|Budget Amount *help
¥2,300,000 (Direct Cost : ¥2,300,000)
Fiscal Year 1998 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1997 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1996 : ¥900,000 (Direct Cost : ¥900,000)
Analysis of trophic levels by using nitrogen and carbon stable-isotope ratios is advantageous to conventional food-habit analysis by gut-content examination, in that the former reflects a long-term food history of an individual animal, while the latter gives a food composition only immediately before capture. The present studies examined inter-individual variability of food-habits of pelagic fishes, meso-and bathypelagic fishes and shrimps in Sagami Bay and adjacent waters, by applying nitrogen and carbon stable-isotope ratio method along with conventional gut-content analysis.
In Japanese anchovy, the individual stable-isotope ratios of both larvae and adults were clustered into two groups, with a variation of ca. 1.7% in nitrogen. In meso-and bathypelagic shrimps, Bentheogennema borealis, a non-migrant, deep-sea species, showed significantly lower delta^<13>C and higher delta^<15>N values than the two vertical migrants. Of the latter, Sergiaprehensilis showed higher delta^<15>N values in larger individuals, coinciding to the result of gut-content analysis (strong carnivory). Acanthephyra quadrispinosa, another migrant, showed delta^<15>N values similar to S.prehensilis but difference between sizes was less marked, suggesting that A.quadrispinosa take foods of higher trophic levels from relatively young stages. Maurolicus muelleri, a vertical migrant, showed inter-individual variations of delta^<15>N of ca. 1.5 times those of the three non-migrating mesopelagic fishes of the genus Cyclothone, suggesting that the former utilizes food resources from both the epi-and mesopelagic layers.
In summary, the present results demonstrated that the delta values provide useful information on food characteristics and food history of individual animals and that these characteristics are closely related to other ecological characteristics of individuals, such as growth, vertical migration, and distributional depths.