Back-Calculated Fish Lengths, Percentages of Scale Growth, and Scale Measurements for Two Scale Measurement Methods used in Studies of Salmon Growth

Scale measurements, percentages of annual scale growth, and back-calculated fish lengths were examined for the INPFC method (75 0 anterior reference line) and Traditional method (anterior-posterior reference line) on scales of chum salmon (Oncorhynchus keta) for three ages, two stocks, and two brood years. Mean measurements of annual increments of scale growth were greater for the INPFC method than the Traditional method. Differences in percentages of scale growth and back-calculated fish lengths for the two methods were tested using the Hotelling onesample T2 test. Percentages of annual scale growth differed significantly (p ::; 0.003) between the two methods for seven of nine tests. Mean percentage of annual scale growth was greater in the first year for the Traditional method and in the final year for the INPFC method; intermediate years were similar. Back-calculated fish lengths computed by the Fraser-Lee method differed significantly between the INPFC and Traditional method (p ::; 0.004) for seven of nine tests. Although differences in back-calculated lengths of the two methods were statistically significant, the biological differences were small (-1 cm).