Isotope-ratio mass spectrometry isotopic make up of the sample is obtained. For example, carbon isotope ratios are measured relative to the international standard for C. The C standard is produced from a fossil belemnite found in the Peedee Formation, which is a limestone formed in the Cretaceous period in South Carolina, U.S.A. The fossil is referred to as VPDB (Vienna Pee Dee Belemnite) and has C:C ratio of 0.0112372. Oxygen isotope ratios are measured relative the standard, V-SMOW (Vienna Standard Mean Ocean Water). It is critical that the sample be processed before entering the mass spectrometer so that only a single chemical species
Standard weight in fish relationships representing a species across its range are used. As fish grow in length, they increase in weight. The relationship between weight and length is not linear. The relationship between length ("L") and weight ("W") can be expressed as: When the equation is for standard weight, the standard weight for a given length is written as W. The exponent "b" is close to 3.0 for most species. The coefficient "a" varies between species. If the exponent "b" is greater than three for a certain fish species, that species tends to become relatively fatter or have more girth as it grows