Stable isotopic composition of otoliths in identification of spawningstocks of Pacific herring (Clupea pallasi) in Puget Sound

摘要

Otoliths of Pacific herring (Clupea pallasi) were collected from Puget Sound, Washington, and were analysed for oxygen and carbon isotope ratios (delta O-18 and delta C-13). It was expected that if adult herring spawn at different localities with different delta O-18 and delta C-13 values, these isotope variations would constitute a natural tag that can be used to distinguish the herring spawning stocks. For a test project, we took aragonite powder samples from the surface of otolith nuclei and the second summer otolith rings, respectively. Isotopic composition of otolith nuclei from the Georgia Strait had lowest isotope values (from -8.2 parts per thousand to -2.0 parts per thousand VPDB (Vienna Peedee belemnite) in delta O-18 and -6.8 parts per thousand to -3.9 parts per thousand VPDB in delta C-13), significantly different from those collected from two southern Puget Sound spawning grounds (from -3.9 parts per thousand to -0.9 parts per thousand VPDB in delta O-18 and -5.6 parts per thousand to -2.0 parts per thousand VPDB in delta C-13). This isotopic identification is consistent with the biological observation and the actual sample collection. Stable isotopic information extracted from the summer otolith rings, in contrast, showed two types of herring in 1999 corresponding to the migratory and non-migratory stocks in Puget Sound. The rate of the two types of herring was about 70% versus 30%.