Trophodynamic similarities of three sympatric clupeoid species throughout their life histories in the Kii Channel as revealed by stable isotope approach

Trophic similarity/difference among multispecies pelagic fish is a focal point in understanding the processes of climate impacts on their population dynamics. We tested trophic overlap of Japanese anchovy Engraulis japonicus, Japanese sardine Sardinops melanostictus, and Pacific round herring Etrumeus teres in the Kii Channel, Japan, by comparing the carbon and nitrogen stable isotope ratios among these clupeoid species from the larval to adult stages throughout the year. Space and time were both significant factors of variations of the isotopic composition values for the three species, and fish size was also significant for sardine and round herring. The isotopic composition values of the three species were homogeneous when compared with those of plankton and some other non-clupeoid species. Moreover, the isotopic composition values of the three clupeoid species collected simultaneously showed closer similarities than those in different areas and dates in all life stages. Thus, spatial and temporal differences in food availability were more apparent compared with interspecific differences in prey items specific to each species. Our analysis indicated strong trophic overlaps throughout the life histories among the three clupeoid species. Hence, they are concluded to be ecologically congeneric (directly competing) species in terms of trophic positions in the pelagic ecosystem.