Chaetognaths in the diet of Pacific saury (Cololabis saira) in the northwestern Pacific Ocean

概要

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The feeding of Pacific saury (Cololabis saira) on chaetognaths was investigated off the east coast of Japan. 58.1% of the saury examined contained chaetognath remains. Most saury contained only a couple of chaetognaths, but about one-third of the saury had over 100 in their gut-suggesting encounters with chaetognath swarms. The chaetognath Sagitta elegans was commonly ingested, and the mean calculated length of S. elegans ingested by saury was significantly larger than the mean length of S. elegans collected by net from the water, indicating selectivity of larger prey sizes by saury. Sagitta elegans ingested at the Oyashio region feeding grounds in July were significantly larger than those ingested in the mixed/transition water off Sanriku in November. Correlation analysis of saury size versus ingested S. elegans size suggests that saury at the Oyashio feeding grounds in July do not eat S. elegans of lengths directly proportional to the saury’s length. But, saury do seem to select S. elegans directly proportional to their own body length in the region of the Subarctic Front. Though size of saury and S. elegans affects predatorprey interactions, additional unknown factors are also recognized as being influential.
2008-08-20