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Ageing Studies

Understanding a stock's status is dependent on how well the age structure is measured or inferred. For instance, only the use of age-structured models can assist in the measurement of an "over-fished state and over-fishing thresholds" of a particular species, described by national standards and spelled out within the Magnusun-Stevens Fishery Conservation and Management Act. This law, updated periodically, governs much of what we do in the fishery science and management business. Therefore, ageing fish is an important activity for the goal of maintaining sustainable fishery harvests.

Some fish species are easy to work with in this respect. These fish may be short-lived, average growth can be readily estimated, and age is related to body size. Also, growth may be fairly constant over time. For these species, age structure can be estimated from sampling many fish lengths or weights. Increasingly, as new species are added to the roster for management, we find species that are not so easy to work with when inferring age-structure. These fish may exhibit high individual variation in growth rate, or large variation in annual recruitment levels or are simply difficult to age because of unclear growth patterns in scales, bones and otoliths (the typical structures used to age fish).

Increasingly, we are being called upon to address ageing needs in a production fashion. That is, verify and validate how we interpret growth structures, estimate ageing precision and error, and age increased numbers of samples annually, perhaps even setting targets to track year-class strength over time.

Since the 1980's our laboratory's focus has been on species managed largely from federal waters within the Gulf of Mexico and has included several reef fishes (snappers and groupers) and certain coastal pelagic species (mackerels). But the potential species needs list is large. For example, just within the Gulf reef fish management plan, there are 49 species noted as commonly landed and 42 species listed within the management unit, meaning more information is desired to address their status. As the number of species being managed grows, our list also grows and we strive to coordinate with other federal, state and university laboratories to efficiently divide up the workload.