Ju et al; Demographic assessment of Callinectes sapidus 



315 



-1  



a, -2- 



-4 



20 40 60 80 100 120 



Carapace width (mm) 



140 



160 



180 



200 



Figure 2 



Plot of natural log (lipofuscin index) versus carapace width (mm) of subsampled crabs collected from 1998-99 and 

 1999-2000 in winter dredge surveys in Chesapeake Bay. Each regression line represents one sex during one year as 

 described in Tabic 1. 



ing seasons (ages 0.4-0.6 yr) (Fig. 4). It seems likely that 

 juvenile modes were skewed towards older juvenile ages 

 because small crabs (40 mm CW) were excluded from anal- 

 ysis. In the 1999-2000 WDS sample, modal analysis sup- 

 ported a second subannual mode for age-1 crabs, which in- 

 fers a bimodal recruitment pattern during the summer and 

 fall ofl998 and may not have occurred in 1997 (i.e. 1998-99 

 WDS samples). Several lipofuscin values actually exceeded 

 the third dominant mode (the fourth mode for 1999-2000 

 WDS samples), which suggests that several crabs at- 

 tained ages >3 years. Nevertheless, these individuals 



could not be statistically distinguished from the last domi- 

 nant mode. 



There was a large discrepancy between the individuals 

 assigned age classes by lipofuscin index and those assigned 

 by CW criteria. Lipofuscin measures suggested that most 

 crabs could attain 120 mm CW in less than two complete 

 years of life (Table 4). Conversely, the index predicted that 

 some individuals could grow quite slowly, remaining <60 

 mm CW into their second year of life ( Fig. 3A). Although the 

 samples analyzed did not include every animal from the 

 WDS, the age structure suggested a pattern of declining 



