MEPS 334:255-262 (2007)  -  doi:10.3354/meps334255

Density-dependence in post-recruit Japanese seaperch Lateolabrax japonicus in the Chikugo River, Japan

Jun Shoji1,2,*, Masaru Tanaka1

1Laboratory of Estuarine Ecology, Field Science Education and Research Center, Kyoto University, Sakyo, Kyoto 606-8502, Japan
2Present address: Takehara Fisheries Research Station, Center for Education and Research of Field Science, Hiroshima University, Minato-machi 5-8-1, Takehara, Hiroshima 725-0024, Japan

ABSTRACT: Density-dependence in feeding, growth, and mortality was evident in the post-recruit riverine period (15–20 mm in length) of Japanese seaperch Lateolabrax japonicus located within the estuarine turbidity maximum of the Chikugo River, Japan. Based on otolith microstructure analysis, the weight-specific growth coefficient (G, d–1) and abundance-at-age were estimated for post-recruit Japanese seaperch from 1990 to 2000. Abundance at recruitment (15 mm, A15) and at 20 mm (A20), and the mortality coefficient during the post-recruit period (M, d–1) were estimated for each year using the larval production method. The A15 varied by a factor of 24 during the 11 yr period, and its variability had a significant effect on G, M, A20, and the ratio of M to G as an index of Japanese seaperch relative recruitment potential. G was low, and M, ratio of M to G, and A20 were high when recruitment was successful. A lower coefficient of variation (%) was observed in A20 (25.0) than in A15 (33.5) for the 11 yr. A significant effect of A15 was also found on the prey ingestion of the post-recruit Japanese seaperch. Mean gut fullness (gut content weight per unit body weight) was low when recruitment was successful. Density-dependent regulation through competition for prey resources operates on Japanese seaperch in the post-recruit period corresponding with the migration from Ariake Bay to the Chikugo River, a spatially restricted nursery.

KEY WORDS: Fish early life stages · Density-dependence · Survival · Estuarine turbidity maximum · Ariake Bay

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