Area 5: Sag Harbor, N.Y., 1963 



A 0.4-ha. lot along the eastern shore of Shelter 

 Island in Sag Harbor was treated. The water over 

 tliis lot is about 3 m. deep at low tide, and maxi- 

 mum curi'ents are about 2.7 km. per hour. 



On September 27, 1963, Polystream (Granular) 

 was used for the first time to control oyster drills. 



Effect on gastropods. — Within an hour of tlie 

 treatment divers noticed that all visible snails were 

 at least partially swollen. A week later divers ol)- 

 served many affected thick-lipped drills, Atlantic 

 oyster drills, northern moon shells, and both knob- 

 bed and channeled whelks. 



Ten drill traps were placed on the treated lot and 

 an adjacent area before the treatment. The traps 

 in each area collected between 200 and 300 oyster 

 drills. After the treatment, traps were examined 

 only once. They collected only 10 oyster drills on 

 the treated area but gathered 127 on the control 

 area. I did not count the two species of drills 

 separately. 



Effect 011 nxsockifed anbmds. — Divers observed 

 that the treatment did not affect associated animals 

 and plants, such as flounders, bay scallops, mud 

 crabs, and sea lettuce. 



Effect on predation. — No determinations were 

 made. 



Area 6: Oyster Bay Harbor, N.Y., 1965 



Oyster Bay Harbor on the north shore of Long 

 Island is about 8 km. long. The oyster beds are 

 in water from 3.5 to 10 m. deep at low tide and 

 water currents do not exceed 2.7 Imi. per hour. 



On April 30, 1965, lot 25, 3.2 ha., was treated 

 with Polystream-sand. 



Effect on gastropods. — The divers made no ob- 

 servations. The treatment killed 89 percent of the 

 oyster drills (100 percent of the thick-lipped drills 

 and 46.6 percent of the Atlantic oyster drills) and 

 reduced their numbers from 4.2 to 0.5 per square 

 meter (table 4). 



Effect on associated animals. — The divers made 

 no observations. 



Effect on predation. — Lot 25 was planted with 

 small oysters in 1965, 1966, and 1967. Each year 

 oysters were grown on the bed during their first 

 summer of life and then transplanted to another 

 bed the following spring. WTien first planted in 

 June, July, August, and early September, the oys- 

 tei-s were about 5 to 10 mm. long. By late Novem- 

 ber most of them had grown to 40 to 60 mm. 



Predation on the oysters w-as light in each of the 

 3 years. On October 1, 1965, examination of the 

 bed showed that less than 5 percent of the oysters 

 had been killed by oyster drills and starfish com- 

 bined. On July 22, 1966, divers observed that no 

 oystei-s had been drilled. By October 9, 1967, oys- 

 ter drills and starfish had killed 4.3 percent of the 

 oysters on one section of the lot and 8.1 percent 

 on another section. Predation by starfish was re- 

 sponsible for most of the mortality. 



Area 7: Norwalk Harbor, Conn., 1966 



Norwalk Harbor is interspersed with se\'eral 

 small islands that protect oyster beds in channels 

 and bays from storms. Water over the beds is from 

 2 to 6 m. at low tide, and the strongest currents 

 run about 3.5 km. per hour. 



Lot 42 in Norwalk Harbor was treated with 

 Polystream (Granular) on August 24, 1966. Depth 

 of water at mean low tide averages about 3 m.; 

 maximum current is 3.5 km. per hour. Divers re- 

 ported that strong currents carried off the lot a por- 

 tion of the granules. 



Effect on gastropods. — Before the treatment, 

 divers counted up to five oyster drills of both spe- 

 cies on each cluster of oysters. Within an hour after 

 the treatment all visible thick-lipped drills and 

 Atlantic oyster drills on clusters of oysters were 

 swelling. 



On September 8, 1966, 14 days after the treat- 

 ment, divers observed that most oyster drills at- 

 tached to clusters of oysters had fallen to the bot- 

 tom. In a few instances, however, one or two oj'ster 

 drills that were protected by being attached on 

 the underside of clusters were unaffected and some 

 were feeding on oysters. 



On frequent inspections of the lot divers found 

 that most oyster drills remained stunned, in a 

 semiswollen condition, until November. A small 

 number of drills may have recovered before the 

 water dropped below 10° C, the temperature at 

 which they normally become dormant. 



As far as divers coidd determine, the treatment 

 of lot 42 on August 24 did not kill many oyster 

 drills but only immobilized them and prevented 

 them from feeding. I suspected that a higher per- 

 centage would have been killed if the treatment 

 with Polystream had been made in late April or 

 early May. 



To determine more precisely the effect of Poly- 

 stream in the summer, however, an oyster comjiany 



CONTROL OF OYSTER DRILLS WITH POLYSTREAIM 



293 



