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In the Western Mediterranean Sea, forage fishes have changed in abundance, body condition, growth, reproduction, and distribution in the last decades. Different hypotheses have been proposed to explain these changes, including increase in fishing mortality; changes in environmental conditions affecting species fitness, and planktonic productivity and quality; recovery of top predators; and increase in competitors. We investigated the main drivers and changes of the pelagic ecosystem and their effects using an ecosystem-based modelling approach. Specifically, we (1) quantified the potential historical contribution of various drivers of change, (2) investigated changes in temporal trends and spatial distributions of main ecosystem components, and (3) identified ecological consequences of these changes in top predator and competitors, their fisheries and ecosystem traits during 2000–2020. We updated an established Ecopath food-web model representing the Spanish and French Mediterranean sub-areas (GSA06 and GSA07) in 2000 with recent available data. We applied the temporal dynamic Ecosim module, and tested historical time series of fishing effort, fishing mortality and environmental factors as potential drivers. Observed biomass and landings of key species were used to validate model projections. A spatial-temporal Ecospace model was developed to project species distribution changes. Results showed historical biomass and catch changes driven by a combination of high fishing pressure and environmental change (i.e. increase in temperature and salinity, and decline in primary productivity). Small pelagic fish showed significant temporal changes and predicted shifts in their distributions, following a latitudinal gradient. Predators and competitors showed changes as well, displaying heterogeneous spatial patterns, while fisheries landings declined. Overall, results matched observations (e.g., decline of sardine, fluctuations of anchovy and increases in bluefin tuna) and ill

The Mediterranean Sea stands out as one of the most vulnerable ecosystems on global scale, facing an array of cumulative impacts, including high climate risks. Climate velocity drives species shifts and redistributions, which has led to changes at different ecosystem levels. However, it is necessary to examine how commercial marine species respond at regional and seasonal levels, which is often the optimal management scale. Here, we analyzed time series data on bottom-trawl fisheries landings (2007 to 2021) and explored seasonal variations using climate velocity and relative climate exposure as metrics of potential range shifts (1987 to 2021) in the Western Mediterranean Sea. Additionally, we examined the impact of climate connectivity, using climate velocity trajectories and temperature preferences, along with life-history traits of commercial species. The outcomes of our study showed fluctuations in climate velocity across diverse spatial and seasonal scales. We identified a relationship between the abundance of most captured commercial species and seasonal climate velocity. These variations were also influenced by the temperature preferences and the life-history traits of these species and, play a key role in the climate connectivity between the network of Marine Protected Areas. We conclude that climate velocity metrics are valuable to comprehend how economically important marine species respond in the Western Mediterranean Sea at regional and seasonal levels. Using this knowledge, we can develop climate-smart management strategies, contributing to biodiversity conservation and the preservation of crucial ecosystem services, while mitigating the risks associated with future maladaptation.

By evaluating genetic variation across the entire genome, one can address existing questions in a novel way while raising new ones. The latter include how different local environments influence adaptive and neutral genomic variation within and among populations, providing insights into local adaptation of natural populations and their responses to global change. Here, under a seascape genomic approach, ddRAD data of 4609 SNPs from 398 sardines (Sardina pilchardus) collected in 11 Mediterranean and one Atlantic site were generated. These were used along with oceanographic and ecological information to detect signals of adaptive divergence with gene flow across environmental gradients. The studied sardines constitute two clusters (FST=0.07), a pattern attributed to outlier loci, highlighting putative local adaptation. The trend in the number of days with sea surface temperature above 19oC, critical threshold for successful sardine spawning, was crucial at all levels of population structuring with implications on species’ key biological processes. Outliers link candidate SNPs to the region's environmental heterogeneity. Our findings provide evidence for a dynamic equilibrium where population structure is maintained by physical and ecological factors under the opposing influences of migration and selection. This dynamic in nature system, warrants continuous monitoring under a seascape genomic approach that might benefit from a temporal and more detailed spatial dimension. Our results may contribute to complementary studies aimed at providing deeper insights into the mechanistic processes underlying population structuring. Those are key for understanding and predicting future changes and responses of this highly exploited species in the face of climate change.

By evaluating genetic variation across the entire genome, one can address existing questions in a novel way while raising new ones. The latter include how different local environments influence adaptive and neutral genomic variation within and among populations, providing insights into local adaptation of natural populations and their responses to global change. Here, under a seascape genomic approach, ddRAD data of 4609 SNPs from 398 sardines (Sardina pilchardus) collected in 11 Mediterranean and one Atlantic site were generated. These were used along with oceanographic and ecological information to detect signals of adaptive divergence with gene flow across environmental gradients. The studied sardines constitute two clusters (FST=0.07), a pattern attributed to outlier loci, highlighting putative local adaptation. The trend in the number of days with sea surface temperature above 19oC, critical threshold for successful sardine spawning, was crucial at all levels of population structuring with implications on species’ key biological processes. Outliers link candidate SNPs to the region's environmental heterogeneity. Our findings provide evidence for a dynamic equilibrium where population structure is maintained by physical and ecological factors under the opposing influences of migration and selection. This dynamic in nature system, warrants continuous monitoring under a seascape genomic approach that might benefit from a temporal and more detailed spatial dimension. Our results may contribute to complementary studies aimed at providing deeper insights into the mechanistic processes underlying population structuring. Those are key for understanding and predicting future changes and responses of this highly exploited species in the face of climate change.

The need to better understand the trade-offs between food production, trade and consumption; social and environmental impacts of food systems and food health requirements remains a challenge. Additionally, there is an urgency to transform the food system to reach the dietary patterns required to address the current diet-environment-health trilemma. Transformative changes are required to deal with the food system crisis. To this end, it is necessary to strengthen the links in the food chain and establish solid alliances between production and consumption with the objective of designing alternative food systems. In this context, the Agroecosystems History Laboratory of Pablo de Olavide University and Alimentta-Think tank for the transition of agrifood systems, organised the IX International Congress of Agroecology between the 19th and the 23rd of January, 2023, in Seville (Spain). Its theme was “Cultivating local agroecological-based food systems”. Within the Congress, a hybrid panel of “Sowing initiatives with transformative potential in the fishing sector” was held to bring together initiatives with the capacity to generate transformative changes and enhance the value of fisheries in the field of agroecology and food sovereignty. The panel included communications related to seafood consumption, food sovereignty, co-management, inequalities, collaborative experiences, waste management, transformation processing and commercialisation. As a conclusion of the panel, a new perspective is required to redesign the agrifood systems and promote desirable multiple transformative changes that help to establish analytical and political action strategies in the field of fisheries as a food system

By evaluating genetic variation across the entire genome, one can address existing questions in a novel way while raising new ones. The latter includes how different local environments influence adaptive and neutral genomic variation within and among populations, providing insights into local adaptation of natural populations and their responses to global change. Here, under a seascape genomic approach, ddRAD data of 4609 single nucleotide polymorphisms (SNPs) from 398 sardines (Sardina pilchardus) collected in 11 Mediterranean and one Atlantic site were generated. These were used along with oceanographic and ecological information to detect signals of adaptive divergence with gene flow across environmental gradients. The studied sardines constitute two clusters (FST = 0.07), a pattern attributed to outlier loci, highlighting putative local adaptation. The trend in the number of days with sea surface temperature above 19°C, a critical threshold for successful sardine spawning, was crucial at all levels of population structuring with implications on the species' key biological processes. Outliers link candidate SNPs to the region's environmental heterogeneity. Our findings provide evidence for a dynamic equilibrium in which population structure is maintained by physical and ecological factors under the opposing influences of migration and selection. This dynamic in a natural system warrants continuous monitoring under a seascape genomic approach that might benefit from a temporal and more detailed spatial dimension. Our results may contribute to complementary studies aimed at providing deeper insights into the mechanistic processes underlying population structuring. Those are key to understanding and predicting future changes and responses of this highly exploited species in the face of climate change

Understanding ecological, and socio-economical vulnerabilities is fundamental towards developing and implementing regional adaptation strategies to climate change. The Portuguese coast is situated in a transition zone between temperate ecosystems to the north, and subtropical with Mediterranean characteristics, to the south, with distinct oceanographic regions (north, centre, and south), fish assemblages and socioeconomic realities of fish communities across these regions. We develop a framework to assess fisheries climate vulnerability in each port. A total of 32 ecological and socio-economic indicators were used to measure exposure, sensitivity, and adaptive capacity of the fishing sector to climate change by combining i) environmental projections ii) information from fishing communities (surveys at ports) and iii) landings and socio-economic data from official statistics offices. The vulnerability to climate change across regions, and its expected impact on fishing fleets and local communities, was low-moderate. Such information will enable fishing communities and decision makers to respond to expected climate change effects and direct/indirect associated activities. This framework comprises background information for developing mandatory EU climate adaptation plans that aim to improve the resilience of fisheries socio-economic systems.

An accelerating rate of warming along spatial gradients is leading to changes in climate velocity, (i.e., speed and direction of isotherm movements). Using climate velocity to assess the threat of climate change has enabled researchers to document global patterns of poleward changes in biodiversity. However, less is known about regional, sub-regional and seasonal responses of commercial marine species, which often represents the efficient scale of management. Using climate velocity as a metric of potential range shifts (1987-2021), we explore how seasons, shifts in fisheries landings (2007-2021), temperature preferences and life-history traits influence the distribution of commercial species in the Western Mediterranean Sea. We found spatial and seasonal differences in climate velocities and some changes in climatic areas (i.e., novel and vulnerable climate areas, climate refugia and climate corridors). The most captured commercial species exhibits a strong relationship with seasonal climate velocity. Shifts in landings also differ in relation to community temperature preferences and life-history traits. Our results suggest that climate velocity is a useful metric that can help to understand regional and sub-regional responses of commercial marine species in the Western Mediterranean Sea. This provides insights into climate-smart management, thereby contributing to the conservation of biodiversity and associated ecosystem services to avoid future maladaptation.

The need to better understand the trade-offs between food production, trade and consumption; social and environmental impacts of food systems and food health requirements remains a challenge. Additionally, there is an urgency to transform the food system to reach the dietary patterns required to address the current diet-environment-health trilemma. Transformative changes are required to deal with the food system crisis. To this end, it is necessary to strengthen the links in the food chain and establish solid alliances between production and consumption with the objective of designing alternative food systems. In this context, the Agroecosystems History Laboratory of Pablo de Olavide University and Alimentta-Think tank for the transition of agrifood systems, organised the IX International Congress of Agroecology between the 19th and the 23rd of January, 2023, in Seville (Spain). Its theme was “Cultivating local agroecological-based food systems”. Within the Congress, a hybrid panel of “Sowing initiatives with transformative potential in the fishing sector” was held to bring together initiatives with the capacity to generate transformative changes and enhance the value of fisheries in the field of agroecology and food sovereignty. The panel included communications related to seafood consumption, food sovereignty, co-management, inequalities, collaborative experiences, waste management, transformation processing and commercialisation. As a conclusion of the panel, a new perspective is required to redesign the agrifood systems and promote desirable multiple transformative changes that help to establish analytical and political action strategies in the field of fisheries as a food system.

Small pelagic fish (SPF) species such as European sardine Sardina pilchardus, European anchovy Engraulis encrasicolus, round sardinella Sardinella aurita and European sprat Sprattus sprattus play important ecological roles in the Mediterranean Sea marine ecosystem. However, changes in SPF abundance and biomass have recently been observed in the basin. Therefore, uncovering the trophic importance of SPF to their predators is key to unravelling potential ecological causes and consequences of SPF population changes related to predator dynamics. Here, we reviewed 101 published studies reporting the presence of the SPF species named above in the diet of marine predators inhabiting the Mediterranean Sea. We found that the number of species preying on SPF was highest for teleost fish species, followed by elasmobranchs, seabirds, marine mammals, cephalopods and sea turtles. These predators were both commercial and non-commercial taxa, and vulnerability ranged from medium to very high. From a conservation point of view, most predator species were considered Least Concern by the IUCN, with few exceptions such as the Balearic shearwater Puffinus mauretanicus, a Critically Endangered species. Geographic information showed that the European sardine was more important in the diet of predators from the western Mediterranean basin, while European anchovy consumption was higher on the eastern side. Round sardinella was consumed in high amounts in the Tyrrhenian Sea, and European sprat was anecdotally consumed. The importance of SPF in the diet of Mediterranean predators may indicate bottom-up control of the marine ecosystem; however, limited temporal information precluded the evaluation of temporal changes, highlighting the need to develop new studies in this area.

Small pelagic fish (SPF) are key organisms for the functioning of pelagic marine ecosystems. In recent decades, these species have undergone significant changes in biomass, growth and body condition in the Mediterranean Sea. Seasonal and spatial information about changes in biological and ecological traits of SPF and their relationship with environmental variables is still missing. Here, we have investigated along a latitudinal gradient in the Northwestern Mediterranean Sea the seasonal patterns of fish fitness (in terms of body condition, fat content and reproduction activity) of two important Mediterranean SPF, European anchovy (Engraulis encrasicolus) and European sardine (Sardina pilchardus). We used non-parametric multivariate analyses and Generalized Additive Models (GAMs) to investigate which environmental and trophic variables could explain observed variations during 2018–2019. Mean fat content values, relative condition index (Kn) and gonadosomatic index (GSI) were calculated monthly. We also measured individual’s stable isotope composition in muscle. Chlorophyll-a, sea surface temperature and salinity were used as environmental descriptors. The results revealed spatial and temporal variations for both species in terms of body condition, fat content and reproduction indices, as well as of stable isotopic values. GAMs showed that the variability in fitness for both species was mostly explained by environmental variables, in addition to the spatial and seasonal factors. Trophic variables contributed to explain the variability of the indices, mostly in the case of anchovy. This study provides insights into the spatial and seasonal interplay of the fitness of two important commercial species along a latitudinal gradient, and contributes to understand the fluctuations of SPF population and recent declining trends to inform proactive fisheries management at local and regional scale.

Sardine and anchovy have shown important changes in landings, biomass, abundance and body condition with time in the Western Mediterranean Sea. Several hypotheses have been proposed to explain these changes, including the negative interaction with jellyfish blooms. Increases in jellyfish blooms may be one of the reasons for a decline in these fish stocks because several jellyfish species have been shown to feed on fish larvae and juveniles. The main aim of the present study was to test the plausible relationship between jellyfish blooms and stock dynamics (abundance, biomass, and fitness) of anchovy and sardine, and its fisheries within an ecological context of the western Mediterranean Sea. Our main hypothesis was that jellyfish blooms, in combination with other environmental drivers, could have negative effects due to their predation on early stages of small pelagic fish (direct mortality) or due to predation on zooplankton, which is also prey of the small pelagic fish at different ontogenetic stages (direct competition). To test our hypothesis, we developed Bayesian Generalized Linear Mixed Models to compare landings, biomass, abundance, and Kn condition factor of both species with several climatic indices, oceanographic variables, and the occurrences of jellyfish blooms. Our results revealed that the jellyfish bloom occurrence had a high probability of negatively and broadly affecting both species in addition to changes in environmental conditions. This suggests that jellyfish blooms should be added to the likely causes of change when analyzing small pelagic fish change.

Small pelagic fish (SPF) species such as European sardine Sardina pilchardus, European anchovy Engraulis encrasicolus, round sardinella Sardinella aurita and European sprat Sprattus sprattus play important ecological roles in the Mediterranean Sea marine ecosystem. However, changes in SPF abundance and biomass have recently been observed in the basin. Therefore, uncovering the trophic importance of SPF to their predators is key to unravelling potential ecological causes and consequences of SPF population changes related to predator dynamics. Here, we reviewed 101 published studies reporting the presence of the SPF species named above in the diet of marine predators inhabiting the Mediterranean Sea. We found that the number of species preying on SPF was highest for teleost fish species, followed by elasmobranchs, seabirds, marine mammals, cephalopods and sea turtles. These predators were both commercial and non-commercial taxa, and vulnerability ranged from medium to very high. From a conservation point of view, most predator species were considered Least Concern by the IUCN, with few exceptions such as the Balearic shearwater Puffinus mauretanicus, a Critically Endangered species. Geographic information showed that the European sardine was more important in the diet of predators from the western Mediterranean basin, while European anchovy consumption was higher on the eastern side. Round sardinella was consumed in high amounts in the Tyrrhenian Sea, and European sprat was anecdotally consumed. The importance of SPF in the diet of Mediterranean predators may indicate bottom-up control of the marine ecosystem; however, limited temporal information precluded the evaluation of temporal changes, highlighting the need to develop new studies in this area

Small pelagic fish (SPF) are key organisms for the functioning of pelagic marine ecosystems. In recent decades, these species have undergone significant changes in biomass, growth and body condition in the Mediterranean Sea. Seasonal and spatial information about changes in biological and ecological traits of SPF and their relationship with environmental variables is still missing. Here, we have investigated along a latitudinal gradient in the Northwestern Mediterranean Sea the seasonal patterns of fish fitness (in terms of body condition, fat content and reproduction activity) of two important Mediterranean SPF, European anchovy (Engraulis encrasicolus) and European sardine (Sardina pilchardus). We used non-parametric multivariate analyses and Generalized Additive Models (GAMs) to investigate which environmental and trophic variables could explain observed variations during 2018–2019. Mean fat content values, relative condition index (Kn) and gonadosomatic index (GSI) were calculated monthly. We also measured individual’s stable isotope composition in muscle. Chlorophyll-a, sea surface temperature and salinity were used as environmental descriptors. The results revealed spatial and temporal variations for both species in terms of body condition, fat content and reproduction indices, as well as of stable isotopic values. GAMs showed that the variability in fitness for both species was mostly explained by environmental variables, in addition to the spatial and seasonal factors. Trophic variables contributed to explain the variability of the indices, mostly in the case of anchovy. This study provides insights into the spatial and seasonal interplay of the fitness of two important commercial species along a latitudinal gradient, and contributes to understand the fluctuations of SPF population and recent declining trends to inform proactive fisheries management at local and regional scale

Sardine and anchovy have shown important changes in landings, biomass, abundance and body condition with time in the Western Mediterranean Sea. Several hypotheses have been proposed to explain these changes, including the negative interaction with jellyfish blooms. Increases in jellyfish blooms may be one of the reasons for a decline in these fish stocks because several jellyfish species have been shown to feed on fish larvae and juveniles. The main aim of the present study was to test the plausible relationship between jellyfish blooms and stock dynamics (abundance, biomass, and fitness) of anchovy and sardine, and its fisheries within an ecological context of the western Mediterranean Sea. Our main hypothesis was that jellyfish blooms, in combination with other environmental drivers, could have negative effects due to their predation on early stages of small pelagic fish (direct mortality) or due to predation on zooplankton, which is also prey of the small pelagic fish at different ontogenetic stages (direct competition). To test our hypothesis, we developed Bayesian Generalized Linear Mixed Models to compare landings, biomass, abundance, and Kn condition factor of both species with several climatic indices, oceanographic variables, and the occurrences of jellyfish blooms. Our results revealed that the jellyfish bloom occurrence had a high probability of negatively and broadly affecting both species in addition to changes in environmental conditions. This suggests that jellyfish blooms should be added to the likely causes of change when analyzing small pelagic fish change

European anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) are crucial species for the marine ecosystem of the Northwestern Mediterranean Sea. They account for a high percentage of fish landings and they represent an important economic income. Concerns over their stock status are rising in recent years as biomass, growth, reproductive capacity and body condition of both species are declining. Therefore, there is an urgent need for a continuous and fast body condition monitoring scheme. Energy storage variability has important implications for both fish recruitment and population structure. Direct condition indices, such as bomb calorimetry, are highly reliable for measuring the energy content, but extremely time-consuming. Alternatively, fatmeter analysis and relative condition index (Kn) have been proposed as effective indirect methods. The aim of this study is to test the application of fatmeter as a surrogate of bomb calorimetry to infer the energy content of both small pelagic fishes. For the validation, fatmeter values were compared with both energy density (ED; via bomb calorimetry) and Kn values. Individuals of both species were sampled monthly in Barcelona harbor for a year in order to assess seasonal variations in energy content. Our results highlight that fatmeter measurements are strongly correlated with calorimetry for sardine, while a weaker but significant correlation was found for anchovy. The observed differences between the two species are related to their breeding strategies. Based on this study, fatmeter analysis appears to be a faster and suitable method to evaluate the energy content of both species routinely., In addition, we provide a linear model to infer ED from fatmeter values of both small pelagic fish. Eventually, these findings could allow for the avoidance of bomb calorimetry and could be used to implement body condition monitoring protocols, and to boost continuous large-scale monitoring

Sustainable fishing practices must ensure human wellbeing by safeguarding the integrity of marine life-supporting systems. Unfortunately, a significant challenge to fisheries management is that sustainable fishing levels can decline, often synergistically, by co-occurring with climate-driven environmental stressors. Within one of the most impacted marine areas in the world, and encompassing a number of highly targeted commercial species, the small pelagic fish community of the western Mediterranean Sea has recently shown signs of collapse. In this study, we identify a worrying coincidence where fishing hotspots for the commercially valuable European sardine Sardina pilchardus and anchovy Engraulis encrasicolus occur in marine areas mostly affected by climate change. To identify these areas, we overlayed detailed, spatially explicit measurements of fishing pressure with the finest-scale maps of cumulative climate change impacts onto these species. According to our results, doubly impacted marine areas largely occur in the north-western Mediterranean Sea, with climate and fisheries mostly affecting European sardine. Reducing local stressors (i.e., fishing pressure) in highly impacted areas may contribute to maintain these communities within a “safe operating space” (SOS), where they remain resilient to climate change. Accordingly, the redistribution and/or reduction of fishing intensity may alleviate pressure in those areas already affected by climate change. Sustainable fishing strategies may benefit, therefore, from the SOS concept and the spatial assessments provided in this study

We investigated the main drivers of eggs and larvae distributions of European sardine and anchovy from the NW Mediterranean Sea. We used Generalized Additive Models and satellite environmental data. Mainly sea surface temperature, but also currents, surface height, and primary production were significantly correlated with both species’ early stages distributions. Anchovy optimal temperature upper limit was not detected, but sardine eggs and larvae presented a small-ranged bell-shape curve relationship to SST with an upper SST threshold around 13 °C. Sardine spawning during winter appeared to be dependant not only on in-situ environmental conditions but also on summer conditions prior to the spawning event. Model predictions of the larval and spawning habitat distribution showed clear differences between developmental stages and between species, confirming a worsening of the sardine habitat with time. Considering the further increase of surface temperature predicted in the years to come, the survival of the sardine in the region could be compromised

European anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) are two of the most important small pelagic fish species in terms of biomass and commercial interest in the Mediterranean Sea. Their populations are clearly influenced by environmental variations, making them good bio-indicators of climate-driven changes. Here, we reviewed the different environmental factors documented to affect anchovy and sardine biology by using a systematic review approach on methodologies used to study environmental effects on these species, variables identified to play a role, and relationships found between ecological variables and the environment. Our results show that available studies were heterogeneously distributed, being more abundant for anchovy adults in the Western Mediterranean. Among all the environmental factors found significant, temperature, depth, salinity and chlorophyll-a concentration were the most studied for both species. Further emphasis was placed on the effect of these four variables, with various relationships found for the different life stages and areas. This review provides a general insight of what is known about how the environment influences growth, spawning, abundance and distribution of anchovy and sardine in the Mediterranean Sea, and identifies gaps of knowledge for future research. Our study sets a knowledge baseline for future studies about climate variability and change in the Mediterranean basin

Sustainable fishing practices must ensure human wellbeing by safeguarding the integrity of marine life-supporting systems. Unfortunately, a significant challenge to fisheries management is that sustainable fishing levels can decline, often synergistically, by co-occurring with climate-driven environmental stressors. Within one of the most impacted marine areas in the world, and encompassing a number of highly targeted commercial species, the small pelagic fish community of the western Mediterranean Sea has recently shown signs of collapse. In this study, we identify a worrying coincidence where fishing hotspots for the commercially valuable European sardine Sardina pilchardus and anchovy Engraulis encrasicolus occur in marine areas mostly affected by climate change. To identify these areas, we overlayed detailed, spatially explicit measurements of fishing pressure with the finest-scale maps of cumulative climate change impacts onto these species. According to our results, doubly impacted marine areas largely occur in the north-western Mediterranean Sea, with climate and fisheries mostly affecting European sardine. Reducing local stressors (i.e., fishing pressure) in highly impacted areas may contribute to maintain these communities within a “safe operating space” (SOS), where they remain resilient to climate change. Accordingly, the redistribution and/or reduction of fishing intensity may alleviate pressure in those areas already affected by climate change. Sustainable fishing strategies may benefit, therefore, from the SOS concept and the spatial assessments provided in this study

European anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) are crucial species for the marine ecosystem of the Northwestern Mediterranean Sea. They account for a high percentage of fish landings and they represent an important economic income. Concerns over their stock status are rising in recent years as biomass, growth, reproductive capacity and body condition of both species are declining. Therefore, there is an urgent need for a continuous and fast body condition monitoring scheme. Energy storage variability has important implications for both fish recruitment and population structure. Direct condition indices, such as bomb calorimetry, are highly reliable for measuring the energy content, but extremely time-consuming. Alternatively, fatmeter analysis and relative condition index (Kn) have been proposed as effective indirect methods. The aim of this study is to test the application of fatmeter as a surrogate of bomb calorimetry to infer the energy content of both small pelagic fishes. For the validation, fatmeter values were compared with both energy density (ED; via bomb calorimetry) and Kn values. Individuals of both species were sampled monthly in Barcelona harbor for a year in order to assess seasonal variations in energy content. Our results highlight that fatmeter measurements are strongly correlated with calorimetry for sardine, while a weaker but significant correlation was found for anchovy. The observed differences between the two species are related to their breeding strategies. Based on this study, fatmeter analysis appears to be a faster and suitable method to evaluate the energy content of both species routinely., In addition, we provide a linear model to infer ED from fatmeter values of both small pelagic fish. Eventually, these findings could allow for the avoidance of bomb calorimetry and could be used to implement body condition monitoring protocols, and to boost continuous large-scale monitoring

Small pelagic fish (SPF) in the western Mediterranean Sea are key elements of the marine food web and are important in terms of biomass and fisheries catches. Significant declines in biomass, landings, and changes in the age/size structure of sardine Sardina pilchardus and anchovy Engraulis encrasicolus have been observed in recent decades, particularly in the northern area of the western Mediterranean Sea. To understand the different patterns observed in SPF populations, we analyzed key life history traits [total length at age, length at maturity, gonadosomatic index (GSI), and body condition (Kn)] of sardine and anchovy collected between 2003 and 2017, from different fishing harbors distributed along a latitudinal gradient from northern to southern Spain. We used Generalized Linear Models (GLM) to estimate the length at maturity and Generalized Additive Models (GAMs) to test the relationship with environmental variables (seawater temperature, water currents, and net primary productivity). The life history traits of both species presented seasonal, interannual and latitudinal differences with a clear decline in length at age, length at first maturity, and body condition, for both species in the northern part of the study area. In the southern part, on the contrary, life history traits did not present a clear temporal trend. The environmental conditions partially explained the long-term changes in life history traits, but the selected variables differed between areas, highlighting the importance of regional oceanographic conditions to understand the dynamics of small pelagic fish. The truncated length-at-age pattern for both species with the disappearance of the larger individuals of the population could have contributed to the poor condition of small pelagic fish populations in the northern part of the western Mediterranean Sea in recent years. In the south area, recent declines in body condition for sardine and anchovy were observed and could be a possible first s

This work combines state-of-the-art methods (DNA metabarcoding) with classic approaches (visual stomach content characterization and stable isotope analyses of nitrogen (δ15N) and carbon (δ13C)) to investigate the trophic ecology of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) at high taxonomic and spatial resolution in the Western Mediterranean Sea. Gut contents observed are in accordance with the dietary plasticity generally described for anchovy and sardine, suggesting a diet related to the opportunistic ingestion of available prey in a certain area and/or time. Genetic tools also showed modest inter-specific differences regarding ingested species. However, inter-specific and intra-specific differences in ingested prey frequencies and prey biomass reflected a latitudinal signal that could indicate a more effective predation on large prey like krill by anchovy versus sardine, as well as a generalized higher large prey ingestion by both species southwards. In fact, both species presented lower δ15N in the northernmost area. This latitudinal gradient indicates changes in the trophic ecology of anchovy and sardine that coincide with previously described better biological conditions for fish in the southern part of the study area as well as higher landings of both species in recent years.

We quantified the incidence of microplastics in the gut contents of the European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) in the Northwestern Mediterranean Sea and tested which variables influence this abundance, including the prevalence of parasites (i.e., trematoda larvae and nematodes). We detected a 58% occurrence of microplastics ingestion in sardines and a 60% in anchovies. With respect to sardines, the individuals with lower body conditions were found to have the highest microplastics ingestion probabilities, whereas in anchovies such probabilities were observed in individuals with higher gonadosomatic indices and smaller size. The areas with the highest microplastics ingestion probabilities were the Gulf of Alicante for sardines and the Gulf of Lion - Ebro Delta for anchovies. Both species showed a positive relationship between parasites and microplastics ingestion. These results highlight that both parasitism and ingestion of microplastics are concerns for the health of marine stocks and human consumers.

We quantified the incidence of microplastics in the gut contents of the European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) in the Northwestern Mediterranean Sea and tested which variables influence this abundance, including the prevalence of parasites (i.e., trematoda larvae and nematodes). We detected a 58% occurrence of microplastics ingestion in sardines and a 60% in anchovies. With respect to sardines, the individuals with lower body conditions were found to have the highest microplastics ingestion probabilities, whereas in anchovies such probabilities were observed in individuals with higher gonadosomatic indices and smaller size. The areas with the highest microplastics ingestion probabilities were the Gulf of Alicante for sardines and the Gulf of Lion - Ebro Delta for anchovies. Both species showed a positive relationship between parasites and microplastics ingestion. These results highlight that both parasitism and ingestion of microplastics are concerns for the health of marine stocks and human consumers.

We quantified the incidence of microplastics in the gut contents of the European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) in the Northwestern Mediterranean Sea and tested which variables influence this abundance, including the prevalence of parasites (i.e., trematoda larvae and nematodes). We detected a 58% occurrence of microplastics ingestion in sardines and a 60% in anchovies. With respect to sardines, the individuals with lower body conditions were found to have the highest microplastics ingestion probabilities, whereas in anchovies such probabilities were observed in individuals with higher gonadosomatic indices and smaller size. The areas with the highest microplastics ingestion probabilities were the Gulf of Alicante for sardines and the Gulf of Lion - Ebro Delta for anchovies. Both species showed a positive relationship between parasites and microplastics ingestion. These results highlight that both parasitism and ingestion of microplastics are concerns for the health of marine stocks and human consumers.

Improving the knowledge on the biology, ecology and distribution of marine resources exploited by fisheries is necessary to achieve population recovery and sustainable fisheries management. European hake (Merluccius merluccius) is one of the most important target species in the Mediterranean Sea and is largely overexploited by industrial fisheries. Here, we used two methodological approaches to further investigate the seasonal variation in the spatial distribution of European hake considering ontogenetic changes and trophic ecology in the western Mediterranean Sea. Our main aim was to explore if spatial changes in hake distribution were related to trophic behavior, in addition to key environmental factors. We employed a hierarchical Bayesian species distribution modeling approach (B-SDM), using spatial data from two oceanographic surveys conducted during winter and summer. We analyzed how the environmental variables, together with abundance and mean weight distribution of the main preys identified for European hake, affected the seasonal distribution of the species. Results revealed clear differences in the distribution of the European hake between seasons, which were indeed partially correlated to the distribution of their main preys, in addition to the environment. Stable isotope values and Bayesian isotopic mixing models (MixSIAR) revealed substantial seasonal and ontogenetic differences in trophic habits of European hake, partly matching the spatial distribution results. These findings could have implications for a future seasonal-based adaptive fisheries management, as local depletion of prey, or variation in size and condition may affect European hake presence in this area. Moreover, this study illustrates how the sequential application of methodologies provides a more holistic understanding of species seasonality, which is essential to understand the phenological processes of exploited species and their potential shifts due to environmental changes.

European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) are crucial species for the marine ecosystem of the NW Mediterranean Sea. They account fora high percentage of fish landings and they represent a relevant source of economic interest for the fishery sector (Palomera et al., 2007). [...]

Improving the knowledge on the biology, ecology and distribution of marine resources exploited by fisheries is necessary to achieve population recovery and sustainable fisheries management. European hake (Merluccius merluccius) is one of the most important target species in the Mediterranean Sea and is largely overexploited by industrial fisheries. Here, we used two methodological approaches to further investigate the seasonal variation in the spatial distribution of European hake considering ontogenetic changes and trophic ecology in the western Mediterranean Sea. Our main aim was to explore if spatial changes in hake distribution were related to trophic behavior, in addition to key environmental factors. We employed a hierarchical Bayesian species distribution modeling approach (B-SDM), using spatial data from two oceanographic surveys conducted during winter and summer. We analyzed how the environmental variables, together with abundance and mean weight distribution of the main preys identified for European hake, affected the seasonal distribution of the species. Results revealed clear differences in the distribution of the European hake between seasons, which were indeed partially correlated to the distribution of their main preys, in addition to the environment. Stable isotope values and Bayesian isotopic mixing models (MixSIAR) revealed substantial seasonal and ontogenetic differences in trophic habits of European hake, partly matching the spatial distribution results. These findings could have implications for a future seasonal-based adaptive fisheries management, as local depletion of prey, or variation in size and condition may affect European hake presence in this area. Moreover, this study illustrates how the sequential application of methodologies provides a more holistic understanding of species seasonality, which is essential to understand the phenological processes of exploited species and their potential shifts due to environmental changes

Understanding the trophic ecology of marine predators is pivotal to assess their ecological role in the ecosystems and develop management actions. Despite the ecological importance of predatory pelagic fish species, the trophic role that individual species play within marine communities in many marine basins, such the Mediterranean Sea, remains unclear. In the present study, we aimed to provide new integrative information about the trophic ecology at different temporal scales of Atlantic bonito (Sarda sarda), little tunny (Euthynnus alletteratus) and swordfish (Xiphias gladius) in the north-western Mediterranean Sea. To quantify the trophic habits of these three species, we used stable isotopic analysis and isotopic mixing models from different tissues that integrate trophic information at different temporal scales (~1 month for liver, ~ several months for muscle, >1 year for fin). We found clear and consistent differences in the trophic habits among the three species and time spans within the same species. Although preying mainly on clupeiforms, Atlantic bonito and little tunny present a temporal segregation in the species preference, with Atlantic bonito preying mainly on European sardine and round sardinella at long-term, while little tunny preyed mainly on European anchovy. In the other hand, swordfish shows a more generalist trophic strategy with high preference for demersal prey. This study emphasises the utility of this integrative approach for trophic studies due to its capacity for monitoring trophic habits over different time spans

The general objective of the workshop was to create a dialogue between stakeholders of the pelagic system of the Northwest Mediterranean Sea (fishers, managers, NGO and scientists); focusing on the dynamics of small commercial pelagic fish (targeting sardine and anchovy) and the fishing activity associated with them. The workshop started with a scientific overview of the current knowledge derived from several research projects (e.g., EU Spelmed, Spanish Plan Estatal Pelweb). Then, factors and processes that may be affecting our understanding of the dynamics of the pelagic system were identified. Finally, stakeholders mentioned and discussed several proposals to improve the management of the fishing resources. The analysis was done from an ecological, social, economic and fisheries management perspective. All the information was integrated using qualitative network modelling techniques with the assistance of Dr. Jeffrey Dambacher, from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), (Tasmania, Australia). Sixteen stakeholders representing the fisheries sector, scientific institutions, environmental organizations and the regional administration participated in the workshop

In the Northwestern Mediterranean Sea, the European sardine (Sardina pilchardus) and the European anchovy (Engraulis encrasicolus) are the most important small pelagic fish in terms of biomass and commercial interest. During the last years, these species have experimented changes in their abundance and biomass trends in the Northwestern Mediterranean Sea, in addition to changes in growth, reproduction and body condition. These species are particularly sensitive to environmental fluctuations with possible cascading effects as they play a key role in connecting the lower and upper trophic levels of marine food webs. It is therefore essential to understand the factors that most profoundly affect sardine and anchovy dynamics. This study used a two-step approach to understand how the environment influences the adult stages of these species in the Northwestern Mediterranean Sea. First, we explored the effects of environmental change over time using Random Forests and available datasets of species occurrence, abundance, biomass and landings. We then applied species distribution models to test the impact of the extreme pessimistic and optimistic Intergovernmental Panel on Climate Change (IPCC) pathway scenarios, and to identify possible climate refuges: areas where these species may be able to persist under future environmental change. Findings from the temporal modeling showed mixed effects between environmental variables and for anchovy and sardine datasets. Future pathway projections highlight that both anchovy and sardine will undergo a reduction in their spatial distributions due to future climate conditions. The future climate refuges are the waters around the Rhone River (France) and the Ebro River (Spain) for both species. This study also highlights important knowledge gaps in our understanding of the dynamics of small pelagic fish in the region, which is needed to progress towards an ecosystem approach to fisheries management

We quantified the incidence of microplastics in the gut contents of the European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) in the Northwestern Mediterranean Sea and tested which variables influence this abundance, including the prevalence of parasites (i.e., trematoda larvae and nematodes). We detected a 58% occurrence of microplastics ingestion in sardines and a 60% in anchovies. With respect to sardines, the individuals with lower body conditions were found to have the highest microplastics ingestion probabilities, whereas in anchovies such probabilities were observed in individuals with higher gonadosomatic indices and smaller size. The areas with the highest microplastics ingestion probabilities were the Gulf of Alicante for sardines and the Gulf of Lion - Ebro Delta for anchovies. Both species showed a positive relationship between parasites and microplastics ingestion. These results highlight that both parasitism and ingestion of microplastics are concerns for the health of marine stocks and human consumers

Variability in body condition and energy storage has important implications for fish recruitment and ecosystem structure. Understanding strategies for energy allocation to maintenance, reproduction and growth is essential to evaluate the state of the fish stocks. In this study, we address the energetics dynamics of the annual cycle of anchovies (Engraulis encrasicolus) and sardines (Sardina pilchardus) in the north-western Mediterranean Sea using indirect and direct condition indices. We assessed and validated the use of morphometric, biochemical and energetic indices for both species. Annual patterns of the relative condition index (Kn), gonadosomatic index (GSI), lipid content (% lipids) and energy density (ED) were linked to the energy allocation strategy. Our results highlight that anchovy mainly rely on income energy to reproduce, while sardine accumulate the energy during the resting period to be used in the reproduction period. Consequently, variability in the lipid content and ED between seasons was lower in anchovy than in sardine. In both species, we observed an early decline in energy reserves in late summer-early fall, which may be related to unfavourable environmental conditions during spring and summer. Regarding the use of different condition indices, both direct indices, lipid content and ED, were highly correlated with Kn for sardine. ED was better correlated with Kn than lipid content for anchovy. For the first time, a relationship between ED of gonads and GSI for sardine and anchovy was provided, highlighting the importance of the energy invested in reproduction. This work provides new insights into the energy dynamics of sardine and anchovy. We also demonstrate which are the most suitable indices to measure changes in the physiological condition of both species, providing tools for the future monitoring of the populations of these two commercially and ecologically important fish species

Mediterranean marine ecosystems are fundamentally driven by their pelagic communities and small and medium-size pelagic fishes (SMPF) play crucial ecological roles. Although fluctuations of the populations of these organisms have been mainly attributed to environmental variability and overfishing, there is still a lack of understanding on specific mechanisms that drive their population changes. In recent decades a decline in landings, biomass and body condition of sardine and anchovy in the Mediterranean Sea has been observed and several hypotheses to explain these changes have been formulated. Therefore, accurate scientific data at species and community level is needed in order to understand the most likely causes of these declines. Within this context, this PhD thesis aims to improve the knowledge of the seasonal dynamics and functioning of the pelagic compartment focusing in the trophic relationships and energy dynamics of SMPF in the northwestern Mediterranean Sea. I used different methods to advance on the knowledge about the ecological and functional role of several pelagic fish species in the western Mediterranean Sea, including clupeoids, horse mackerels and mackerels. Specifically, stable isotope and stomach content analyses in combination with direct and indirect body condition indeces, were used to study seasonal variation in energy content in relation to their breeding strategies, feeding preferences and trophic role in the pelagic food-web. Results showed stability in the trophic structure through the year with a trophic segregation of small pelagic fish depending on the ontogenetic stage. Seasonal differences in energy density were highly related with the spawning season and food availability. To integrate the new findings and to test the role of potential pressures on main pelagic species, I developed qualitative food-web models. Overall, results provide pivotal information to assist the adaptive management of pelagic fish species in the region., Els ecosistemes marins mediterranis estan fonamentalment dirigits per les seves comunitats pelàgiques on els peixos pelàgics petits i mitjans (SMPF) exerceixen funcions ecològiques crucials. Si bé les fluctuacions de les seves poblacions s'han atribuït principalment a la variabilitat ambiental i la sobrepesca, encara hi ha una manca de comprensió sobre els mecanismes específics que impulsen els canvis en la població. En les últimes dècades s'ha observat una disminució en la biomassa, en els desembarcaments i en la condició de la sardina i l'anxova al mar Mediterràni, i s'han formulat diverses hipòtesis per explicar aquests canvis. Actualment, es necessiten dades científiques precises a nivell d'espècies i comunitats per comprendre les causes més probables d'aquestes disminucions. En aquest context, aquesta tesi doctoral pretén millorar el coneixement de la dinàmica estacional i el funcionament del compartiment pelàgic, centrant-se en les relacions tròfiques i la dinàmica energètica dels SMPF al nord-oest del Mar Mediterrani. Diferents tècniques es varen fer servir per avançar en el coneixement del paper ecològic i funcional de diverses espècies de peixos pelàgics al mar Mediterrani occidental, incloent clupèids, sorells i verats. En concret, es varen utilitzar anàlisi d'isòtops estables i de contingut estomacal en combinació amb índexs directes i indirectes de condició corporal, per estudiar la variació estacional del contingut d'energia en relació amb les seves estratègies de reproducció, preferències tròfiques i paper tròfic en la comunitat pelàgica. Els resultats van mostrar estabilitat en l'estructura tròfica al llarg de l'any amb una segregació tròfica dels peixos pelàgics petits en funció de l'etapa ontogenètica. Les diferències estacionals en la densitat energètica van estar altament relacionades amb la temporada de reproducció i la disponibilitat d'aliments. Per integrar tota aquesta informació i testar el paper de les pressions potencials en les principals, Los ecosistemas marinos mediterráneos están fundamentalmente condicionados por sus comunidades pelágicas donde los peces pelágicos pequeños y medianos (SMPF) desempeñan funciones ecológicas cruciales. Si bien las fluctuaciones de sus poblaciones se han atribuido principalmente a la variabilidad ambiental y la sobrepesca, todavía hay una falta de comprensión sobre los mecanismos específicos que impulsan los cambios en las poblaciones pelágicas. En las últimas décadas se ha observado una disminución en la biomasa, en los desembarques y en la condición de la sardina y la anchoa del noroeste del mar Mediterráneo, y se han formulado varias hipótesis para explicar estos cambios. Actualmente, se necesitan datos científicos precisos a nivel de especies y comunidades para comprender las causas más probables de estas disminuciones. En este contexto, esta tesis doctoral pretende mejorar el conocimiento de la dinámica estacional y el funcionamiento del compartimento pelágico, centrándose en las relaciones tróficas y la dinámica energética de los SMPF en el noroeste del mar Mediterráneo. Se usaron diferentes técnicas para avanzar en el conocimiento del papel ecológico y funcional de varias especies de peces pelágicos en el Mar Mediterráneo occidental, incluyendo clupeoides, jureles y caballas. En concreto, se utilizó el análisis de isótopos estables y de contenido estomacal en combinación con índices directos e indirectos de condición corporal, para estudiar la variación estacional del contenido de energía en relación con las estrategias de reproducción de los SMPF, las preferencias tróficas y el papel trófico en la comunidad pelágica. Los resultados mostraron estabilidad en la estructura trófica a lo largo del año con una segregación trófica de peces pelágicos pequeños en función del estadío ontogenético. Las diferencias estacionales en la densidad energética estuvieron altamente relacionadas con el periodo de reproducción y la disponibilidad de alimentos. Para integrar toda es, Postprint (published version)

En la última década ha habido un declive en las poblaciones de sardina (Sadina pilchardus) y boquerón (Engraulis encrasicolus) en el noroeste del Mediterráneo tanto a nivel de capturas como de biomasa y también en su estado de condición. El actual declive se ha relacionado con un alto impacto de la pesca o con efectos ecosistémicos como un cambio en la alimentación debido a una peor calidad o cantidad del plancton (Brosset et al., 2017; GFCM, 2016). A pesar de que hay disponible diferentes estudios sobre la biología, ecología y gestión de estas dos especies, esta información está fragmentada y un mayor esfuerzo es necesario para poder integrar toda la información disponible y desarrollar un conocimiento robusto para poder gestionar mejor estas especies. Por ello actualmente en el Instituto de Ciencias del Mar de Barcelona (ICM-CSIC) estamos llevando a cabo dos proyectos muy relacionados entre ellos. El proyecto SPELMED: “Evaluación del estado de las poblaciones y alternativas de gestión específicas para las poblaciones de peces pelágicos pequeños del noroeste del Mediterráneo” (Framework Contract No. EASME/EMFF/2016/032, Specific Contract No. 2, 2018), y el proyecto PELWEB "Ganadores, perdedores y cambios de la red trófica pelágica del Mediterráneo Occidental: de consecuencias ecológicas a proyecciones futuras" (proyecto Estatal de I+D+I RETOS, 2018-2020). Este último proyecto acaba de iniciarse. El proyecto SPELMED abarca las subareas geográficas (GSA) 6 - Norte de España (GSA) 7 – Golfo de León, y se centra en las poblaciones de Sardina pilchardus (sardina) y Engraulis encrasicolus (boquerón), sin olvidar el ecosistema marino y las interacciones con la pesca. SPELMED tiene tres objetivos específicos y cada uno de ellos subdivididos: [...]

During the last years small pelagic fish species (SPF), such as European sardine (Sardina pilchardus) and European anchovy (Engraulis encrasicolus), have experimented changes in their abundance, biomass and spatial distribution in the Northwestern Mediterranean Sea. Different hypotheses have been related to these changes, such as: (1) an increase in fishing impact, (2) changes in the environmental conditions that can directly influence annual recruitment, growth and condition of organisms; (3) the recent recovery of some pelagic predators such as Bluefin tuna (Thunnus thynnus); and (4) inter-specific competition for food between the expanding round sardinella (Sardinella aurita). We firstly tested these hypotheses in the northwestern Mediterranean Sea (in Geographical Sub-Areas GSA06, Spain, and GSA07, France) using a statistical modelling approach in order to understand which one of these factors may have mostly affected these species, and secondly we developed scenarios to predict their future biomass and distributions using a multi-modelling platform. In particular, using a spatial Redundancy Analysis (RDA) we tested the four mentioned main hypotheses as possible causes of European sardine and anchovy observed biomass declines in the area. Secondly, we modeled future environmental and management scenarios including IPCC projected environmental variables using Species Distribution Models and a food-web modeling approach (Ecopath with Ecosim -EwE). Spatial RDAs highlighted that the variability in the distribution of sardine in Spain (GSA06) was due to a combination of effects that included environmental conditions (bathymetry, sea surface temperature, primary production and sea surface salinity), fishing factors (considering AIS and VMS intensity), the expansion of the occurrence of Bluefin tuna feeding habitat, as well as an increase of round sardinella. Similar results were found for European anchovy in this area, although fishing factors were the most important

Small pelagic fishes (SPF) in the western Mediterranean Sea are key elements of the marine food web and are important in terms of biomass and catches. Significant declines in biomass, landings and changes in the age/size structure of European anchovy Engraulis encrasicolus and European sardine Sardina pilchardus have been observed in recent decades in the northwestern Mediterranean Sea (in GSA06 Northern Spain and GSA07 Gulf of Lions, France). Instead, SPF in the southwestern Mediterranean Sea (GSA01 Alboran Sea, Spain) showed different patterns without a clear trend. Fluctuations of SPF have been related to local and regional scale environmental changes, driving annual recruitment and growth, mainly by river runoff, temperature and primary production. To understand the different patterns observed in SPF populations in the western Mediterranean Sea, we analysed seasonal and inter-annual variability of key life-history traits (size at first maturity, gonadosomatic index and body condition) collected in different fishing harbours of Spain distributed along a latitudinal gradient from Tarragona and Torrevieja, in GSA06, norther Spain, to Malaga, in GSA01, southern Spain. Results showed a clear decline in size at first maturity and body condition of sardine and anchovy since 2008 until 2017, with minimum values in 2012 and 2014 in the north of the area. On the contrary, in the south inter-annual fluctuations in body condition did not present a clear temporal trend while size at first maturity increased. However, in absolute terms, levels of energy stored and energy invested in reproduction were lower in the southern area compared with the northern populations. Maximum values of body condition of European sardine also differed between areas at seasonal scale. The decline in size at first maturity may have been translated into lower reproductive capacity in the north, since younger females have proportionally lower fecundity and shorter spawning season. Overall, the most

The small pelagic fish studied in the present work, European anchovy (Engraulis encrasicolus) and European sardine (Sardina pilchardus) have a major role in marine ecosystems, and in particular in the Northwestern Mediterranean Sea. However, in the last decade declines in landings and body condition of both species have been observed in the Northwestern Mediterranean Sea. Therefore, it is necessary to advance on our knowledge about their biological and ecological key traits in order to understand the potential factors that affect the population of European sardine and anchovy in this area. In this study we developed an analysis of their body energy cycle, throughout a year, in different areas of the Catalan coast and evaluate seasonal and spatial fluctuations by means of indirect and direct methods to estimate physiological condition. Specifically, we used energy density measures of dry fish, the Kn index, the GSI index and Fatmeter measurements and we compared them between species, months, locations and methodologies. A significant relationship between the values of the Fatmeter and the energy density measures was found in the case of sardine. Moreover, our results confirmed that seasonality can affect the energetic content of these two species due to their strategies of energy accumulation in relationship with their reproduction periods

[EN] Mediterranean marine ecosystems are fundamentally driven by their pelagic communities and small and medium-size pelagic fish (SMPF) play crucial ecological roles. Although fluctuations of the populations of these organisms have been mainly attributed to environmental variability and overfishing, there is still a lack of understanding on specific mechanisms that drive their population changes. In recent decades a decline in landings, biomass and body condition of sardine and anchovy in the northwestern Mediterranean Sea has been observed and several hypotheses to explain these changes have been formulated. Therefore, accurate scientific data at species and community level is needed in order to understand the most likely causes of these declines. Within this context, this PhD thesis aims to improve the knowledge of the seasonal dynamics and functioning of the pelagic compartment focusing in the trophic relationships and energy dynamics of SMPF in the northwestern Mediterranean Sea. I used different methods to advance on the knowledge about the ecological and functional role of several pelagic fish species in the western Mediterranean Sea, including clupeoids, horse mackerels and mackerels. Specifically, stable isotope and stomach content analyses in combination with direct and indirect body condition indices, were used to study seasonal variation in energy content in relation to their breeding strategies, feeding preferences and trophic role in the pelagic food-web. Results showed stability in the trophic structure through the year with a trophic segregation of small pelagic fish depending on the ontogenetic stage. Seasonal differences in energy density were highly related with the spawning period and food availability. To integrate the new findings and to test the role of potential pressures on main pelagic species, I developed qualitative food-web models. Results showed that an increase of sea surface temperature in combination with an increase of explotation o, [ES] Los ecosistemas marinos mediterráneos están fundamentalmente condicionados por sus comunidades pelágicas donde los peces pelágicos pequeños y medianos (SMPF) desempeñan funciones ecológicas cruciales. Si bien las fluctuaciones de sus poblaciones se han atribuido principalmente a la variabilidad ambiental y la sobrepesca, todavía hay una falta de comprensión sobre los mecanismos específicos que impulsan los cambios en las poblaciones pelágicas. En las últimas décadas se ha observado una disminución en la biomasa, en los desembarques y en la condición de la sardina y la anchoa del noroeste del mar Mediterráneo, y se han formulado varias hipótesis para explicar estos cambios. Actualmente, se necesitan datos científicos precisos a nivel de especies y comunidades para comprender las causas más probables de estas disminuciones. En este contexto, esta tesis doctoral pretende mejorar el conocimiento de la dinámica estacional y el funcionamiento del compartimento pelágico, centrándose en las relaciones tróficas y la dinámica energética de los SMPF en el noroeste del mar Mediterráneo. Se usaron diferentes técnicas para avanzar en el conocimiento del papel ecológico y funcional de varias especies de peces pelágicos en el mar Mediterráneo occidental, incluyendo clupeoides, jureles y caballas. En concreto, se utilizó el análisis de isótopos estables y de contenido estomacal en combinación con índices directos e indirectos de condición corporal, para estudiar la variación estacional del contenido de energía en relación con las estrategias de reproducción de los SMPF, las preferencias tróficas y el papel trófico en la comunidad pelágica. Los resultados mostraron estabilidad en la estructura trófica a lo largo del año con una segregación trófica de peces pelágicos pequeños en función del estadío ontogenético. Las diferencias estacionales en la densidad energética estuvieron altamente relacionadas con el periodo de reproducción y la disponibilidad de alimentos. Para integrar to, [CAT] Els ecosistemes marins mediterranis estan fonamentalment condicionats per les seves comunitats pelàgiques on els peixos pelàgics petits i mitjans (SMPF) exerceixen funcions ecològiques crucials. Si bé les fluctuacions de les seves poblacions s'han atribuït principalment a la variabilitat ambiental i la sobrepesca, encara hi ha una manca de comprensió sobre els mecanismes específics que impulsen els canvis en la població. En les últimes dècades s'ha observat una disminució en la biomassa, en els desembarcaments i en la condició de la sardina i el seitó al nord-oest del mar Mediterrani, i s'han formulat diverses hipòtesis per explicar aquests canvis. Actualment, es necessiten dades científiques precises a nivell d'espècies i comunitats per comprendre les causes més probables d'aquestes disminucions. En aquest context, aquesta tesi doctoral pretén millorar el coneixement de la dinàmica estacional i el funcionament del compartiment pelàgic, centrant-se en les relacions tròfiques i la dinàmica energètica dels SMPF al nord-oest del mar Mediterrani. Es varen fer servir diferents tècniques per avançar en el coneixement del paper ecològic i funcional de diverses espècies de peixos pelàgics al mar Mediterrani occidental, incloent clupeoids, sorells i verats. En concret, es varen utilitzar anàlisi d'isòtops estables i de contingut estomacal en combinació amb índexs directes i indirectes de condició corporal, per estudiar la variació estacional del contingut d'energia en relació amb les seves estratègies de reproducció, preferències tròfiques i paper tròfic en la comunitat pelàgica. Els resultats van mostrar estabilitat en l'estructura tròfica al llarg de l'any amb una segregació tròfica dels peixos pelàgics petits en funció de l'etapa ontogenètica. Les diferències estacionals en la densitat energètica van estar altament relacionades amb la temporada de reproducció i la disponibilitat d'aliments. Per integrar tota aquesta informació i testar el paper de les pressions pote

Mediterranean marine ecosystems are fundamentally driven by their pelagic communities and small and medium-size pelagic fishes play crucial ecological roles. Although fluctuations of their populations have been mainly attributed to environmental variability and overfishing, there is still a lack of understanding on specific mechanisms that drive population changes, impairing the capability to predict future dynamics. Therefore, accurate scientific data at species and community level is needed at inter-annual and seasonal resolution. We used a multidisciplinary approach to advance on our knowledge about the ecological and functional role of several pelagic fish species in the western Mediterranean Sea, including clupeoids, horse mackerels and mackerels. We used energy density, stable isotope (nitrogen and carbon) and stomach content analyses to study seasonal variation in energy content in relation to their breeding strategies, feeding preferences and trophic role in the pelagic food-web. Results showed seasonal differences in energy density highly related with the spawning season and food availability, and differences in energy density and trophic niche between species. To integrate the new findings we developed a qualitative model combining sign directed graphs with an analysis of Bayesian belief networks to test the role of potential pressures on main species. Overall, results provide pivotal information to assist the adaptive management of pelagic fish species in the region