days later they saw a large number of healthy 

 flounders (only about 1 percent were still affected) 

 and mud crabs on the two treated beds. 



Polystreaih was used m all later commercial 

 treatments because these experiments showed it 

 was much less toxic than Drillex to associated 

 animals, particularly arthropods. 



Effect on predation. — I made no careful quanti- 

 tative determinations; however, periodic observa- 

 tions of the lot indicated that predation by oyster 

 drills on oysters on the treated lots during 1963 

 was slight. 



Area 3: Northport Harbor, N.Y., 1%5 



On April 28, 1965, which was 2 years after the 

 initial treatment, lot 1 was treated again with 

 Polyst ream-sand. 



Effect on gastropods. — Eight days after the 

 treatment divers observed that every snail was 

 swollen. 



The treatment killed 64 percent of the oyster 

 drills (77.2 percent of the thick-lipped drills and 

 8.6 percent of the Atlantic oyster drills) and re- 

 duced their numbers from 31.5 to 11.4 per m.* 

 (table 4). 



Effect on associated animals. — Nine days after 

 the treatment divers found 6 stunned adult floim- 

 ders and one dead juvenile on the bed among about 

 50 healthy floimders of mixed ages. The only her- 

 mit crab they saw was healthy. 



Before treatment the number of young clams 

 (5-7 mm. long) on the bed was 158 per square 

 meter ; 28 days after the treatment the number of 

 clams was 125 per square meter. Thus, apparently 

 only about 20 percent were killed. 



Effect on predation. — I made no quantitative de- 

 terminations. Periodic observations of the lot indi- 

 cated, however, that predation by oyster drills 

 during 1965 was slight. 



Area 4: Northport Harbor, N.Y., 1966 



On May 9, 1966, 3 years after the initial treat- 

 ment, lot 2 was treated again, this time with Poly- 

 stream (Granular). 



Effect on gastropods. — ^Three days after the 

 treatment divers found that all thick-lipped drills, 

 Atlantic oyster drills, northern moon shells, and 

 New England nassas were swollen. 



The treatment killed 92 percent of the oyster 

 drills (94.5 percent of the thick-lipped drills and 

 71.7 percent of the Atlantic oyster drills) and re- 

 duced their numbers from 27 to 2.1 per square 

 meter (table 4). 



Effect on associated animals. — No observations 

 were made by divere. 



Effect on predation. — I made no careful quan- 

 titative determinations. Several observations of 

 the lot indicated, however, that predation by oyster 

 drills during 1966 was slight. 



Table 4. — Density of oyster drills, before and after treatments with Polystream and sand or Polystream (Granular), on oyster 



lots in N.Y., Conn., R.T., and Mass., 1966-67 



Lot DO. and area 



Date of 

 ' (hectares) treat- 

 ment 



Formulation 



Drills per m.' 



Before treatment 



After treatment 



Killed • 



E. caudttta U. cinerea E. eaudata V. clnerea 



E. caudata U. cinerea 



Both 



species 



combined 



25(3.2) 4/30/65 



1(2.4-3.2) 4/28/65 



2(2.0) 6/0/66 



208(1.8) 9/15/66 



I8» 4/ ?/67 



40» 4/29/67 



49> 4/29/67 



42(2.8) 5/ 1/87 



50> 6/ 1/67 



19 Control 



RI(0* 6/ 1/67 



FP(0.08) - 5/29/67 



FP Control 



Poly-sand.-. 

 Poly-sand.-. 

 Poly (Qran.) 

 Poly (Oran.) 

 Poly (Oran.) 

 Poly (Gran.) 

 Poly (Oran.) 

 Poly (Gran.) 

 Poly (Qran.) 



None 



Poly (Gran.) 

 Poly (Gran.) 

 None 



Number Number Number Number Percent Percent Percent 



3.3 0.9 0.0 0. S 100.0 4&6 88.7 



25.2 6.3 5.7 5.7 77.2 8.6 64.0 



24.1 2.9 1.3 0.8 94.5 71.7 92.3 



14.0 J0.9 77.5 



7.6 0.9 2^4 1.6 68.0 520 



12.0 4.7 2.2 1.6 82.2 66.7 77.8 



6.6 0.7 a 9 0.0 84.6 100.0 86.4 



3.0 0.3 0.9 1.0 66.7 .. 43.6 



12.6 1.3 1.7 a 6 86.4 65.6 83.6 



188 0.7 19.6 1.7 



ao 6.5 ao ao loo.o 100.0 



0.0 40.8 0.0 2.2 94.5 94.6 



0.0 37.2 0.0 33.2 



'Lot25,OysUrBay,N.Y.;Lotsl,2, Northport, N.Y.; Lots 205, 18,40, 49,42,50, and 19, Norwalk.Conn.; RI, Charlestown Pond, R.I.; FP, Fresh Pond 



Mass. 



' Actual number of hectares treated on these beds Is unknown, bat I estimated that areas treated ranged between 1.2 and 6.0 hectares. 



• Both species. 



< If count increased, no perceutage is given for tbi? species 



292 



U.S. FISH AND WILDLIFE SERVICE 



