Stable nitrogen isotope analysis of amino acids
The δ 15NAAs measurements were
performed only for some copepods and chum salmon samples to minimize
experimental effort. We selected representative 3–6 samples from six
copepod species for δ 15NAAs
measurements so as to cover theδ 15NBulk range of each species.
Collagen samples from the bone sections of two individuals of O.
keta (IDs: OK2 and OK8) were used forδ 15NAAs measurements. Samples
for δ 15NAAs were prepared based
on amino acid derivatization procedures, and theδ 15NAAs values were determined
by gas chromatography/combustion/isotope-ratio mass spectrometry (See
Text S3).