N-methylcarbaraate) were added to the chlorin- 

 ated benzenes to increase their killing effect on the 

 snails. In laboratory experiments, orthodichloro- 

 benzene mixed with dry sand in the ratio of 1 to 19, 

 by volume, and then spread over shallow pans 

 killed most oyster drills ; and when used to form a 

 barrier in small troughs it prevented them from 

 crossing the barrier for several months. 



Ijoosanoff, MacKenzie, and Davis ' stated that 

 for 14 months small barriers consisting of ortho- 

 dichlorobenzene and sand continued to affect oys- 

 ter drills on contact but were not toxic to larvae 

 and juveniles of sea squirts, Molgula manhattensh, 

 common shipworms. Teredo sp., Atlantic oyster 

 drills, eastern white slippers, Cr&pidiila plana, 

 and mud blister worms, Polydora sp., which set 

 and grew within 2.5 cm. (1.0 inch) of the barriers. 

 These observations showed that orthodichloroben- 

 zene was only a contact poison. In large outdoor 

 troughs siltation reduced the effectiveness of chlo- 

 rinated benzenes by forming a covering layer that 

 kept the oyster drills from touching the chemicals. 



Field Tests 



Loosanoff (1961) reported that oyster drills can 

 be greatly reduced in numbers by spreading chem- 

 ically treated sand over shellfish beds. The combi- 

 nation that gave good results consisted of 95 

 percent dry sand and 5 percent orthodichloroben- 

 zene containing 1 to 3 percent, by weight, of Sevin. 

 The chemicals were mixed with the sand in large 

 commercial cement trucks. The treated sand, 

 loaded on the deck of a boat, was then spread over 

 the oyster bed by a Iiigh-pressure stream of water. 



Davis, Loosanoff, and MacKenzie ^ reported the 

 results of treatments of several small oyster beds. 

 They emphasized the effects of chemical treat- 

 ments on organisms other than oysters and clams. 

 On July 16, 1961, a bed of about 1.6 ha. (4 acres) 

 in Great South Bay, Long Island, N.Y., was 

 treated with 9.5 kl. jjer hectare (5 yards per acre) 

 of sand mixed with 1.9 hi. (50 gallons) of ortho- 

 dichlorobenzene containing 6 kg. (13 pounds) (2 

 percent by weight) of Sevin. As the sand'de- 



I Loosanoff, V. L., C. L. HacEenzle, Jr., and H. C. Davis. 



1960. Progress report on chemical methods of control of moUnscan 

 enemies. Bur. Commer. Pish. Blol. Lab., Mllford, Conn., Bull 24 

 (8). 20 pp. 



•Davis, H. C, V. L. Loosanoff, and C. L. MacKenzie, Jr. 



1961. Field tests of a chemical method for the control of marine 

 gastropods. Bur. Commer. Fish. Blol. Lab., Mllford, Conn., Bull. 

 26 (3), 9 pp. 



scended, several small fish were killed and common 

 jellyfish were carried to the bottom. Shortly after 

 tlie sand reached the bottom, sea squirts were 

 found partially contracted ; oyster drills and other 

 snails were greatly swollen; and a number of 

 liermit crabs, Pagumn sp., and mud crabs, Neo- 

 panope texana, were dead. They did not determine 

 whether this experimental treatment eventually 

 killed the oyster drills. Another bed, which was off 

 the east end of Long Island in 9 m. of water, was 

 treated in like manner. Because of strong water 

 currents over the area, little sand actually reached 

 the bottom that was to be treated and, as a result, 

 the treatment was not effective. This failure indi- 

 cated that in an area with strong currents it was 

 very difficult to control oyster drills with sand 

 treated with a chlorinated benzene. 



In treatments along the Connecticut shore the 

 effects of the chemicals on animals inhabiting the 

 bottom varied somewhat depending on location of 

 the bed. In open waters, divers noticed only a small 

 effect on fish, hermit crabs, mud crabs, and anne- 

 lids. In ai-eas where waters were shallower and 

 currents slower, however, the effect was greater. 

 In all tests, fish, hermit crabs, and mud crabs fed 

 and moved normally in an area within a few days 

 after a treatment. Fish, perhaps attracted by the 

 exposed white feet of swollen gastropods, were 

 more numerous after a treatment. Most pelagic 

 common shrimp that were in the immediate area 

 at the time the treated sand was spread were ap- 

 parently killed. Once the chemicals were on the 

 bottom, however, shrimp moved in again and re- 

 mained uninjured. Oysters and mussels, Mytilus 

 edidis, when present, were pumping normally with- 

 in an hour of the treatment. Starfish, Asterias for- 

 besi, were irritated by treated sand falling on their 

 aboral surface, and small sores soon appeared. In 

 a number of treated areas starfish consumed swol- 

 len oyster drills and northern moon shells, Poli- 

 nices sp. Davis et al.' also reported that the treat- 

 ment did not reduce the intensity of setting of 

 oyster and starfish larvae in the area. 



Polystream* (trademark of Hooker Chemical 

 Corporation for a mixture of polychlorinated ben- 

 zenes containing a minimum of 95 percent total of 

 active triclilorobenzene, tetrachlorobenzene, and 



' See footnote 2. 



< Trade names referred to In this publlcatloD do not Imply 

 endorsement of commercial products. 



286 



U.S. FISH AND WILDLIFE SERVICE 



