Northwestern Mediterranean Sea Research Articles

Rapid Restratification Processes Control Mixed Layer Turbulence and Phytoplankton Growth in a Deep Convection Region

AbstractThe Gulf of Lion, Northwestern Mediterranean Sea, is one of few oceanic regions where deep convection occurs. We investigate the restratification following a convection event using measurements from an ocean glider equipped with turbulence microstructure sensors. This unique combination of instruments provides a high‐resolution description of the mixed layer with regard to turbulence, stratification and chlorophyll. We observe a rapid restratification process that proceeds over a timescale of days to one week. We find that restratification exerts a leading order control on surface mixed layer turbulence variability, as abrupt changes in turbulence dissipation rates are associated with the formation of near‐surface stratification. The near‐surface formation of stratification occurs through both the diurnal variability in surface buoyancy fluxes and through lateral advective processes. We conclude that daily near‐surface processes that influence stratification control mixed layer turbulence levels, and thus the phytoplankton response in the critical transition period to spring bloom.

Selectivity-based management for reversing overexploitation of demersal fisheries in North-western Mediterranean Sea

Bottom trawling in the Mediterranean Sea has compromised the availability of demersal fishery resources, primarily due to decades of overexploitation beyond sustainability thresholds. Low selective bottom trawl nets have exacerbated this situation by catching large numbers of under-sized or immature individuals of targeted and not-targeted commercial species that are subsequently discarded. EU legislation requires EU Mediterranean countries to recover demersal fish stocks to sustainable levels by January 2025. This is a challenging requirement under current management scenarios that mainly focus on reducing fishing hours, compromising the activity of the fleets. While social networks among fishing fleets and fisherman associations are essential for facilitating the transition to sustainable exploitation, improving the selectivity of bottom trawl gears is proposed as a viable option beyond reducing fishing hours. This study presents the benefits of improving bottom trawlers net selectivity in multi-species NW Mediterranean coastal and deep-sea fisheries to reduce the catch of non-commercial sizes and discards. Data from selectivity experiments and literature review, fish market landings and a regional monitoring program in the FAO geographical sub-area 6 were used. Results indicate that in the short term, enhanced selectivity leads to an increase in the proportion of fish that are closer to their minimum conservation reference sizes or sizes at maturity, while minimising the impact on commercial catches. Sustainability may be achieved, though beyond 2025, with measures complementing selectivity. These include the adoption of semi-pelagic otter doors to mitigate the impact of trawlers on the seabed and the expansion of no-take marine reserves to ensure habitat recovery and spillover effects.

Meta-analysis of the Cetacea gut microbiome: Diversity, co-evolution, and interaction with the anthropogenic pathobiome

Despite their critical roles in marine ecosystems, only few studies have addressed the gut microbiome (GM) of cetaceans in a comprehensive way. Being long-living apex predators with a carnivorous diet but evolved from herbivorous ancestors, cetaceans are an ideal model for studying GM-host evolutionary drivers of symbiosis and represent a valuable proxy of overall marine ecosystem health. Here, we investigated the GM of eight different cetacean species, including both Odontocetes (toothed whales) and Mysticetes (baleen whales), by means of 16S rRNA-targeted amplicon sequencing. We collected faecal samples from free-ranging cetaceans circulating within the Pelagos Sanctuary (North-western Mediterranean Sea) and we also included publicly available cetacean gut microbiome sequences. Overall, we show a clear GM trajectory related to host phylogeny and taxonomy (i.e., phylosymbiosis), with remarkable GM variations which may reflect adaptations to different diets between baleen and toothed whales. While most samples were found to be infected by protozoan parasites of potential anthropic origin, we report that this phenomenon did not lead to severe GM dysbiosis. This study underlines the importance of both host phylogeny and diet in shaping the GM of cetaceans, highlighting the role of neutral processes as well as environmental factors in the establishment of this GM-host symbiosis. Furthermore, the presence of potentially human-derived protozoan parasites in faeces of free-ranging cetaceans emphasizes the importance of these animals as bioindicators of anthropic impact on marine ecosystems.

Limited spatiotemporal larval mixing of the Norway lobster from no‐take marine protected areas in the northwestern Mediterranean Sea

Abstract The larvae of many marine species are pelagic drifters in the vast oceans, yet they are the first and, for sessile species, the only way to connect with other populations. Connectivity is of particular interest in designing and assessing marine protected areas (MPAs), as it is considered a factor of renewal and stability. In this study, we focused on larval mixing between MPAs, investigating mixing rates during and at the end of their pelagic life, and how this is affected by the timing of larval release. We used a particle transport model coupled to the climatological hydrodynamics of the northwestern Mediterranean Sea to simulate the trajectories of Nephrops norvegicus larvae. Larvae were released from four no‐take MPAs, where fishery activity is banned, and started mixing between 7 and 12 days old. At settlement time, larval mixing mainly occurred between two pairs of MPAs labelled AxB (49.4% ± 5.8%) and CxD (23.7% ± 10.7%), respectively, located on the northern and southern sides of a thermal front. Percentages of larval mixing between these pairs changed, and other MPA combinations were formed with delayed larval release times. Mixing of larvae released from the same MPA tended to decrease with increasing delays between release times. This variability in mixing was related to the latitudinal distribution of MPAs along the continental slope and the spatiotemporal dynamics of the regional hydrodynamics, with a strong impact from a thermal front. Larval mixing modelling is a useful measure for understanding connectivity in marine environments and can suggest new conservation decisions. It identifies MPAs that are spatially distributed to facilitate the convergence of larvae from various protected areas. It also underlines that recognizing the significance of hydrodynamic variability when designing MPAs is crucial for promoting efficient connectivity among these areas.

Evaluation of the exposure of the Mediterranean biodiversity to marine litter: the ASI – plastic busters MPAs projects connection

A number of marine species in the Mediterranean are threatened by the presence of several pressure factors, which include climate change, collisions with vessels, entanglement and ingestion of marine litter, especially plastic. Risk reduction policies can only be conceived starting from an accurate analysis of the exposure to such pressure factors. To estimate spatial abundance of both marine species and plastic litter and to assess the exposure risk, a two-stage analysis approach was applied, using aerial survey data from the ACCOBAMS Survey Initiative (ASI), in synergy with the Plastic Busters MPAs (PB MPAs) project. First, a detection function was fitted to observation data to obtain detection probabilities for individuals, then a Generalized Additive Model (GAM) was employed to estimate the spatial distribution of relative abundance, based on survey observations. A bivariate Local Indicator of Spatial Association (LISA) was then applied to the maps of relative abundance to derive risk maps of exposure of marine species to marine litter. The maps, obtained with a spatial resolution of about 10 km, allow us to identify areas with the highest neighboring abundance of taxa and marine litter, in particular for the MPAs studied by the PB MPAs project, which include the North-Western Mediterranean (Pelagos Sanctuary and Tuscan Archipelago), the Ionian and Aegean Sea (Zakynthos), and the Strait of Sicily (Cabrera Archipelago).

Nesting of Caretta caretta in Tuscany area (north-western Mediterranean Sea): insights of a recent colonisation phenomenon

Nesting of Caretta caretta in Tuscany area (north-western Mediterranean Sea): insights of a recent colonisation phenomenon

Distribution and in vivo Observations of the Boa Dragonfish Stomias boa (Stomiidae) in Deep-Sea Canyon Ecosystems of the Northwestern Mediterranean Sea

Distribution and in vivo Observations of the Boa Dragonfish Stomias boa (Stomiidae) in Deep-Sea Canyon Ecosystems of the Northwestern Mediterranean Sea

Trace and rare earth elements in phytoplankton from the Tyrrhenian Sea (Italy).

Plankton plays a very crucial role in bioaccumulation and transfer of metals in the marine food web and represents a suitable bioindicator of the occurrence of trace and rare earth elements in the ecosystem. Trace elements and REEs were analyzed by ICP-MS in phytoplankton samples from the northwestern Mediterranean Sea. Metal concentrations in phytoplankton were found strongly influenced by seasons and depth of collection (- 30m, - 50m). Principal component analysis (PCA) has shown that Al, As, Cr, Cu, Ga, and Sn concentrations were related to summer and autumn in samples collected at 30m depth, while Fe, Mn, Ni, V, and Zn levels related strongly with summer and spring at 50m depth. Fe, Al, and Zn were the most represented elements in all samples (mean values respectively in the ranges 4.2-8.2, 9.6-13, and 1.0-4.4mgkg-1) according to their widespread presence in the environment and in the earth crust. Principal component analysis (PCA) performed on REEs showed that mostly all lanthanides' concentrations strongly correlate with summer and autumn seasons (- 30m depth); the highest ∑REE concentration (75µgkg-1) was found in winter. Phytoplankton REE normalized profile was comparable to those of other marine biota collected in the same area according to the suitability of lanthanides as geological tracers.

Targeting fin whale conservation in the North-Western Mediterranean Sea: insights on movements and behaviour from biologging and habitat modelling.

Biologging and habitat modelling are key tools supporting the development of conservation measures and mitigating theeffects of anthropogenic pressures on marine species. Here, we analysed satellite telemetry data and foraging habitat preferences in relation to chlorophyll-a productivity fronts to understand the movements and behaviour of endangered Mediterranean fin whales (Balaenoptera physalus) during their spring-summer feeding aggregation in the North-Western Mediterranean Sea. Eleven individuals were equipped with Argos satellite transmitters across 3 years, with transmissions averaging 23.5 ± 11.3 days. Hidden Markov Models were used to identify foraging behaviour, revealing how individuals showed consistency in their use of seasonal core feeding grounds; this was supported by the distribution ofpotential foraging habitat. Importantly, tracked whales spent most of their time in areas with no explicit protected status within the study region. This highlights the need for enhanced time- and place-based conservation actions to mitigate the effects of anthropogenic impacts for this species, notably ship strike risk and noise disturbance in an area of exceptionally high maritime traffic levels. These findings strengthen the need to further assess critical habitats and Important Marine Mammal Areas that are crucial for focused conservation, management and mitigation efforts.

Filling the gap: The unique isotopic niche of medium-sized and large sharks in the northwestern Mediterranean Sea

The Mediterranean Sea is considered a biodiversity hotspot and hosts a broad diversity of shark species. Unfortunately, many shark populations have suffered a long story of overexploitation and their abundance has strongly declined over the last decades. A few studies have addressed the trophic role of sharks in the northwestern Mediterranean Sea, yet little is known about their isotopic niches. In this study, the isotopic niches of six shark species (Alopias vulpinus, Galeorhinus galeus, Hexanchus griseus, Isurus oxyrinchus, Prionace glauca and Squalus acanthias) from the northwestern Mediterranean Sea were determined and compared with those of sympatric predatory teleosts and marine mammals. Overall, δ13C and δ15N values were similar amongst all the shark species except for the three individuals of G. galeus, whose high δ15N values indicate recent immigration from a distinct area with a different isotopic baseline and hence were excluded from further analysis. The mixing models identified cephalopods as the dominant prey of the other five shark species and revealed that the medium-sized and large shark species studied here filled unique isotopic niches. Their trophic positions were similar to those of predatory teleosts and small dolphins but lower than those of larger dolphins, pilot whales and beaked whales. The high contribution of cephalopods to the diet of sharks in the northwestern Mediterranean Sea might be indicative of fish scarcity and deserves further research in the context of potential ontogenetic diet changes.

Assessing the Plastisphere from Floating Plastics in the Northwestern Mediterranean Sea, with Emphasis on Viruses.

Plastics in the ocean create the "plastisphere", a diverse habitat hosting various life forms. Other than the pollution induced by plastics, the co-occurrence of primary producers, symbiotic organisms, decomposers, and pathogens within the plastisphere raises questions about how they influence the dynamics of marine ecosystems. Here, we used a shotgun DNA-sequencing approach to describe the species thriving on floating plastics collected in two Mediterranean sites. Our findings revealed many species of bacteria, eukaryotes, viruses, and archaea on each plastic. Proteobacteria was dominant (70% of reads in the entire dataset), with other groups such as Ascomycota fungi (11%) and Bacteroidetes (9%) also being represented. The community structure was not affected by the polymeric composition or the plastic shape. Notably, pathogenic Vibrio species, including V. campbelli, V. alginolyticus, and V. coralliilyticus, were among the most abundant species. Viruses, despite showing lower relative abundances, occurred in all samples, especially Herpesvirales, Caudovirales, and Poxviridae groups. A significant finding was the presence of the White Spot Syndrome virus (WSSV). This pathogen, responsible for devastating outbreaks in aquaculture systems, had not been previously reported in the marine plastisphere. Our study emphasizes the need for further investigation into the ecological and economic impacts of plastisphere organisms in the ocean.

Size at Sexual Maturity of Deep-Sea Unexploited Caribbean Metanephrops binghami (Boone, 1927) and Overexploited Mediterranean Nephrops norvegicus (Linnaeus, 1758) Using Morphometric and Gonadal Staging Approaches

The deep-sea Caribbean lobster (Metanephrops binghami) and the Norway lobster (Nephrops norvegicus) are Nephropidae species of high commercial interest. Although the first one still remains unexploited, the second is overexploited in the Mediterranean Sea. For effective fisheries management, size at sexual maturity is an essential indicator to protect immature individuals from exploitation. The estimation of this indicator can, however, be biased due to the difficulty of differentiating juveniles from adults by their size structure due to the natural process of molting. This study aims to estimate the size at sexual maturity of M. binghami and N. norvegicus females by comparing the effectiveness of the morphometric method versus the macroscopic evaluation of gonad maturity. Samples of M. binghami were collected from the Colombian Caribbean Sea in August and December 2009, March and May 2010, and August 2020 to May 2021. Samples of N. norvegicus were collected from the northwestern Mediterranean Sea from 2019 to 2022. Similar sizes at sexual maturity were found for M. binghami between the morphometric approach (ranging from 28.6 to 33.9 mm cephalothorax length, CL) and the gonadal staging approach (31.4 mm CL). Conversely, for N. norvegicus, the morphometric approach yielded higher measurements (between 27.2 and 30.4 mm CL) than the gonadal approach (26.0 mm CL). This discrepancy might stem from the intense fishing overexploitation conditions of N. norvergicus, leading to a physiological adaptation that enables earlier gonadal maturation at faster rates than morphometric adaptation. Further research is required to elucidate these discrepancies and the effect of overexploitation on physiological (i.e., mature gonads) and functional maturity (i.e., capacity to brood eggs at a larger size).

An update on the biological parameters of the Norway lobster (Nephrops norvegicus) in the northwestern Mediterranean Sea

Abstract The Norway lobster, Nephrops norvegicus, is one of the most valuable fishery resources in many coastal countries of the Mediterranean Sea and the northeastern Atlantic Ocean. In the Mediterranean Sea, several stocks are being overexploited, with ecological, economic, and social consequences. To perform an adequate stock assessment and provide guidance on maximum sustainable yield, reliable biological parameters of the species are required. Considering that biological parameters may change over time in overexploited populations, in the present study, we updated key biological parameters for the N. norvegicus stock of the northwestern Mediterranean Sea: size at which 50% (L50) of females were in reproductive condition, length–weight relationship, and individual size structure. Moreover, daily landings were combined with the spatial position of the vessels tracked by their Vessel Monitoring System (VMS), to obtain information on the geographical distribution and time series of Landings Per Unit Effort (LPUE), as well as total landings from 2008 to 2021. Our results suggest overexploitation of the resource, revealing a severe reduction in size at 50% maturity, an earlier spawning and brooding period, and a clear decrease of LPUE over time.

Mercury Mobility in Epibenthic Waters of a Deltaic Environment

AbstractMercury (Hg) cycling at the sediment‐water interfaces (SWI) encompasses multiple homogeneous and heterogeneous biogeochemical reactions whose result is not yet elucidated. Estuarine SWIs, where the organic matter mineralization is active, constitute experimental sites particularly suitable for scrutinizing Hg speciation and mobilization. Here, we present high‐resolution vertical concentration profiles of Hg species, including inorganic divalent Hg () and monomethyl Hg (MMHg) in solid and dissolved (<0.22 μm) phases, on both sides of the SWI of the proximal part of the Rhône prodelta (northwestern Mediterranean Sea) using sediment cores and dialyzers implemented for a 67‐day‐long period. Concentrations of the dissolved species were <0.10 nM in the sediment pore waters but reached up to 0.58 nM in the epibenthic water zone, a concentration level that is ∼200 times higher than that of the water column. Conversely, MMHg concentrations were low (<0.5 pM) above the SWI and increased to up to 4.6 pM in the sulfate‐reducing zones of the sediment. The dynamic of the Hg species interconversions was explored using one‐dimensional transport‐reaction equations. This model allowed us to constrain the depth intervals where various species are produced or consumed and to approximate the reaction rates. We conclude that the epibenthic zone of the Rhône prodelta is a location of intense mobilization of inorganic HgII associated with organic matter mineralization and MMHg distribution in pore water is controlled by microbiological in situ reactions, but sedimentary MMHg does not diffuse in the overlying water column.

The Heatwave of Summer 2022 in the North-Western Mediterranean Sea: Some Species Were Winners

The warming trend of the Mediterranean Sea is a long-term process. It has resulted in a northwards and westwards range expansion and abundance increase of thermophilic species, both native and non-indigenous, and in a shrinking of the range of cold-affinity species. Marine heatwaves (MHWs) are relatively short-term extreme episodes that are responsible for spectacular mortality events in some species and have been extensively reported in the literature. In contrast, the species that benefit from MHWs (the ‘winners’) have been much less studied. A record-breaking MHW occurred in 2022 in the north-western Mediterranean Sea. We focus on three ‘winner’ species, the thermophilic green macroalgae Penicillus capitatus and Microdictyon umbilicatum and the endemic seagrass Posidonia oceanica. Penicillus capitatus, which is mainly present in the area as an inconspicuous turf of entangled filaments (espera stage), produced the erect paintbrush-like stage where sexual reproduction takes place. Microdictyon umbilicatum, usually uncommon, bloomed to the point of clogging fishing nets. Finally, a mass flowering of P. oceanica occurred in late August–September, followed the following year (April–May 2023) by the extensive production and dissemination of fruits and seeds. Both processes, the long-term warming trend and one-off heatwaves, both ‘losers’ and ‘winners’, shape the change in structure and functioning of Mediterranean ecosystems.

Growth rates of marine prokaryotes are extremely diverse, even among closely related taxa.

Marine prokaryotes play crucial roles in ocean biogeochemical cycles, being their contribution strongly influenced by their growth rates. Hence, elucidating the variability and phylogenetic imprint of marine prokaryotes' growth rates are crucial for better determining the role of individual taxa in biogeochemical cycles. Here, we estimated prokaryotic growth rates at high phylogenetic resolution in manipulation experiments using water from the northwestern Mediterranean Sea. Experiments were run in the four seasons with different treatments that reduced growth limiting factors: predators, nutrient availability, viruses, and light. Single-amplicon sequence variants (ASVs)-based growth rates were calculated from changes in estimated absolute abundances using total prokaryotic abundance and the proportion of each individual ASV. The trends obtained for growth rates in the different experiments were consistent with other estimates based on total cell-counts, catalyzed reporter deposition fluorescence in situ hybridization subcommunity cell-counts or metagenomic-operational taxonomic units (OTUs). Our calculations unveil a broad range of growth rates (0.3-10 d-1) with significant variability even within closely related ASVs. Likewise, the impact of growth limiting factors changed over the year for individual ASVs. High numbers of responsive ASVs were shared between winter and spring seasons, as well as throughout the year in the treatments with reduced nutrient limitation and viral pressure. The most responsive ASVs were rare in the in situ communities, comprising a large pool of taxa with the potential to rapidly respond to environmental changes. Essentially, our results highlight the lack of phylogenetic coherence in the range of growth rates observed, and differential responses to the various limiting factors, even for closely related taxa.

Phytoplankton spring bloom in the NW Mediterranean Sea under climate change

The spring phytoplankton bloom is the main event influencing ecosystem richness in the pelagic realm of the Northwestern Mediterranean Sea (NW Med Sea). The Marine Strategy Framework Directive requires the achievement of a good ecological status for the pelagic habitat, and phytoplankton bloom phenology has been used as an indicator of the status of offshore waters. In this work we investigate interannual changes in the timing and magnitude of the phytoplankton bloom in the NW Med Sea, using phenological metrics. Daily maps of Chl-a concentration from 1998 to 2022 obtained by CMEMS were used to analyse bloom phenological metrics in 5 representative sites in the area. Chlorophyll-a data from 1998 to 2007 were used for determining the climatological behaviour, while 2008–2022 was identified as the study period. For this latter period, yearly spring bloom were identified and interannual variability and overall trends were analysed for each of the phenological metrics considered. Winter oceanographic and meteorological data were analysed to investigate possible correlations with the subsequent spring bloom. The frequency of anomalous years is increasing, both for bloom intensity and sea temperature. Bloom analysis revealed a negative trend only in some areas, but a steep decrease in the last 7 years was noticeable for all sites considered. Correlations of the Chl-a concentration during bloom with oceanographic variables revealed the importance of temperature, both marine and atmospheric, while Mixed Layer Depth played a lesser role. This work contributes to a better understanding of the dynamics of an area already under severe threat from human activities.

Seasonal stratification leads to changes within the benthic food web of the Gulf of Lions (northwestern Mediterranean)

Due to its extensive continental shelf, the Gulf of Lions, situated in the northwestern Mediterranean Sea, plays a crucial role in providing ecological services amidst various natural and anthropogenic pressures. Exposed to the impacts of climate change and suitable for marine energy development projects, the conservation of marine biodiversity in this environment raises significant concerns. To detect any potential disturbances in the functioning of the terrigenous mud community on the continental shelf, we conducted stable carbon and nitrogen isotope analyses on suspended particulate organic matter, sediments, and benthic fauna. Since seasonality is a structuring factor for the functioning of such an oligotrophic ecosystem, we conducted two sampling campaigns in 2018 to capture contrasting scenarios of water column stratification — one in April during well-mixed conditions and high phytoplankton production, and another in September at the end of the summer thermal stratification period characterized by low primary productivity. Stable isotope analysis revealed changes in the structure of the benthic food web in response to seasonal stratification of the water column. While isotopic niches of taxa remained evenly distributed, the total niche space contracted between sampling dates, primarily affecting low trophic level consumers. The observed contraction aligns with that reported at the base of the pelagic food web. These results enhance our understanding of the functioning of the continental shelf of the Gulf of Lions. The intense trawling pressure on the study site affected sampling. In this context, this research contributes not only to the knowledge of seasonal trophic variations but also provides a reference state to understand the future of this Mediterranean continental shelf.

Edible Sea urchin (Paracentrotus lividus) larval dispersal and connectivity modelling in the northwestern Mediterranean Sea

The edible sea urchin (Paracentrotus lividus) is of significant economic importance due to high demand for its consumption in various Mediterranean countries. This echinoderm plays a crucial ecological role by regulating the dynamics of seaweed and seagrass through its grazing behaviour. The abundance of sea urchin is variable in time and space, but it is currently potentially declining in the Mediterranean Sea, and likely to be negatively affected by global change. Therefore, gaining a more comprehensive understanding of sea urchin larval dispersal patterns over an extended period could contribute to our understanding of how their dynamics relate to population connectivity. To investigate the trajectories of larval dispersal of this sea urchin in the Northwestern Mediterranean Sea, we combined a Lagrangian model (Ichthyop) with a hydrodynamic model (MARS3D). This study covered the years 2010–2018 and aimed to quantify the connectivity between the preferred habitats of the sea urchin (seagrasses and rocky substrates). The present study explores seasonal variations in dispersal routes and habitat connectivity relationships for two spawning scenarios identified in the literature (spring and autumn). The results enable us to identify dispersal routes, and their regularity over time. They highlight a consistent connection between Sardinia, Corsica, and the coastlines of the Ligurian and Tyrrhenian Seas, indicating a lack of genetic structuring within the edible sea urchin population in this area, particularly in Corsica. The connectivity matrices confirm the observed dispersal trajectories and highlight certain areas of significant and enduring local retention over time. The results also reveal minimal seasonal variability. Conversely, interannual variability appears pronounced, particularly in relation with trends in the warming of surface waters in the Mediterranean, which seem to impact the dispersal routes taken by P. lividus larvae. Lastly, a connectivity map was created to explore spatial resource management perspectives, aiming to identify frequent connections over an extended time period and assign varying levels of intensity to them. This approach can provide guidance with regard to resource management issues for different coastal areas that can be connected by larvae.

Analysis of the state of conservation of Trachurus trachurus in the Western Mediterranean Sea based on the interannual (2009–2020) changes in their life history traits

Horse mackerel is a semi-pelagic fish widely distributed in the eastern Atlantic, where it represents a species of interest for fisheries and is subject to intense exploitation, leading to its global classification as a vulnerable species by IUCN. In the Northwestern (NW) Mediterranean Sea, the knowledge of their distribution, abundance and main biological parameters is fundamental to achieve their sustainable exploitation and contribute to the ecosystem approach to fisheries management. The time series (2009–2020) data set analyzed in this study came from two geographical subareas (GSAs) defined by the General Fisheries Commission for the Mediterranean (GFCM), Northern Spain (GSA06) and Northern Alboran Sea (GSA01) sampled in July during the MEDiterranean International Acoustic Survey (MEDIAS). Our results suggest that in summer, a higher concentration and aggregation of fish exists in GSA01, with a density ten times greater than in GSA06. Possible life history changes can be inferred through the analysis of the biological parameters of Trachurus trachurus in the NW Mediterranean Sea. In both GSAs, the annual decline of the size at first maturity (L50) and condition factor (Kn) was prominent. Moreover, the population structure lacked adult modes that could guarantee a successful recuperation of future stocks. Nonetheless, fish inhabiting GSA01 seem to have a better adaptive response to the events responsible for these alterations. In comparison, GSA01 is under less fishing pressure and the upwelling occurring in this area contributes to a higher availability of food, in addition to reducing the increases in sea surface temperature due to climate change during the study period.