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For small pelagic fish, the physical and feeding environments during the larval and juvenile periods significantly affect recruitment to standing stock. To understand the variation in environmental conditions experienced by larvae and juveniles, this study determined the distribution of larval and juvenile Pacific saury Cololabis saira over a distance of more than 6900 km in an east–west direction in relation to the ocean environment in winter. Specimens were collected from the western and central parts of the North Pacific Ocean, mainly in January and February 2018 and 2020. Larvae (≤39.9 mm) were broadly distributed around the Kuroshio Current and the Kuroshio Extension Current. Larval densities in the water masses around the Kuroshio Extension Current were as high as, or even significantly higher than, those around the Kuroshio Current, which is considered the main spawning ground. Most juveniles (≥40.0 mm) were captured north of the Kuroshio Extension Current, where sea surface temperatures were lower and chlorophyll a concentrations were higher. The generalized additive model analysis also suggested that, compared to larvae, juveniles tended to be distributed in areas with lower sea surface temperatures and in more eastern areas. The extensive distribution of Pacific saury larvae and juveniles indicates that it is necessary to focus not only on the marine environment around the Kuroshio region but also on the Kuroshio Extension region to understand the recruitment variability of this species. [ABSTRACT FROM AUTHOR]

The development of management strategies for the promotion of sustainable fisheries relies on a deep knowledge of ecological and evolutionary processes driving the diversification and genetic variation of marine organisms. Sustainability strategies are especially relevant for marine species such as the European sardine (Sardina pilchardus), a small pelagic fish with high ecological and socioeconomic importance, especially in Southern Europe, whose stock has declined since 2006, possibly due to environmental factors. Here, we generated sequences for 139 mitochondrial genomes from individuals from 19 different geographical locations across most of the species distribution range, which was used to assess genetic diversity, diversification history and genomic signatures of selection. Our data supported an extensive gene flow in European sardine. However, phylogenetic analyses of mitogenomes revealed diversification patterns related to climate shifts in the late Miocene and Pliocene that may indicate past divergence related to rapid demographic expansion. Tests of selection showed a significant signature of purifying selection, but positive selection was also detected in different sites and specific mitochondrial lineages. Our results showed that European sardine diversification has been strongly driven by climate shifts, and rapid changes in marine environmental conditions are likely to strongly affect the distribution and stock size of this species. [ABSTRACT FROM AUTHOR]

Fishing operations of floating lift net have a close relationship with its distribution, as the distribution of floating lift net can affect fish catches. Along with the development of satellite image technology, it can be utilized to monitor the distribution of floating lift net. This research aims to determine the distribution pattern of floating lift net in Palabuhanratu Bay Waters and identify fishing operations on floating lift net in Palabuhanratu Bay Waters. Primary data collection was carried out by interviewing and observing fishermen. Secondary data collection utilized Sentinel-2 satellite imagery in 2019-2023 in the waters of Palabuhanratu Bay, then the results of satellite image recordings were manually digitized using ArcGIS software. The points of distribution of floating lift net resulting from manual digitization were analyzed using nearest neighbor analysis, the results of which were in the form of the T index. The results of the nearest neighbor analysis (T index) in Palabuhanratu Bay Waters in 2019-2023 were 1.23, 1.09, 1.14, 0.90, and 0.95, which means that for 5 years the distribution pattern of floating lift net in Palabuhanratu Bay Waters is random. Floating lift net operation consists of preparation, going to the fishing ground, lowering the net (setting), pulling the net (hauling), and homing back to the fishing base. Floating lift net operations is carried out in one day fishing. The catches of floating lift net in Palabuhanratu Bay waters includes small pelagic fish. [ABSTRACT FROM AUTHOR]

Energy content has long been proposed as a fundamental, integrated, and reliable indicator of the condition of individuals as it reflects past bioenergetics and influences future life‐history traits. There is a direct biochemical link between energy density and body composition described by four main compounds in fish (protein, lipid, ash, and water), with proteins and lipids being the sources of energy. If relationships between water content, or lipid content, and energy density have been well described in relative terms, the absolute mass variations in the proximate composition have been overlooked and thus their interpretation is often equivocal. In our study, based on a large and unique dataset on the proximate composition and energy density of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) from sampling in the Bay of Biscay and the English Channel, we aimed to better explain the patterns between water content and other proximate components or energy density, based on the dynamics of proteins, lipids, and water absolute masses. For the first time, we defined good, intermediate, and poor condition states in wild fish, based on water content, corresponding to the different dynamics of lipids and proteins in the metabolism of individuals. Anchovy and sardine exhibited remarkably similar patterns of variation in the compounds and in the limits between the condition states with respect to water content. Those patterns revealed that water mass remained constant for a given fish size whatever its condition state, and that variability in water content only resulted from the variation in lipid and protein masses. Furthermore, the differential dynamics of proteins and lipids, with only lipids mobilized in the good condition state, only proteins in the poor condition state, and both proteins and lipids in the intermediate condition state, elucidates the nonlinear pattern observed in the relationship between energy density and water content. Overall, our results highlight the importance of monitoring the intraspecific variations in water content to predict the proximate composition and energy content in small pelagic fish and better assess individual and population conditions in changing ecosystems as well as to better parameterize bioenergetic models. [ABSTRACT FROM AUTHOR]

The effect of the combination of marine toxins produced by algal blooms, in conjunction with varying environmental characteristics on organisms in the water column, is a poorly explored research field. Pelagic fish species of commercial importance, such as anchoveta (Engraulis ringens) in central Chile, may be exposed to these combined factors in a climate change scenario. This is observed from documented changes in the length of the upwelling season, frequency of upwelling events, and the increased frequency of atmospheric rivers affecting the southern spawning zone of this species. This study evaluated the integrity of hair cells in neuromasts, mechanosensory organs present in fish larvae, under exposure to different combinations of the algal bloom-produced okadaic acid OA (1 ng mL1), and two temperature (12 and 14°C), and salinity treatments (historically more frequent: 34 PSU- 12°C; expected: 32 PSU - 14°C). Viable hair cells were counted in newly hatched larvae from the Biobıo region, central Chile. Results showed a significant decrease in the average number of viable hair cells per neuromast (from 6.1 ± 1.6 to 4.0 ± 1.2) under lower salinity treatments (32 PSU) compared to normal conditions. Additionally, a seasonal trend was observed with fewer viable cells (from 7.4 ± 1.2 to 4.4 ± 1.1) as the fish species' reproductive period progressed. The combined effect of OA exposure and modifications with the environmental factors also resulted in a significant decrease of up to 70% in the number of viable hair cells in larvae exposed to OA and high temperatures, indicating damage influenced by the toxin along with a synergistic and/or additive role of temperature. These findings reveal how the lipophilic toxin okadaic acid, produced by harmful algal blooms, interacts with abiotic environmental factors affecting coastal ecologically and socio-economically important organisms. This emphasizes the need to consider multiple factors when studying the effects of marine toxins. [ABSTRACT FROM AUTHOR]

Small pelagic fish (SPF) are crucial in marine food webs, transferring energy from plankton to higher trophic levels. This study focuses on herring (Clupea harengus) and sprat (Sprattus sprattus), addressing knowledge gaps in their feeding ecology in a nursery area, the Dutch Wadden Sea. We conducted a year-long, monthly survey, and used DNA metabarcoding to analyse zooplankton samples and stomach contents of two size classes of herring and sprat. Intra-, interspecific, and seasonal variations in fish condition, stomach fullness, and diet composition, along with selective feeding, were studied. Our study showed that condition and diet composition of herring and sprat, along with zooplankton density, exhibited a clear seasonal pattern. Juvenile herring and sprat displayed opportunistic feeding behaviour, rather than showing distinct prey selection. Besides copepods, we regularly observed (larvae of) benthic invertebrates in their diet. This emphasizes the crucial role of SPF as energy transfer agents, not solely between trophic levels, but also from benthic to pelagic habitats. Furthermore, fish post-larvae were part of the diet of larger herring (10–15 cm). Because of its unprecedented temporal and taxonomical detail, this study advances the understanding of seasonal dynamics of dominant components at the base of the Wadden Sea food web. [ABSTRACT FROM AUTHOR]

Indonesia's marine resources are abundant, with fishing being a primary focus. The effective management of these resources requires an understanding of the factors that influence them, such as sea surface temperature (SST), El Niño-Southern Oscillation (ENSO) as indicated by the Southern Oscillation Index (SOI), and chlorophyll-a levels as food sources. This research aimed to elucidate the relationships among those factors at Madura Strait by utilizing their characteristics in response to the electromagnetic wavelengths that can be found Landsat 9 OLI/TIRS satellite images. This research utilized the satellite's Thermal Infrared Sensor (or Band 10) (10.6-11.19 µm) to obtain the SST levels as well as the OceanColor 2 (OC2) algorithm to process Band 2 (0.45-0.51 µm) and Band 3 (0.53-0.59 µm) in order to obtain the chlorophyll-a levels. The results were the mean values of the SST (21.42 and 20.60°C) and the chlorophyll-a levels (0.77 and 0.87 mg/m³) from the periods of June through August 2 022 and December 2 022 through February 2023, respectively. Furthermore, a correlation test and t-test were conducted, which indicated that the chlorophyll-a levels were contradictory with the SST, SOI, and total pelagic fish catches (which were in alignment). The t-test results only indicated significant correlations between the SST and chlorophyll-a levels (-0.806) and between the SST and SOI (0.732), while the other correlation was not significant. [ABSTRACT FROM AUTHOR]

This article discusses the feeding behavior of Atlantic herring in coastal waters, specifically in Greifswald Bay in the Baltic Sea. The researchers found that adult herring caught in the fall had unexpectedly consumed demersal fishes and large invertebrates, rather than the expected zooplankton. This behavior was consistent over multiple years of sampling. In contrast, herring stomachs in the spring were mostly empty. The study highlights the importance of considering the feeding traits of marine fish in population models and the need for more holistic approaches in food web science. [Extracted from the article]

The need to transition from traditional single-species fisheries management approaches towards ecosystem-based fisheries management (EBFM), or an ecosystem approach to fisheries, is widely recognised. EBFM is particularly important when considering management actions for economically valuable fisheries for small pelagic forage fish, given their key ecological role. Management strategy evaluation (MSE) is an effective approach to advance the quantitative implementation of EBFM by enabling stakeholders to explore trade-offs among competing ecosystem-related objectives. This paper puts forward six different approaches to advance EBFM with MSE explicity, by taking advantage of data and research already available and by guiding future research. These approaches can be grouped into those which (i) involve the operating model and/or link directly to the operating model while potentially providing additional performance metrics to evaluate ecosystem objectives, (ii) can be incorporated into the performance metrics, and (iii) involve the harvest control rule of the management procedure. This review demonstrates that immediate steps can be taken to implement EBFM targeted at quantitative tactical management, even without a complex, data-rich ecosystem operating model. [ABSTRACT FROM AUTHOR]

Abstract Climate change is recognised to lead to spatial shifts in the distribution of small pelagic fish, likely by altering their environmental optima. Fish supply along the Northwest African coast is significant at both socio-economic and cultural levels. Evaluating the impacts of climatic change on small pelagic fish is a challenge and of serious concern in the context of shared stock management. Evaluating the impact of climate change on the distribution of small pelagic fish, a trend analysis was conducted using data from 2363 trawl samplings and 170,000 km of acoustics sea surveys. Strong warming is reported across the Southern Canary Current Large Marine Ecosystem (CCLME), extending from Morocco to Senegal. Over 34 years, several trends emerged, with the southern CCLME experiencing increases in both wind speed and upwelling intensity, particularly where the coastal upwelling was already the strongest. Despite upwelling-induced cooling mechanisms, sea surface temperature (SST) increased in most areas, indicating the complex interplay of climatic-related stressors in shaping the marine ecosystem. Concomitant northward shifts in the distribution of small pelagic species were attributed to long-term warming trends in SST and a decrease in marine productivity in the south. The abundance of Sardinella aurita, the most abundant species along the coast, has increased in the subtropics and fallen in the intertropical region. Spatial shifts in biomass were observed for other exploited small pelagic species, similar to those recorded for surface isotherms. An intensification in upwelling intensity within the northern and central regions of the system is documented without a change in marine primary productivity. In contrast, upwelling intensity is stable in the southern region, while there is a decline in primary productivity. These environmental differences affected several small pelagic species across national boundaries. This adds a new threat to these recently overexploited fish stocks, making sustainable management more difficult. Such changes must motivate common regional policy considerations for food security and sovereignty in all West African countries sharing the same stocks.

The effect of the combination of marine toxins produced by algal blooms, in conjunction with varying environmental characteristics on organisms in the water column, is a poorly explored research field. Pelagic fish species of commercial importance, such as anchoveta (Engraulis ringens) in central Chile, may be exposed to these combined factors in a climate change scenario. This is observed from documented changes in the length of the upwelling season, frequency of upwelling events, and the increased frequency of atmospheric rivers affecting the southern spawning zone of this species. This study evaluated the integrity of hair cells in neuromasts, mechanosensory organs present in fish larvae, under exposure to different combinations of the algal bloom-produced okadaic acid OA (1 ng mL−1), and two temperature (12 and 14°C), and salinity treatments (historically more frequent: 34 PSU- 12°C; expected: 32 PSU - 14°C). Viable hair cells were counted in newly hatched larvae from the Biobío region, central Chile. Results showed a significant decrease in the average number of viable hair cells per neuromast (from 6.1 ± 1.6 to 4.0 ± 1.2) under lower salinity treatments (32 PSU) compared to normal conditions. Additionally, a seasonal trend was observed with fewer viable cells (from 7.4 ± 1.2 to 4.4 ± 1.1) as the fish species’ reproductive period progressed. The combined effect of OA exposure and modifications with the environmental factors also resulted in a significant decrease of up to 70% in the number of viable hair cells in larvae exposed to OA and high temperatures, indicating damage influenced by the toxin along with a synergistic and/or additive role of temperature. These findings reveal how the lipophilic toxin okadaic acid, produced by harmful algal blooms, interacts with abiotic environmental factors affecting coastal ecologically and socio-economically important organisms. This emphasizes the need to consider multiple factors when studying the effects of marine toxins.

Abstract Declines in individuals' growth in exploited fish species are generally attributed to evolutionary consequences of size‐selective fishing or to plastic responses due to constraints set by changing environmental conditions dampening individuals' growth. However, other processes such as growth compensation and non‐directional selection can occur and their importance on the overall phenotypic response of exploited populations has largely been ignored. Using otolith growth data collected in European anchovy and sardine of the Bay of Biscay (18 cohorts from 2000 to 2018), we parameterized the breeder's equation to determine whether declines in size‐at‐age in these species were due to an adaptive response (i.e. related to directional or non‐directional selection differentials within parental cohorts) or a plastic response (i.e. related to changes in environmental). We found that growth at age‐0 in anchovy declined between parents and their offspring when biomass increased and the selective disappearance of large individuals was high in parents. Therefore, an adaptive response probably occurred in years with high fishing effort and the large increase in biomass after the collapse of this stock maintained this adaptive response subsequently. In sardine offspring, higher growth at age‐0 was associated with increasing biomass between parents and offspring, suggesting a plastic response to a bottom‐up process (i.e. a change in food quantity or quality). Parental cohorts in which selection favoured individuals with high growth compensation produced offspring high catch up growth rates, which may explain the smaller decline in growth in sardine relative to anchovy. Finally, on non‐directional selection differentials were not significantly related to the changes in growth at age‐0 and growth compensation at age‐1 in both species. Although anchovy and sardine have similar ecologies, the mechanisms underlying the declines in their growth are clearly different. The consequences of the exploitation of natural populations could be long lasting if density‐dependent processes follow adaptive changes.

Cenderawasih Bay is one of the territorial waters of Indonesia with high fishery potential. In 2022, the Indonesian Goverment revealed that the bay's small pelagic fishery potential reached 135, 140 t, yet the utilization rate remains at only 0.3, indicating underutilization. This shows the necessity of estimating fish distribution in the bay to maximize the use of small pelagic fisheries resources. The hydroacoustic method, known for its extensive survey coverage and minimal environmental impact, can be employed to estimate the distribution of small pelagic fish. Therfore, this research aims to investigate the distribution of acoustic parameters of small pelagic fish using a split beam echosounder, specifically the SIMRAD EY-60, to obtain fish SV value and distribution data. SV (Scattering Volume) values were coverted to TS (Target Strength) values and projected onto a spatial distribution map. The distribution of fish exhibited a varied range of values, with the highest SV value ranging from -59.7 to -57.4 dB and the highest TS values ranging from -59.4 to -46.7 dB. Fish distribution was more concentrated in areas with warmer temperatures and dispersed evenly across different salinity ranges, with a higher concentration of fish detected in areas with elevated chlorophyll levels. [ABSTRACT FROM AUTHOR]

Simple Summary: Between 2019 and 2022, scientific pelagic trawl surveys in the Western Black Sea monitored the biomass of sprat and moon jellyfish and their spatial variability in the summer. Investigations into the correlation patterns between the two plankton-feeding species revealed that gelatinous plankton can have a weak-to-moderate effect on the spatial distribution of sprat assemblages in coastal areas. Over the past few decades, various causal connections between commercial small pelagic fish species and gelatinous zooplankton have been reported in the Black Sea, which affect the pelagic ecosystem. Recently, moon jellyfish regained dominance among gelatinous plankton; however, biomass fluctuations and interactions with small pelagic fish remain poorly understood. During the summers of 2019–2022, scientific pelagic trawl surveys in the Western Black Sea enabled simultaneous monitoring of small pelagic fish biomass, with sprat as the key species and moon jellyfish as an incidental catch. In total, 153 trawl hauls were conducted across four depth strata from 15 to 100 m, and a "swept area" method was used for biomass estimation. The sprat stock biomass ranged from 10,698 to 29,177 t, with an average value of 19,432 ± 4834 t. The total biomass of moon jellyfish was 2002 ± 868.73 t, and dense aggregations were observed in the coastal waters during certain years. Two scenarios of spatial interactions between planktivorous species were identified and linked to the formation of A. aurita aggregations. We found that changes in jellyfish density were associated with weak-to-moderate effects on the spatial distribution of sprat assemblages in coastal areas. [ABSTRACT FROM AUTHOR]

The Northwest Pacific Ocean is one of the most productive fisheries in the world, with small pelagic fish constituting a substantial portion of its fishery resources. Changes in abiotic factors can affect the distribution of marine fish, but there are limited studies on the relationship between abiotic factors and fish density in a vertical direction. This study used acoustic measurement data collected by the scientific research vessel “Songhang” equipped with a Simrad EK 80 scientific echosounder from June to July 2022, to estimate the small pelagic fish resource density in different water layers from 0 to 200 m. Furthermore, Generalized Additive Models (GAMs) were established for various water layers, combined with remote sensing data such as temperature (Temp), salinity (Sal), net primary productivity (Nppv), as well as latitude (Lat) and longitude (Lon) data, to analyze the influence of abiotic factors on abundance density of small pelagic fish species. The results showed that mean abundance and biomass densities estimated based on the acoustic method were 3.12×105±1.42×106 ind/n mile2 and 5768.39±26224.76 kg/n mile2, respectively. Small pelagic fish resources exhibited a predominant concentration within the 0–50 m layers and displayed a significant accumulation phenomenon near the Kuroshio Extension area in each water layer. The GAMs results indicated that abiotic factors affecting fish density vary across different water layers. Temp and Lon factors appeared in optimal GAMs for all water layers and significantly contributed to fish density. Variations in temperature lead to differences in the vertical distribution of fishery resources. Our results emphasized the necessity of exploring the relationship between abiotic factors and fish density within different water layers. This research can provide scientific support for developing and managing fishery resources in the Northwest Pacific Ocean.

Declines in individuals' growth in exploited fish species are generally attributed to evolutionary consequences of size‐selective fishing or to plastic responses due to constraints set by changing environmental conditions dampening individuals' growth. However, other processes such as growth compensation and non‐directional selection can occur and their importance on the overall phenotypic response of exploited populations has largely been ignored. Using otolith growth data collected in European anchovy and sardine of the Bay of Biscay (18 cohorts from 2000 to 2018), we parameterized the breeder's equation to determine whether declines in size‐at‐age in these species were due to an adaptive response (i.e. related to directional or non‐directional selection differentials within parental cohorts) or a plastic response (i.e. related to changes in environmental). We found that growth at age‐0 in anchovy declined between parents and their offspring when biomass increased and the selective disappearance of large individuals was high in parents. Therefore, an adaptive response probably occurred in years with high fishing effort and the large increase in biomass after the collapse of this stock maintained this adaptive response subsequently. In sardine offspring, higher growth at age‐0 was associated with increasing biomass between parents and offspring, suggesting a plastic response to a bottom‐up process (i.e. a change in food quantity or quality). Parental cohorts in which selection favoured individuals with high growth compensation produced offspring high catch up growth rates, which may explain the smaller decline in growth in sardine relative to anchovy. Finally, on non‐directional selection differentials were not significantly related to the changes in growth at age‐0 and growth compensation at age‐1 in both species. Although anchovy and sardine have similar ecologies, the mechanisms underlying the declines in their growth are clearly different. The consequences of the exploitation of natural populations could be long lasting if density‐dependent processes follow adaptive changes. [ABSTRACT FROM AUTHOR]

In this study, the effects of chemical refining on the physicochemical indices, environmental pollutants, lipid functional groups, relaxation characteristics, fatty acid profiles, and triglyceride (TG) molecular species in crude oil extracted from small fish in Mauritania were evaluated. The acid, peroxide, and iodine values of crude oil were identified as 5.52 mg KOH/g, 1.73 meq/kg, and 200.78 g/100 g oil, respectively. After refining, these values were determined to be 0.29 mg KOH/g, 0.76 meq/kg, and 210.80 g/100 g oil, respectively. The polychlorinated biphenyls and arsenic content of crude oil were identified as 32.30 μg/kg and 1.00 mg/kg, respectively. After refining, these were not detected. The content of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) accounted for as much as 87.55% of the polyunsaturated fatty acids in the refined oil, indicating that high-quality fish oil is suitable as a food supplement. The correlation coefficient of the infrared spectra before and after refining was 0.968, and the relaxation time and peak shape data were almost similar before and after purification. Meanwhile, there were no significant differences (P ≥ 0.05) in fatty acid profiles between the crude and refined oils, except for C16:0 (P

Small pelagic fish (SPF) are fundamental components of marine food webs and are subject to boom and bust periods ascribed to the interactive effects of fishing and climate, which vary depending on species' demography and life-history traits and determine the signal that we observe in fisheries time series. However, it is poorly understood how the biology of SPFs and habitat structure shape their population demography and responses to fishing and climate. This study evaluates the influence of life-history traits and the environment on the demography and the response to exploitation and climate for 14 populations of SPFs occurring in the European Atlantic Seas. Using age-structured population matrix models we calculated elasticities to characterize the contribution of recruitment to population growth rate. We then evaluated the association between biological traits and environmental conditions (mean, seasonality, and predictability) with average recruitment elasticity and demography. Finally, we quantified the effects of biological traits and geography in shaping the temporal responses of each population's recruitment elasticities to demography, exploitation, and climate. For all species, population growth rate correlated positively with the elasticity to the recruitment, implying that long-term persistence is driven by the contribution of recruitment. Greater elasticity was found for populations with younger spawners, earlier maturation, and higher somatic growth rate inhabiting less predictable thermal ecosystems but with more temporally similar wind conditions. Among populations, fast growers had a stronger negative relationship between demographic structure and the importance of recruitment. At high fishing pressure, populations became increasingly dependent on recruitment though this relationship was less important for fast growers which, on average, sustained higher levels of exploitation. In turn, fast-maturing populations responded more strongly to the mean, seasonality, and predictability of the environmental conditions, especially towards eastern and southern geographically extremes. The results highlight the importance of recruitment for the population growth of SPFs and illustrate how the contribution of recruitment varies among and within populations as a function of environmental conditions and life-history traits defining an ordination of SPFs along a slow-fast continuum with implications for population dynamics and the responses to endogenous and exogenous factors. [ABSTRACT FROM AUTHOR]

The thread herring Opisthonema oglinum (Lesueur, 1818) is a small pelagic fish distributed in the western margin of the Atlantic Ocean from the United States to Argentina. It is a target species for diverse commercial fisheries, including the Brazilian industrial purse seine fleets that operate in the Southeastern Brazilian Bight. To investigate the geographic variation in the thread herring populations in this fishing ground, sagittal otoliths were collected from two areas: Rio de Janeiro (RJ: 23°04′ S, 44°03′ W) and Santa Catarina (SC: 26°05′ S, 48°18′ W). Otolith shape analyses and multi-elemental signatures were statistically evaluated using elliptical Fourier descriptors and elemental/Ca ratios. Remarkable differences in the thread herring otoliths between the two areas were found. The previous scenario in which the thread herring constitutes a single panmictic population in the Atlantic Ocean is now debatable. The implications of these results in terms of rational fisheries management for this species are highlighted. [ABSTRACT FROM AUTHOR]

Otolith shape analysis has been one of the most used approaches to study population structure in the past decades. Currently, two sets of shape descriptors are used to perform otolith shape analysis, namely, Elliptic Fourier descriptor (EFd), which focuses on the overall otolith shape differences, and Discrete Wavelet descriptor (DWd), which is sensible to local differences along the otolith contour. Here, the authors conducted a comparative analysis of the performance of both the descriptors in reconstructing the population structure and connectivity patterns in a small pelagic fish species with a wide geographical distribution and fast growth rate, the European sardine Sardina pilchardus (Walbaum, 1792), for the first time. A combination of each otolith shape descriptor and shape indices was explored using multivariate statistical methods. The two otolith shape descriptors showed similar, although limited, overall classification success associated with the population dynamic characteristics of the species. Both descriptors point to migration among adjacent areas, such as northern Atlantic locations, eastern Mediterranean and even across well‐defined physical obstacles, such as the Strait of Gibraltar, among Atlantic and western Mediterranean locations. Both descriptors supported the division of the populations of Mediterranean waters into three main groups but slightly differed in the group limits of the Atlantic waters. A comparison of the present results with those from previous otolith shape analysis studies using EFd on a decadal time scale revealed differences in the population structure and connectivity patterns compared to the earlier period. These differences not only may be attributed to changes in environmental variables leading to changes in population dynamics but can also be the result of the sardine biomass sharp decrease that occurred in the past decade. [ABSTRACT FROM AUTHOR]

The sex ratio, length–weight relationship (LWR) and diets based on stomach contents of whiting (Merlangius merlangus) were investigated in the south-eastern Black Sea, Turkey. A total of 3507 females (7.5–24.0 cm), 1602 males (9.4–20.0 cm), and 78 unidentified sex (5.5–16.5 cm) whiting were caught during monthly sampling from February to December 2017. The sex ratio was dominated by females, and their ratio (♀:♂, 1:0.46) significantly deviated from 1:1. The LWR indicated a negative allometric growth for males, while females had a positive allometric growth pattern. The stomach content analysis based on the relative importance index (IRI%) indicated exclusively piscivorous diets dominant by Sprattus sprattus and Engraulis encrasicolus made up more than 91 IRI% of the total diets of M. merlangus. The modified Costello-Amundsen's graphical analyses evinced the specialized feeding strategy of M. merlangus throughout this study. The contribution of these two preys to the diets of M. merlangus showed considerable seasonal variations that were totally dependent on their abundance. Sprattus sprattus contributed to more than 98% of the total diets during June, July and August, while in the following months, E. encrasicolus appeared to take its position. Based on fish size, a general trend of a rise in prey diversity was found with increasing fish size. Also, the contribution of S. sprattus tended to decrease with increasing predator size, which is replaced by a rise in E. encrasicolus contribution. Hence, larger M. merlangus predominantly fed on E. encrasicolus while smaller size predators preferred to feed on S. sprattus. [ABSTRACT FROM AUTHOR]

IntroductionSmall pelagic fishes constitute large proportions of fisheries and are important components linking lower and higher trophic levels in marine ecosystems. Many small pelagic fishes in the Northwest Pacific spawn upstream in the Kuroshio and spend their juvenile stage in the Kuroshio Front area, indicating that the Kuroshio Current system impacts their stock fluctuations. However, the distribution of these fish relative to the Kuroshio has not been determined due to dynamic spatio-temporal fluctuations of the system. Here, the recent development of environmental DNA (eDNA) monitoring enabled us to investigate the distribution patterns of four economically important small pelagic fishes (Japanese sardine Sardinops melanostictus, Japanese anchovy Engraulis japonicus, chub mackerel Scomber japonicus, and blue mackerel Scomber australasicus) in the Kuroshio Current system. MethodsThe influence of environmental factors, such as sea water temperature, salinity, oxygen concentration, chlorophyll-a concentration, and prey fish on the occurrence and quantity of target fish eDNA was analyzed using generalized additive models. In addition, the detection (presence) of target fish eDNA were compared between the offshore and inshore side areas of the Kuroshio axis.ResultsSea water temperature showed important effect, especially on the distribution of Japanese sardine and Japanese anchovy, whereas the distribution pattern of chub mackerel and blue mackerel was greatly influenced by the eDNA quantity of Japanese sardine and Japanese anchovy (especially potential prey fish: Japanese anchovy). In addition, we found that the four target fish species could be observed in areas on the inshore side or around the Kuroshio axis, while they were hardly found on the offshore side.ConclusionBased on eDNA data, we succeeded in revealing detailed spatial distribution patterns of small pelagic fishes in the Kuroshio Current system and hypothesized predator–prey relationships influence their distribution in small pelagic fish communities.

The aim of this article is to present the multidimensional challenges associated with the exploitation of small pelagic fish in the West Africa region. The method involved collecting statistical data on the production and trade of these fish from research centres located in countries along the West African coastline. Field surveys were also conducted with experts and key stakeholders in fisheries to gather qualitative information on fisheries resource governance and working conditions within the value chain. These empirical data are enriched by a narrative review of scientific literature. Our results show an average annual production of small pelagic fish estimated at 1.3 million tonnes. Although this performance has improved over the past decade, primarily due to increased catches in Mauritania, it remains insufficient to meet the needs of a rapidly growing population. Indeed, per capita consumption of small pelagic fish has decreased by two kilograms over the past decade, currently standing at five kilograms per individual per year. The trade deficit in pelagic fish is increasing. This situation is set to worsen in the coming years due to various factors such as the current state of overexploitation of pelagic stocks, degradation of marine ecosystems, and climate change. Additionally, the emergence of fishmeal and fish oil industries, as well as the lack of adequate port infrastructure, hampers the value addition of the small pelagic fish value chain for human consumption. On the governance front, several challenges remain. Current public policies are often directive and ineffective, particularly concerning artisanal fisheries. The management of migrant fishers also remains problematic, exacerbating the pressure on already vulnerable stocks. Despite the establishment of regional institutions, interviews with experts highlight a lack of integration and synergy in fisheries resource governance. In a context where issues of food security and climate change are becoming increasingly urgent, it is imperative to design and implement robust regional strategies to address these critical challenges.Haut du formulaire Bas du formulaire • The study analyses the multidimensional challenges facing West African fisheries. • The article highlights the need for local stakeholder integration in decision making. • The study offers a comprehensive diagnosis as a basis for targeted interventions. • Criticism of small pelagics management and a call for strong regional policies. • The study links regional analysis to global food security and climate change issues. [ABSTRACT FROM AUTHOR]

Non‐stationary driver‐response relationships are increasingly being recognized by scientists, underlining that a paradigm shift out of conventional stationary relationships is crucial. Japanese sardine (Sardinops melanostictus, Clupeidae) is a typical small pelagic fish in the northwestern Pacific with considerable fluctuations in productivity, bringing about great economic and ecological concerns. Numerous studies suggest that the population dynamics of Japanese sardine is an integrated process affected by multiple density‐dependent, fishing and climatic drivers. However, little has hitherto been done to incorporate the non‐stationary effects of multiple drivers, impeding progresses in understanding the population dynamics and in developing management strategies. In this study, we adopted variable coefficients generalized additive models to reveal the non‐stationary effects of density dependence, fishing pressure and climatic conditions on the population dynamics of Japanese sardine. Results suggest that the dynamics of Japanese sardine from 1976 to 2018 could be divided into four periods: the 1980s when suitable climatic conditions from strong Siberian High pressure system sustained high abundance; the 1990s when negative density‐dependent effects and degrading climatic conditions due to temperature increase led to population collapse; the 2000s when negative triple effects, particularly high fishing pressure, restricted the population increase; and the 2010s when favourable climatic conditions with re‐strengthening Siberian High pressure system accompanied by low fishing pressure contributed to the population recovery. The study highlights that precise identifications of population status and climatic conditions are helpful to achieve good trade‐offs between resource exploitation and protection and to facilitate ecosystem‐based management for Japanese sardine fisheries. [ABSTRACT FROM AUTHOR]

Small pelagic fish are important marine ecosystem components and highly variable fisheries resources. In the California Current upwelling system, Pacific sardine (Sardinops sagax) has supported important fisheries in the past, but contrary to expectations, remains at low biomass despite recent warm ocean conditions. We developed a data-driven, process-based population model that reproduces fluctuations of the US Pacific sardine population based on ocean temperature, early life stage and adult food, and upwelling strength. The lack of sardine recovery after 2014 can be explained by reduced food availability. Ensemble projections for the 21st century driven by downscaled ocean-biogeochemical simulations under three Earth system models (ESMs) show a likely recovery to early 2000s sardine abundance and catch by mid-century, due to increased recruitment. Ecological process uncertainty (ensemble configuration range) is of the same magnitude as uncertainty among ESM projections, and uncertainty related to the thermal optimum of early life stages dominates after 2070. Even for a fish species presumably favoured by warmer conditions, future climate projections entail risks of stock declines in food-limited years and when passing unknown thermal optima. Quantification of combined environmental driver impacts and sources of uncertainty to projections under novel conditions open new pathways for environment-responsive fisheries management strategies. [ABSTRACT FROM AUTHOR]

Small pelagic fishes are used for human consumption, fishmeal and fish oil. They constitute 25% of global fish catch and have been of considerable conservation concern because of their intermediate position in aquatic food webs, often being a dominant dietary component of marine predators. This paper provides an overview of trends in abundance and fishing pressure on small pelagic fish stocks from single‐species scientific assessments that constitute 60% of global small pelagic catch. While most individual stocks have exhibited wide variability in abundance (typical of small pelagics compared with other fish taxa), across stocks there has been remarkable stability in average fishing pressure and biomass since 1970. On average, since 1970, the biomass of assessed small pelagic stocks is estimated to have been slightly above the biomass that would produce maximum sustainable yield, but estimation of this quantity for highly fluctuating stocks is quite uncertain. There were significant differences among assessed regions, with the Mediterranean and Black Sea of greatest concern for high and growing fishing pressure. The 40% of global small pelagic fish catch not covered by single‐species quantitative stock assessments since 1970 comes largely from Asia, where catches have continued to increase. At regional levels, the average abundance of assessed small pelagic fish is largely unrelated to average fishing pressure, which we argue results both from the portfolio effect, where numerous stocks fluctuate with little correlation in abundance, and from the short life span of small pelagics coupled with recruitment largely independent of spawning abundance. [ABSTRACT FROM AUTHOR]

Abstract The northward expansion of round sardinella (Sardinella aurita) in the Mediterranean Sea, together with declines and fluctuations in biomass and landings of European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) observed in recent decades, may suggest potential inter‐specific competition in the pelagic domain. The coexistence of sympatric zooplanktivorous fish species might therefore be exposed in part to trophic niche overlap and competition for food. Combining visual diet characterization under the microscope with DNA metabarcoding from stomach contents of fish collected in spring results show that predation on relatively large krill is equally important for sardinella than for the other two niche overlapping species. Furthermore, an important overlap is found in their isotopic niche, especially with anchovy, using nitrogen (δ15N) and carbon (δ13C) stable isotopes in muscle tissue. In fact, the three fish species are able to feed effectively in the whole prey size spectrum available during the sampled season, from the smallest diatoms and copepods to the larger prey (i.e., decapods and euphausiids), including fish larvae. Moreover, effective predation upon other large prey like siphonophores, which is observed only when multi‐proxy analyses in stomach contents are applied, might also be relevant in the diet of sardinella. The overlapping diet composition in spring, together with the effective use of food resource by sardinella, can be of special interest in potential future scenarios with warmer water temperature leading to lower zooplankton and/or higher jellyfish availability, where sardinella may take advantage over other species due to its feeding plasticity.

Among the various species of small pelagic fish, Sardinella sindensis (Day ,1878) has high economic and ecological importance and is one of the most important species exploited by fishermen. In recent years, the catch rate of this species has increased, and due to the limited data available on its stock in southern waters, it is not possible to use models based on the complementary data to assess its stock. In the present study, the catch-maximum sustainable yield (CMSY) model was used to determine the stock status of Sardinella sindensis in southern waters. Catch data related to the last 23 years (1997- 2019) were collected and entered into the model to calculate fisheries reference points. The value for B/BMSY by the model was estimated to be more than 1.0 and the value of F/FMSY was less than 1.0, which indicates the healthy stock status of this species in the southern waters of Iran. The maximum sustainable yield (MSY) was estimated to be 86,000 tons. In recent years, the catch rate has been exceeded this amount and has caused the stock to move gradually towards the overfishing zone. Based on the results, it is suggested to control and manage the fishing activities regionally (specially in Hormozgan province) by taking into account the fishery potentials, monitoring the exploitation status with regard to the environmental factors affecting the stocks of this species.

Diet and trophic interactions of seven species of planktivorous fishes: European anchovy Engraulis encrasicolus, European sardine Sardina pilchardus, round sardinella Sardinella aurita, European sprat Sprattus sprattus, red bandfish Cepola macrophthalma, damselfish Chromis chromis and bogue Boops boops were studied in the Bay of Marseille (North-Western Mediterranean Sea) from March to September 2017. Taxonomic composition and size distribution of prey were studied using stomach content analysis, and compared to prey availability determined by continuous zooplankton sampling at a fixed point. Frequently consumed items included copepods, decapod larvae and fish eggs. Comparatively, E. encrasicolus consumed more calanoid copepods (i.e. Centropages spp.), S. pilchardus, S. aurita and S. sprattus consumed more harpacticoid copepods (i.e. Microsetella/Macrosetella spp.), C. macrophthalma consumed more decapod larvae, C. chromis consumed more pteropods and B. boops consumed more benthic polychaetes. Sardina pilchardus consumed the widest diversity of prey. Prey size distribution and average prey size significantly differed among species. The prey–predator size ratio (PPSR) was highest for B. boops and lowest for S. aurita. Carbon and nitrogen stable isotope composition of species overlapped, probably due to the ingestion of particulate organic matter from the same sources at the base of the planktonic food web in the Bay of Marseille. Furthermore, trophic niche overlap supported the hypothesis of potential trophic competition between Engraulidae and Clupeidae. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the reproductive biology of the small pelagic Sardinella aurita Valenciennes, 1847 in the Canary Islands, to enable its reliable assessment and advise on appropriate management measures for a fishing resource showing a declining trend in landings. Reproductive biology and sexual patterns of round sardinella were examined from monthly random samples of commercial catches landed by the artisanal purse-seine fleet. The landings' length frequencies, ranging between 9–32 cm (based on the total lengths, TL), were recorded from 2013–2019. The overall mean value of TL was 20.9 cm, with annual mean values between 20–22 cm, except in 2016 (TL = 19 cm). The overall sex ratio M:F was 1:0.92, with males significantly predominant. Sex ratios fluctuated as a function of size and month: females were more abundant in the larger length classes, as well as before and after spawning, whereas males were more abundant in the smaller length classes and during spawning. Based on gonad maturity stages and gonadosomatic index, round sardinella spawns during almost all the year, with a peak in January–February and a resting period during October–November. The length at first maturity was estimated at TL of 18.2 cm, notably smaller than the value obtained for the NW African coastal waters where the demographic structure in round sardinellas' landings is totally different. [ABSTRACT FROM AUTHOR]

Food availability is thought to exert a bottom-up control on the population dynamics of small pelagic fish; therefore, studies on trophic ecology are essential to improve their management. Sardina pilchardus is one of the most important commercial species in the Adriatic Sea, yet there is little information on its diet in this area. Adult sardines were caught in the Gulf of Trieste (northern Adriatic) from spring 2006 to winter 2007. Experimental catches conducted over 24-h cycles in May, June and July showed that the sardines foraged mainly in the late afternoon. A total of 96 adult sardines were analysed: the number of prey varied from a minimum of 305 to a maximum of 3318 prey/stomach, with an overall mean of 1259 ± 884 prey/stomach. Prey items were identified to the lowest possible taxonomical level, counted and measured at the stereo-microscope. Overall, sardines fed on a wide range of planktonic organisms (87 prey items from 17 μm to 18.4 mm were identified), with copepods being the most abundant prey (56%) and phytoplankton never exceeding 10% of the prey. Copepods of the Clauso-Paracalanidae group and of the genus Oncaea were by far the most important prey. The carbon content of prey items was indirectly estimated from prey dry mass or body volume. Almost all carbon uptake relied on a few groups of zooplankton. Ivlev's selectivity index showed that sardines positively selected small preys (small copepods < 1 mm size), but also larger preys (such as teleost eggs, decapod larvae and chaetognaths), confirming their adaptive feeding capacity. [ABSTRACT FROM AUTHOR]

Interactions between cetaceans and the purse seine fishery in coastal waters of mainland Portugal were investigated using onboard observations over a period of 15 years (2003–2018). In 10% of the fishing sets, there were interactions with one of three species of cetaceans: common dolphin (Delphinus delphis), bottlenose dolphin (Tursiops truncatus), and harbour porpoise (Phocoena phocoena). The common dolphin was the most frequently observed species, occurring in 89% of all interaction events, and the only species with observed mortality. Therefore, this study focused only on the interactions with common dolphins.A generalized additive model (GAM) was applied to observer data to investigate how the fishing activity and the abundance of small pelagic fish influenced the probability of occurrence of interactions between the common dolphin and the purse seine fishery between 2003 and 2018. The results revealed significant annual and geographic variation in the occurrence of interactions, and a significant influence of fishing effort and catch per unit effort of sardine (Sardina pilchardus).A second GAM in a hurdle model was used to model the number of common dolphins that interacted with the fishing activity as a function of fishing seasonality and the local abundance of pelagic fish. There was a significant effect of the seasonality of the fishing activity and catch per unit effort of sardine and chub mackerel (Scomber colias) on the number of common dolphins interacting with the fishery.The results of this study suggest that the probability of interactions and the number of common dolphins interacting with the fishery were affected by the local abundance of sardine and chub mackerel.As the common dolphin population appears to be increasing in the study area, the risk of by‐catch also increases, thus the monitoring of the Portuguese purse seine fishery is important to inform the implementation of management plans, and also as a response to global efforts for sustainable fisheries and marine mammal conservation. [ABSTRACT FROM AUTHOR]

The anchovy (Engraulis encrasicolus, Linnaeus, 1758), one of the most important small pelagic fish species in the Adriatic, is currently described as a species that can be considered overfished. From 2013 to 2020, samples of anchovy eggs and larvae were collected through scientific surveys during the summer months. The collected ichthyoplankton data were combined with environmental data (measured satellite sea surface temperature and chlorophyll data, numerically simulated salinity, maps of primary production) to identify anchovy spawning habitats and environmental conditions affecting the anchovy early life stages. For this large dataset, a nonlinear method called Growing Neural Gas Network analysis was used to explain the multiple dependencies between anchovy and the explanatory environmental variables and represent them in 9 patterns called Best Matching Unit (BMU). Obtained values of anchovy early life stages abundances (eggs/m2; larvae/m2) showed a clear negative trend, which was easily observed both in the time series and in the annual spatial distributions. Among all measured environmental parameters that were previously mentioned, salinity showed a significant increase, which can be attributed to the cyclonic phase of the bimodal oscillatory system of the Adriatic and Ionian Seas. The calculated BMUs showed several interesting results that shed new light on previous findings: (a) there is a split between the richer northern and poorer southern parts of the Adriatic in terms of anchovy eggs and larvae abundances, (b) the Kvarner Bay, the west coast of Istria and the area around Dugi otok are consistently rich spawning grounds, (c) decreased abundance in the southern areas is a result of the influence of salinity, (d) an increase in chlorophyll can lead to an increase in egg count, (e) the positive effects of upwelling can be negated by an increase in salinity, (f) increased primary production is followed by increased egg count. Upwelling, as one of the factors that can influence larval and egg abundance by bringing nutrients up from the seafloor, showed increased spatial and temporal variability during the investigated period, which depended on the wind regime. Our analysis showed that neural network analysis can successfully describe the effects and interplay of environmental factors on the abundance of anchovy early life stages.

Species distribution models (SDMs) are a commonly used tool, which when combined with earth system models (ESMs), can project changes in organismal occurrence, abundance, and phenology under climate change. An often untested assumption of SDMs is that relationships between organisms and the environment are stationary. To evaluate this assumption, we examined whether patterns of distribution among larvae of four small pelagic fishes (Pacific sardine Sardinops sagax, northern anchovy Engraulis mordax, jack mackerel Trachurus symmetricus, chub mackerel Scomber japonicus) in the California Current remained steady across time periods defined by climate regimes, changes in secondary productivity, and breakpoints in time series of spawning stock biomass (SSB). Generalized additive models (GAMs) were constructed separately for each period using temperature, salinity, dissolved oxygen (DO), and mesozooplankton volume as predictors of larval occurrence. We assessed non-stationarity based on changes in six metrics: 1) variables included in SDMs; 2) whether a variable exhibited a linear or non-linear form; 3) rank order of deviance explained by variables; 4) response curve shape; 5) degree of responsiveness of fishes to a variable; 6) range of environmental variables associated with maximum larval occurrence. Across all species and time periods, non-stationarity was ubiquitous, affecting at least one of the six indicators. Rank order of environmental variables, response curve shape, and oceanic conditions associated with peak larval occurrence were the indicators most subject to change. Non-stationarity was most common among regimes defined by changes in fish SSB. The relationships between larvae and DO were somewhat more likely to change across periods, whereas the relationships between fishes and temperature were more stable. Respectively, S. sagax, T. symmetricus, S. japonicus, and E. mordax exhibited non-stationarity across 89%, 67%, 50%, and 50% of indicators. For all species except E. mordax, inter-model variability had a larger impact on projected habitat suitability for larval fishes than differences between two climate change scenarios (SSP1-2.6 and SSP5-8.5), implying that subtle differences in model formulation could have amplified future effects. These results suggest that the widespread non-stationarity in how fishes utilize their environment could hamper our ability to reliably project how species will respond to climatic change.

Anchovy (Engraulis japonicus), a commercially and biologically important fish species in Korean waters, is a small pelagic fish sensitive to environmental change. Future changes in its distribution in Korean waters with significant environmental change remain poorly understood. In this study, we examined the projected changes in the seasonal anchovy habitat in Korean waters in the 2050s under three representative concentration pathways (RCPs; RCP 2.6, RCP 4.5, and RCP 8.5) by using a maximum entropy model (MaxEnt). The MaxEnt was constructed by anchovy presence points and five environmental variables (sea surface temperature, sea surface salinity, sea surface current speed, mixed layer depth, and chlorophyll-a concentration) from 2000–2015. Future changes in the anchovy habitat in Korean waters showed variation with seasonality: in the 2050s, during winter and spring, the anchovy habitat area is projected to increase by 19.4–38.4%, while in summer and fall, the habitat area is projected to decrease by up to 19.4% compared with the historical period (2000–2015) under the three different RCPs. A substantial decline (16.5–60.8%) is expected in summer in the East China Sea and the Yellow Sea—main spawning habitat. This considerable decrease in the spawning habitat may contribute to a decline in the anchovy biomass, relocation of the spawning area, and changes in the reproduction timing in Korean waters. Our findings suggest that seasonal variation of the anchovy habitat should be considered to ensure effective future management strategies for the effect of climate change on fisheries resources, particularly for environmentally sensitive species, such as anchovy.

Among the various species of small pelagic fish, Sardinella sindensis (Day, 1878) has high economic and ecological importance and is one of the most important species exploited by fishermen. In recent years, the catch rate of this species has increased, and due to the limited data available on its stock in southern waters, it is not possible to use models based on the complementary data to assess its stock. In the present study, the catch-maximum sustainable yield (CMSY) model was used to determine the stock status of Sardinella sindensis in southern waters. Catch data related to the last 23 years (1997-2019) were collected and entered into the model to calculate fisheries reference points. The value for B/BMSY by the model was estimated to be more than 1.0 and the value of F/FMSY was less than 1.0, which indicates the healthy stock status of this species in the southern waters of Iran. The maximum sustainable yield (MSY) was estimated to be 86,000 tons. In recent years, the catch rate has been exceeded this amount and has caused the stock to move gradually towards the overfishing zone. Based on the results, it is suggested to control and manage the fishing activities regionally (specially in Hormozgan province) by taking into account the fishery potentials, monitoring the exploitation status with regard to the environmental factors affecting the stocks of this species. [ABSTRACT FROM AUTHOR]

The influence of phytoplankton biomass on small pelagic fish groups was studied at three sites along the Western Pemba Channel, to assess the contribution of seasonality. Sampling took place at the three sites in the coastal waters of Tanga, Tanzania. The study used in-situ data from July 2016 to January 2017, remotely-sensed chlorophyll-a data from August 2016 to August 2017 and 2019-2020, and small pelagic fish catch data from the same periods as the remotely-sensed data. The dominant groups at all the three sites were diatoms, dinoflagellates, and cyanobacteria, with diatoms having the highest number of species compared to the other two. In comparison to the southeast monsoon season, phytoplankton species and biomass were significantly higher during the northeast monsoon season. The most plentiful fish were anchovies, which had high peaks in both seasons, followed by sardinella, while mackerel had the lowest catch. Chlorophyll-a and anchovy catches showed a positive correlation; however, the relationship was not significant (r = 0.47, df = 11, p = 0.12). Both variables showed the highest peaks in October, while other fish groups showed very weak and insignificant positive or negative correlations. These findings suggest that factors other than phytoplankton biomass contribute to controlling small pelagic fish availability. [ABSTRACT FROM AUTHOR]

Bycatch small pelagic fish during the fishing season can be oversupplied so that its price goes down. The study aims to analyze the proximate of local fish powder from the by-catch and probiotics of Probio_FM in the fish feed in Bangka Belitung. The method was the data compared with the Indonesian National Standard, SNI 01-2715-1996/Rev: 92 about the raw material of animal feed as fish powder and fish feed with six different treatments. The study found that the bycatch or trash from small pelagic fish could be used as a fish powder or fish feed. The proximate analysis on fish powder and fish feed with probiotics Probio_FM included as the quality of SNI. Crude protein values from 25.75% until 66.96% that was above SNI standard I (1.5%), II (2.5%), and III (3.0%) could be followed up into an economical business. Fermented activity from Probio_FM could degrade the protein and other components proximate such as ash content, crude protein, crude fat, crude fiber, calcium, Phosphor, and NaCl. The amino acids from protein were getting simpler and easier being absorbed by fish in culture or livestock farms. Probio_FM was assumed to degrade the protein value and other components proximate due to the utilization of nitrogen and ammonia derived from the process fish protein hydrolyzation of probiotic bacteria. The production of local feed should be implemented to reach feed security and very important to be developed into a community business. Proximate analysis of bycatch could support sustainable good aquaculture practices in the future. [ABSTRACT FROM AUTHOR]

Climate‐induced fluctuations in marine fish populations have been raising great scientific concerns. Previous studies generally dedicate to parameterization of climatic, environmental, and biological variability patterns with focuses on their empirical or incompletely mechanistic relationships. Little consideration on physiological characteristics of organisms prevents from exploring mechanisms behind the apparent relationships. Therefore, incorporating physiological information into investigation on climate–environment–biology relationships is essential to understand climate‐induced biological variability. Small pelagic fishes play unparalleled roles in the Kuroshio ecosystem and show dramatic fluctuations in response to environmental changes, serving as ideal research targets in studies on climate‐induced biological variability. This study focuses on Japanese sardine, chub mackerel, and Japanese anchovy, three key small pelagic fishes in the Kuroshio ecosystem with distinct physiological characteristics, with attempts to incorporate thermal niches into investigations on their responses to climate variability. The recruitment suitable index (RSI) is developed considering both sea surface temperature (SST) and species thermal niche. Results show that the RSI significantly increase explanations on variations in resource abundance indices of the three key small pelagic fishes. Responses of small pelagic fishes to climate variability show differences by species and stocks. In addition, variations in the Siberian High pressure system and Atlantic Multidecadal Oscillation contribute highly to variations in resource abundance indices through affecting the SST and further the RSI. This study demonstrates importance of physiological information for understanding climate‐induced biological variability and effectiveness of combining thermal niches with the investigation on mechanistic climate–environment–biology relationships, which should be extensively considered in the future studies. [ABSTRACT FROM AUTHOR]

This study presents updated stock assessments and risk analyses of overexploitation for the aggregate small pelagic fish complex and the dominant genus of the complex, Decapterus, for improving the management of the small pelagic fishery in Fisheries Management Area (FMA) 715. The analyses herein used non-equilibrium biomass dynamics models with available data on annual catch and catch per unit effort for 2005 to 2016. Fishing effort was standardised into the number of 20-meter length overall purse-seine vessels. The analyses show that the maximum sustainable yield (MSY) of the aggregate fish was about 121,600 tonnes, caught by 876 purse-seiners, while the MSY of the mackerel scad, Decapterus macarellus (Cuvier, 1833), was about 67,900 tonnes, caught by 805 purse-seiners. Since the mackerel scad and the aggregate fish stocks have been overexploited, a rebuilding strategy would be necessary to restore the stocks to a level capable of producing MSY (BMSY). After achieving the BMSY, it is recommended that a target reference point be implemented for the catch level with the maximum overexploitation risk level of 50 % in 10 years. The catch level meeting this requirement for mackerel scad would equal 80 % of its MSY, which could be achieved by controlling fishing effort at 427 purse-seiners. At this effort level, the fishery would produce 95,800 tonnes of aggregate fish catch with 54,300 tonnes of mackerel scad. These reductions in fishing efforts will be needed to maintain the future sustainability of the fish stocks in FMA 715. [ABSTRACT FROM AUTHOR]

Rough scad Trachurus lathami is a key pelagic fish in the Argentinean continental shelf (ACS, south‐west Atlantic Ocean), with recent increases in abundance. It is a main prey of fishes and marine mammals, and shares the environment with commercially relevant pelagic species (Engraulis anchoita and Scomber colias), playing an important role linking lower and upper trophic levels in the ecosystem. This study aims to determine the ontogenetic changes in the diet composition, feeding strategy, trophic niche breadth and trophic level of T. lathami in the North Patagonian Shelf (43°–45°30′S). The stomach contents of adult fish (n = 238) were analysed. The results suggest a clear ontogenetic shift in the diet at a size of ~190 mm. Smaller individuals (160–190 mm) were specialized on misidaceans, and showed the highest trophic level, while larger T. lathami (221–230 mm) consumed decapods (Peisos petrunkevitchi) and teleosts (eggs and larvae). Trophic niche breadth was higher at the medium‐sized class (191–220 mm), which mainly preyed on copepods (Calanoides carinatus) and chaetognaths (Sagitta spp.), evidencing a more diverse diet and a rather generalist strategy. Updated information on the trophic ecology of T. lathami evidences its extremely plastic feeding behaviour, being able to adapt its trophic niche to the most readily available food items from the mesopelagic community. [ABSTRACT FROM AUTHOR]

Essential fatty acids are suggested to be key elements in trophodynamic processes in small pelagic fish. Small pelagic fish generally acquire these fatty acids from phytoplankton and zooplankton lipids; however, little is known about the utilization characteristics of fatty acids. To clarify this, we measured the fatty acid composition of Japanese sardine, Sardinops melanostictus, during the feeding and spawning periods. A comparison of fatty acid composition between sardine and zooplankton in the feeding period indicated that sardine preferentially retained high levels of specific long-chain polyunsaturated fatty acids (LC-PUFAs), such as docosahexaenoic acid (DHA) and arachidonic acid, in the muscles compared to those in dietary organisms. Further, a comparison of sardines between the feeding and spawning periods demonstrated that the levels of these LC-PUFAs in the muscle decreased during the spawning period. Instead, the levels of LC-PUFAs in the ovary (especially DHA) increased with ovary-somatic development, indicating that in the sardine, these LC-PUFAs are transferred from the muscle to the gonad during the spawning period. [ABSTRACT FROM AUTHOR]

The northward expansion of round sardinella (Sardinella aurita) in the Mediterranean Sea, together with declines and fluctuations in biomass and landings of European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) observed in recent decades, may suggest potential inter-specific competition in the pelagic domain. The coexistence of sympatric zooplanktivorous fish species might therefore be exposed in part to trophic niche overlap and competition for food. Combining visual diet characterization under the microscope with DNA metabarcoding from stomach contents of fish collected in spring results show that predation on relatively large krill is equally important for sardinella than for the other two niche overlapping species. Furthermore, an important overlap is found in their isotopic niche, especially with anchovy, using nitrogen (δ15N) and carbon (δ13C) stable isotopes in muscle tissue. In fact, the three fish species are able to feed effectively in the whole prey size spectrum available during the sampled season, from the smallest diatoms and copepods to the larger prey (i.e., decapods and euphausiids), including fish larvae. Moreover, effective predation upon other large prey like siphonophores, which is observed only when multi-proxy analyses in stomach contents are applied, might also be relevant in the diet of sardinella. The overlapping diet composition in spring, together with the effective use of food resource by sardinella, can be of special interest in potential future scenarios with warmer water temperature leading to lower zooplankton and/or higher jellyfish availability, where sardinella may take advantage over other species due to its feeding plasticity. [ABSTRACT FROM AUTHOR]

Japanese sardine (Sardinops melanostictus) in the Sea of Japan expanded their distribution from the coast to offshore with an increase in population biomass; however, little is known about the suitability of the offshore habitat for this species. Using lipid analysis, this study compared the body condition of juvenile sardine between an area off the Noto Peninsula (offshore) and the Tsushima Strait (coast), with respect to habitat conditions during the summer, from 2015 to 2017. Sardine in the offshore area had larger bodies and higher lipid contents than those in the coastal area. Regarding the sardine diet, lipid content of the offshore zooplankton was clearly higher than that of the coastal zooplankton. Hence, we found a positive effect of this dietary lipid content on sardine lipid content, suggesting that these lipid measurements could explain the trophic relationship between sardine and zooplankton. The higher lipid content in offshore zooplankton was mainly attributed to the abundance of large‐sized copepods and lower water temperatures. Such lipid measurements might involve habitat‐specific characteristics of zooplankton assemblage. In conclusion, compared to the coastal area, the offshore area is considered a more favorable habitat for the sardine in terms of lipid availability. [ABSTRACT FROM AUTHOR]

Forecasts indicate that rising temperatures towards the future and the expansion of dead zones will change environmental suitability for fish early stages. Therefore, we assessed the chronic effects of warming (26 °C), hypoxia (<2–2.5 mg L−1) or their combination on mortality rate, growth, behaviour, energy metabolism and oxidative stress using Atherina presbyter larvae as a model species. There were no differences between the treatments in terms of mortality rate. The combination of warming and hypoxia induced faster loss of body mass (+22.7%). Warming, hypoxia or their combination enhanced boldness (+14.7–25.4%), but decreased exploration (−95%–121%), increased the time in frozen state (+60.6–80.5%) and depleted swimming speed (−45.6–50.5%). Moreover, routine metabolic rate was depleted under hypoxia or under the combination of warming and hypoxia (−56.6 and 57.2%, respectively). Under hypoxia, increased catalase activity (+56.3%) indicates some level of antioxidant defence capacity, although increased DNA damage (+25.2%) has also been observed. Larvae also exhibited a great capacity to maintain the anaerobic metabolism stable in all situations, but the aerobic metabolism is enhanced (+19.3%) when exposed to the combination of both stressors. The integrative approach showed that changes in most target responses can be explained physiologically by oxidative stress responses. Increased oxidative damages (lipid peroxidation and DNA damage) and increased interaction between antioxidant enzymes (superoxide dismutase and catalase) are associated to increased time in frozen state and decreased swimming activity, growth rates and boldness. Under all stressful situations, larvae reduced energy-consuming behaviours (e.g. depleted exploration and swimming activity) likely to stabilize or compensate for the aerobic and anaerobic metabolisms. Despite being an active small pelagic fish, we concluded that the sensitive larval phase exhibited complex coping strategies to physiologically acclimate under thermal and hypoxic stress via behavioural responses. [Display omitted] • Combined warming and hypoxia had no effect on mortality in sand smelt larvae. • Larvae reduced growth rates, boldness and activity under all stressful situations. • Hypoxia or combined warming and hypoxia depleted routine metabolic rate. • Combined warming and hypoxia enhanced the aerobic metabolism in sand smelt larvae. • Hypoxia enhanced the antioxidant defense, though damaged DNA increased. [ABSTRACT FROM AUTHOR]

Omega-3 long-chain polyunsaturated fatty acids (hereafter, omega-3), including eicosapentaenoic-acid (EPA) and docosahexaenoic-acid (DHA), are essential nutritional compounds for humans, providing several benefits related to cardiovascular and neural health. Human intake of omega-3 occurs mostly via seafood, particularly fish. The primary source of omega-3 in aquatic systems is represented by primary producers, from which omega-3 are transferred throughout the food web. Nitrogen is an essential nutrient for primary producers and can be supplied to surface waters as nitrate upwelled from below, or as ammonium and other regenerated nitrogen forms recycled in situ. Eastern Boundary Upwelling Systems (EBUS) are the most productive marine systems on Earth, together covering only 2% of the ocean’s surface area but supporting 25% of the global fish catch, thereby providing food for humans. In EBUS, nitrate and other nutrients are advected to the surface to support the proliferation of a phytoplankton community dominated by known omega-3 producers (i.e., diatoms). Given current climate change-related projections of ocean warming, acidification, deoxygenation, and increased upwelling intensity, phytoplankton community composition in EBUS may change. Additionally, the global production of EPA + DHA is expected to decrease by up to 30%, rendering its supply for human consumption insufficient by 2050. Here we discuss the state of knowledge related to omega-3 transfer from phytoplankton to small pelagic fish in EBUS, including factors that can influence omega-3 production, links to nitrogen cycling, climate change implications for the omega-3 supply to humans, and suggestions for future research directions to improve our understanding of omega-3 in the ocean.