[A-OS26] [JJ] 海洋生物資源保全のための海洋生物多様性変動研究

[AOS26-P03] 炭素14分析によるサケの繁殖時の炭素源推定

*山口 保彦¹、野畑 重教¹、川上 達也²、白井 厚太朗¹、本多 健太郎³、宮入 陽介¹、横山 祐典¹、永田 俊¹ (1.東京大学　大気海洋研究所、2.東京大学　大学院農学生命科学研究科、3.水産研究・教育機構　北海道区水産研究所)

キーワード：放射性炭素、同位体分析、海洋生態系、サケ、ベーリング海、大槌湾

There has been increasing interest in understanding the responses of Pacific salmon to marine climate variation. Chum salmon (Oncorhynchus keta) is the second most abundant salmonid in the North Pacific Ocean, and important for the fisheries in the northern Japan (especially Hokkaido and Iwate). For migrating animals like salmon, breeding strategy would be one of key factors for their sensitivity to changing environments. Do they prepare their eggs from recently ingested nutrients during/after migration to Japan ('income' breeders) or from body stores which are mainly produced in the Bering Sea ('capital' breeders)? Here, to address this important ecological question, we propose radiocarbon analysis as a new useful method to locate oceanic regions where Japanese chum salmon obtained their carbon resource. To our knowledge, this study is the first study to utilize radiocarbon (Δ¹⁴C) value as an indicator of salmon ecology in the ocean. We determined bulk Δ¹⁴C, δ¹³C, and δ¹⁵N values of muscle and gonad (eggs) samples from female chum salmons collected during October-December 2015 at Otsuchi Bay, Japan. We also analyzed bulk Δ¹⁴C values of plankton net samples collected in the Bering Sea, to constrain the Δ¹⁴C values of salmon's diets in the Bering Sea. The gonad samples generally showed lower Δ¹⁴C values, which overlap with the range of the plankton net samples in the Bering Sea. On the other hand, the muscle samples generally showed higher Δ¹⁴C values, which overlap with the range of fishes collected around Sanriku area, Japan. These results suggest that Japanese chum salmon (at least individuals from Otsuchi Bay) produce eggs mainly using the carbon resource obtained in the Bering Sea before migration to Japan (i.e., capital breeders), while their muscle tissues are affected by feeding around Japan.