and 10 dead polychaetes. On the inspections made 

 along the shoreline, just inside the other treated 

 section, there were only two dead toadfish and one 

 dead blue crab. Undoubtedly, a high percentage of 

 fish, blue crabs, and shrimp was killed at the time 

 of treatment. Divers did not see any fish or shrimp, 

 live or dead, either on or off treated areas. 



Effect on predation. — No determinations were 

 made. 



Area 10: Fresh (Quahog) Pond, Falmouth, Mass., 1%7 



Fresh Pond, about 2.0 ha., is a tidal pond on the 

 east shore of Buzzard's Bay. It is connected with 

 the Bay by a long, narrow creek only about 1 m. 

 wide and 0.3 m. deep at the entrance of the pond. 

 The area for growing oysters is from to 2 m. 

 deep. Winds generate the principal currents in the 

 pond. 



On May 29, 1967, a 0.08-ha. section of the pond 

 was treated with Polystream (Granular) . 



Effect on ga.stropods.—^N\th.\n an hour of the 

 treatment divers observed that all snails were 

 beginning to swell. 



By July 11, the treatment had killed 95 percent 

 of the Atlantic oyster drills (no thick-lipped drills 

 were present) and reduced their numbers from 

 40.8 to 2.2 per squai-e meter (table 4) . 



An untreated area in another section of the pond 

 that served as a control for the treatment had an 

 average on May 29 of 37.2 Atlantic oyster drills 

 per square meter. On July 11 this control plot 

 had 33.2 drills per square meter. 



Effect on associated animals. — Because the 

 treatment extended to the shoreline of the pond, a 

 number of observations could be made by walking 

 along the shore. An hour after the treatment I 

 observed 2 flounders (5 cm. long), 5 green crabs, 

 Carcinus maenas, and 200 shrimp all dying, and 

 100 mummichogs stunned. I also observed three 

 small schools of silversides swimming through the 

 area; all these fish were healthy. New England 

 nassas and mud snails, Nassarius obsoletus, were 

 begimiing to swell. 



On July 11, 1967, divei-s examined the area 

 again. The only animal affected other than snails 

 was a tautog which weighed about 1.8 kg. All New 

 England nassas and mud snails were dead. 



Effect on predation. — The area had no oysters. 



RECOMMENDATIONS FOR USING 

 POLYSTREAM 



During this study I made a number of observa- 

 tions on the use of Polystream (Granular), the 

 form now most commonly used on commercial oys- 

 ter beds to control oyster drills. These observations 

 are listed below and should be emphasized for 

 those who might wish to use this product : 



1. The bed to receive a treatment should have a 

 firm bottom, free of silt. 



2. Treatments should be made in late April or 

 early May when oyster drills first become active 

 after a period of winter dormancy. 



3. Polystream (Granular) should be spread at 

 slack current. 



4. Most successful treatments have been made in 

 water less than 6 m. deep, where currents are less 

 than 2.7 km. per hour. Wliere currents are stronger 

 than this, planted oysters appear to prevent the 

 Polystream (Granular) from being carried off a 

 bed. 



5. Polystream (Granular) treatments are suc- 

 cessful on beds planted with seed oysters. 



6. In certain shallow areas, where little or no 

 current flows, a smaller quantity of Polystream 

 (Granular) may be successful. 



SUMMARY 



1. Five experimental and 10 commercial treat- 

 ments of oyster beds were made with Polystream 

 in the States of Connecticut, New York, Rhode 

 Island, and Massachusetts. 



2. Immediately after a treatment, oysters, clams, 

 and other organisms accumulated small residues 

 of Polystream in their tissues. These residues, how- 

 ever, were gradually lost or greatly diminished. 

 For instance, oysters and clams lost the residue of 

 Polystream within 119 days. If they were trans- 

 planted from a treated to an untreated bed, how- 

 ever, they lost the residue within a week. 



3. All oyster drills were killed in areas where 

 water current velocities were low. On a typical 

 bed, in an area where current velocities were be- 

 tween 0.9 and 2.7 km. per hour, liowever, about 

 85 percent of thick-lipped drills and 66 percent of 

 Atlantic oyster drills were killed. Apparently, no 

 oyster drills were killed where current velocities 

 were strong. 



4. On treated beds where current velocities were 

 low, significant percentages of fish, small clams. 



296 



U.S. FISH AND WILDLIFE SERVICE 



