Authorship：Lead author  

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Publisher：Estuarine, Coastal and Shelf Science  

© 2019 Elsevier Ltd Apostichopus japonicus (Japanese sea cucumber) is of ecological and economic importance in the coastal waters of Japan. To assess the apparent abundance of A. japonicus, density data of visible A. japonicus are required; however, the activity of this species on the sea floor changes with variations in sea water temperature. For example, at high sea water temperatures, A. japonicus takes shelter in the gaps of rocks or oyster shells. This change in its visibility on the sea floor makes it difficult to determine the apparent abundance of this species. In the present study, we aimed to clarify the optimal survey timing to assess the apparent abundance of A. japonicus based on the relationship between the density of visible A. japonicus and sea water temperature. Between 2010 and 2013, we evaluated how the density (ind. 100 m−2) of visible A. japonicus changes with sea water temperature in an area preferred by these organisms, Maizuru Bay, Kyoto, Japan, every 2 weeks. Seasonal changes in the density were consistent with seasonal variations in sea water temperature. Density increased when sea water temperature decreased and was at a maximum at minimum sea water temperatures. In addition, the density tended to change significantly over a short period. In some cases, the density after the lowest sea water temperature in March 2011 declined by half from 65 to 27 in just 2 weeks. Owing to considerable variations in the density of visible A. japonicus, we believe it is important to establish the appropriate survey timing to quantify the apparent abundance of this species, with our data suggesting that surveys should be performed during the season with the lowest sea water temperatures. Furthermore, at the lowest sea water temperatures in 2010, 2011, 2012, and 2013, the maximum densities were 99.0 (9.1 °C), 65.0 (9.7 °C), 41.3 (9.8 °C), and 8.7 (8.9 °C), respectively. Over 4 years, the density decreased to approximately 10% of that in the year with the peak density. Considering this decrease, it is suggested that A. japonicus in Maizuru Bay is overfished. Therefore, it is possible that the density of visible A. japonicus at the lowest sea water temperatures provides useful information for assessing the apparent abundance of this species.

DOI： 10.1016/j.ecss.2019.106384

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Publisher：Journal of Ethology  

© 2019, Japan Ethological Society. Habitat preference is thought to be genetically programmed in fishes. However, fishes can choose habitat based on their personal experience of an environment. We investigated whether the environment in which fish are raised affects habitat preference in red sea bream Pagrus major juveniles, and tested if the formed preference lasts until later life stages. Juveniles were reared in tanks with a substrate of either sand or artificial seaweed for 40 days. Naive fish were raised without either type of substrate. In the preference test, individual fish were allowed to choose either a sand or artificial seaweed microhabitat. The tested fish were then kept in barren tanks, and similar tests conducted again on days 30 and 100. Sand and seaweed treatment fish preferred the corresponding habitat immediately after the rearing treatment, whereas naive fish did not exhibit any preference. These preferences were maintained when fish were tested on day 30, but not on day 100. The present study suggests that habitat preference is acquired through the rearing environment at the nursery stage, and that this preference lasts for at least 30 days. The formation of habitat preference should help juveniles to choose an optimal microhabitat in a fluctuating environment.

DOI： 10.1007/s10164-019-00605-6

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Publisher：Nippon Suisan Gakkaishi (Japanese Edition)  

DOI： 10.2331/suisan.WA2651

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Tokyo  

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.

DOI： 10.1007/s12562-017-1174-1

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Canadian Science Publishing  

The low return rate of fish released for stock enhancement has often been attributed to hatchery-reared fish having inferior behavioral characteristics. We tried to improve the behavioral characteristic of red sea bream (Pagrus major) juveniles by using a net-chasing treatment. The fish were provided with 2 min of net chasing twice daily for 3 weeks, following which their behavioral characteristics (emergence from a start area, avoidance response to novel stimulus, and foraging following transfer between tanks) were individually tested and compared with a control group. A predator exposure test was then conducted using marbled rockfish (Sebastiscus marmoratus). Net-chased fish exhibited a shorter latency to emergence, a higher avoidance rate, and an earlier foraging time than the control fish, indicating that the net-chasing treatment may improve adaptability for environmental change and alertness to a novel object. The net-chased fish also exhibited a better survival rate than the control fish, with an odds ratio of 6.76. We suggest that net-chasing training represents an easy and efficient method for improving the behavior of fish for stock enhancement.

DOI： 10.1139/cjfas-2017-0073

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Public Library of Science  

DOI： 10.1371/journal.pone.0173073

CiNii Article

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPANESE SOC FISHERIES SCIENCE  

We aimed to confirm the reproduction of Manila clam Ruditapes philippinarum in Maizuru Bay, and also determine the cause of their mortality. Using seedling collectors, we obtained 5 to 60 juveniles per collector, demonstrating that this species is reproducing in the bay. Depletion of clams in Maizuru Bay was investigated by setting clams on coastal area sea beds in the summer. Predation was found to be more effective in depleting clams than environmental factors. Laboratory experiments revealed that juveniles less than 5 mm in shell length were preyed upon by 6 out of 13 fish species, whereas Japanese rock crab preyed upon clams from juveniles to adults.

DOI： 10.2331/suisan.1600017

Web of Science

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PUBLIC LIBRARY SCIENCE  

Recent studies in streams and ponds have demonstrated that the distribution and biomass of aquatic organisms can be estimated by detection and quantification of environmental DNA (eDNA). In more open systems such as seas, it is not evident whether eDNA can represent the distribution and biomass of aquatic organisms because various environmental factors (e.g., water flow) are expected to affect eDNA distribution and concentration. To test the relationships between the distribution of fish and eDNA, we conducted a grid survey in Maizuru Bay, Sea of Japan, and sampled surface and bottom waters while monitoring biomass of the Japanese jack mackerel (Trachurus japonicus) using echo sounder technology. A linear model showed a high R-2 value (0.665) without outlier data points, and the association between estimated eDNA concentrations from the surface water samples and echo intensity was significantly positive, suggesting that the estimated spatial variation in eDNA concentration can reflect the local biomass of the jack mackerel. We also found that a best-fit model included echo intensity obtained within 10-150 m from water sampling sites, indicating that the estimated eDNA concentration most likely reflects fish biomass within 150 m in the bay. Although eDNA from a wholesale fish market partially affected eDNA concentration, we conclude that eDNA generally provides a 'snapshot' of fish distribution and biomass in a large area. Further studies in which dynamics of eDNA under field conditions (e.g., patterns of release, degradation, and diffusion of eDNA) are taken into account will provide a better estimate of fish distribution and biomass based on eDNA.

DOI： 10.1371/journal.pone.0149786

Web of Science

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Authorship：Lead author   Language：English   Publisher：Springer Japan  

DOI： 10.1007/s12562-015-0881-8

CiNii Article

CiNii Books

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Other Link： http://hdl.handle.net/2433/202068

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Language：Japanese   Publisher：The Japanese Society of Fisheries Science  

DOI： 10.2331/suisan.79.612

CiNii Article

CiNii Books

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Authorship：Lead author  

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Authorship：Lead author  

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