35- 



30 



oi 25 



z 



20 



O 15 



< 



UJ 



> 

 <25 



Fresh water 

 Salt water 



Female 



J L 



20 



15 



Male 



_L 



_L 



_L 



J_ 



J_ 



_L 



20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99 100-109 110-119 120-129 130-139 



WIDTH ( MM. ) 



Figure 2. — Relative growth per molt of female and male blue crabs in fresh and salt water, St. Johns River, 



Fla., April 1 to November 1.5, 1964 and 1965. 



water than in summer; salinities at the salt 

 water station were 4.3 p.p.t. lower. Mean water 

 temperature was 15° C. in salt water (range, 

 8.3°-22.9° C.) and 12.3° C. in fresh water (range, 

 3.8°-18.2° C). Salinity at the Cedar Point Creek 

 site averaged 14.5 p.p.t. (range, 6-23.3 p.p.t.). 



Relative growth ])er molt in winter was similar 

 to that in summer. Crabs were less active and 

 consumed less food but generally were in good 

 condition. 



MOLT INTERVAL 



Information was collected on molting in summer 

 and winter. 



SUMMER 



More than one-half (1,256) of the molts in 

 summer (April 1 to November 15) from crabs 

 that molted more than once ])rovided information 

 on molt interval. 



Molt intervals appeared to be affected by the 

 size of crabs and by season but not by sex and 

 salinity. I found little difference in molt interval 



between males and females or between salt and 

 fresh water. The time between molts increased 

 with increasing body size (table 3). The smallest 

 crabs (20-29 mm. \\ide) molted after an average 

 of 11 days, and those over 120 mm. wide after 

 an average of 42 days. Molt intervals of crabs 

 within each size grouj) varied greatly but usually 

 were shortest during the warmest months, June 

 to September. Most juveniles 30 to 39 mm. wide 

 in Aju-il reached harvestable size after 4 months, 

 but crabs that had the same width in Jime were 

 harvestable after 3 months A\-ith the same numbei 

 of molts. Crabs that molted after particularly 

 long i)eriods grew little or died. 



Information was obtained on the tmie needed 

 for the terminal molt of 101 female blue crabs 

 (83-139 mm. wide). The final molt interval for 

 85 ])ercent of these crabs ranged from 25 to 50 

 days. Two females molted in as few as 18 days. 

 Large crabs (above 110 mm. \\ide) averaged 5 

 days longer than smaller ones. In salt water 

 (crabs averaged 106 mm. wide), the mean interval 



GROWTH OF JUVENILE BLUE CRABS IX ST. JOHNS RIVER, FLA. 



28.5 



