explain their concurrent size and biomass decline, which caused a fishery crisis. Combining the observed diet composition of bluefin tuna, their modelled daily energy requirements, their population size, and the abundance of prey species in the area, we calculated the proportion of the prey populations that were consumed by bluefin tuna annually over 2011–2013. To assess whether tuna could alter the size structure of the three small pelagic fish populations (anchovy, sardine, and sprat (Sprattus sprattus)), the size distributions of the consumed prey species were compared with those of the wild populations. We estimated that the annual consumption of small pelagic fish by bluefin tuna is less than 2% of the abundance of these populations. Furthermore, size selectivity patterns were not observed. We thus concluded that tuna predation is unlikely to be the main cause of major changes in the small pelagic fish populations from this area.