Tabt.e 7. — Percentane of males amonq juvenile blue crabs 

 collected at selected stations in the St. Johns River. Distance 

 upstream in kilometers is shown in parentheses 



all males and generally were larger than 100 mm. 

 wide (relatively few mates are available to the ma- 

 ture males that remain above Palatka). Juvenile 

 blue crabs under 100 mm. and usually over 30 mm. 

 occurred irregularly between Palatka and Welaka. 

 Nearly all juveniles above Welaka were over 100 

 mm. wide; the smallest blue crab I caught was 

 25 mm. 



In summary, juveniles, primarily beyond the 

 initial crab stages, enter the St. Johns in waves 

 dui'ing the latter part of the spawning season. The 

 time of the first wave appeared to depend on the 

 time of initial spawning. Many firet and second 

 crab stages entered in early winter. Individuals as 

 small as 8 mm. wide moved at least 135 km. up- 

 sti-eam. Juvenile blue crabs were widely distrib- 

 uted but concentrated the year around in certain 

 localities. Those less than 40 mm. wide were most 

 common in shallower waters; those more than 40 

 mm., in deeper areas. Females predominated in the 

 lower river and males m the upper river. 



FOOD OF BLUE CRABS 



Blue crabs eat a great ^-ariety of foods. Fish, 

 alive and dead, are eaten regularly (dead fish are 

 used as bait in the commercial fishery) . The diet of 

 blue crabs includes many types of aquatic vege- 

 tation (Truitt, 1939), and they have been repoited 

 to eat oysters (Lunz, 1947) and other bivalves 



(Carriker, 1951). Darnell (1958) found that blue 

 crabs of Lake Pontchartrain, La., fed principally 

 on mollusks (clams, mussels, and snails), crusta- 

 ceans (mostly crabs but also barnacles and mide- 

 termined forms), and to a lesser degree on insects, 

 hydroids, annelid worms, fish, algae, and vascular 

 plants. 



Little is known of the foods that sustain lan^al 

 crabs. Most successful foods for growth of zoeae 

 in the laboratoi-y are yellow dinoflagellates (San- 

 doz and Rogers, 1944) and Artemia nauplii and 

 Arhacm eggs (Costlow and Bookhout, 1959). The 

 megalops is omnivorous and will eat pieces of fish, 

 shellfish, and aquatic plants (Van Engel, 1958). 



Of the 695 blue crab stomachs collected at four 

 localities— Clapboard Creek (15 km. upstream 

 from mouth of St. Jolms River), Dmin Creek (30 

 km. upstream). Trout River (40 km. upstream), 

 and buoy 24, Picolata (95 km. upstream) — 668 

 contained food. Classes of food as percentage 

 fi-equency of occurrence were: 



Food item Percent 



Mollusks 32. 4 



Crustaceans 19. 4 



Organic debris 17. 



Fish 15. 6 



Plants 8. 5 



Annelids 5. 



Insects 1-4 



Bryozoans -6 



Classes of food as percentage of the total volume 

 of food per stomach were : 



Food item Percent 



Mollusks 39. 



Organic debris 19. 8 



Fish 19. 4 



Crustaceans 15. 



Plants 3. 9 



Annelids 1.8 



Insects .9 



Bryozoans -1 



Table 8. — Monthly size distribution of juvenile blue crabs collected at buoy S4, Picolata, St. Johns River, Fla., 1962 



28 



U.S. FISH AND WILDLIFE SERVICE 



