MAY JUNE JULY AUG, SEPT. OCT. NOV. 



1962 



MAY JUNE JULY AUG. SEPT. OCT. 



1963 



JULY AUG. SEPT. OCT. 



1964 



Figure 2. — Catches of mud crabs on traps in treated area of Lewis Gut, Bridgeport, Conn. 



Area 2: Northport Harbor, N.Y., 1963 



Noithpoit Harbor on the north shore of Long 

 Island is about 6.5 km. long. The oyster beds are in 

 water 4.5 to 7.5 m. deep at low tide, and water cur- 

 rents rarely exceed 1.8 km. per hour. 



On May 21 and 28, 1963, 1 made a series of com- 

 parative treatments. The i^urpose was to determine 

 whether Drillex (a mixture of Polystream and 2 

 percent by weight of Sevin) is more lethal to oyster 

 drills than Polystream alone. The experiment had 

 four 2-ha. lots. Two lots received an application 

 of 11.5 kl. of treated sand per hectare. They were 

 designated as 1 (for Polystream) and 1 x (for 

 Drillex). The remaining two lots which received 

 19.0 kl. of treated sand per hectare were desig- 

 nated as 2 and 2 x. 



Effect on gastropods. — -The treatments had a 

 very deleterious effect on gastropods. A few hours 

 after the treatments, divers observed that nearly 

 eveiy visible gastropod on all four lots was 

 swollen ; on lots treated with Drillex, however, the 

 drills expanded faster and sooner. Ten days after 

 tlie treatments, most thick-lipped drills were 

 drawn deeply into their shells but some were still 



swollen. Northern moon shells were observed in 

 tliree conditions — partially expanded, dormant 

 with their operculum flush with their aperture, 

 and dead. Twenty-three days after the treatments 

 divers noted that all visible thick-lipped drills 

 were dead on lots 2 and 2 x, and only a small num- 

 ber were alive on lots 1 and 1 x. No northern moon 

 sliells were observed either dead or alive; even 

 their shells were gone. Hermit crabs had probably 

 carried them off the bed. 



Because many flounders were swimming over 

 the beds and crabs were numerous when the snails 

 were swollen, these fish had ample opportunity to 

 feed on the paralyzed drills. I observed no snails 

 being consumed, however; instead, they appeared 

 to die directly from the toxic effects of the 

 chemicals. 



Examination of the bottom showed that Poly- 

 stream alone killed almost as many oyster drills as 

 Drillex. 



Effect on associated animals. — Divers observed 

 that during the applications of Drillex-sand a 

 small number of flounders, many hermit crabs, 

 sin-imp, and annelids were killed; however, 10 



CONTROL OF OYSTER DRILLS WITH POLYSTREAM 



291 



