Engraulis Japonicus Research Articles

Relationship between stable cesium concentration and body size of Japanese flounder Paralichthys olivaceus and the effect of a size-dependent shift in diet.

To understand the relationship between the radioactive cesium (Cs) concentration in muscle of Japanese flounder Paralichthys olivaceus and the species' biological characteristics (size, sex, and age) under conditions of ecological equilibrium (i.e., distributed among ecosystem components over sufficient time, and with nearly constant ratios of Cs concentration in organisms to the concentration in water) as existed before the accident at the Fukushima Dai-ichi Nuclear Power Station (FDNPS), Japan, in 2011, we examined stable Cs, as it is thought to exist in equilibrium in the environment and behave similarly to radioactive Cs in aquatic animals. The concentration of stable Cs in 241 P. olivaceus (range 216-782 mm total length [TL]) collected in Sendai Bay, approximately 90 km north of the FDNPS, in June-July 2015 was expressed as an exponential function with size as an independent variable; the results show the concentration of stable Cs doubled with an increase in TL of 442 mm. Next, to evaluate the cause of the size-dependent change in stable Cs concentration, we examined 909 individuals (200-770 mm TL) collected in September 2013-July 2015 to determine their feeding habit based on size. Analysis of the frequency of occurrence of prey organisms in stomach contents showed that sand lance Ammodytes japonicus (55-180 mm standard length [SL]) was the most consistently consumed across size classes. Analysis on a wet-mass basis showed that A. japonicus and anchovy Engraulis japonicus (65-130 mm SL) were the main food of P. olivaceus sized 200-599 mm TL, whereas chub mackerel Scomber japonicus (120-230 mm SL) and two species of flatfishes (180-205 mm SL) were abundant in the diet of P. olivaceus sized ≥600 mm TL. All these prey items were presumed to have similar concentrations of stable Cs. Based on the above, the effect of diet on the relationship between stable Cs in muscle and fish size was considered negligible. That the diet of P. olivaceus largely did not change with size was also confirmed by C and N stable isotope ratios in P. olivaceus and their prey species. Therefore, the Cs-size relationship is probably determined by changes in the balance between the rate of Cs intake from food and seawater and the excretion rate during growth, both of which change as functions of body mass. Values of stable Cs concentrations among environmental components and animals appear to be a valid indicator for understanding the radioactive Cs distribution in the marine environment and aquatic animals under the equilibrium state, as existed before the 2011 nuclear accident.

Engraulisin: A novel marine derived cell penetrating peptide with activity against drug resistant bacteria

Cell penetrating peptides (CPP) with their intrinsic ability to penetrate plasma membranes facilitate intracellular uptake of various macromolecules. Although a substantial number of CPPs have been reported over the last three decades, the number is still inadequate when compared to the theoretically feasible peptides with similar physicochemical composition.Marine organisms, due to their hostile environment, are an immense source of several high-valued therapeutically relevant peptides. Various marine derived antibacterial, antimycotic and anticancer peptides have demonstrated improved activity in comparison to peptides of terrestrial origin. While a significant number of marine bioactive peptides exist, cell penetrating peptides from marine organisms remain unravelled.In this study, we report Engraulisin from Engraulis japonicus, a computationally derived novel cell penetrating peptide of marine origin. Engraulisin manifest successful uptake in mammalian cells at 5 μM concentration with negligible cytotoxicity observed through MTT assay. Analysis of its cellular uptake mechanism revealed significant inhibition at 4 °C suggesting endocytosis as the major route of cellular entry. Interestingly, the novel peptide also demonstrated selective antimicrobial activity against Methicillin-resistant Staphylococcus aureus (MRSA). Additionally, molecular dynamics simulation with POPC and POPG bilayer system unveiled significance of positively charged residues in forming a stable membrane interaction. Engraulisin represents a novel marine-derived cell penetrating peptide which can be explored for cellular delivery of pharmaceutically relevant molecules.

Recruitment of Engraulis japonicus and its environmental drivers: An EDM analysis

Anchovies are the key trophic links between secondary production and higher trophic levels, and their recruitment changes have the potential to cascade and affect higher trophic levels. Therefore, understanding the stock-recruitment relationships and the external drivers of recruitment has important ecological and fishery management implications. In this study, we employed empirical dynamic modelling (EDM) to analyze the recruitment dynamics of Japanese anchovy (Engraulis japonicus) in the Yellow Sea large marine ecosystem (YSLME), based on data from surveys of the YSLME. The results indicated that biological effects between the YSLME Japanese anchovy stock and its recruitment were deterministic and bidirectional (interplay of causality in both directions). Japanese anchovy recruitment was also driven by other external factors, chief among these was fishing pressure which plays a decisive role in overall recruitment of the YSLME. In contrast, climate related factors act more locally on recruitment. We conclude that the decline in Japanese anchovy biomass is mainly caused by overfishing. This has important implications for rebuilding and subsequent management of Japanese anchovy stock: under current climate pressure, the EDM showed that reducing fishing pressure would promote recovery of stock biomass and recruitment.

Acoustic Target Strength According to Different Growth Stages of Japanese Anchovy (Engraulis japonicus): A Comparison of Juvenile and Adult Fish

Japanese anchovy (Engraulis japonicus) is an economically important species found in the coastal waters of the northwestern Pacific Ocean. To conduct effective acoustic surveys on the spawning or fishing grounds of this species, the target strength (TS, dB re 1 m2) during its growth stages must be understood. However, knowledge regarding the TS of juvenile Japanese anchovies is limited. To address this knowledge gap, we measured the TS and proposed equation models for juvenile Japanese anchovies while describing the TS differences between young and adult anchovies. We evaluated 21 live anchovies using 38, 120, and 200 kHz transducers. TS models were fitted for the juvenile stage of anchovies, considering different frequencies. The mean TS values of young and adult anchovies were similar to those reported in previous TS studies, whereas the TS values of juvenile anchovies were significantly lower. Thus, applying the same TS equation based on the acoustic characteristics of anchovies at different growth stages, especially for juvenile anchovies, may not be appropriate. These findings underscore the importance of adopting a suitable TS equation specific to the growth stages of Japanese anchovies for accurate data analysis in acoustic surveys conducted on spawning and fishing grounds.

Temperature sensitivity of the interspecific interaction strength of coastal marine fish communities

The effects of temperature on interaction strengths are important for understanding and forecasting how global climate change impacts marine ecosystems; however, tracking and quantifying interactions of marine fish species are practically difficult especially under field conditions, and thus, how temperature influences their interaction strengths under field conditions remains poorly understood. We herein performed quantitative fish environmental DNA (eDNA) metabarcoding on 550 seawater samples that were collected twice a month from 11 coastal sites for 2 years in the Boso Peninsula, Japan, and analyzed eDNA monitoring data using nonlinear time series analytical tools. We detected fish–fish interactions as information flow between eDNA time series, reconstructed interaction networks for the top 50 frequently detected species, and quantified pairwise, fluctuating interaction strengths. Although there was a large variation, water temperature influenced fish–fish interaction strengths. The impact of water temperature on interspecific interaction strengths varied among fish species, suggesting that fish species identity influences the temperature effects on interactions. For example, interaction strengths that Halichoeres tenuispinis and Microcanthus strigatus received strongly increased with water temperature, while those of Engraulis japonicus and Girella punctata decreased with water temperature. An increase in water temperature induced by global climate change may change fish interactions in a complex way, which consequently influences marine community dynamics and stability. Our research demonstrates a practical research framework to study the effects of environmental variables on interaction strengths of marine communities in nature, which would contribute to understanding and predicting natural marine ecosystem dynamics.

Temperature sensitivity of the interspecific interaction strength of coastal marine fish communities.

The effects of temperature on interaction strengths are important for understanding and forecasting how global climate change impacts marine ecosystems; however, tracking and quantifying interactions of marine fish species are practically difficult especially under field conditions, and thus, how temperature influences their interaction strengths under field conditions remains poorly understood. We herein performed quantitative fish environmental DNA (eDNA) metabarcoding on 550 seawater samples that were collected twice a month from 11 coastal sites for 2 years in the Boso Peninsula, Japan, and analyzed eDNA monitoring data using nonlinear time series analytical tools. We detected fish-fish interactions as information flow between eDNA time series, reconstructed interaction networks for the top 50 frequently detected species, and quantified pairwise, fluctuating interaction strengths. Although there was a large variation, water temperature influenced fish-fish interaction strengths. The impact of water temperature on interspecific interaction strengths varied among fish species, suggesting that fish species identity influences the temperature effects on interactions. For example, interaction strengths that Halichoeres tenuispinis and Microcanthus strigatus received strongly increased with water temperature, while those of Engraulis japonicus and Girella punctata decreased with water temperature. An increase in water temperature induced by global climate change may change fish interactions in a complex way, which consequently influences marine community dynamics and stability. Our research demonstrates a practical research framework to study the effects of environmental variables on interaction strengths of marine communities in nature, which would contribute to understanding and predicting natural marine ecosystem dynamics.

Evaluation of Yellow Sea anchovy (Engraulis japonicus) fishery for management strategies using a data-limited management toolkit

Most fisheries in developing countries are data-limited, which creates a huge challenge to the fishery management. Therefore full utilization of the available information is essential. Japanese anchovy (Engraulis japonicus) plays a key role in the marine ecosystem, but the anchovy population in the Yellow Sea of China has declined in the recent decades, which is also a data-limited fishery. In order to implement robust management strategies to recover the anchovy stock, based on the available information as well as the associated uncertainties, here we examine its management strategy evaluation using a computer software package data-limited management toolkit (DLMtool). Results indicated that fishing pressure on the Yellow Sea anchovy should be slightly reduced and the length at first capture should exceed the length at first maturity. These are high probably conductive to anchovy population recovery. We also selected some management procedures performed well in this study, such as minlenLopt1. Paying attention to quantitative population dynamics and perfecting data collection are important for future anchovy fisheries management against uncertainties in both model and data.

Environmental DNA in the Kuroshio reveals environment-dependent distribution of economically important small pelagic fish

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.

Use of Ensemble Model for Modeling the Larval Fish Habitats of Different Ecological Guilds in the Yangtze Estuary

Estuaries provide nursery habitats for a variety of fish species of different ecological guilds and have complicated environmental conditions. In this study, we applied ensemble species distribution models (SDMs) to four abundant and different ecological guild larval fish species (Hemiculter bleekeri (freshwater guild), Pseudolaubuca sinensis (freshwater guild), Coilia mystus (brackish water guild), and Engraulis japonicus (marine guild)) to explore their suitable habitats and the fish–habitat relationships in the Yangtze Estuary. The results showed that random forest (RF) demonstrated the best performance in all single algorithms and the surface range envelop (SRE) model was scarcely accurate. The ensemble SDMs demonstrated a superior predictive ability compared with any single algorithm, with the true skill statistic (TSS) and the area under the receiver operating characteristic curve (AUC) scores being above 0.899 and 0.641, respectively. Binary presence–absence maps showed the different spatial distribution patterns of the four species. We primarily found the freshwater species (P. sinensis and H. bleekeri) present in the South Branch (west of 122° E), whereas we found the marine species (E. japonicus) anywhere except inside the South Branch (west of 121.8° E). The area for P. sinensis (1615.93 km2) was relatively larger than that for H. bleekeri (1136.87 km2). We predicted that the brackish water species (C. mystus) would most likely be present inside the North Branch (west of 122° E), Eastern Chongming, and outside the South Branch (east of 121.8° E). Salinity, as a key environmental variable, contributed to the spatial variability. A low salinity (sea surface salinity (SSS) < 3) was beneficial for P. sinensis and H. bleekeri but was not suitable for E. japonicus. The SSS suitable range for C. mystus was 5–10 and 12–20. Multiple ecological guild species dwelled in the confluence of salt and fresh water. Our results will play an important role in the design of specific conservation strategies for fishery resources in this area.

Overcoming gaps in a seasonal time series of Japanese anchovy abundance to analyse interannual trends

Monitoring and understanding the level of exploitation and stock status of target and bycatch species are essential for effective fishery management and conserving biological diversity. Pursuit of these objectives is often challenging where yield statistics are unavailable, especially when scientific surveys are spatially and seasonally unbalanced. To address this issue, we attempt to combine recently developed methods to construct an assessment framework using Japanese anchovy (“anchovy”; Engraulis japonicus) in the Bohai Sea as an example. First, based on data from surveys conducted in spring, summer and autumn in the Bohai Sea during 2009–2019, we developed a seasonal spatio-temporal model for anchovy to interpolate missing observations thereby obtaining a continuous time series of abundance. Then, we fitted the abundance maximum sustainable yield (AMSY) model using the spring, summer, autumn, and seasonal average indices of abundance to obtain long-term trends in the stock status of anchovy. The model indicated that at the end of the survey series in 2019 there was a 17.6%–22.6% probability that the anchovy stock was in a sustainable state, 51.1%–69.3% probability it was in a period of recovery and 10.3%–29.8% probability it was declining. The relative stock size gained significant recovery throughout the study period, reaching a healthy level during 2016–2018. Our assessment framework enabled the estimation of anchovy stock status in the Bohai Sea in the absence of yield data, a process which will facilitate the assessment of other fishery resources in waters without yield statistics to provide estimates of local stock status for managers to take measures to avoid local depletion of those resources.

Metabolic Rates of Japanese Anchovy (Engraulis japonicus) during Early Development Using a Novel Modified Respirometry Method.

The allometric relationship between metabolic rate (VO2) and body mass (M) has been a subject of fascination and controversy for decades. Nevertheless, little is known about intraspecific size-scaling metabolism in marine animals such as teleost fish. The Japanese anchovy Engraulis japonicus is a planktotrophic pelagic fish with a rapid growth and metabolic rate. However, metabolic rate measurements are difficult in this species due to their extremely small body size after hatching. Herein, the metabolic rate of this species during its early developmental stage was measured for 47 individuals weighing 0.00009-0.09 g (from just after hatching to 43 days old) using the micro-semi-closed method, a newly modified method for monitoring metabolism developed specifically for this study. As a result, three distinct allometric phases were identified. During these phases, two stepwise increases in scaling constants occurred at around 0.001 and 0.01 g, although the scaling exponent constant remained unchanged in each phase (b^ = 0.683). Behavioral and morphological changes accompanied the stepwise increases in scaling constants. Although this novel modified respirometry method requires further validation, it is expected that this study will be useful for future metabolic ecology research in fish to determine metabolism and survival strategy.

Interannual Variation of Ichthyoplankton Community Structure in the Yellow River Estuary, China

To understand the community structure dynamics of fish eggs and larvae in the Yellow River estuary, four trawl surveys were annually conducted between 2011 and 2014, including at 13 stations in 2011 and 18 stations between 2012 and 2014. A total of 2540 eggs and 143 larvae were collected during the four surveys, comprising 25 species, 8 orders, 16 families, and 20 genera. During the survey period, species numbers of eggs first decreased and then increased, while abundances first increased and then decreased. Larval species numbers exhibited the same trends as for eggs, while larval abundances fluctuated across the four years of the study. The primary species represented by the eggs were Konosirus punctatus, Sillago sihama, and Cynoglossus joyeri, while the larval species primarily comprised Amblychaeturichthys hexanema, Chaeturichthys stigmatias, and Engraulis japonicus. Cluster analysis of species compositions for eggs and larvae revealed the presence of four groups, wherein groups 1–3 comprised communities from 12, 3, and 2 stations, respectively, that were primarily distributed in the eastern part of the estuary. In contrast, group four only comprised communities from one station at the western part of the estuary near Bohai Bay. All biodiversity indices were lowest in 2012 and biodiversity of fish egg and larval communities were most correlated with the water depth among the parameters that were measured. Overall, interannual variation in the distribution and diversity of fish egg and larval communities in the Yellow River estuary reflected the responses of fish to environmental variability.

Potential impact of predation by larval Spanish mackerel on larval anchovy in the central Seto Inland Sea, Japan

Japanese anchovy is used as an essential dried fish material from the larval to adult stages. In the central Seto Inland Sea, Japan, the catch of larval anchovy has markedly decreased to <3.9% of the maximum recorded in 2002 since 2013; however, the reason causing this reduction has not been well understood. The abundance of recruit fish, including larvae and early juveniles, has decreased in the last decade, despite abundant eggs, suggesting that the majority of larvae do not survive before recruitment. In contrast, the stock of Japanese Spanish mackerel, whose larvae are the major predator of larval anchovy, has increased in the Seto Inland Sea. It is hypothesized that an increase in the density of Spanish mackerel may have a top-down control on the decrease in anchovy recruitment by an increase in predation opportunities. In this study, we investigated the abundance of Spanish mackerel and anchovy larvae using a bongo net in the field in 2018 and 2019. The average densities of larvae in late May were 1.5–3.3 individuals (inds)/100 m3 and 1058–1346 inds/100 m3 for the Spanish mackerel and the anchovy, respectively; both were higher than those in 2002–2005. We constructed a Stella model, simulating the growth and survival of larval anchovy until they reached the commercial sizes by taking into account consumption by larval Spanish mackerel. The model suggested that the consumption of larval anchovy by larval Spanish mackerel accounted for <4% of the initial abundance of anchovy in 2018, which was not greater than that in 2005. In contrast, the reduction in the growth rates of larval anchovy due to reduced maternal conditions can adversely affect their survival. Thus, the results did not fully support the hypothesis mentioned above.

Comparative early growth patterns across four dominant fish species in a marine protected area in the East China Sea

Multiple marine protected areas have been established to protect spawning and recruitment fish stocks in the East China Sea. However, inadequate knowledge on early life histories for most species could be the main limiting factor for the effectiveness of these marine protected areas. To address the knowledge gap, the juvenile specimen of four dominant species (Amblychaeturichthys hexanema, Engraulis japonicus, Pampus argenteus and Trachurus japonicus) were collected in the Wentai marine protected area. Comparative analysis was carried out to explore the early growth patterns of these species. Through otolith microstructure analysis, we estimated daily age for 319 individuals and reconstructure the hatching pattern. The result helps more accurately identify hatching time of the four species, and hatching time of P. argenteus was found to shift to an earlier time. Consistent with the differing ecological characteristics, significant differences in growth rate and response pattern to SST were detected among the four species. The revealed early life characteristics and adaptive pattern to experienced thermal conditions could contribute to ecosystem-based fisheries management.

Exploring reconfiguration of trends in CPUE to model sustainable TAC options for the pivotal YSLME anchovy fishery

Sustainable utilization of exploited fish stocks generally relies on characterizing key aspects of their population dynamics using mathematical models to evaluate their stock status. In this study, the Anchovy population (Engraulis japonicus) in the Yellow Sea large marine ecosystem (YSLME) was evaluated by using the ‘Just Another Bayesian Biomass Assessment’ (JABBA) model. Catch and the anchovy scientific survey biomass index data from 1989 to 2021 in its nominal or raw form, plus three adjusted CPUE trends using data acquired from the China Fishery Statistical Yearbook were each used to fit JABBA to explore the performance of reconfigured CPUE for setting a total allowable catch (TAC) quota to sustain the YSLME commercial anchovy fishery. Results showed contrasting trends in estimated biomass from the fishery independent surveys, and nominal and reconfigured commercial fishery CPUE, with the latter producing the most plausible results. The JABBA output based on the scientific survey biomass index indicated a 56.7% probability that the anchovy stock is currently healthy with 1.04B2021/BMSYand 0.51F2021/FMSYratios, whereas JABBA estimates based on the nominal commercial CPUE-based were overly optimistic (100% probability stock was healthy). JABBA outputs based on the first two reconfigured CPUEs (FacpueyandFECcpuey) countered this overoptimism, with the survey biomass index-based assessment results lying between the extremes. This improvement in the modelled assessment was achieved because the reconfigured CPUE time series accommodated technological progress in fishing vessels and gear performance. Therefore, in instances where survey biomass index data are unavailable, we recommend using the two improved fishery CPUEs and combining the results of the two assessments to guide fishery management. Management reference points, however, should preferably be based on the more conservative of the two reconfigured CPUEs as a precautionary approach for setting a total allowable catch (TAC) whilst concomitantly considering the role of anchovy as prey for other economically important fish in the system.We encourage researchers to extensively review and improve the quality and availability of fisheries statistical data worldwide in the shared endeavour towards obtaining more realistic stock assessments.

Larval Fish Spatiotemporal Dynamics of Different Ecological Guilds in Yangtze Estuary

Estuaries, as important fish nursery habitats, usually include a variety of larval fishes of different ecological guilds and exhibit complicated changing environmental conditions. We carried out a survey to examine the spatiotemporal dynamics of different ecological guild larval fishes and their relationships with environmental factors in the springs and summers from 2018 to 2020 in the Yangtze Estuary (China). The aims of the study were to provide detailed information on the characteristics of the larval fish assemblage and to explore the spatiotemporal variation in different ecological guild species and the effects of environmental variables on assemblage structure. More than 140,000 fish larvae from 26 families and 99 species were gathered during the six cruises, with the spring being the most prolific. The assemblage was dominated by a few species and was divided into three ecological guilds. Engraulidae was the most abundant family, followed by Cyprinidae and Gobiidae. Hemiculter bleekeri (freshwater), Pseudolaubuca sinensis (freshwater), Coilia mystus (brackish water), and Engraulis japonicas (marine) were the predominant species. Seasonal variations in larval fish assemblage structure were closely influenced by temperature, and the fluctuation in salinity mainly determined the spatial distribution of the larval fish community. Freshwater flows also played an important role in shaping the larval fish assemblage structure and dynamics. The conclusions improve the understanding of the ecological dynamics of larval fish assemblages in environmentally heterogeneous areas and may be applicable to other estuary ecosystems.

Biological interactions potentially alter the large-scale distribution pattern of the small pelagic fish, Pacific saury Cololabis saira

We aimed to understand the effect of biological interactions on the distribution of small pelagic fishes. Surveys were conducted during 2003-2019 using sea surface trawl nets in the western and central North Pacific Ocean, covering an area between 143° E and 165° W, to estimate the distributions of 4 small pelagic fishes: Pacific saury Cololabis saira, Japanese sardine Sardinops melanostictus, chub mackerel Scomber japonicus, and Japanese anchovy Engraulis japonicus. These species are potential competitors, as they all occupy a similar niche. Japanese anchovy was abundant during 2003-2012, while Japanese sardine and chub mackerel were abundant during 2013-2019. Only Pacific saury was distributed throughout the survey area, while the others occurred within the area west of 180° longitude (WA). Pacific saury and its potential competitors showed adjacent distributions, with a slight overlap along sea surface temperature gradients in the WA. This distribution pattern remained even when Japanese sardine expanded its distribution to colder waters and increased in abundance after 2013, resulting in a shift in the distribution of Pacific saury to colder waters and a period of high densities of Japanese sardine. Such a distribution shift of Pacific saury was not observed in the area east of 180° longitude, where no Japanese sardine was observed. These results suggest the possibility that biological interactions such as inter-species competition can be an important factor in determining the distribution of small pelagic fishes.

Spawning Phenology and Early Growth of Japanese Anchovy (Engraulis japonicus) off the Pacific Coast of Japan

The reproduction and early growth of fish are essential elements that affect recruitment and provide breakthrough points for understanding population fluctuations. In this study, larval and juvenile Japanese anchovy (Engraulis japonicus) were collected from five coastal waters off the Pacific coast of Japan in 2020 and 2021 to gain more insight into life history traits such as reproduction and early growth of this species on the basis of otolith microstructure analysis. The spawning period appeared to be related to temperature and chlorophyll-a concentrations, showing latitudinal gradient variation among fishing areas. We detected a significant positive allometric growth pattern between standard length and body weight. The Gompertz model best fits the growth of standard length, showing an initial stage of growth that was quick and accelerating. The mean daily growth rate for standard length was 0.64 ± 0.09 mm per day. A series of mixed-effect models was constructed to investigate the sources of differences in the mean growth rates among individuals. The results revealed regional variability in fish growth, with individuals in the central Pacific stock growing faster. Individuals that grew slower were heavier than those of the same length, indicating a trade-off between length growth and weight growth. The mean growth of individual fish was positively influenced by environmental factors (surface water temperature and chlorophyll-a concentration), and individuals within the same school of fish displayed a striking homogeneity of growth. Our research demonstrates the significance of including both physiological characteristics and environmental influences in early growth studies on fish.

Development of a prey-predator species distribution model for a large piscivorous fish: A case study for Japanese Spanish mackerel Scomberomorus niphonius and Japanese anchovy Engraulis japonicus

One of the major challenges of species distribution models (SDMs) is incorporating the influence of prey on the predator. An ensemble modeling approach, the prey-predator species distributabion model (PPSDM), uses environmental variables (sea surface temperature, bathymetry, sea surface salinity, and sea surface current) and a biotic variable (predicted prey distribution: Japanese anchovy) to predict a piscivorous fish (Japanese Spanish mackerel) habitat in the China Seas. PPSDM comprised selected preferable single algorithms from nine algorithms, including tree-based models, machine learning models, regression models, an envelope-style method, and a classification model. Compared with that obtained when using habitat without the Japanese anchovy distribution, the regression models, machine learning models and a classification model have significant improvements. However, tree-based models have only slightly improved. The PPSDM results well reflected the ontogenetic migration of Japanese Spanish mackerel. We found that the wintering ground was distributed in regions with temperatures between 11 and 17 °C and salinities between 33.6 and 34.1. The bottom topography was also closely correlated with Japanese Spanish mackerel, and the suitable habitat was at 50–100 m isobaths as topography determined the position of isotherms (11, 17 °C), salinity isolines (33.6, 34.1), and fronts (temperature, salinity) in winter. The relationships among different climatic indices, temperature, and Japanese Spanish mackerel were analyzed. We found that the East Asian monsoon significantly influenced the Japanese Spanish mackerel habitat by affecting temperature variation. In the future, the suitable habitat of Japanese Spanish mackerel is projected to decrease by 21%, 28%, 36%, and 42% under RCP2.6, RCP4.5, RCP6.0, and RCP8.5, respectively. The Japanese Spanish mackerel in the northern Yellow Sea is projected to experience the ‘cul de sac’ effect, which would drive this species toward local extinction. The Japanese Spanish mackerel in the China Seas will probably shift northeastward through the Tsushima Strait, and the Sea of Japan may form the main habitat at the end of the century.

Revisiting the role of early life growth for survival potential in three clupeoid species

AbstractJohan Hjort's “critical period” hypothesis, which postulates that year‐class strength is determined in the short period following the onset of exogenous feeding, has rarely been supported by empirical data. Instead, the current understanding is that recruitment is determined by cumulative mortality throughout early life. Recent studies relied on the measure of growth autocorrelation derived from otolith daily increment widths to test the link between growth rate achieved during the post‐hatch period and during subsequent phases of the larval stage. Based on this approach, we revisit the role of larval growth in driving survival potential in three clupeoid species: Japanese sardine Sardinops melanostictus, Japanese anchovy Engraulis japonicus, and Pacific round herring Etrumeus micropus throughout the larval stage, using a combination of published datasets of otolith increment widths. Strong growth autocorrelation was detected for all three species throughout the larval stage, suggesting that initial growth determines to some extent growth rates achieved later in life. The extent of autocorrelation was reduced in sardine relative to anchovy and round herring at older ages. This interspecific difference could be attributed to differences in sensitivity to variability of environmental factors such as water temperature and food availability. The present findings suggest that the effect of early growth rate persists into later life stages for driving survival potential, which could reconcile the classic concept of “critical period” and the current “growth–survival” paradigm.