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

Yasue, N., Doiuchi R., and Takasuka, A. 2013. Trophodynamic similarities of three sympatric clupeoid species throughout their life histories in the Kii Channel as revealed by stable isotope approach. – ICES Journal of Marine Science, 71: . 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.

Reproductive Biology of Round Herring Etrumeus teres (Dekay, 1842) from the Egyptian Mediterranean Water at Alexandria

Maturity stages of round herring Etrumeus teres were divided anatomically into six stages. Monthly distribution of such maturity stages showed that E. teres had prolonged spawning season extended from December to May for females and to July for males. The observed sex ratio was 1 : 2 (male: female). Gonadosomatic index (GSI) values were high during breeding season for both sexes. Hepatosomatic index (HIS) values for females increased from December to April and from December to July for males. Both sexes of E. teres showed the same correlation between GSI and HSI during their breeding season. The absolute and relative fecundity increased with increasing of length and weight. Histologically, the ovarian cycle of E. teres was classified into six stages and the testicular cycle into five stages. Female of E. teres was a multiple spawner and had prolonged spawning season with a group-synchronous ovarian which contained oocytes at all stages of development. Also, different sizes of spermatocytes at different developmental stages of maturation were observed during the same season. This may reflect the suitability of the specific reproductive behavior of male and its adaptation to the prolonged spawning season with females.