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European sardine Sardina pilchardus is a commercially valuable coastal pelagic fish species. Spain is one of the largest sardine suppliers in Europe and the Iberian stock is of particular significance. Kudoa parasites are known to infect sardines causing the so-called ‘soft flesh’ condition; however, data on the occurrence of ‘soft flesh’ in this sardine stock are limited. This study investigates the occurrence of Kudoa-induced ‘soft flesh’ in the Iberian sardine stock caught in 2023 off the northern Spanish Atlantic coast (Division 8.c). Five hundred specimens were examined for ‘soft flesh’ by manual texture testing and visual inspection 48 h post-catch using standardized procedures. ‘Soft flesh’ was detected in 5.4% (27/500) of the sardines. Microscopic examination of muscle samples revealed the presence of Kudoa thyrsites–like myxospores in all ‘soft flesh’–affected fish, which based on SSU rDNA gene sequence analysis was identified as K. thyrsites. The unsightly appearance of infected fillets represents a substantial food quality issue for the Iberian sardine stock that could reduce marketability and consumer confidence in both local and international markets. This is particularly relevant since larger Iberian sardines, which are highly appreciated by consumers, appear to be the most affected.

Marine litter impacts oceans and affects marine organisms, representing a potential threat for natural stocks of pelagic fish species located at the first levels of the marine food webs. In 2013–2014, on a seasonal basis, marine litter and microplastics in stomach contents from Sardinia pilchardus and Engraulis encrasicolus were evaluated. Selected species are plankitivores of great ecological and commercial importance in the Adriatic Sea. Collected data were correlated to possible factors able to affect ingested levels as well as species, season of sampling, biometry and sex of animals. Almost all tested samples (80 organisms for each species) contained marine litter (over 90% of samples from both species) and also microplastics; while any meso- or macroplastics were recorded. On average, recorded items were as follows: 4.63 ( S. plichardus ) and 1.25 ( E. encrasicolus ) per individual. Sardines evidenced a higher number of microplastics characterised by a smaller size than those recorded in anchovies . For sardines, sex, Gastro Somatic Index and sampling season showed negligible effects on the number of ingested litter; conversely, anchovies showed differences related with both sex of animals and dominant colour of ingested materials with prevalence for black and blue colours.

Population dynamics of small pelagic fishes (SPF) and their management in Japan were reviewed for Japanese sardine Sardinops melanostictus, Japanese anchovy Engraulis japonicus, chub mackerel Scomber japonicus, and Pacific saury Cololabis saira. The catch and biomass of SPF generally showed decadal-scale variability with prominent species replacements since the 1900s. The causes of species replacements were generally associated with climatic/oceanic variability, particularly “regime shifts,” of which the 1988/89 regime shift was the most influential since the 1970s. Variability in the early survival rate is a key factor for population fluctuations, and the proposed hypothetical mechanisms of recruitment variability are summarized herein. Although overfishing during the 1990s and early 2000s prevented the recovery of Pacific stocks of sardine and chub mackerel, they have been recovering since the mid-2000s owing to strong year classes and reduced exploitation rates. The fundamental cause of overfishing was derived from a mismatch between investments in larger purse seine fleets during the 1980s and poor ocean productivity since the 1988/89 regime shift, when dominant SPF began to shift from sardine to anchovy. Recommendations for fisheries management of SPF around the Japanese Archipelago are proposed, considering climate change and naturally and drastically changing SPF populations.

Upwelling of nutrient-rich, subsurface water sustains high productivity in the ocean's eastern boundary currents. These ecosystems support a rate of fish harvest nearly 100 times the global mean and account for >20% of the world's marine fish catch. Environmental variability is thought to be the major cause of the decadal-scale biomass fluctuations characteristic of fish populations in these regions, but the mechanisms relating atmospheric physics to fish production remain unexplained. Two atmospheric conditions induce different types of upwelling in these ecosystems: coastal, alongshore wind stress, resulting in rapid upwelling (with high vertical velocity, w); and wind-stress curl, resulting in slower upwelling (low w). We show that the level of wind-stress curl has increased and that production of Pacific sardine (Sardinops sagax) varies with wind-stress curl over the past six decades. The extent of isopycnal shoaling, nutricline depth, and chlorophyll concentration in the upper ocean also correlate positively with wind-stress curl. The size structure of plankton assemblages is related to the rate of wind-forced upwelling, and sardine feed efficiently on small plankters generated by slow upwelling. Upwelling rate is a fundamental determinant of the biological structure and production in coastal pelagic ecosystems, and future changes in the magnitude and spatial gradient of wind stress may have important and differing effects on these ecosystems. Understanding of the biological mechanisms relating fisheries production to environmental variability is essential for wise management of marine resources under a changing climate.

Populations of small pelagic fish are strongly influenced by climate. The inability of managers to anticipate environment-driven fluctuations in stock productivity or distribution can lead to overfishing and stock collapses, inflexible management regulations inducing shifts in the functional response to human predators, lost opportunities to harvest populations, bankruptcies in the fishing industry, and loss of resilience in the human food supply. Recent advances in dynamical global climate prediction systems allow for sea surface temperature (SST) anomaly predictions at a seasonal scale over many shelf ecosystems. Here we assess the utility of SST predictions at this \"fishery relevant\" scale to inform management, using Pacific sardine as a case study. The value of SST anomaly predictions to management was quantified under four harvest guidelines (HGs) differing in their level of integration of SST data and predictions. The HG that incorporated stock biomass forecasts informed by skillful SST predictions led to increases in stock biomass and yield, and reductions in the probability of yield and biomass falling below socioeconomic or ecologically acceptable levels. However, to mitigate the risk of collapse in the event of an erroneous forecast, it was important to combine such forecast-informed harvest controls with additional harvest restrictions at low biomass.

Integrated information from different parts of the Mediterranean Sea was used to model the spatial and temporal variability of the distribution grounds of the sardine population. Acoustic data from the North Aegean Sea (Eastern Mediterranean), the Adriatic Sea (Central Mediterranean), the Sicily Channel (Central Mediterranean) and Spanish Mediterranean waters (Western Mediterranean) were analysed along with satellite environmental and bathymetric data to model the potential habitat of sardine during summer, autumn and early winter. Generalized additive models were applied in a presence-absence approach. Models were validated in terms of their predictive ability and used to construct maps exhibiting the probability of sardine presence throughout the entire Mediterranean basin as a measure of habitat adequacy for sardine. Bottom depth and sea surface temperature were the environmental variables that explained most of the data variability. Several areas along the Mediterranean coastline were indicated as suitable habitat for sardine in different seasons. An expansion of these areas over the continental shelf, up to 100 m depth, was consistently noticed from summer to winter. This was attributed to the horizontal movements of sardine related to spawning (i.e. winter period) and the peculiarities of the Mediterranean Sea where areas favouring growth, feeding and spawning processes tend to be localised and prevent a long range, offshore migration as opposed to large upwelling ecosystems. Moreover, within the study period, a positive relationship between the extent of sardine preferred habitat and landings was revealed for both summer and winter seasons throughout the entire Mediterranean Sea.

The detection of causal interactions is of great importance when inferring complex ecosystem functional and structural networks for basic and applied research. Convergent cross mapping (CCM) based on nonlinear state-space reconstruction made substantial progress about network inference by measuring how well historical values of one variable can reliably estimate states of other variables. Here we investigate the ability of a developed optimal information flow (OIF) ecosystem model to infer bidirectional causality and compare that to CCM. Results from synthetic datasets generated by a simple predator-prey model, data of a real-world sardine-anchovy-temperature system and of a multispecies fish ecosystem highlight that the proposed OIF performs better than CCM to predict population and community patterns. Specifically, OIF provides a larger gradient of inferred interactions, higher point-value accuracy and smaller fluctuations of interactions and α -diversity including their characteristic time delays. We propose an optimal threshold on inferred interactions that maximize accuracy in predicting fluctuations of effective α -diversity, defined as the count of model-inferred interacting species. Overall OIF outperforms all other models in assessing predictive causality (also in terms of computational complexity) due to the explicit consideration of synchronization, divergence and diversity of events that define model sensitivity, uncertainty and complexity. Thus, OIF offers a broad ecological information by extracting predictive causal networks of complex ecosystems from time-series data in the space-time continuum. The accurate inference of species interactions at any biological scale of organization is highly valuable because it allows to predict biodiversity changes, for instance as a function of climate and other anthropogenic stressors. This has practical implications for defining optimal ecosystem management and design, such as fish stock prioritization and delineation of marine protected areas based on derived collective multispecies assembly. OIF can be applied to any complex system and used for model evaluation and design where causality should be considered as non-linear predictability of diverse events of populations or communities.

The European sardine (Sardina pilchardus, Walbaum 1792) is indisputably a commercially important species. Previous studies using uneven sampling or a limited number of makers have presented sometimes conflicting evidence of the genetic structure of S. pilchardus populations. Here, we show that whole genome data from 108 individuals from 16 sampling areas across 5000 km of the species’ distribution range (from the Eastern Mediterranean to the archipelago of Azores) support at least three genetic clusters. One includes individuals from Azores and Madeira, with evidence of substructure separating these two archipelagos in the Atlantic. Another cluster broadly corresponds to the center of the distribution, including the sampling sites around Iberia, separated by the Almeria–Oran front from the third cluster that includes all of the Mediterranean samples, except those from the Alboran Sea. Individuals from the Canary Islands appear to belong to the Mediterranean cluster. This suggests at least two important geographical barriers to gene flow, even though these do not seem complete, with many individuals from around Iberia and the Mediterranean showing some patterns compatible with admixture with other genetic clusters. Genomic regions corresponding to the top outliers of genetic differentiation are located in areas of low recombination indicative that genetic architecture also has a role in shaping population structure. These regions include genes related to otolith formation, a calcium carbonate structure in the inner ear previously used to distinguish S. pilchardus populations. Our results provide a baseline for further characterization of physical and genetic barriers that divide European sardine populations, and information for transnational stock management of this highly exploited species towards sustainable fisheries.

Background Nutrition therapy is the cornerstone of treating diabetes mellitus. The inclusion of fish (particularly oily fish) at least two times per week is recommended by current international dietary guidelines for type 2 diabetes. In contrast to a large number of human studies examining the effects of oily fish on different cardiovascular risk factors, little research on this topic is available in patients with type 2 diabetes. The aims of this pilot study were to investigate the effects of a sardine-enriched diet on metabolic control, adiponectin, inflammatory markers, erythrocyte membrane fatty acid (EMFA) composition, and gut microbiota in drug-naïve patients with type 2 diabetes. Methods 35 drug-naïve patients with type 2 diabetes were randomized to follow either a type 2 diabetes standard diet (control group: CG), or a standard diet enriched with 100 g of sardines 5 days a week (sardine group: SG) for 6 months. Anthropometric, dietary information, fasting glycated hemoglobin, glucose, insulin, adiponectin, inflammatory markers, EMFA and specific bacterial strains were determined before and after intervention. Results There were no significant differences in glycemic control between groups at the end of the study. Both groups decreased plasma insulin (SG: −35.3 %, P  = 0.01, CG: −22.6 %, P  = 0.02) and homeostasis model of assessment - insulin resistance (HOMA-IR) (SG: −39.2 %, P  = 0.007, CG: −21.8 %, P  = 0.04) at 6-months from baseline. However only SG increased adiponectin in plasma compared to baseline level (+40.7 %, P  = 0.04). The omega-3 index increased 2.6 % in the SG compared to 0.6 % in the CG ( P  = 0.001). Both dietary interventions decreased phylum Firmicutes (SG and CG: P  = 0.04) and increased E. coli concentrations (SG: P  = 0.01, CG: P  = 0.03) at the end of the study from baseline, whereas SG decreased Firmicutes / Bacteroidetes ratio ( P  = 0.04) and increased Bacteroides-Prevotella ( P  = 0.004) compared to baseline. Conclusions Although enriching diet with 100 g of sardines 5 days a week during 6 months to a type 2 diabetes standard diet seems to have neutral effects on glycemic control in drug-naïve patients with type 2 diabetes, this nutritional intervention could have beneficial effects on cardiovascular risk. Furthermore, both dietary interventions decreased HOMA-IR and altered gut microbiota composition of drug-naïve patients with type 2 diabetes. Trial registration Trial number and name of the registry: NCT02294526 , ClinicalTrials.gov