Geographical variations in carbon and nitrogen stable isotope ratios in squid

Abstract

The magnitude of geographical variations of stable isotope ratios of carbon and nitrogen was examined in ten squid species captured in seven areas of the world's oceans. The average of all 139 squid was −17.4±1.4‰ for δ 13 C and 11.6±1.6‰ for δ 15 N. The δ 13 C of squid showed a clear-cut negative correlation with the latitude of the sampling locations, reflecting the well-known latitudinal characteristics of phytoplankton δ 13 C, while squid δ, 15 N did not correlate with the latitude significantly. The δ 15 N reflected the regional characteristics of nitrogen metabolism such as denitrification and N 2 fixation, and it was conspicuous in the intraspecific variation in Sthenoteuthis oualaniensis ranging from 10.0±1.5‰ off Japan to 16.3±0.6‰ off Peru in the Pacific Ocean. Significant isotopic variations were also found in the local area among the five species off Japan in the Pacific Ocean and among the three species in the Japan Sea. Attention must be paid to the isotopic variations of primary producers as well as those of squid in examining the trophic positions of squid.