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 of known-age fish can all age classes in a population be validated. If such studies are not possible, fish should be aged by several methods, and the possibility of errors in age estimates must be considered.

The life history traits of 42 marine fish species were grouped according to the theoretical classifications of life history strategies. This provides a conceptual framework of management options, because life history strategies are the underlying determinants for population responses to climate and ocean changes, they can be used to classify typical population responses. When faced with providing management advice for species for which there is no information on absolute or relative biomass, such as newly exploited species, life history traits can be used to classify the species into a strategist grouping and the appropriate management options can be selected from the conceptual framework.

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Large fluctuations in the trends of Pacific salmon production in this century have been linked to trends in climate in the Pacific that are in turn associated with climate trends throughout the Northern Hemisphere. The close correspondence in the persistence of climate trends and the synchrony of the changes is evidence that a common event may cause the regime shifts. The trends or regimes can be characterized by stable means in physical data series or multiyear periods of linked recruitment patterns in fish populations. The regime concept is important in fisheries management because the natural shifts in abundance may be large and sudden, requiring that these natural impacts be distinguished from fishing effects. An equally important consideration is that biological and physical mechanisms may change when regimes shift, resulting in conditions that may not be characterized in the earlier part of the data series. Fluctuations in Pacific salmon abundance in this century were synchronous with large fluctuations in Japanese sardine abundance, which can be traced back to the early 1600's. The synchrony in the fluctuations suggests that Pacific salmon abundance may have fluctuated for centuries in response to trends in climate. The concept of regimes and regime shifts stresses the need to improve our understanding of the mechanisms that regulate the dynamics of fish and their ecosystems.

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