Small Fish Research Articles

Comparing standard‐ and reduced‐size passive integrated transponder (PIT) tags for monitoring juvenile wild spring Chinook Salmon

AbstractObjectivesAnnual migration monitoring can help to discern patterns and environmental factors that impact growth, survival, and movement timing in small fish. Mark–recapture methods form the basis for such monitoring, and the standard 12‐mm passive integrated transponder (PIT) tag has emerged as an essential tool for studies of juvenile salmonids. A smaller, 9‐mm PIT tag now provides the potential to conduct mark–recapture studies on smaller fish. We evaluated relative performance of the 9‐mm tag, which is similar in design to its 12‐mm predecessor.MethodsFor this comparison, we tagged and released approximately 8400 wild spring Chinook Salmon Oncorhynchus tshawytscha parr in Valley Creek, Idaho, from 2011 to 2013. Tag‐size cohorts were of similar average body size and were tagged in equal numbers. We estimated survival and detection probability for each cohort over two river segments.ResultsIn both segments, survival varied among years, but we observed no significant differences between tag‐size groups. At Valley Creek, average detection rates of fish with 9‐mm tags were a little less than one‐half the rates of fish with 12‐mm tags and were significantly lower in all 3 years. At Lower Granite Dam, detection rates were again lower for 9‐mm tags, but the differences were much smaller (3%–12%) and were not statistically significant.ConclusionWe found that 9‐mm tags can be as effective as 12‐mm tags and may allow for better inference to smaller (<55‐mm) non‐tagged fish. However, the lower detection rates of the 9‐mm tags could lead to less precise estimates, and site‐specific detection rates should be considered for studies that rely on these tags.

A shortfin mako shark circling a finless porpoise with damaged caudal fin.

Research on predator-prey interactions between sharks and cetaceans remain limited. Here, we report on a video of a shortfin mako shark circling a finless porpoise with a damaged caudal fin in the Seto Inland Sea, Japan. The finless porpoise was neither emaciated nor inactive, but unable to swim effectively due to the complete lack of a caudal fin. Some circumstantial evidence, including a bite mark on the porpoise's head, strongly suggests that the mako shark attacked it. Furthermore, the possible time difference between the two injuries the porpoise sustained may reflect the shark's hunting tactics. While mako sharks primarily feed on small fish and cephalopods, this observation suggests they also may prey on live cetaceans more often than previously thought.

ANALISIS KELAYAKAN MODEL BIOMEDIS EKSPERIMENTAL PADA KASUS DIABETES MELLITUS MENGGUNAKAN MODEL ORGANISME IKAN ZEBRA (Danio rerio)

Introduction : Animal models are essential for research into diabetes, as they allow scientists to study the disease in a controlled environment. Small freshwater fish known as zebrafish (Danio rerio) are being employed more and more as model organisms in studying human diseases. They are genetically similar to humans, and they share many of the same metabolic pathways. This study aims to assess the viability of utilizing zebrafish as a model organism in the study of diabetes mellitus. Method: This study was examined in three databases, including Google Scholar, PubMed, and Scopus, and 19 publications were included. For that database, we ran the following search query in the titles. A literature review was performed in this study, and Prisma flow diagrams were employed to enhance the clarity and transparency of the review process. A method for summarizing the characteristics of the Zebrafish that make it a desirable model organism for Diabetes Mellitus research. Result: The findings of this study show that zebrafish may be used to investigate the genetics, development, and treatment of diabetes since their glucose metabolism and reactive metabolite production pathways are remarkably similar to those of humans. Similar findings were made regarding the functional conservation in adipose biology, pancreatic anatomy, lipid metabolism, and glucose homeostasis. Conclusion:The conclusion of this study is that the Zebrafish can be used as one of the animal models for identifying new targets for the precaution and medication of diabetes mellitus.

The performance of anchovy purse seine in the North Coastal Java Sea, Indonesia

Small pelagic fishes including anchovies in Indonesia are caught by using different types of fishing gears. However, the anchovy purse seine commonly used polyethylene (PE) as material webbing which is less effective in the North Coastal Java Sea. This study aims to describe the design and construction of the anchovy purse seine and the characteristics of this gear construction. The research was carried out in the North Coastal Java Sea of Indonesia between May and June 2021. The main data from the nine anchovy purse seine units were collected using purposive sampling. The sampling method was performed by identifying and measuring the components of the number of anchovy purse seiners. The ratio of the length of the head rope to the length of the ground rope is between 0.926 and 0.991, so the net is not exactly rectangular, but almost trapezium in shape. The anchovy purse seine was constructed using webbing polyamide (PA) with 8 mm–9 mm in mesh size, which is considered a small mesh size. It is assembled with some ropes, floats, and sinkers. The anchovy purse seine is characterized by the dominant buoyancy value, 48 % larger than the sinking force. The sinking speed is 0.15 m/s, and the sinking time is 164 s. The anchovy purse seine's design and construction are suitable for operating in the waters of North Coast of Java.

Skin swabbing protocol to collect DNA samples from small-bodied fish species

Fish species are commonly used as experimental models in the laboratory. DNA is routinely collected from these animals to permit identification of their genotype. The current standard procedure to sample DNA is fin clipping, which involves anaesthetising individuals and removing a portion of the caudal fin. While fin clipping reliably generates good quality DNA samples for downstream applications, there is evidence that it can alter health and welfare, and impact the fish’s behaviour. This in turn can result in greater variation in the data collected. In a recent study we adapted a skin swabbing protocol to collect DNA from small-bodied fish, including sticklebacks and zebrafish, without the use of analgesics, anaesthetics or sharp instruments. A rayon-tipped swab was used to collect mucus from the flank of the fish, which was then used for DNA extraction. We subsequently demonstrated that compared to fin clipping, skin swabbing triggered fewer changes in stress axis activation and behaviour. We also found that gene expression and behaviour data collected from swabbed fish were less variable than similar data collected from fish that had been fin clipped. This potentially allows smaller sample sizes in experimental groups to be used after skin swabbing, thereby reducing animal use. Here we provide a detailed protocol explaining how to collect DNA samples from small laboratory fish using skin swabs.

Marine heatwaves alter the nursery function of coastal habitats for juvenile Gulf of Alaska Pacific cod

Marine Heatwaves (MHWs) can directly influence survival of marine fishes, particularly for early life stages, including age-0 juveniles during their residence in coastal nursery habitats. However, the ability of nurseries to support high fish densities, optimize foraging and growth, and protect against predators may be altered during MHWs. Gulf of Alaska Pacific cod (Gadus macrocephalus) larval, juvenile, and adult abundances declined dramatically following MHW events in 2014–2016 and 2019. To evaluate coastal nursery function during MHWs, we compared diet composition, recent growth, size, condition, and abundance of age-0 juveniles throughout their first summer before, during, and between MHWs. Diet shifted to larger prey during MHWs, particularly mysids, but diet did not appear to influence growth. We observed faster growth rates during MHWs, yet even when accounting for growth, we could not explain the higher body sizes observed in August during MHWs. Together with lower abundance and the near absence of small fish in the nursery by August during MHWs, these patterns highlight potential for size-selection and a reduced ability of nursery habitats to buffer against environmental variability during MHWs, with only a small number of large “super survivors” persisting through the summer.

A passive fish sampling method is representative for size but selective for parasite load

Fish capture in industrial aquaculture is both necessary (i.e., for transfer, monitoring and harvesting) and difficult. The most logistically feasible methods rely heavily on crowding, a process that is detrimental to fish welfare and production outcomes. Jump nets, which rely on passive capture via jumping behaviour, present a welfare-friendly alternative. But reliance on behaviour means capture is not guaranteed, and limited knowledge of their capture rate and sampling biases means they are not yet used to their full potential. Here, in sea-cages stocked with Atlantic salmon Salmo salar, we investigated how capture rate varied with net size, position, and time of day, and if salmon caught via jump net were representative of the sea-cage population. A comparison of jumping rates into surface rings (without nets) indicated that larger jump nets will catch more fish. Capture rate was highest in rings positioned in the centre of cages, and during the morning and evening. Jump nets sampled representatively for fish size but caught salmon with marginally lower condition (<2% difference) and with three times higher parasitic salmon louse (Lepeophtheirus salmonis) loads than fish caught using lift nets. Our results indicate that jump nets can be used as a size-representative sampling tool and to target lice infected salmon for treatment.

Sperm handling and management in the teleost model fish Japanese medaka (Oryzias latipes)

Japanese medaka (Oryzias latipes) has been used as a model organism in different research fields, including reproductive physiology. Sperm motility is the most important marker for male fertility in fish and, thus, reproduction success. However, because of small volume of ejaculate and short motility duration, it is still challenging to manage the sperm collection and analysis in small model fish. In the present study, we aimed to investigate sperm motility and to optimize sperm collection, short-term sperm storage, and cryopreservation in Japanese medaka (Oryzias latipes). Using two different approaches for sperm collection: testes dissection and abdominal massage, different housing conditions and activating the sperm with different activation solutions, we investigated immediate sperm motility. In the second part of this study, we used different osmolalities of immobilization solution, Hank's Balanced Salt Solution (HBSS) for sperm storage at 0, 2 and 3 h after sperm collection. Finally, the sperm were cryopreserved using methanol as cryoprotectant and HBSS as extender at two different osmolalities, and post-thaw sperm motility was investigated. The highest post-activating sperm motility was achieved in the groups activated by the extender at 300 mOsm/kg. The quality of sperm remained unaffected by co-housing with females or with males only. Furthermore, Hanks’ Balanced Salt Solution (HBSS) with an osmolality of 600 mOsm/kg demonstrated its efficacy as a suitable extender for sperm storage, preserving motility and progressivity for 3 h. The highest post-thaw motility was around 35%. There were no significant differences between post-thaw motility in different groups. We also found that post-thaw incubation on ice can maintain the motility of the sperm for up to one hour after thawing.

Non-model method for the stock status assessing and catch forecasting of the Flounder 26+28 subdivisions ICES in the Baltic Sea

The aim of this article: to assess the flounder stock state in the 26+28 ICES subdivisions of the Baltic Sea and forecast its catch in the Russian part of the 26th ICES subdivision using non-model methods.Methods used: The qualitative condition of the stock was assessed by length (LBI method — Length Based Indicators). To develop catch recommendations for flounder stock in 26+28 ICES subdivision, as well as in the Russian sea area, was used an approach for a stock category 3 (ICES classification), based on a combined biomass index for fish from bottom trawl surveys. The assessment was based on the ratio of the average values of population indices of the last two years to the previous values for three years. All methods have been successfully tested at the international level within the framework of seminars and Working Groups of the International Council for the Exploration of the Seas (ICES), in which Russian specialists took part.Novelty: In conditions of insufficient completeness and quality of available information to justification the flounder catch, using models of the exploited stock, for the Russian water area of the 26th ICES subdivision of the Baltic Sea, non-model methods for assessing the state and predicting its catch were used for the first time. Result: to solve problems of rational management and conservation of fish stocks, the LBI method, as a non-model assessment tool, allows timely identification of qualitative changes occurring in the stock. The flounder stock is within biologically safe limits. The fishery is aimed at preserving small and large fish (conservation option), the stock is exploited optimally. It is possible to maintain the species’ production level at least at the current level.Practical significance: In modern conditions the current level of information support for forecasting the flounder stock state and catch in the Baltic Sea will make it possible to solve problems related to the management of this resource in the near future.

Spatial structure and potential processes linking fish and benthic communities in a protected reef ecosystem in SE Brazil

Top-down and bottom-up processes can mediate the structuring of biological communities. Several studies have provided separate support for those processes in pelagic and benthic compartments of reef systems but studies focusing on whole-reef processes are less common. Here, we sampled 3 ‘reef compartments’ in the Alcatrazes Archipelago in Southeastern Brazil: benthic cover of colonial organisms, solitary organisms, and reef fish (i.e. pelagic) to identify the groups responsible for spatial community structure among reefs. A dynamic mosaic structure best defines the assemblages of each compartment, with substantial changes observed among sites over 2 consecutive years and at 2 depth strata, separated by a sharp thermocline. Changes in benthic cover of colonial organisms are largely due to the extent of the blooming of Sargassum canopies, algal turfs, and the zoanthid Palythoa caribaeorum. Solitary organisms show a consistent monotonic change in the abundance of sea urchins, ascidians, and snails. Fish assemblage structure differed among reefs; however, we observed that large invertivore fish tended to concentrate in warmer water above the thermocline and small fish of different feeding habits were found in deeper and colder water in all reefs. We observed a potential strong link between the reefscape and solitary organisms, with a negative relationship between the abundance of urchins and the cover of Sargassum spp. suggesting top-down control. A second link is indicated by a positive relationship between low-lying cover composed of articulated turf and P. caribaeorum and larger invertivorous fish, suggesting bottom-up control through the provision of favorable foraging grounds.

Fatty acid content and profile of round sardinella (Sardinella aurita), an expanding thermophilic species in the NW Mediterranean

Over the past few decades, due to sea warming driven by global climate change, the habitat range of round sardinella (Sardinella aurita) has expanded into the north-western Mediterranean Sea. This study evaluates the fatty acid content and fatty acid profile of this small, warm-water pelagic fish caught in this area, specifically the northern Catalan coast. The findings provide important insights into the nutritional status of the species under changing environmental conditions. The study confirms that fatty acid content varies according to the individual specimen’s maturity stages (immature, pre-spawners, and spawners). Pre-spawners showed higher fat levels compared to spawners, whose lipids are allocated to their gonads to enhance the survival of their offspring. While a high content of omega-3 polyunsaturated fatty acids (n-3 PUFAs) was generally found at all stages of maturity, pre-spawners had higher levels of EPA but lower levels of DHA than immature individuals and spawners. Moreover, compared to small pelagic fish more typical of the temperate waters in the region (European anchovy, Engraulis encrasicolus, and European sardine, Sardina pilchardus), round sardinella generally have a higher level of PUFAs, especially DHA. Encouraging consumption of this warm water species could provide significant nutritional benefits while reducing fishing pressure on European sardine and European anchovy, whose populations are currently in a very poor state.

Individual Identification of Medaka, a Small Freshwater Fish, from the Dorsal Side Using Artificial Intelligence

Individual Identification of Medaka, a Small Freshwater Fish, from the Dorsal Side Using Artificial Intelligence

Global and local behaviour of brown trout (Salmo trutta, L.) and chub (Squalius cephalus, L.) inside a laboratory vertical slot fishway model

Fish passes are commonly installed to partially reinstate river connectivity for fish species. They are designed according to the hydrological context and the biological features of the target species. Vertical slot fishways (VSF) still need a design optimization for small fish species, potentially relying on a better knowledge of fish behaviour inside the pools. This work studied the behaviour of two common fish species in France rivers: brown trout (Salmo trutta L.) and chub (Squalius cephalus L.) while passing through a VSF model. Fish movements were recorded by video tracking and analyzed following two steps: (i) global fish passages and (ii) fish behaviour inside one pool (trajectories, use of resting zones, movement patterns, position, and orientation before a successful upstream move). The mean total efficiencies (i.e. number of individuals that managed to pass and stay upstream over the total number of individuals studied) were 23.6 and 35.7% for trout and chub, respectively. Two behaviours were observed: direct passages in the upstream pool and passages with stops in one or more “resting” zones. Direct passages induced short transit times (several seconds) while a resting behaviour induced longer times (up to several minutes). A preferential resting zone, where flow conditions were the least constraining, was highlighted. Finally, the distance of fish from the slot was identified as a key parameter to ensure a successful passage. These results highlight the importance of the presence of resting zones and their hydraulic conditions for small fish passage success in VSF.

Conformity of the Work Plan with the Budget Implementation Document at the Marine and Fisheries Service of Central Lombok Regency

The writing of this article is aimed at finding out the suitability of the work plan with the Budget Implementation Document at the Marine and Fisheries Service of Central Lombok Regency by using descriptive qualitative. The results and discussion can be seen from the Details of the DPA Expenditure Activities of the Central Lombok Marine and Fisheries Service has reflected the conformity with the performance of the service which can be seen in the Central Lombok Regent Regulation No. 83 of 2016 concerning the Position, Organizational Structure, Main Tasks and Functions of the Central Lombok Regency Marine and Fisheries Service. As for activities and expenditures that are samples are Expenditure on Fishing Management activities in Rivers, Lakes, Reservoirs, Swamps, and Other Reservoirs that can be Pursued in 1 (one) Regency/City Region with official travel expenses, Small Fishermen Empowerment Activities in the Regency/City Region with competition prize spending, and Small Fish Cultivation Empowerment Activities with fish health and environmental management training expenses.

Phylogenomic analyses in the complex Neotropical subfamily Corydoradinae (Siluriformes: Callichthyidae) with a new classification based on morphological and molecular data

Abstract The family Callichthyidae, which comprises the subfamilies Corydoradinae and Callichthyinae, represents one of the largest families within the Siluriformes. Corydoradinae, the largest subfamily of Callichthyidae, alone accounts for &amp;gt;200 valid species, with new species being described frequently. This subfamily holds significant popularity among catfish enthusiasts worldwide, mainly because Corydoras are small, peaceful, and colourful fishes. Recognizing the existence of polyphyletic groups within Corydoradinae, the aim of this study was to construct a new phylogenetic hypothesis using genomic data (ultraconserved elements) and to re-evaluate the synonymized genera using the most recent morphological data. Our results supported the monophyly of Corydoradinae and identified seven distinct groups of species, each one with an associated pre-available generic name. These genera, namely Corydoras, Aspidoras, Scleromystax, Gastrodermus (resurrected), Osteogaster (resurrected), Brochis (resurrected), and Hoplisoma (resurrected), were all validated based on evidence derived from molecular and morphological analyses. A taxonomic key for the Corydoradinae genera is provided.

Small Fish Big Impact: Improving Nutrition during Pregnancy and Lactation, and Empowerment for Marginalized Women.

Undernutrition and micronutrient deficiencies such as anemia are considered significant public health challenges in Bangladesh, which enhancing fish consumption is a well-established food-based intervention to address these. This paper documents the establishment of community-based fish chutney production and reports the impact of its consumption on mid-upper arm circumference (MUAC) and hemoglobin (Hb) levels among targeted 150 pregnant and lactating women (PLW) in rural Bangladesh. A fish chutney was developed using locally available ingredients followed by a series of laboratory tests, including nutrient composition, shelf-life and food safety. A community-based fish chutney production process was designed to: (1) supply locally available ingredients for processing; (2) establish two fish drying sites; (3) initiate a community-based production site; and (4) distribute fish chutney to PLW for one year by six women nutrition field facilitators. Then a pre- and post-intervention study was designed for a selected 150 PLW to receive 30 g of fish chutney daily for 12 months. Differences in mean MUAC and Hb levels pre- and post-consumption were analyzed using one-way analysis of variance. Consumption of 30 g of fish-chutney resulted in significant increases of the mean values of Hb levels and MUAC among the targeted PLW.

Validation of a new acoustic telemetry transmitter for the study of predation events in small fishes.

Acoustic telemetry has emerged as an important tool for studying the movement and behavior of aquatic animals. Predation-sensing acoustic transmitters combine the functions of typical acoustic transmitters with the added ability to identify the predation of tagged animals. The objective of this paper was to assess the performance of a newly miniaturized acid-based predation-sensing acoustic transmitter (Innovasea V3D; 0.33 g in air). We conducted staged predation events in the laboratory where acoustically tagged rainbow trout (Oncorhynchus mykiss) were fed to largemouth bass (Micropterus nigricans) at 3.3-7.0, 9.0-10.8, 16.0-20.0, and 22.0-25.8°C. We also conducted false-positive tests where tagged rainbow trout were held at 10.0 and 16.8°C without the risk of predation. Predation events were successfully identified in 92% of the staged predation trials. Signal lag (i.e., the time required for a predation tag to indicate that predation occurred) ranged from 0.11 to 6.29 days and decreased strongly with increasing water temperature and increased with increasing body mass of the tagged prey. Tag retention in the gut of the predator was much more variable than signal lag and was influenced by water temperature and individual predators but not by prey mass. No false positives were detected after 60 days at either temperature (n = 27 individuals). Although the relationships between water temperature, signal lag, and retention time are likely species-specific, the data reported here provide useful information for the use of these transmitters to study predation in wild fishes, especially for temperate, freshwater fish.

Effect of Heat Shock Treatment on the Virulence of Grass Carp Reovirus in Rare Minnow Gobiocypris rarus

The mode and outcome of fish–virus interactions are influenced by many abiotic factors, among which water temperature is especially important in poikilothermic fish. Rare minnow Gobiocypris rarus is a eurythermal small cyprinid fish that is sensitive to infection with genotype II grass carp reovirus (GCRV). HSP70, a conservative and key player in heat shock response, is previously identified as an induced pro-viral factor during GCRV infection in vitro. Here, rare minnow was subjected to heat shock treatment (HST), 1 h treatment at 32 °C followed by reverting to a normal temperature of 24 °C, and subsequently challenged with GCRV-II at a dosage of 1 × LD50. The effect of HST on GCRV virulence in vivo was evaluated by calculating virus-associated mortality and viral load in both dead and survival fish. The results revealed that HST enhanced the mortality of rare minnow infected with GCRV; the fact that viral loads in the tissue samples of HST-treated fish were significantly higher than those in samples of the control group at 6, 8 d p.i. reflected a faster infection process due to HST. Quantitative gene expression analysis was further employed to show that the expression levels of Hsp70 in intestine and liver tissues from the HST group declined faster than muscle tissue after HST. HST W/O GCRV challenge upregulated proinflammatory cytokines such as MyD88 and Nf-κB, which was in consistence with the inflammation observed in histopathological analysis. This study shed light on the complexity of the interaction between fish abiotic and biotic stress response, which suggested that HST, an abiotic stress, could enhance the virulence of GCRV in Gobiocypris rarus that involved modulating the gene expression of host heat shock, as well as a pro-inflammatory response.

Climate change impacts on small pelagic fish distribution in Northwest Africa: trends, shifts, and risk for food security

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.

Migration patterns of the Japanese sardine in the Sea of Japan by combining the microscale stable isotope analysis of otoliths and an ocean data assimilation model

The Japanese sardine (Sardinops sagax melanostictus) is a small pelagic fish found in the Sea of Japan, the marginal sea of the western North Pacific. It is an important species for regional fisheries, but their dispersal and migration patterns during early life stages remain unclear. In this study, we analyzed the stable oxygen isotope ratios of otoliths of young-of-the-year (age 0) Japanese sardines collected from the northern offshore and southern coastal areas of the Sea of Japan in 2015 and 2016. The ontogenetic shifts of the geographic distribution were estimated by comparing the profiles of life-long isotope ratios and temporally varying isoscape, which was calculated using the temperature and salinity fields produced by an ocean data assimilation model. Individuals that were collected in the northern and southern areas hatched and stayed in the southern areas (west offshore of Kyushu) until late June, and thereafter, they can be distinguished into two groups: one that migrated northward at shallow layer and one that stayed around the southern area in the deep layer. A comparison of somatic growth trajectories of the two groups, which was reconstructed based on otolith microstructure analysis, suggested that individuals that migrated northward had significantly larger body lengths in late June than those that stayed in the southern area. These results indicate that young-of-the-year Japanese sardines that hatched in the southern area may have been forced to choose one of two strategies to avoid extremely high water temperatures within seasonal and geographical limits. These include migrating northward or moving to deeper layers. Our results indicate that the environmental variabilities in the southern area could critically impact sardine population dynamics in the Sea of Japan.