NIPPON SUISAN GAKKAISHI
Online ISSN : 1349-998X
Print ISSN : 0021-5392
ISSN-L : 0021-5392
Current issue
Displaying 1-25 of 25 articles from this issue
Foreword
2023 Awards of Excellence for the Science Paper
Achievement Awards for Young Scientist in Fisheries Science 2023
Originals
  • EIJI TANAKA
    Article type: Original
    2024 Volume 90 Issue 4 Pages 306-312
    Published: July 15, 2024
    Released on J-STAGE: July 20, 2024
    Advance online publication: July 05, 2024
    JOURNAL FREE ACCESS
    Supplementary material

     Parameters in the Beverton and Holt model of stock and recruitment of the Tsushima Warm Current stock of Japanese anchovy Engraulis japonicus incorporating the effect of capture of whitebait into the mortality process were estimated using time series of number of recruits, spawning stock biomass and catch number for whitebait over 1977–2019. An equation expressing the relation between stock and recruitment was derived from the differential equation describing the density-dependent mortality process of whitebait with fishing coefficient, and a catch equation for the whitebait was derived using the equation. The unknown parameters were estimated by minimizing the residual sum of squares of number of recruits on a log scale. The estimations showed that the number of recruits at saturation under the average of past exploitation levels to that without capture was 70%. The point estimate of survival rate from egg to whitebait, exploitation rate averaged over 1977–2019, and averaged survival rate for whitebait span were 1.2 (×10−4, CI 1.0–2.0×10−4), 0.26 (SE 0.08), and 0.27 (0.10), respectively. The estimates of CV (Coefficient of Variation) at egg stage, whitebait one, and recruitment were 0.41, 0.78, and 0.34, and this suggested that the fluctuation at whitebait stage was amplified due to the fluctuation of initial mortality rate and variation at recruitment stabilized by density-dependent natural mortality. The results of the estimations and modification of the model were discussed.

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  • MIKIMASA JOH, SATOSHI KATAYAMA, TAKAHIRO TAKASHIMA, OSAMU MURAKAMI
    Article type: Original
    2024 Volume 90 Issue 4 Pages 313-322
    Published: July 15, 2024
    Released on J-STAGE: July 20, 2024
    Advance online publication: July 05, 2024
    JOURNAL FREE ACCESS
    Supplementary material

     An age-determination method using otolith-thin sections and the relationship between age and body length of pointhead flounder Cleisthenes pinetorum, an important fisheries resource, were investigated in the Pacific Ocean off southern Hokkaido Island, Japan. In otolith-surface observation, the age determined by three readers varied even for young fish and the coincidence rate of two determinations by the same reader was only 58%. In contrast, in thin-section observation, the coincidence rate was 93%, and the surface method tended to result in overestimation compared with the thin-section method. The von Bertalanffy growth formulae were estimated for males and females as Lt=232×(1−e(−0.57×(t−0.26))) and Lt=299×(1−e(−0.43×(t−0.29))), respectively. Estimated growth was faster than that in the same area with the surface method and than that of Ishikari Bay, off the western coast of Hokkaido Island. This study proposed an accurate age-determination method for pointhead flounder and the results are fundamental for understanding ecology and for precise stock assessment.

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  • KENTA OGAWA, YUSUKE MATSUSHITA, HIROMASA OCHI, TSUNEO HONJO
    Article type: Original
    2024 Volume 90 Issue 4 Pages 323-333
    Published: July 15, 2024
    Released on J-STAGE: July 20, 2024
    Advance online publication: July 03, 2024
    JOURNAL FREE ACCESS
    Supplementary material

     The occurrence of two groups of Chattonella spp. (C. antiqua + C. marina, and C. ovata) along with environmental factors were investigated in southern Harima-nada, eastern Seto Inland Sea, Japan, from 1984 to 2021. The frequency of red tide occurrence (>10 cells/mL) decreased for C. antiqua + C. marina after 1990, whereas it increased for C. ovata from 2002. Since 1997, the cell density of C. antiqua + C. marina reached a maximum between early to mid-July, which was one month earlier than that before 1997. These temporal changes were suggested to be influenced by long-term increases in water temperature and decreases in dissolved inorganic nitrogen (DIN) concentrations.

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  • TETSUYA MIKADO, SATORU JINNO, MAKIKO HIRAI, YUJI TOMARU, GOH ONITSUKA, ...
    Article type: Original
    2024 Volume 90 Issue 4 Pages 334-343
    Published: July 15, 2024
    Released on J-STAGE: July 20, 2024
    Advance online publication: July 05, 2024
    JOURNAL FREE ACCESS

     A red tide of the harmful dinoflagellate Karenia mikimotoi occurred in Uwajima Bay from early September to mid-November 2020, the latest occurrence observed in this bay. Although genes of K. mikimotoi had been detected since the winter, low water temperatures associated with the offshore shift of the Kuroshio Current and the existence of competing species apparently delayed its bloom. The Kyucho in mid- and late-August potentially promoted the bloom by raising water temperature, dispersing competing species, and supplying nutrients to the bottom layer. In addition, typhoons approaching in early September appeared to have caused plankton to accumulate in the inner parts of Uwajima Bay by the west wind and to have reduced the duration of sunshine, consequently promoting the bloom of K. mikimotoi.

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  • KEITA ABE
    Article type: Original
    2024 Volume 90 Issue 4 Pages 344-354
    Published: July 15, 2024
    Released on J-STAGE: July 20, 2024
    Advance online publication: July 17, 2024
    JOURNAL FREE ACCESS
    Supplementary material

     Amid fisheries reforms, Japan is considering expanding the number of fish species subject to catch limits, a regulation that could potentially have economic impacts on fishers. This study estimates the demand curve for splendid alfonsino using daily reports from the Tokyo Metropolitan Central Wholesale Market. The results suggest that the price flexibility is low, indicating that prices are unlikely to rise significantly even if supply decreases because of the catch limits. Simulations using these estimates of the demand curve showed that a 30% decrease in supply could result in a 27–34% reduction in annual sales revenue. In scenarios where catch competition occurs, the decline in sales revenue is significantly larger, underscoring the critical importance of effective measures for managing economic impacts.

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