Estimating Trophic Level and Food-web Structure for Japanese Anchovy in the Offshore and Inshore Waters by using Carbon and Nitrogen Stable Isotope Ratios

Abstract

The trophic level (TL) of the Japanese anchovy Engraulis japonicus was estimated using carbon / nitrogen stable isotope ratios (δ¹³C / δ¹⁵N). δ¹⁵N signature of the anchovy was high in Sagami Bay (inshore waters) and low in the offshore waters. Although the intra-sample variations of the δ¹⁵N and TL were small in offshore and large in inshore waters, each mean TL was approximately same in the offshore and inshore waters. However, the δ¹³C signature for the anchovy was significantly different between the offshore and inshore waters. It was suggested that the food-web structures differed between the two waters because the starting points of the food-webs were different. Furthermore, it showed complicated food-web structures because offshore populations of Japanese anchovy, migratory fish, came to Sagami Bay.