COMMERCIAL SEASONS 



1952 



1953 



20 40 60 80 100 120 140 160 



20 40 60 80 100 120 140 160 



TOTAL LENGTH (MM.) 



Figure 5. — Monthly length distributions of commercially caught shrimp, M. vollenhovenii, from the lower 



St. Paul River, Liberia. 



impossible because of overlapping age groups 

 (Miller, 1960). Length distributions of the 

 western crawfish plotted by month was nearly 

 identical because: recruitment in each size 

 interval was relatively proportionate following 

 a molt; there was little variance in growth in- 

 crement of the same length crawfish; there 

 was no identifiable modal length increase by 

 month ; and growth in the adults was a func- 

 tion of food availability, not age. 



The second explanation was rejected because 

 I could see no evidence in the length distribu- 

 tions to support the entrance of the large adults 

 into the fishery in early summer (fig. 5). If 

 age group one does not die off naturally in 

 December but migrates upstream or into ad- 

 jacent swampy areas, then I speculate that 

 these shrimp, as age group two, survivors con- 

 tribute very little to the population. 



