Geographical variations in the trophic ecology of Japanese anchovy, Engraulis
japonicus, inferred from carbon and nitrogen stable isotope ratios |
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Authors: | Hiroshige Tanaka Akinori Takasuka Ichiro Aoki Seiji Ohshimo |
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Institution: | (1) Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-8657, Japan;(2) Seikai National Fisheries Research Institute, Fisheries Research Agency, 1551-8 Taira, Nagasaki 851-2213, Japan;(3) National Research Institute of Fisheries Science, Fisheries Research Agency, 2-12-4 Fukuura, Kanazawa, Yokohama Kanagawa, 236-8648, Japan |
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Abstract: | Carbon and nitrogen stable isotope ratios of Japanese anchovy (Engraulis japonicus) and their stomach contents were examined and compared among various regions around Japan. Geographical variations in the
isotope ratios were found between inshore and Pacific offshore regions. While most of the anchovy samples had isotope ratios
around −17.6‰ for δ13C and 10.0‰ for δ15N as median values, higher (more enriched) isotope values were found in the anchovy sampled from inshore regions. On the contrary,
lower (more depleted) values were found mostly in the anchovy from the Pacific offshore region including the Kuroshio Extension
and Kuroshio-Oyashio transition zones. Higher carbon isotope ratios in the inshore regions may reflect a carbon source from
benthic primary producers in addition to phytoplankton possibly through the consumption of the larvae of benthic organisms
such as bivalves or decapods, which were found in the stomach contents of the inshore anchovy. Variations in the nitrogen
isotope ratio may reflect not only differences in the trophic level of prey species, but also variations in the baseline level
of food webs. Stable isotope ratios are potentially a useful tool for understanding the stock/population structure and migration
of anchovy. The present findings indicate the potential importance of the “inshore–offshore” variations in the biology of
Japanese anchovy populations in the northwestern Pacific waters. |
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