Effects of water temperature and prey density on recent growth of chub mackerel Scomber japonicus larvae and juveniles along the Pacific coast of Boso-Kashimanada
2019
Taga, M. ((Ibaraki Prefectural Fisheries Research Institute, Hitachinaka, Ibaraki (Japan)), (Kyoto University, Kyoto (Japan). Field Science Education and Research Center)) | Kamimura, Y. | Yamashita, Y.
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.
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