Steelhead trout otoliths for age, race, and stock analysis

Graduation date: 1971Presentation date: 1971-03-12Growth characteristics of otoliths were used to determine age, and to separate known races and stocks of steelhead trout (Salmo\ud gairdneri). Otoliths were the first calcified structures observed in X-ray photographs of steelhead embryos, and a continuous record of events through life was interpreted from these structures. A direct\ud relationship was established between otolith length and fork length of the fish. Freshwater and saltwater annuli, and spawning checks on otoliths were used to describe 27 life history patterns. A significant difference in nucleus diameters of otoliths was used to separate summer and winter races. Significant differences in freshwater growth characteristics were used subjectively to separate wild from\ud hatchery-reared stocks of steelhead. The use of otoliths represents a valid technique to supplement those now available for management\ud of this species