were swollen ; a few weeks later most of these gas- 

 tropods, as well as mud snails, were dead. 



To evaluate the number of oyster drills killed, 

 I used drill traps. The catch per trap per week fell 

 from 16 drills before the treatment to 0.4 drill 

 afterwards. One year later the average catch of 

 oyster drills increased, primarily by recruitment 

 of young drills, to about two per trap per week. 

 In 1964, the average catch rose to about 5 per trap 

 per week, again as a result of recruitment by young 

 oyster drills; by July 1965 it rose to 13 per trap 

 per week (fig. 1). 



E-ffect on associated animals. — During 1961, 

 divers observed that only a small number of fish — 

 primarily sea robins, Prionotns caroUnus; pipe- 

 fish; flounders; mummichogs, FundvZus heterocli- 

 tus; and eels, Anguilla rostrata — were present in 

 Lewis Gut before or after the treatment. Immedi- 

 ately after the application of chemicals only the 

 pipefish appeared to be affected, i.e., more slug- 

 gish than usual. A few hours later, however, mum- 

 michogs were dying along the shore as some of the 

 finer sand coated with Polystream was churned up 

 in the water by wave action. 



This treatment had a slight effect on several 



organisms. Hermit crabs were affected to some 

 degree. A number of them had no shells; appar- 

 ently, a small quantity of treated sand entered the 

 shell and caused enough irritation to compel them 

 to leave. The abdomens of a number of these crabs 

 had been bitten off. Most mud crabs were unaf- 

 fected, but between 5 and 10 percent were twitch- 

 ing abnormally immediately after the treatment. 

 The treatment also compelled many nereids and 

 nemerteans to emerge from their burrows. A few 

 weeks later all animals not killed by the initial 

 treatment appeared to be normal. 



Catches on drill traps indicated that the treat- 

 ment did not reduce the population of mud crabs. 

 The weekly catch of these crabs on drill traps fol- 

 lowed the same pattern each year: Each trap 

 caught an average of about 15 crabs per week in 

 May, June, and July ; about 10 crabs during Au- 

 gust; and (because of recruitment of young crabs) 

 18 to 23 crabs in the fall (fig. 2) . 



Effect on predation. — In midsummer of 1962 an 

 oyster company planted 3,500 hi. ( 10,000 bushels) 

 of seed oysters in Lewis Gut. Periodic examination 

 of the oysters through early winter showed little 

 loss from predation by oyster drills. 



290 



JUNE JULY AUG. SEPT. OC 



1962 

 Figure 1. — Catches of oyster drills on traps in treated area of Lewis Gut, Bridgeport, Couu. 



U.S. FISH AND WILDLIFE SERVICE 



