New Method for Ageing Chinook Salmon (Onchorhynchus tshawytscha) Using Dorsal Fin Rays, and Evidence if Its Validity

Abstract

Age of spawning chinook salmon (Oncorhynchus tshawytscha) was estimated using a combination of thin cross-sections from the dorsal fin rays and scales. The latter were used when freshwater growth could not be interpreted from fin rays. Fish of known age were used when available. Results were compared with ages obtained from scales only. Due to scale resorption a significant proportion of the older fish ages was undetected using only scales. Determinations of freshwater age from fin rays and from scales were in agreement 88.5 ± 8.7 to 92.3 ± 7.2% at the 95% confidence level. Thus, the fin ray method provided virtually the same freshwater age as did the scale method. Also, fin rays provided quite acceptable estimation of ocean age. It is recommended that managers use a combination of scales and fin rays to estimate the total age of spawning chinook salmon.