Size relations of two instars of the blue crab,Callinectes sapidus

Two successive blue crab instars were examined for size variation. Data assembled from Chesapeake Bay crabs show that linear measurements of an instar may vary by as much as 50% of the mean dimension. The size ranges of the two instars (penultimate and ultimate) that were examined overlap considerably. The average crab size for the instars may change significantly with sample locality, or, at a particular locality, may change with date.