Knowing the age structure of wild populations is fundamental for understanding the ecology of fish populations. For many species of fish, age can be determined with reasonable certainty using hard parts which produce a characteristic growth increment over time e.g. otoliths, scales, or spines. Age determination of crustaceans, however, is difficult because they lack permanent hard structures. As they grow, crustaceans periodically molt their calcareous exoskeleton which removes all external evidence of age or previous size. At each molt an internal space is created which is filled over time by the growth of soft tissue. As a result crustacean soft tissue growth may be continuous while carapace size, the most frequently used measure of growth and age, is a discontinuous function of time. For crustaceans such as the commercially important blue crab, Callinectes sapidus, methods such as a model analysis of length frequency data have been used in lieu of accurate age information for estimating population dynamics.
The critical need for age structure information among invertebrate populations
has lead to a search for alternative methods for age determination.
The most successful have taken a biochemical approach, and followed the
accumulation of condensation products produced as a consequence of peroxidation
reactions in cells. In neural tissues which undergo limited postmitotic
division, these products can accumulate over the life of an organism.
First described for humans by Hannover in 1842, these heterogeneous mixtures,
termed lipofuscins, are now recognized as one of the most clearly discernible
markers of age in cells. using extraction methods, we have modified
and refined previous approaches for the extraction of these hydrophobic
products from tissues and have streamlined the approach and increased sensitivity
to allow precise measurements of lipofuscins content in numbers sufficient
to adequately represent field populations.
The blue crab is an economically and ecologically important species in
the Chesapeake Bay. Therefore, they require a resource management
program, however, this has proven difficult. Understanding the age
structure of a stock population is critical for stock management,
but it is difficult to attain precise and realistic age structures of population
using current methods; such as size and weight to determine age.
Estimates of precise age are difficult because blue crabs don't have any
permanent hard structures such as otoliths, scales, etc. and are molt periodically.
In order to solve the crab population dynamics problem and help the crab
fishery, my research focuses on establishing and applying the new biochemical
technique of age pigment to estimate the age of crabs.
