
Blue Crabs 
Ecology 
, The common blue crab, Callinectes sapidus, frequents creeks, 
ditches and ponds in salt marshes. Much of its population, particularly 
the medium and large-sized individuals, moves outward from the marsh into 
deeper water with ebbing tides and returns with flood tides. Saltmarsh 
ponds are likely to be inhabited by smaller individuals which do not migrate 
with the tides. The blue crab is largely aquatic but may stay on moist 
banks for extended periods. Unlike the fiddler, it does not inhabit burrows, 
individuals that remain in ditches or creeks temporarily drained by the 
tide are likely to bury themselves in the mud or hide under other cover. 
Methods of Study 
Evidence of DDI spray effects upon blue crabs was obtained by 
two procedures: (1) General observations consisting of visual estimates 
of effects upon populations and (2) studies in creek and ditch sections 
enclosed by screen barriers. 
General Observations 
Observations made on the 1.6 area one day after the first 
spraying seemed to indicate a nearly complete kill of the crabs present at 
spraying. The few crabs that were not dead appeared feeble. There was 
evidence that new crabs entering the area continued to be killed. Live 
crabs were not seen in any numbers until twc weeks after spraying. By the 
time of the September spraying, active crabs were again present in the 1.6 
and 0.8 areas but not in numbers as great as prior to the first treatment. 
The second spraying also caused very heavy mortality within 2 hours. The 
total number found dead was only about half that encountered after the first 
spraying and the individuals appeared to average smaller in size. A few 
live crabs were found in heavy vegetation. 
In general, the results on the 0.8 area were similar to those on 
the 1.6 area though the mortality, 16 hours after both the first and second 
treatments, did not appear to be as sudden or as complete. On this area, 
however, a larger proportion of individuals was noted with tremors. Two 
and a half days after the first spraying there were a few more live crabs 
than had been observed in the 1.6 area. 
The 0.4 dosage caused much less mortality than the two higher 
ones. The first spraying resulted in only a slight kill, but dead crabs 
were decidedly more numerous after the second treatment. as in the case 
of fish and fiddler crabs this increase in mortality may be attributed to 
the higher application during the second spraying. The toxic effects of 
DDT did not appear to last over six days. 
Both the first and second sprayings in the 0.2 area resulted in 
only light mortality. A few dead crabs and some with tremors were found. 
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