Lipofuscin concentration versus length as indicators of age in decapods. Using the norway lobster (Nephrops norvegicus) as a model.

Tese mest. , Biologia Marinha, 2008, Universidade do AlgarveDirect age estimation is not possible in crustaceans, because they lack permanent calcified parts with age marks. Because of the importance of estimating the age structure of an exploited population for stock assessment and management, indirect techniques are used to estimate age, the most common being length frequency analysis (statistical separation of length distributions associated to each age class by identifying modes and estimating their variances). Since the 1980’s, several authors have proposed a technique for direct estimation of crustacean age: the levels of fluorescent pigments (lipofuscins) in postmitotic cells (such as those in the brain), assuming the accumulation of these pigments does not decelerate with age, thereby providing a better indicator for age, particularly in older groups, where length frequency analysis does not work well. The technique involves the histological quantification of lipofuscin granules present in the cells, requiring considerable amount of work and resources. In this work, available data for the Norway lobster (from wild populations and simulations) was used, and the lipofuscin accumulation was modelled according to suggestions that it’s accumulation is linearly dependent on age, and evidence that it has either a normal or a lognormal distribution within each age group. Expected lipofuscin distribution at length was generated according to the previous assumptions. The results suggest that lipofuscin distribution at age still has a considerable amount of overlap from age class to age class, and that it’s much higher requirements, in terms of time, equipment and cost, do not favour or justify it’s systematic use as an age indicator for the Norway lobster