EXPERIMENTAL RESULTS IN OTHER AREAS 



Wood and Roberts (1963) reported that in the 

 laboratory Polystream alone killed 50 to 78 percent 

 of large Atlantic oyster drills from the Eastern 

 shore of Virginia and that a mixture of Poly- 

 stream and Sevin killed 66 to 77 percent. Thus, 

 they felt that Sevin was not needed. They also in- 

 dicated that if oyster drills are in poor condition, 

 they are more easily killed by Polystream. There- 

 fore, they recommended that treatments should be 

 made in the early spring when oyster drills are 

 emerging from winter dormancy. 



Haven, Castagna, Chanley, Wass, and Whit- 

 comb (1966) reported the results of a field test in 

 Hog Island Bay, Va. A 0.4-ha. section of bottom 

 was treated with 9.5 kl. of sand mixed with Poly- 

 stream containing 2 percent of Sevin. The oyster 

 drills were not killed by the treatment, they depos- 

 ited egg cases at a normal rate, and they destroyed 

 as many oysters on the treated plots as on un- 

 treated control plots. I believe the reason for the 

 ineffectiveness was that the treated sand soon sank 

 as deep as 4 cm. into a layer of silt on the bed ; thus, 

 the drills could move over the bottom without 

 contacting significant quantities of the chemicals. 

 Haven et al. (1966) also reported that the Poly- 

 stream-Sevin treatment had a deleterious effect on 

 other living organisms and that growth of oysters 

 and clams was apparently retarded. 



RESULTS OF COMMERCIAL 

 TREATMENTS 



I used se\ eral methods to evaluate the effective- 

 ness of treatments in killing oyster drills and their 

 effects on organisms inhabiting oyster beds. Ten 

 commercial treatments of oyster beds are described. 



METHODS USED IN EVALUATION 



Oyster companies used a standard rate of 1.9 hi. 

 of Polystream per hectare (50 gallons per acre) of 

 oyster bed. In early treatments, they mixed Sevin 

 with Polystream at the rate of 2 percent by weight. 

 The Polystream was mixed with either dry sand or 

 a granular clay [the mixture is termed Polystream 

 (Granular)] which carried it to the bottom and 

 dispersed it. 



Several techniques were used to evaluate the 

 effects of treating commercial oyster beds with 



Polystream and Sevin. On numerous occasions 

 SCUBA divers examined each bed carefully for 

 20 to 30 minutes to determine the gross effects of 

 the chemicals on all visible living animals and 

 plants. Often they made the first examination 

 within an hour of a treatment and followed it by 

 many subsequent periodic examinations during the 

 next 2 to 3 years. They examined certain beds once 

 a month during collections to determine survival 

 rates of oysters. 



In 1961-63, drill traps were used to estimate the 

 effectiveness of treatments in controlling oyster 

 drills. Because mud crabs enter drill traps in large 

 numbers, I estimated the effect of treatments on 

 these populations. 



From 1964^67 I made quantitative determina- 

 tions of the number of drills per unit area with a 

 hydraulic sampler, which pumps through a mesh 

 bag all bottom material from within a ring enclos- 

 ing areas of 1 or 1.5 m.^ All coarse material is 

 retained within the bag, carried to the surface, and 

 sorted. This sampling method, which is carried out 

 by divers, provides an accurate measure of the 

 density of oyster drills and other mollusks on a 

 shellfish bed if enough samples are taken. I took 

 about 25 random samples on beds 2 to 6 ha. in size 

 a few days before and again about a month after 

 a treatment. I determined the percentage of oyster 

 drills killed by comparing their densities before 

 and after treatments. Actually, the Atlantic oyster 

 drills on many beds were too few in number for 

 me to determine the precise percentage of this 

 species killed. 



EFFECTS OF TREATMENTS IN DIFFERENT AREAS 



Ten commercial treatments in four States were 

 made with Polystream. Each treatment will be 

 described separately by areas. 



Area 1: Lewis Gut, Bridgeport, Conn., 1962 



Lewis Gut is a long narrow arm of Bridgeport 

 Harbor. The water is about 1 to 3 m. deep at low 

 tide, and maximum currents run at about 4.5 km. 

 per hour (2.5 knots). On June 27 and 29, 1962, 

 an oyster company treated 12 ha. of this area with 

 a mixture of Polystream-Sevin and sand. 



Eifect on gastropods. — Divers observed that 

 within an hour after the treatment nearly all thick- 

 lipped drills, Atlantic oyster drills, northern moon 

 shells, and both knobbed and channeled whelks 



CONTROL OF OYSTER DRILLS WITH POLYSTREAM 



289 



