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Estuaries are one of the most productive ecosystems in the world, supporting a variety of flora and fauna. Primary productivity by phytoplankton is a rich source of organic carbon, substantial for the aquatic food web. Monitoring phytoplankton (i.e., chlorophyll-a) is essential to assess the health of estuaries and other continental shelves subjected to constant anthropogenic stress (e.g., developmental activities). In this study, a three-endmember combination Spectral Decomposition Algorithm (SDA) was developed to estimate the phytoplankton in the micro-tidal Yura estuary of Japan using Landsat-8 (30 m), and Sentinel − 2A (10 m). The endmember water, phytoplankton, and submerged aquatic vegetation (SAV) yielded the best results with both the satellite sensors (R2 > 0.80) owing to the limited influence of non-phytoplankton suspended solids (NPSS) in the estuary. Chlorophyll-a was used as the proxy for phytoplankton. The estimated root mean square error (RMSE) was relatively higher in Landsat-8 (RMSE = 0.187 µg/L) than the Sentinel-2A (RMSE = 0.162 µg/L). The results were validated using the ground truth data of the Yura Estuary (26 sampling points). Furthermore, the results indicate low chlorophyll-a concentration in the Yura estuary (< 2µg/L) except near the shorelines (~ 6 µg/L). A good fit (R2 = 0.79) between observed chlorophyll-a and turbidity indicated phytoplankton-dominated turbidity in the tide-less estuary of Japan. The estimated maximum turbidity was 1.4 FTU using both sensors, suggesting a low anthropogenic influence on the Yura Estuary. The study demonstrates a successful application of the spectral decomposition algorithm (SDA) in the coastal waters which could further be used to assess the horizontal and temporal variability in phytoplankton in estuarine water. [ABSTRACT FROM AUTHOR]

Yellow-phase Japanese eel Anguilla japonica (Temminck & Schlegel, 1846) utilize a variety of anthropogenically impacted habitats. An extensive understanding of the trophic ecology and habitat use is necessary for the conservation of this endangered species. In this study, we analysed the trophic ecology and feeding habitat of Japanese eels in two small rivers, the Akugawa River and Takase River in Wakayama Prefecture, Japan, dominated by an urban landscape and agricultural land use, respectively. The main goals were to assess the dietary diversity and trophic niche width for eels of two size classes (small eels: ≤ 240 mm total length, large eels: > 240 mm total length) in both habitats. The suitability of both rivers as a feeding habitat for eels was also evaluated. The trophic ecology of eels was inferred based on analysis of carbon and nitrogen stable isotopes, as well as stomach contents. Our results indicated that both rivers are suitable habitats to accommodate this eel, but to varying degrees. The dietary diversity of small eels and trophic niche width differed between rivers, indicating limiting factors, such as insufficient food sources and unfavourable abiotic habitat requirements for small eels in urban rivers. Also, the body condition of eels was found to be lower in the urban Akugawa River than in the Takase River. [ABSTRACT FROM AUTHOR]

The selection of a suitable method for tagging fish with transmitters is essential to ensure the feasibility of telemetry studies. Here, using a micro-acoustic transmitter, we examined the effects of tagging methods such as external attachment and surgical implantation on tag retention, and growth and survival of hatchery-reared spotted halibut at the release size (ca. 8–10 cm in total length). Fish with surgical implantation showed higher survival and retention rates than those with external attachments. However, the tagging methods did not influence the growth of the tagged fish. These findings indicated that surgical implantation of acoustic transmitters can be applied to small-sized spotted halibut. Overall, the findings can enhance the study about post-release movement of hatchery-reared fish at the release size to manage and conserve flatfish stocks. [ABSTRACT FROM AUTHOR]

The present study assessed the impact of regime shifts on the ecosystems that support fisheries in the coastal area of Kyoto Prefecture, the Sea of Japan. Ecopath models were constructed during cold (1985) and warm (2013) regime periods, when the fishery structures were different. Both models evaluated by pre-balance diagnostics were reliably constructed. Multiple ecosystem indicator values were compared between the two periods to assess changes in the ecosystem structure and the impact of fisheries on the ecosystem. The major change in catches in the coastal area of Kyoto Prefecture between 1985 and 2013 was that the Japanese sardine drastically declined and Spanish mackerel increased. The primary production requirements of fisheries (%PPR) were higher in 1985, reflecting the greater impact of sardine. The mean trophic level of catch and system omnivory index suggested that stability of trophic network increased after the sharp decline in sardine biomass. The %PPR, the loss of secondary production due to fisheries exploitation and probability analysis of fishery sustainability suggested that the fishery structure in 2013, which was dominated by set nets, contributed to a more sustainable fishery than the structure in 1985, when fishery was dominated by purse seines and set nets. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "Trophic ecology of Japanese eels in small rivers of urban and agricultural areas" published in Fisheries Science. The correction addresses several minor errors in the original article, including the correction of the author's email address and the correction of information regarding the QuAAtro2-HR AutoAnalyzer and the range of body weights for a specific river. Additionally, errors in the formatting of tables in the original article have been corrected. The correction notice emphasizes that Springer Nature, the publisher, remains neutral in terms of jurisdictional claims and institutional affiliations. [Extracted from the article]

This study aimed at characterizing the distribution of black sea bream Acanthopagrus schlegelii, a major target fish of commercial and recreational fishing, using environmental DNA (eDNA). Twelve survey stations were aligned along an inshore-offshore axis in Tango Bay, southwestern Japan. Water samples were taken from the surface and bottom layers at each station monthly from May 2017 through April 2018 (twice in June 2017 and excluding October 2017). Quantitative polymerase chain reaction (qPCR) with species-specific primers and probe was used to detect DNA of black sea bream in water samples. Throughout the year, eDNA was abundant at inshore stations, especially at stations close to the river mouth in the innermost part of the bay. In May and June, eDNA was detected even at the most offshore station 19 km from the coast, whereas eDNA was detected exclusively within 3 km from the coastline during the months of July through April. The eDNA detected offshore in May and June were likely to have originated from eggs and/or larvae, as this species spawns pelagic eggs in early summer. These results through the use of eDNA indicated that black sea bream is highly dependent on coastal areas in its life history. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) has been utilized for the detection of target species, and its application in biomass estimation has great potential. However, there are several factors that may hinder this application, such as species-specific eDNA emission, interspecific interactions, and the effect of feeding. In this experiment, we quantified eDNA emission in the striped jack Pseudocaranx dentex and the jack mackerel Trachurus japonicus in single- and mixed-species tanks for 10 days over a 12-day experimental period. eDNA concentrations of both of these species peaked on the first day of the experiment and later stabilized. The linear mixed-effects model revealed that the temporal factor, being highest immediately after their introduction into experimental tanks, had significant effects on eDNA concentration, whereas fish species and feeding factors did not. Rearing conditions of mixed or single species were not significant either. Taken together with previous studies, eDNA emission may be equal in fishes that have similar morphology and behavior, and their interspecific interaction may be negligible for eDNA detection. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) can be a powerful tool for detecting the distribution and abundance of target species. This study aimed to test the longevity of eDNA in marine sediment through a tank experiment and to use this information to reconstruct past faunal occurrence. In the tank experiment, juvenile jack mackerel (Trachurus japonicus) were kept in flow-through tanks with marine sediment for two weeks. Water and sediment samples from the tanks were collected after the removal of fish. In the field trial, sediment cores were collected in Moune Bay, northeast Japan, where unusual blooms of jellyfish (Aurelia sp.) occurred after a tsunami. The samples were analyzed by layers to detect the eDNA of jellyfish. The tank experiment revealed that after fish were removed, eDNA was not present in the water the next day, or subsequently, whereas eDNA was detectable in the sediment for 12 months. In the sediment core samples, jellyfish eDNA was detected at high concentrations above the layer with the highest content of polycyclic aromatic hydrocarbons, reflecting tsunami-induced oil spills. Thus, marine sediment eDNA preserves a record of target species for at least one year and can be used to reconstruct past faunal occurrence. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "Impacts of regime shift on the fishery ecosystem in the coastal area of Kyoto prefecture, Sea of Japan, assessed using the Ecopath model." The article was originally published without open access, but the author later decided to make it an open access publication. The copyright of the article has been changed to © The Author(s) 2024, and it is now distributed under the terms of the Creative Commons Attribution 4.0 International License. The original article has been corrected. Springer Nature, the publisher, remains neutral regarding jurisdictional claims and institutional affiliations. [Extracted from the article]

Eel movement patterns have been frequently studied to learn about their movements within the fresh- and brackish waters of the same river before their spawning migrations. Although otolith microchemistry analyses estimated that the eels used fresh-, brackish, and marine water habitats, inter-river movements of Japanese eels via the sea have not been observed. In previous studies silver eels appear to migrate for spawning in October-December, and so eels that migrate to the sea during this period have been considered as migrating for spawning. In the progress of our acoustic telemetry study on eel movement patterns, we found the first evidence that Japanese eels move between distant rivers via the sea. During the study in the Akugawa River, Wakayama Prefecture, Japan, we released 15 acoustically tagged yellow-phase eels on 8 April 2019. Three of the 15 tagged eels released into the Akugawa River were later caught in the ~ 15 km distant Hidari-Aizu River by a local angler during early mid-July 2020. This showed that 2 of 3 tagged eels migrated seaward in October and December. The other tagged eel had been detected only at a releasing point until 30 June 2019 and due to an unknown reason was never detected again before capture in the Hidari-Aizu River. The remaining 12 tagged eels stayed in the Akugawa River during the study period. These findings indicate that Japanese eels may migrate seaward for purposes other than just spawning. This information is valuable for understanding the eels' life-history diversity and for future conservation plans. [ABSTRACT FROM AUTHOR]

Land use features can have a significant impact on the flux and stoichiometry of nutrients from the watershed to the sea along the freshwater continuum. Traditional agricultural watersheds designated as a Globally Important Agricultural Heritage System (GIAHS) may have unique features on nutrient dynamics. Here, we conducted seasonal, high-resolution spatial surveys for concentrations of dissolved inorganic phosphorus (DIP) and nitrogen (DIN) and stable isotopes of water and nitrate of the GIAHS in Japan (Kunisaki Peninsula). The highest upstream DIN concentrations (mean = 83 μM) were observed in the non-irrigation period in autumn. 17O isotopes of nitrate suggested that microbial nitrification in forest soil was the primary source (> 95%) of total nitrate. Spatial differences in DIP and DIN concentrations among the upstream, midstream, and downstream waters were small, with high DIN/DIP ratios (> 50) were exported from the watershed to coastal seas. Nutrient concentrations exhibited different dynamics during summer when irrigation was taking place with average DIP concentrations increasing from upstream (0.5 μM) to downstream (2.1 μM) waters. A generalized linear model showed that the proportion of paddy fields, cultivated land, residential area as well as forest were the primary drivers of DIP concentrations. DIN concentrations decreased moving downstream likely due to denitrification in the anaerobic irrigation ponds and paddy fields. This study showed that the traditional agricultural landscapes mitigated the excess DIN loading from forested areas while supplying the essential DIP for coastal production, suggesting an important forest-river-sea connection system that manages nutrient inputs to coastal waters. [ABSTRACT FROM AUTHOR]

Although recreational fishing is popular in Japan, few estimates have been made of its economic value to the country. This study aims to (1) evaluate the economic value of recreational fishing in Tango Bay, Kyoto Prefecture using the travel cost method (TCM); and (2) explore the development of related regional economies around Tango Bay. The TCM analysis showed that 150,000 anglers visit Tango Bay annually, and the estimated total annual travel cost and total annual consumer surplus of recreational fishing there are approximately JPY 3.8 billion and JPY 11.7 billion, respectively. The annual commercial fisheries production of Kyoto Prefecture in 2017 was JPY 3.0 billion. Thus, in Tango Bay, coastal fish resources not only have a direct use value as food, but also a large indirect value as targets for recreational fishing. The importance of recreational fishing relative to commercial fishing has increased in Japan similar to in other countries where it is popular. As many people enjoy recreational fishing in Japan, it is expected to have an impact on domestic fish resources. To address this, both commercial and recreational fishing should be included in fish resource management activities aimed at the development of related local economies in Japan. [ABSTRACT FROM AUTHOR]

Japanese eels (Anguilla japonica) utilize a broad range of habitats along the marine-freshwater ecotone during their growth phase in inland waters. This study aimed to analyze the foraging behavior of yellow-phase Japanese eels in connected fresh- and brackish water habitats and to connect foraging behavior and habitat use through the analysis of carbon (δ13C) and nitrogen (δ15N) stable isotopes. Stomach contents of eels collected in fresh- and brackish waters were analyzed to identify food sources. Values of δ13C and δ15N were analyzed in eels and their potential food sources, and used to predict the recent foraging patterns of eels in the Matsukawa-ura, a brackish water lagoon, and in three freshwater tributaries. Eels preyed on the benthic river community and the mudflat community of the lagoon. Gobiid fishes were found to be an important food source for eels in fresh- and brackish water habitats, while Japanese mitten crabs (Eriocheir japonica) and shore crabs (Hemigrapsus spp.) were major prey in fresh- and brackish waters respectively. δ13C values of potential eel prey differed significantly between fresh- and brackish waters and were used to classify three recent patterns of foraging by the 73 eels included in this study: 1) freshwater foraging, 2) brackish water foraging, and 3) multiple-habitat foraging. The data suggested that some eels recently or frequently moved between fresh- and brackish water habitats while others demonstrated a higher fidelity to either fresh- or brackish waters. Isotopic characteristics of prey in the respective foraging habitats revealed the plasticity of habitat use of yellow eels in the study area. This study demonstrates an integrated approach to study habitat use and foraging behavior of eels. Furthermore, the study underlines the need to consider freshwater and estuarine habitats and the connectivity between them for eel management and conservation. [ABSTRACT FROM AUTHOR]

Japanese eel (Anguilla japonica) is a commercially important species; however, its population has declined in recent years. Appropriate conservation management, including habitat protection, is required to reverse this decline. However, their habitat use pattern during the riverine life stage is poorly understood. In this study, we investigated the longitudinal distribution and microhabitat of small-sized (<200 mm total length) and large-sized (≥200 mm total length) Japanese eels observed in 83 and 124 quadrats (1 m × 1 m), respectively, placed at seven stations in the Nikkeshi River in Fukushima Prefecture, Japan. Analysis using generalized linear models revealed that the eel density of both size classes decreased with increasing distance from the river mouth. In addition, the density of small-sized eels, but not large-sized ones, decreased as weir numbers increased. Moreover, analysis using generalized additive models showed that microhabitat uses differed between the size classes. The small-sized eels used near-shore habitats which had low current velocities. Their preferred habitats contained both complex substrates with smaller particle sizes and simple substrates with relatively large particle sizes. In contrast, the large-sized eels used both near-shore habitats with lower current velocities and the center of the river which had high current velocities. They preferred simple riverbed habitats with large particle-sized substrates and no underwater vegetation. These results suggest that there is a size-dependent change in the longitudinal distribution and microhabitat use of Japanese eels during their river life stage. These findings provide valuable information for the conservation and management of Japanese eels in rivers. [ABSTRACT FROM AUTHOR]

The population structure and demographic history of a pelagic lumpsucker, Aptocyclus ventricosus, were investigated on the basis of sequence variation in the mitochondrial cytochrome b gene (1038 bp). The haplotype network clearly recovered two haplotype groups, consisting of western and eastern North Pacific individuals, except for some specimens collected from offshore of Tohoku, northern Japan. The geographic distribution of haplotypes suggests that the ocean currents in the North Pacific have shaped the population structure of the species after historical vicariant events between the Kuril Islands and Kamchatka Peninsula. In addition, the demographic histories of the two haplotype groups were quite different, suggesting that the western North Pacific group experienced a population expansion starting around 10,000 years ago, while the population size of the eastern North Pacific group has remained more stable. [ABSTRACT FROM AUTHOR]

The effects of temperature and prey density on the recent growth rate (RGR) of chub mackerel, Scomber japonicus, were examined. Scomber spp. larvae and juveniles were collected along the Boso–Kashimanada Pacific coast in Japan between March and July in 2015 and 2016. Larvae and juveniles identified as S. japonicus using DNA were subjected to stomach-content and otolith-increment analyses. The effects of temperature and prey density on RGR were analyzed using a generalized linear mixed model (GLMM), which showed that temperature positively affected the RGR of larvae in the body length (BL) classes < 5 mm, 5–7 mm, 7–9 mm and 9–11 mm. Prey density also affected growth in the < 5 mm, 5–7 mm, 7–9 mm and > 11 mm classes and effects of prey density on RGR for larger (> 11 mm) larvae and juveniles were stronger than those for smaller (< 9 mm) larvae. S. japonicus larvae transform into juveniles at around 12 mm BL, and the increased feed demands of juveniles likely lead to prey-density-dependent growth. The otolith increment widths of larvae and juveniles were significantly narrower than those during the same stages in 1-year-old S. japonicus collected from purse seine fisheries operated in the Joban or Kashimanada areas, suggesting growth-dependent mortality. [ABSTRACT FROM AUTHOR]

The ark shell Scapharca broughtonii population has decreased markedly in recent years in Nanao Bay, a semi-enclosed embayment in Japan. Continuous measurement of dissolved oxygen (DO) at the bottom of Nanao Bay was performed, and S. broughtonii survival rates were investigated experimentally and in situ. In summer the DO concentration showed diel variation, with generally sufficient oxygen during the day but concentrations < 2 mg/l at night. In rearing experiments to investigate their physiological state, ark shells were placed in a tank designed to produce hypoxic conditions at night. Blood succinate levels in the ark shells increased, and all individuals were dead after 35 days. The results of the study indicate that the main cause of mortality of S. broughtonii on the seabed in Nanao Bay is hypoxia at night. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) consists of DNA fragments shed from organisms into the environment, and can be used to identify species presence and abundance. This study aimed to reveal the dispersion and degradation processes of eDNA in the sea. Caged fish were set off the end of a pier in Maizuru Bay, the Sea of Japan, and their eDNA was traced at sampling stations located at the cage and 10, 30, 100, 300, 600 and 1000 m distances from the cage along two transect lines. Sea surface water was collected at each station at 0, 2, 4, 8, 24 and 48 h after setting the cage, and again after removing the cage. Quantitative PCR analyses using a species-specific primer and probe set revealed that the target DNA was detectable while the cage was present and for up to 1 h after removing the cage, but not at 2 h or later. Among the 57 amplified samples, 45 (79%) were collected within 30 m from the cage. These results suggest that eDNA can provide a snapshot of organisms present in a coastal marine environment. [ABSTRACT FROM AUTHOR]

The temperate seabass Lateolabrax japonicus is a coastal and partial amphidromous fish that is commercially valuable in Japan. Fish age is an important and sensitive variable for stock structure assessment, and inaccurate aging can result in inappropriate management practices. However, there have been few studies on age determination in this species. By examining monthly changes in marginal increment growth, we validated that otolith increments are formed annually. This information was used to develop an age-determination method using otolith sections. Von Bertalanffy growth models were generated based on standard length and weight data for both sexes in Sendai Bay and Tango Bay, Japan. Differences in standard length- and weight-at-age and growth parameters were observed in both sexes and locations. Females exhibited larger standard lengths and weights at older ages than did males, in both locations. Individuals from Sendai Bay exhibited longer average asymptotic lengths, higher asymptotic weight, higher standard length-at-age and higher weight-at-age compared to their counterparts from Tango Bay. Decreases in growth rates in both Sendai Bay and Tango Bay occurred around the age at maturity, indicating that more energy was allocated to reproduction than growth after reaching maturation. Differences between Sendai Bay and Tango Bay in the age at which the maximum instantaneous growth rate and the asymptotic length are reached were thought to arise from differences in water temperature and biological productivity between the two bays. [ABSTRACT FROM AUTHOR]

Terrestrially derived dissolved organic matter (DOM) plays an important role in providing ligands that regulate iron transport to coastal ecosystems. Fluorescent DOM (FDOM) is widely used to evaluate DOM behavior, but the relationship between iron and FDOM distributions in estuarine and coastal systems is poorly understood. In this study, we investigated the distributions of dissolved iron (DFe < 0.7-µm fraction) and FDOM as measured using fluorescence excitation-emission matrices in the Yura River-Tango Bay system. The DFe distribution was not closely correlated with that of the humic-like FDOM, indicating that humic-like FDOM is not the main regulator of the DFe concentration in this system. The relatively low fluorescence intensity of humic-like FDOM demonstrates that colloidal inorganic iron is the major component of riverine DFe. A large proportion of the riverine DFe (> 94%) was removed in the mixing process, but humic-like FDOM likely supports the transport of DFe to the coastal zone. [ABSTRACT FROM AUTHOR]

Ontogenetic habitat shift and feeding habits in the shallow (< 15 m) and deep (30-80 m) habitats of age-0 Japanese flounder Paralichthys olivaceus in Sendai Bay, the Pacific coast of northeastern Japan, were examined to understand the mechanisms that potentially enable area-specific high recruitment success. The flounder was able to use the shallow nursery habitat for about 1 year, until the next summer of their settlement (June-August) when they had reached 250 mm total length (TL). In addition, age-0 flounder between 150 and 250 mm TL used both shallow and deep habitats from winter to the next summer of their settlement, where species, size, and availability of potential food and susceptibility to predators are considerably different. These area-specific characteristics in Sendai Bay are clearly different from other areas around Japan that have been described in the literature: shorter residence in the shallow habitat and smaller size at emigration to the deep habitat. The characteristics in Sendai Bay seem to be enabled by prolonged good feeding conditions in the shallow habitat, which result from an abundant food supply and relatively lower temperature that does not exceed the uppermost temperature (25 °C) for maximum growth of the age-0 flounder. We consider that the prolonged better feeding conditions in the shallow habitat in the study area for ca. 1 year after settlement contribute to higher recruitment success. [ABSTRACT FROM AUTHOR]

Coastal seas are composed of relatively independent ecosystems, such as estuaries, rocky shores, mangroves, and coral reefs. Such individual ecosystems (IEs) are linked closely to each other by the dispersal and circulation of nutrients and organic matter and the movement of organisms, and form a coastal ecosystem complex (CEC). The CEC is understood as a unit of structure and function of coastal seas. It is characterized by a high degree of species diversity and it plays a large role in fishery and aquaculture production, as it provides important marine services for humans. This special volume compiles recent ecological studies of target species and IEs, to facilitate the conservation of coastal seas and the sustainability and production of their fisheries and aquaculture based on our understanding of the structure and function of the CEC in these environments. [ABSTRACT FROM AUTHOR]

Seasonal changes in the growth rate of larval Japanese anchovy Engraulis japonicus collected by shirasu seine net boats in Osaka Bay in 2008 were estimated using otolith daily growth increments to examine the effects of environmental factors. Larval anchovy were caught from May to November. The range in standard length (SL) of the larval anchovy was 10-35 mm, and larvae of SL 20-25 mm dominated numerically, accounting for more than 40% of all anchovy larvae. Daily growth rates for the last five days before catch increased from May to July, decreased or were stagnant in August and September, increased again in October, and decreased in November. Seawater temperature and density of copepod nauplii were correlated with the daily growth rate. In this study, the relationship between growth rate and temperature showed a skewed dome shape, with an optimum temperature for growth of around 23 °C. These results in summer of 2008 suggest that the growth rate of Japanese anchovy increased with increasing temperature for temperatures < 23 °C, but growth was limited by prey availability and/or other factors, such as low dissolved oxygen, at higher temperatures. Recent environmental improvements in nutrient inputs to Osaka Bay are discussed in relation to larval growth rate. [ABSTRACT FROM AUTHOR]

The Japanese sea cucumber Apostichopus japonicus plays important ecological and economic roles in the coastal areas of Japan. Here, we aim to reveal the relation between habitat characteristics and density of juvenile and adult sea cucumbers in Maizuru Bay. Density of adult sea cucumbers was estimated by underwater visual surveys and bottom trawls and that of newly settled individuals by seedling collectors distributed in the bay. The physical environment of the sea bottom was evaluated from median diameter, total organic carbon, total nitrogen, carbon-to-nitrogen ratio, carbon isotope ratio, nitrogen isotope ratio, depth, slope, and distance from the coastline. Adult sea cucumber density was higher in the east side than the west side of Maizuru Bay, the former having a no-take zone for sea cucumbers. Juvenile sea cucumbers were most abundantly collected in the central part of the bay. High organic matter from the sea, short distance from the coastline, and high seabed gradient (steepness) had a positive effect on the density of adult sea cucumbers, and depth had positive effects on their body size. We suggest that sustainable management of sea cucumbers can be achieved by a combination of the establishment of no-take zones and increased protection of nursery habitats. [ABSTRACT FROM AUTHOR]

Hydrographic conditions and distributions of juvenile temperate sea bass Lateolabrax japonicus were observed in early spring from 2009 to 2012 in the Yura River estuary, which is highly stratified due to its small tides and consequent seawater intrusion into the bottom layer of the river as a salt wedge. In all four studied years, the upstream expansion of their distribution coincided with the timing of the salt wedge intrusion from the lower to upper estuary, indicating that juvenile fish used salt wedge intrusions to ascend the estuary in early spring. However, juveniles sometimes remained in the nearshore area even when the salt wedge intrusion had already occurred, indicating that other triggers are also likely to be necessary. We therefore evaluated the effects of temperature on upstream migration behaviors. The relationship between the mean temperature they experienced from hatch until starting the ascent and mean age of each cohort at the upstream migration fitted with the law of effective cumulative temperature. Most cohorts ascended the river at an effective cumulative temperature of approximately 500 °C-days. This suggests that higher temperatures would lead to a shorter period prior to the upstream migration. [ABSTRACT FROM AUTHOR]

To better understand the habitat choices of Japanese sea cucumber Apostichopus japonicus juveniles, we investigated their responses to various stimuli. Specifically, their phototactic, thigmotactic, and geotactic responses were tested by placing sea cucumber juveniles in appropriately designed test tanks, while their responses to turbulence were tested in tanks in the presence or absence of wind-driven waves. Sea cucumber juveniles showed clear negative phototaxis, but there was no clear evidence of thigmotaxis or geotaxis. The juveniles frequently appeared at the surface of the water in a tank lacking turbulence, but much less frequently in a tank with turbulence. We conclude that sea cucumber juveniles choose their habitat via a combination of phototaxis and their limited ability to attach to hard substrates. [ABSTRACT FROM AUTHOR]

Although many fish species are known to feed on jellyfish, only a few quantitative studies on this subject have been conducted in the field or laboratory. We combined field observations and feeding experiments to quantitatively evaluate the potential feeding capability of the black scraper Thamnaconus modestus on giant jellyfish Nemopilema nomurai in a jellyfish-abundant area. Underwater observations revealed that shoals of T. modestus fed voraciously on jellyfish when the jellyfish were close to the fish's seaweed habitat. Gut contents of field-collected T. modestus almost exclusively consisted of jellyfish. In tank trials, feeding activity of black scraper was high when light intensity was between about 1.1 lx and 50 × 10 lx. The estimated feeding speed of T. modestus on the jellyfish in the Sea of Japan when the jellyfish bloom occurred was 10.0 ± 2.0 times fish body weight per day. The results support the prediction that T. modestus and probably other coastal medusivorous fishes have a substantial capability to eliminate jellyfish blooms. Considering that they are highly dependent on seaweed bed, protection of such habitats for these medusivores may be the most cost-efficient control method for jellyfish blooms. [ABSTRACT FROM AUTHOR]

Populations of sea cucumbers, including the Japanese common sea cucumber Apostichopus japonicus, have been seriously depleted worldwide due to overfishing. Mark-recapture study is an efficient means of collecting ecological data. However, the use of such a method in sea cucumbers is difficult because they lack hard tissues in the body wall. Here we tested the viability of various tagging methods on A. japonicus. First, we applied conventional tags using four different methods [single spaghetti (T-bar) tagging, double spaghetti tagging, ribbon tagging, and Atkins tagging] to ten individuals per method in aquaria for 14 days. Of the methods used, single spaghetti tagging had the highest retention rate. Then we examined the retention rate of single spaghetti tags on ten individual sea cucumbers for up to approximately 6 months in rearing conditions. The single spaghetti tagging method showed a retention rate of 100% over at least 7 days, and 50% of the tags remained embedded after 56 days. The longest duration of tag retention was 174 days, at which time the experiment was terminated. These results indicate that single spaghetti tagging is reliable for both short- and longer-term studies, making it a useful tool for ecological and conservation studies in sea cucumbers. [ABSTRACT FROM AUTHOR]

The feeding ecology of juvenile temperate seabass ( Lateolabrax japonicus) in relation to various prey environments was analyzed in the Yura River estuary from 2008 to 2012. Juveniles mainly fed on copepods and mysids, both in the Yura River estuary and in the adjacent coastal area. The dependency on the mysids increased as juveniles grew from 15 to 25 mm standard length (SL), and the main stomach contents were mysids for juveniles larger than 25 mm SL. The maximum size of food contents increased from 2 to 15 mm with the growth of juveniles from 15 to 25 mm SL. Most prey items smaller and larger than 2 mm were composed of copepods and mysids, respectively. The mean size of ingested food items increased with the size of the juveniles, while the mean number of prey items in each stomach decreased with growth after juveniles reached 22 mm SL. As a result, the stomach content index increased with the size of juveniles. These results indicate that the shift to larger-sized prey items (from copepods to mysids) is important for juveniles to obtain energy efficiently. Mysids were larger and more abundant in the estuaries than those in the coastal area. Therefore, the estuary provided better foraging conditions to juvenile temperate seabass than the coastal area. [ABSTRACT FROM AUTHOR]

Although jellyfish are important predators of fish larvae, many fish species also feed on jellyfish. Therefore, the predator-prey role of jellyfish and fish may switch during the course of their life histories. Here, we investigated such interactions by examining (1) the avoidance behaviour of threadsail filefish Stephanolepis cirrhifer to moon jellyfish Aurelia sp. and (2) the feeding behaviour of filefish on moon jellyfish medusae and polyps. The efficiency of filefish as jellyfish predators was examined by comparing their behaviour with that of black scraper Thamnaconus modestus and red sea bream Pagrus major. Filefish and black scraper were able to avoid medusae and obtain tolerance against nematocysts at a smaller body size compared to red sea bream. Filefish initiated feeding on medusae when they became juveniles of 21.8 mm SL. Feeding trials of yearling filefish on polyps at different temperatures (range 10-30°C) indicated that the highest feeding rate was 3.1 individuals s at 26.8°C. We suggest that the feeding pressure of filefish on jellyfish polyps may have an impact on medusa biomass. [ABSTRACT FROM AUTHOR]

We examined the diel activity pattern of the sea cucumber Apostichopus japonicus with or without the presence of food and predators. We also tested whether they have the capability for time-place learning. In the feeding experiment, juvenile and adult sea cucumbers were fed at either 00:00 or 12:00, at a fixed feeding place for 12 days, and the presence of animals in the feeding area was recorded. In the predator experiment, juvenile sea cucumbers were kept in a tank with or without a filefish, and the emergence of juvenile sea cucumbers outside the oyster shell area was recorded. Juvenile sea cucumbers did not show a diel activity rhythm, whereas adults were nocturnal, but this was altered by feeding at 12:00. Neither juveniles nor adults appeared in the feeding area before feeding time, suggesting an inability for time-place learning. Juvenile sea cucumbers hid under the oyster shells during the daytime and were active at night in the presence of a filefish, but without a filefish, they also showed high activity in the daytime. We suggest that sea cucumbers change their activity depending on the presence of food and predators, but without the influence of time-place learning. [ABSTRACT FROM AUTHOR]

The present study investigated whether red sea bream Pagrus major could learn about feeding and avoidance area through video model observation. In Experiment 1, 45-mm standard length (SL) fish were trained to learn about a feeding area in a tank. In Experiment 2, 114-mm SL juveniles were trained to avoid a hand net by moving into a shelter. Three treatments were established in each experiment: (i) live model observer: fish observed the behavior of a real fish in an adjacent tank; (ii) video model observer: fish observed video playback of a conspecific on a monitor; and (iii) non-observing control. Ten observational trials were performed in both experiments for the live and video model observer. Afterwards, fish from all treatments were conditioned by feed or avoidance training. In Experiment 1, there was no difference in the feed learning process among treatments. In contrast, in Experiment 2, live and video model observers acquired avoidance learning more quickly than control. The result indicates that the video model can be as efficient as the live model for observational learning in fish. This study suggests that video playback may be useful for anti-predator training of seedlings for stock enhancement. [ABSTRACT FROM AUTHOR]

Conditional discrimination in the octopus ( Octopus vulgaris) was studied using successive discrimination training. The experimental animals were divided into two groups, and a barrel-shaped white object (stimulus) was presented to each group. One of the groups was rewarded with food for responding to the stimulus, but only when the tank was aerated, whereas the other group was rewarded with food for responding to the stimulus when the aeration was switched off. The number of trials in which octopuses responded to the stimulus, and the latency of the responses, were significantly different between trials with the aeration on and trials with the aeration off, in both groups. Therefore, the octopuses learned to conditionally discriminate. [ABSTRACT FROM AUTHOR]

It is important to know the characteristics of migration pattern and vital rates of juveniles to understand the early life history and its effect on the population dynamics of fishes. The relationship between growth and migration pattern of juvenile temperate seabass Lateolabrax japonicus in the Yura River estuary was examined by combination of stable carbon isotope ratio (δC) and otolith microstructure. Gut fullness indices were also examined to know the feeding condition of juveniles. δC values of seabass juveniles in the lower estuary and surf zone (LES) were enriched, while those in freshwater zone (FW) were depleted, consistent with δC differences in prey items. The back-calculated growth rates of juveniles in FW were significantly lower than those of juveniles that resided in the LES from 50 days to 90 days old, implying that juveniles with poor growth ascended the river while those with better growth remained in the LES. However, the growth rates of the juveniles, which resided in FW for more than 1 month, caught up with and even overtook those of juveniles in LES within 1 month after ascended the river. The higher water temperature and better feeding conditions would contribute to better growth rates of juveniles in FW than those in LES. [ABSTRACT FROM AUTHOR]

In a recent study most of the temperate-living corals were found to harbor stress-sensitive Symbiodinium clade C, which is common in the tropical zone. In this study, we investigated the genetic variations within Symbiodinium clade C among corals living in temperate waters of Japan (17 genera; 26 species) using rDNA internal transcribed spacers (ITSs) to clarify the genetic differences between climatic zones. We also focused on two widespread coral species, Acropora hyacinthus and Pocillopora damicornis, to compare the genetic differences of Symbiodinium clade C between subtropical and temperate regions. We found multiple haplotypes of Symbiodinium ITSs in clade C, which formed nine subclades. Our data indicate that five genera ( Acropora, Cyphastrea, Stylocoeniella, Porites, Pocillopora) contained host-specific Symbiodinium, while members of the family Faviidae and others contained several Symbiodinium ITS haplotypes from two or three subclades. A comparative analysis using Acropora and Pocillopora also revealed that the temperate zone coral population formed a single subclade of Symbiodinium clade C that was genetically isolated from those of subtropical populations. In summary, the majority of corals living in temperate waters of Japan, such as faviid corals, have several ITS haplotypes which possibly are utilized as an opportunistic survival strategy under severe environmental conditions, whereas Acropora and Pocillopora at the very least harbor temperate zone-specific Symbiodinium. [ABSTRACT FROM AUTHOR]

The amount of ultraviolet (UV)-B radiation reaching the sea surface has increased due to ozone depletion. Several laboratory studies have highlighted the negative impacts of UV radiation on fish using hatchery-reared specimens. However, potential differences in UV tolerance between wild and hatchery-reared fish have been given little consideration. Wild and reared juveniles of red sea bream and black sea bream were exposed to one of four different UV-B radiation levels (1.8; 1.1; 0.4; 0 W/m) for 4 h. Survival rate was measured every 2 h for a period of 24 h (red sea bream) or 48 h (black sea bream) following exposure. Wild and reared juvenile red sea bream were characterized by similar survival rate, with survival declining to almost 0 % 24 h after exposure at the 1.1 and 1.8 W/m levels. In black sea bream, wild individuals showed significantly higher survival than reared fish in levels 1.1 and 1.8 W/m. Melanophore density was also measured since melanin absorbs UV radiation. Wild black sea bream showed higher melanophore density compared to reared individuals, while no such difference was observed in red sea bream. We conclude that wild black sea bream juveniles acquire higher UV tolerance partly by increasing melanophore density through exposure to UV radiation. Our results indicate that the predicted impacts of UV radiation on fish populations solely based on experimentation with hatchery-reared specimens may be overestimated for some species. [ABSTRACT FROM AUTHOR]

We examined the effect of bottom feeding and net chasing as means to improve the maladaptive off-bottom swimming of hatchery-reared Japanese flounder Paralichthys olivaceus juveniles for stock enhancement. Three treatments were tested: (1) a bottom feeding treatment in which fish were fed near the bottom; (2) a net chasing treatment in which fish were chased by a hand net two to four times a day, and (3) a surface feeding treatment in which fish were fed from the surface (control treatment). Foraging behavior at the surface with surface feeding was analyzed 1 day before initiating these treatments and 2 weeks thereafter. A comparison of the pre- and post-treatments revealed that off-bottom swimming was less in the bottom feeding treatment and net chasing treatments. A comparison of off-bottom swimming in the bottom feeding treatment between the pre- and post treatments revealed that bottom fed fish showed less off-bottom swimming than surface fed fish. These findings suggest that fish behavior can be manipulated during the rearing period and that such manipulations can be used to improve the behavior of fish for release. [ABSTRACT FROM AUTHOR]

We examined three sympatric gobies ( Acentrogobius sp. A, Acentrogobius sp. B, and Acentrogobius sp. C) that were recognized as a single species ' Acentrogobius pflaumii' until recently. Our aims were to describe their geographic distribution patterns and clarify their habitat use across the Japanese archipelago. Exhaustive specimen sampling revealed that their distributions overlapped broadly, although the distributional range of Acentrogobius sp. A was somewhat more southerly than those of the other two species, and only Acentrogobius sp. A was found in the Ryukyu archipelago. The species showed significant differences in two environmental factors (water depth and salinity) measured at the collection sites. [ABSTRACT FROM AUTHOR]

Genetic divergence among three morphs of a goby, Acentrogobius pflaumii, was investigated on the basis of sequence variations in a partial section of the mitochondrial cytochrome oxidase subunit I gene. A total of 95 specimens, representing the three morphs, collected almost sympatrically from three sites around the Japanese archipelago, were sequenced, the sequence divergences between the morphs (8.62-15.50%) being much greater than within each morph (0.44-0.57%). In addition, each morph formed a distinct cluster in a neighbor-joining tree. Together with an earlier morphological study, such evidence indicated that each morph clearly represented a distinct species. Based on the determined gene sequences, three morph-specific primers were designed for multiplex haplotype-specific polymerase chain reaction (PCR) to enable quick and easy identification of each morph in future studies, especially for early life ecology given morphological similarities at these stages. [ABSTRACT FROM AUTHOR]

The occurrence and distribution of settling and settled spotted halibut Verasper variegatus were compared with those of Japanese flounder Paralichthys olivaceus in shallow habitats around Shimabara Peninsula, western Japan, to elucidate the settlement and recruitment characteristics of spotted halibut, a rare pleuronectid flatfish in Japan. Push-net sampling conducted at nine sites in March and April 2003 collected spotted halibut from four nurseries located at eastern areas of Shimabara Peninsula in Ariake Bay; Japanese flounder were sampled from eight nurseries. Comparison of microhabitat distributions in a tidal-flat nursery during February-April in 2003-2007 revealed that metamorphosing larvae and juveniles of spotted halibut, which showed the drastic body coloration (black to brown) and behavioral changes (frequent swimming to settlement), were distributed mainly in the lower edge of the intertidal area, whereas Japanese flounder inhabited both intertidal and subtidal areas. Metamorphosing larvae of spotted halibut (12.6-16.5 mm standard length; n = 24) were collected in March when the highest densities were observed, whereas metamorphosing larvae of Japanese flounder (10.0-15.9 mm, n = 55) were observed during March-April. Our results suggest that spotted halibut has a narrower time/space window for recruitment to the specific nurseries compared with Japanese flounder. [ABSTRACT FROM AUTHOR]

Marine fishes often experience major habitat shifts during their life history, and previous studies have shown that the learning capability of fish change ontogenetically and in accordance with such habitat shifts. However, because all of these studies used a single type of conditioned stimuli (CS), they failed to detect qualitative changes in learning capability. Here we tested the hypothesis that preparedness for learning changes ontogenetically in jack mackerel Trachurus japonicus, which undergo a drastic change in habitat preference during their life history as they move from offshore pelagic waters to coastal and demersal rocky reefs. Groups of juveniles measuring 40 mm standard length (SL) (pelagic stage) and 60 mm SL (demersal stage) were conditioned to food rewards in response to three different CS; the presence of a surface structure, mid-water structure, and aeration. The results showed that small juveniles tended to become conditioned to the surface stimulus faster than they did to the mid-water stimulus. Conversely, large juveniles responded to the mid-water stimulus significantly more quickly than they did to the surface stimulus. These results suggest that stimulus-specific learning capability in T. japonicus changes ontogenetically, facilitating adaptation to their life-history strategy. [ABSTRACT FROM AUTHOR]

We aimed to evaluate the effect of social interaction on learning in juvenile jack mackerel Trachurus japonicus. We first compared the learning process between single fish and groups of fish. Reward-conditioned learning was established in eight trials in both treatments, whereas individuals in the group treatment responded to stimuli more frequently in the feeding area than in the single fish. This implies that information about the feeding area was shared in the group and pursuing other individuals gave them a behavioral advantage for feeding. We then investigated whether information on the feeding area can be transmitted through observation of other individuals in aligned tanks. Fish in the control group required six trials to be conditioned to aeration stimuli and feeding location, whereas those in the observation treatment required only three trials for this learning. This result implies that information on the feeding area was transmitted through visual observations. The present research suggests that sharing and transmission of information occur in schools of jack mackerel. Schooling behavior would thus enable optimization of the foraging behavior in this species. [ABSTRACT FROM AUTHOR]

Recruitment in marine fishes is regulated largely by the demographic changes that occur during the early life stages; therefore, a thorough understanding of early life stages is essential for predicting recruitment variability in fishes. Japanese sea bass (JSB), Lateolabrax japonicus, is a coastal marine fish distributed in East Asian coastal waters, and is regarded as highly important for commercial and recreational fisheries, for marine and brackish water aquaculture as well as for stock enhancement. JSB is a typical estuarine dependent temperate fish, which spawns in shelf areas and coastal embayments and the larvae and juveniles are dispersed and transported into shallow nearshore habitats and estuaries where they spend the early life. In this paper, we provide insight into the early life history and ecology of JSB through a revision of the available information and using the data we obtained from a relatively long-term research. We review and discuss the distribution and habitat use, food and feeding, age and growth, mortality and recruitment of larval and juvenile JSB in coastal waters around Japan. We extend our discussions in all available dimensions: habitat-specific, ontogenetic, and spatio-temporal, and highlight the importance of nursery habitats. We also discuss the implications of early life history for recruitment of JSB as well as the possible effects of climate change. At the end, we point out potential areas for future research. [ABSTRACT FROM AUTHOR]

Morphometric analyses of marine pelagic fishes have generally been conducted for stock identification rather than for ecomorphological understanding. Many papers on stock identification of Trachurus japonicus reported polymorphisms in the Japanese Islands waters. However, none of them has found polymorphism in fish less than 100 mm standard length (SL), despite the environmental differences experienced by juvenile cohorts. The objective of this study was to detect ecomorphological polymorphism of juvenile T. japonicus (<100 mm SL) in Wakasa Bay, Japan, where multiple juvenile cohorts appear. From analyses of size frequency distributions and otolith microstructure, five cohorts were recognized in the bay from September 2003 to August 2004. We then compared 17 morphometric characters on body, fin, and otolith morphology, and found cohort-specific and roughly dimorphic pattern (a streamlined morph and a compressed morph). The dimorphism was markedly observed in 50-70 mm SL, and was regarded as specific to the juvenile stage by comparison with the senior dimorphisms (≥100 mm SL). Referring to the literatures on functional morphology, the streamlined morph and the compressed morph were considered to be suitable to body and caudal fin (BCF) periodic propulsion and BCF transient propulsion, respectively. The juvenile dimorphism was interpreted as adaptive in its developmental environments (i.e., ecomorphological dimorphism) by relating the functional differences to the inferred ecological differences: the streamlined morph is adaptive to feed on larval Engraulis japonicus in coastal waters, whereas the compressed morph is adaptive to associate with jellyfishes in offshore waters. [ABSTRACT FROM AUTHOR]

We conducted laboratory experiments to examine the effects of turbidity on the survival of red sea bream Pagrus major and ayu Plecoglossus altivelis altivelis larvae when exposed to either visual (jack mackerel juveniles) or tactile (moon jellyfish) predators. The experiments were conducted in 30-l tanks with three different levels of turbidity obtained by dissolving 0, 50, or 300 ppm kaolin. Predators were introduced to the experimental tanks followed by larvae of either red sea bream (mean ± standard deviation 6.1 ± 0.3 to 11.4 ± 2.1 mm standard length) or ayu (6.6 ± 0.3 and 24.4 ± 1.8 mm). When exposed to jack mackerel, the mean survival rate of larvae was significantly higher in 300 ppm treatments compared with the other turbidity levels. When exposed to moon jellyfish, however, there was a less marked difference in the survival rates among different turbidity treatments. Survival rates of ayu larvae exposed to moon jellyfish were generally lower than those of red sea bream. Our study indicates that anthropogenic increases of turbidity may increase the relative impact of jellyfish predation on fish larvae. [ABSTRACT FROM AUTHOR]

This study examined the ontogenetic change in vertical distribution associated with algae and the thyroid hormone profiles of black rockfish ( Sebastes schlegelii) under rearing conditions. Experimental observations on distribution were carried on black rockfish from the newly born larval stage to juveniles 75 days after birth (DAB). Position was categorized by vertical location [upper layer, mid layer and lower layer (LL)] and by association with artificial algae (floating algae, bottom algae and no association). Position of fish was observed four times a day, at 0400 (dawn), 1200 (noon), 1800 (dusk) and 2400 (midnight) hours. The majority of fish (>80%) reached transforming larval stage [17.8 ± 0.7 mm total length (TL)] at 25 DAB and juvenile stage (24.3 ± 0.6 mm TL) at 35 DAB. Newly born larvae were mainly distributed at surface and middle layers, the shift of vertical distribution to the LL occurred between 10 and 25 DAB, and over 98% of the individuals were distributed near the bottom after 35 DAB. Association behavior with algae was first observed from 20 to 30 DAB depending on the time of day. Percentage of fish associated with bottom algae increased from 25 to 40 DAB and reached 50–70% thereafter. Thyroid hormone (T4) showed two surges at 30 and 50 DAB. The first surge corresponded to the transforming larval stage and the occurrence of association behavior with algae. The results indicate that pelagic larvae settle to the bottom layer before metamorphosis, and association behavior with algae appears at the transforming larval stage. A high T4 concentration at 30 DAB indicates a close relationship with these morphological and behavioral developments. [ABSTRACT FROM AUTHOR]

Juvenile temperate seabass Lateolabrax japonicus were sampled along the Yura River estuary from April to July 2008 to determine their distribution and feeding habits during migration within a microtidal estuary. Throughout the sampling period, juvenile seabass were distributed not only in the surf zone, but also in the freshwater zone, and they were particularly abundant in areas with aquatic vegetation in the freshwater zone. This distribution pattern suggests that the early life history of the temperate seabass depends more intensively on the river (freshwater) than previously considered. Small juveniles in the freshwater zone fed on copepods and chironomid larvae and upon reaching a standard length (SL) of approximately 20 mm did they fed on mysids. In contrast, juveniles (approx. 17–80 mm SL) in the surf zone fed mainly on mysids. [ABSTRACT FROM AUTHOR]

Temperature-dependent sex determination has been demonstrated in some species of fish, and a high temperature during the period of sex differentiation typically produces a male-dominant population. This research investigated the gonadal sex differentiation and effect of rearing temperature on the sex ratio in larval black rockfish Sebastes schlegeli, which is a viviparous species. Two types of gonads were histologically distinguishable in fish 20 mm in total length (TL). The putative ovary started forming an ovarian cavity, while the putative testis was not clearly differentiated until 51 mm TL. In a temperature-controlled experiment, the proportions of females were 45% at 10°C, 46% at 14°C, 50% at 18°C, 63% at 22°C, and 83% (significantly different from 1:1 sex ratio) at 24°C. These results suggest that morphological sex differentiation in black rockfish occurs at approximately 20 mm in TL, and it is possible that high temperatures (24°C) induce not a male- but a female-dominant population in this species. [ABSTRACT FROM AUTHOR]