Evaluation of the stock enhancement of chum salmon inJapan using stable isotope retrospective analysis.

近年来，岩手县的大马哈鱼捕捞量有所下降，但放生的幼鱼数量保持不变。为了阐明这种减少的原因，测量了大马哈鱼鱼鳞的稳定同位素比率。结果表明，鱼鳞肌肉和边缘部位碳氮稳定同位素比值呈正相关。这一发现表明鱼鳞是一种稳定的同位素特征。岩手和北海道种群第二年海洋生命阶段的碳、氮稳定同位素特征均较低。这一发现表明，日本大马哈鱼可能在其生活史的相对早期阶段依赖于较低水平的食物网作为食物。

Chum salmon population in Iwate prefecture has declined in catch for these years, although the numbers of juvenile release remained constant. To elucidate the cause of such decrease, stable isotope ratios of fish scales of chum salmon were measured. As results, carbon and nitrogen stable isotope ratiosof muscle and marginal parts of fish scales are positively correlated. This finding suggested fish scales remain stable isotopic signature of pray items. The carbon and nitrogen stable isotopic signatures of second year in oceanic life stage were lower for both Iwate and Hokkaido populations. This finding suggested Japanese chum salmon might have depended on lower level of food web as food items at relatively early stage in its life history.