Age determination in crustaceans

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Decapod crustaceans, such as American lobster, snow crab and northern shrimp, are an important component of Canadian society and economy; in 2006, lobster alone generated $633,181 million, or 34% of the total landed value of all Canada's wild capture fisheries combined. Sound management of this industry is therefore crucial. One of the more important parameters fisheries scientists rely upon to assess and manage stocks is the age of individuals, which is used to calculate growth and mortality rates, recruitment and productivity. Whereas the age of wild animals can often be determined by examining calcified structures (e.g., bones, scales, otoliths, shells), this method has not been used in decapod crustaceans, due to the presumed loss of all integumental structures at each moult. The research we propose will investigate the potential of a new method for revealing absolute age of individual decapod crustaceans, which is based on observations of growth bands in transverse sections of the eyestalk. The observed growth bands appear different from the micro-scale features previously reported in the shells of various crustaceans. Research is needed to determine if the bands documented in our preliminary work are indicators of age, moult events, or neither. As a first step in answering this question we will use microscopy to determine the precise location, nature and ontogeny of these bands, as well as their potential presence in other body parts (walking legs, swimmerets, gastric mill) and species (8 total). We will then use the knowledge acquired to perform more direct tests of the age-determination hypothesis, based on i- body size - band count relationships in American lobsters from different latitudes, ii- band counts in known-age decapod crustaceans (obtained via rearing of juvenile lobsters as well as a world search of marine laboratories and aquarium facilities), and iii- additional validation using chemical marking techniques. If these bands are confirmed to be age indicators, the implications for future stock assessments and biological studies of lobsters, crabs, and shrimps, both in Canada and around the world, would be substantial. However, even a reliable indicator of moult number would have considerable value in monitoring crustacean populations.