Many calcified structures produce periodic growth increments useful for age determination at the annual or daily scale. However, age determination is invariably accompanied by various sources of error, some of which can have a serious effect on age-structured calculations. This review highlights the best available methods for insuring ageing accuracy and quantifying ageing precision, whether in support of large-scale production ageing or a small-scale research project. Included in this review is a critical overview of methods used to initiate and pursue an accurate and controlled ageing program, including (but not limited to) validation of an ageing method. The distinction between validation of absolute age and increment periodicity is emphasized, as is the importance of determining the age of first increment formation. Based on an analysis of 372 papers reporting age validation since 1983, considerable progress has been made in age validation efforts in recent years. Nevertheless, several of the age validation methods which have been used routinely are of dubious value, particularly marginal increment analysis. The two major measures of precision, average percent error and coefficient of variation, are shown to be functionally equivalent, and a conversion factor relating the two is presented. Through use of quality control monitoring, ageing errors are readily detected and quantified; reference collections are the key to both quality control and reduction of costs. Although some level of random ageing error is unavoidable, such error can often be corrected after the fact using statistical (‘digital sharpening)’ methods.

Accuracy, precision and quality control in age determination, including a review of the use and abuse of age validation methods

A survey of 500 studies published between 1907 and 1980 that included estimates of fish age indicated that only 65% mentioned age validation or attempted to validate the ageing technique In less than 3% was the technique validated for all age classes Among the 35% that did not consider age validation, many did not consider the possibility that ages may be incorrect Among 75 additional publications published in primary journals between 1965 and 1980 that assessed stock dynamics and used fish ages, only 40% mentioned or attempted age validation, and none successfully validated all age groups used in the analysis Many investigators continue to neglect the critical study of age validation despite the clear direction of the early work on age determination We show that estimated ages greater than the maximum validated age must not be considered accurate Use of inaccurate ages has caused serious errors in the management and understanding of fish populations Only by mark-recapture studies or use o

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The Forgotten Requirement for Age Validation in Fisheries Biology

The development of ideas and methods in the quantitative study of the patterns of growth, maturation and longevity in fish is reviewed. Earlier studies on length and age at maturity, von Bertalanffy growth formula parameters, natural mortality and maximum age for clupeiformes, pleuronectiformes, gadiformes and Sebastes spp. are up-dated and extended. The concept of the Growth-Maturity-Longevity (GML) plot is developed and applied. GML plots for the gadiformes and pleuronectiformes occupy the same two-dimensional space, but those for clupeiformes and Sebastes are located differently from them and from each other. The GML parameter suite for long-lived Sebastes spp. is similar to that of certain higher vertebrates of comparable longevity (minke whale and African elephant). It is suggested that the conventional distinction between the growth of fish being indeterminate and that for higher vertebrates determinate is inappropriate; the main difference is whether the approach to the characteristic maximum size is asymptotic, as in fish and some higher vertebrates, or abrupt as in others, including man.

Patterns of reproductive strategy parameters in some marine teleost fishes

Age determination and validation studies of marine fishes: do deep-dwellers live longer?

Pre- and post-bomb radiocarbon in fish otoliths

Fish ages are often estimated by assuming an annual frequency of the band-like, growth-zones recorded in the largest of their otoliths, the sagittae. The total number of growth-zones are normally determined either by counting external growth-zones (whole otolith technique) or by examining otolith cross-sections (otolith section technique). The two techniques do not always yield the same age, however, particularly in older specimens of certain fishes. To resolve this problem, otoliths of the splitnose rockfish Sebastes diploproa were examined morphologically and were assayed for their natural radionuclide concentrations. Four age groups of otoliths were identified based on growth-zone counting; in the first three, whole otolith and otolith section age estimates agreed, while in the fourth, the otolith section age substantially exceeded the whole otolith age. Radiometric analysis demonstrated that all otoliths were deficient in 210Pb activity relative to 226Ra activity with the deficiency decreasing with increasing number of growth-zones. The magnitude of the 210Pb/226Ra radioactive disequilibrium in each otolith group, when compared to the number of growth-zones and the otolith weight histories derived with the two techniques, identifies the growth-zones revealed by otolith sections as annual features. Thus when otolith section age exceeds whole otolith age (usually occurring after 20 to 25 yr of age for this species), the otolith section technique is the correct method of age determination. Estimates of longevity in the genus Sebastes near 80 yr are therefore confirmed.

K. K. Turekian

Papers

Confirmation of longevity in Sebastes diploproa (Pisces: Scorpaenidae) from 210Pb/226Ra measurements in otoliths