Year of publication 2013

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Product type Document

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Edition 1

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Synopsis (short abstract) Information on the age of individuals is often required for models assessing the status of stocks. Techniques used to estimate age of tu have varied across species and agencies, precluding meta-alyses of age and growth. We compared age estimates obtained from commonly used ageing techniques for four important tu species: bigeye tu, yellowfin tu, southern bluefin tu, and albacore tu. Estimates of age from counts of annual increments in transverse-sectioned otoliths were generally higher than thos e from counts of daily increments in transverse and longitudil sections for all species, particularly for fish older than two years. However, annual counts produced younger estimates, on average, relative to daily counts for bigeye and yellowfin tu younger than one year. Estimates derived from daily increments in longitudil and transverse sections were generally similar, although longitudil sections produced relatively older age estimates for individuals older than two years. A linear or non-lin ear increase in the magnitude of differences between ageing methods was the best- approximating model in all cases except when comparing daily-increment counts between transverse and longitudil otolith sections for southern bluefin tu. These observations are consistent with a rrowing of daily increments with increasing age, resulting in under- estimates of age relative to those derived from annual increments. We conclude that (i) daily increments are unsuitable for ageing indivi- duals over two years, especially for southern bluefin and albacore, (ii) longitudil sections are more precise and produce older age estimates than transverse sections for daily-age estimates, (iii) there are considerable differences in these trends between species, likely dependent on longevity, and (iv) parameter estimates and/or conclusions based on meta-alyses using age data derived from different ageing methods are likely confounded with methodological biases. This result demonstrates that greater effort i s required to provide con- sistent, validated methods for routine age determition to support the assessment and magement of these valuable populations.

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Meeting Session Number 15

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Language English

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