
addition, many crabs were found in a sluggish condition. Lortality was apparently 
more severe in flat areas than on well drained banks. Deaths continued to 
occur for at least ten days after the spraying. 
A light but widespread kill occurred on the 0.4 area, with a 
somewhat greater mortality after the second spraying than after the first. 
This is in agreement with the higher mortality of fish and blue crabs | 
occurring in this plot at the same time. However, the severity of kill 
seemed appreciably less in this plot than in the case of the heavier dosage 
areas. «A minimum of 30 dead crabs was found alony 290 feet of a creek 
section after the second spraying. 
Tnere was slight and inconclusive evidence. of mortality on the 
0.2 area following both sprayings. The few dead crabs found were assumed 
to have been killed by DDT. 
kncelosures 
This method of testing DUT effects on fiddler crab populations 
made use of a square frame of sheet metal, 22 inches on a side and l2 inches 
deep, sunk 8-9" into the ground. Though box-like in form, it had no bottom, 
In the fiddler banks where this frame was used, crab burrows did not extend 
more than 10 inches deep. A covering of 3 inch hardware cloth was placed 
over the top to prevent crabs from escaping during high water and to preclude 
depredation by birds, 
Preliminary tests involving the removal.of all crabs within an 
enclosure demonstrated that fiddlers were usually more numerous than their 
burrows. The results of four samplings are given below and indicate that, 
in these instances, the number of fiddlers averaged half again the number 
of holes. 
Ratio of Holes 
Sample No. No. of Holes No. of Crabs to Crabs 
1 25 76 ee 
2 2 80 1-1.9 
3 9h 117 1-1.2 
yy 48 61 ji P13 
In sampling the effects of DDT sprayings, one or more pairs of 
frames were placed in each area. They were set side by side before the 
Spraying in places where comparable conditions of habitat and crab popula- 
tion existed. About a day before the spray was applied, one frame of each 
pair was covered with waterproof paper to protect the crabs in that enclo- 
sure from direct contact with DDI and to serve as a partial check. Burrows, 
classified as small, medium, and large, were counted before and after 
Spraying and the number of active crabs of different sizes seen within the 
enclosures after spraying was noted. Record was made of any dead specimens 
removed, 
Limitations of time and staff, as well as interference by adverse 
weather, prevented a full utilization of this method during both sprayings. 
Observations on enclosures during the second spraying were inconclusive, 
18 
