Abstract: The specimens of red flying squid (Ommastrephes bartramii) were caught by Chinese squid jigging vessels in the waters of 42°N-45°N and 153°E-157°E during July to October in 2012. 20 pairs of beaks were randomly selected to measure their stable carbon and nitrogen isotope values and to investigate the relationships between stable isotope values of beaks and the corresponding biological parameters of the squids, i.e. sex, body size and pigmentation stage. The results indicated that there are no significant differences in stable carbon and nitrogen isotope values of beaks between male and female. Stable carbon isotope values of upper and lower beaks have negative relationships with the body size, while stable nitrogen isotope values of upper and lower beaks have positive relationships with the body size. Pigmentation stage and stable nitrogen isotope values of beaks increase with the growth of squid, and pigmentation stage is associated with the content of catechols in beaks, which could increase the rigidity of beaks and help squid forage high trophic level organisms. As beaks are an important information carrier in feeding ecology studies of O. bartramii, especially in diet shift and migration patterns, they can provide a new tool for estimating the trophic position and function of O. bartramii in north Pacific ecosystem.

Key words: quantification, heavy metal, coastal waters of China, sediment, source apportionment