Age Validation and Revised Natural Mortality Rate for Yellowtail Rockfish

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Abstract
Oxytetracycline (OTC) injections were used in a mark-recapture study undertaken to validate the otolith method of age determination for yellowtail rockfish Sebastes flavidus. Otoliths from recaptured fish were broken across the focus and burned to enhance the contrast of features in the internal structure. The number of opaque and translucent zones laid down in the otolith after the deposition of the fluorescent OTC mark at the time of tagging agreed with the number of years (up to four) that the fish had been at liberty. These results validate the annual pattern of banding in otoliths of fish of ages 8-34 years. A larger sample of fish aged by this technique indicated an instantaneous natural mortality rate (M) of 0.07, a value only 28% of the estimate presently used for stock assessment and management of yellowtail rockfish.