12 3 4 5 6 7 e 9 10 11 12 13 14 15 16 17 18 19 

 CARAPACE WIOIH (MM) 



FiGUKE 5. — Width distribution of blue crabs less than 20 

 mm. wide collected before and after the initial wave in 

 Dunu Creek and Trout River. 



in Dunn Creek and Trout Eiver during December 

 and Januaiy (fig. 6). These crabs were hatched 

 in October and November, and subsequent win- 

 ter temperatures probably inhibited postlarval 

 growtli. They shed tlirougliout the winter but less 

 frequently than in other seasons. 



Waves of early blue crab stages also entered 

 Clapboard Creek in 1962, but no appreciable in- 

 flux was observed during 1963. Small numbers, in- 

 cluding a few first crab stages, occurred among 

 much larger numbers of CaUinectes simills or C. 

 ornahts from July to October 1963. No con- 

 gregations of blue crabs developed, possibly be- 

 cause of competition for food and space from 

 small juveniles of these other species, which were 



established in Clapboard Creek as early as May 

 (Tagatz, 1967). 



The influx of early crab stages was not confined 

 to the lower river but extended 95 km. and more 

 upstream. Early crab stages over 5 mm. wide first 

 appeared at Picolata (buoy 24) during the same 

 month as the initial waves in the lower river — 

 July 1962 and September 1963. In 1962, most early 

 crab stages were widely scattered in shallow areas 

 adjacent to buoy 24; in 1963, waves and sub- 

 sequent growth were clearly evident at this station 

 (fig. 7) . Crabs that made up the waves were larger 

 than those entering lower river areas, and no crabs 

 less than 6 mm. wide were caught. A few early 

 crab stages 8 to 9 mm. wide were collected at Pa- 

 latka (buoy 11). 



In the St. Johns River, some juvenile blue crabs 

 grew to maturity (or a harvestable size of at least 

 120 mm.) between the mouth and Jacksonville, 

 but most females attained maturity between Jack- 

 .sonville and Palatka; most males matured up- 

 stream of Palatka. Juvenile males were less abun- 

 dant than juvenile females in the lower river, and 

 the percentage of males increased with distance 

 upstream (table 7). I found the largest concentra- 

 tions of juvenile crabs 20 to 119 mm. wide at Pico- 

 lata (buoy 24). Because of variation in growth 

 rate and a long spawning season, significant num- 

 bers of crabs were one or more molts away from 

 harvestable size during all seasons (table 8) . Juve- 

 niles 20 to 39 mm. wide were most common in 

 spring and fall. They were more widely distrib- 

 uted in the shallows along shore than larger crabs 

 which remained in the channel. Juveniles 20 to 

 119 mm. wide also concentrated at Palatka (buoy 

 11). Upstream of Palatka, juveniles were nearly 



CARAPACE WIDTH (MMI 



Figure. 6. — Width distribution of blue crabs less than 

 14 mm. wide collected in Dunn Creek and Trout River 

 during December 1962 and January 1963. 



8 9 10 II 12 13 14 IS 

 CARAPACE WIDTH |MM i 



FiQURE 7. — Width distribution of blue crabs 

 mm. wide collected before and after the 

 at Picolata (buoy 24). 



16 17 le 19 



less than 20 

 initial wave 



BIOLOGY OF BLUE CRAB IN ST. JOHNS RIVER, FLORIDA 



27 



