Frequency of Increment Formation on Sagittae of North Pacific Albacore (Thunnus alalunga)

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Abstract
An examination of sagittae from 116 albacore (Thunnus alalunga) caught in the North Pacific, injected with tetracycline, tagged, released, and subsequently recaptured in sport and commercial fisheries showed that detectable increments are formed on these otoliths at an average rate of 0.954 per day. We take this as a confirmation of daily increment formation in North Pacific albacore sagittae. The slight departure of observed mean increment counts from the expected rate of one per day may be due to an occasional interruption of otolith growth, or to a systematic bias in detecting daily increments or interpreting otolith microstructure. The estimated rate of detectable increment formation applies explicitly to albacore of fork lengths between about 50 and 100 cm. If the same rate holds for fish smaller than 50 cm, as is likely, most albacore taken in sport or commercial catches can be aged accurately by applying our methods and expanding the increment count by 5%.

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