treated lot 205, in a moi-e protected area. Tidal 

 currents over this lot run at no more than 0.9 km. 

 per hour and, therefore, did not carry off the Poly- 

 stream (Granular). The water is about 2 m. deep 

 at low tide. On September 15, when the lot was 

 ti'eated, the water temperature was about 21° C. 



A month later determinations with the hy- 

 draulic sampler showed that the treatment killed 

 78 percent of the oyster drills (no separation of 

 species was made) (table 4). 



Effect on associated animals. — On lot 42, divers 

 reported that a large number of pipefish, juvenile 

 flounders, mud crabs, and shrimp were stunned by 

 the chemical an hour after the treatment, but these 

 animals a]3peared to be normal later. They made 

 no observations on lot 205. 



Effect on predation. — In early May 1966, lot 42 

 was planted with 350 hi. of 1-year-old oysters 

 (5,000-6,000 individuals per bushel). On June 17, 

 7 weeks later, oyster drills had killed 4.3 percent 

 of the oysters and had reduced the number of live 

 oysters per cluster from 19 to 18.2. 



By July 25, 12 weeks after the planting, the 

 I'ate of kill by oyster drills had increased tremen- 

 dously. For example, 34 percent of the oysters had 

 been killed around the edges of the bed and 26 per- 

 cent in the center. Thus, during the period of 5 

 weeks, from June 17 to July 25, the average kill 

 was 4.8 oysters per cluster, or nearly one oyster per 

 cluster per week. 



On August 24, the day the lot was treated, a 

 third sampling was made. In areas around the 

 edges of the lot, where oysters were planted thinly, 

 clusters avei-aged only two live oysters each. In the 

 center of the lot the number of live oysters per 

 cluster averaged between 9 and 10. Thus, even in 

 the main portions of the lot about 50 percent of 

 the oysters had been destroyed. Oyster drills 

 caused almost all the mortality; starfish caused 

 only a small amount. 



The fourth sampling was made on September 8. 

 In the main portion of the lot, clusters had an av- 

 erage of ten 1-year-old oysters and, in addition, 

 18.3 live spat had attached to each cluster. By 

 counting small oyster scars I determined that the 

 original 1966 oyster set had averaged about 30 

 per cluster. Thus, even in the center of the lot, 

 oyster drills had destroyed more than a third of 

 the 1966 oyster spat by the time of treatment, 

 August 24. 



By observing these oystei-s through the fall of 

 1966 and into the spring of 1967, I found that 

 virtually no additional oysters were killed by oys- 

 ter drills. On March 31, 1967, clusters in the main 

 portion of the lot averaged 9.3 2-year-olds (in 1966 

 they were 1-year-olds) and 21.5 1-year-olds of the 

 1966 oyster set. No careful determinations were 

 made on lot 205. Later periodic observations indi- 

 cated, however, that predation by oyster drills was 

 slight. 



In the spring of 1967, when these oysters were 

 transplanted to another lot, their volume had in- 

 creased to 2,100 hi., a sixfold increase during one 

 growing season. I did not determine the increase 

 in size of individual oysters. 



Area 8: Norwalk Harbor, Conn., 1967 



Five lots in Norwalk were treated with Poly- 

 stream (Granular) between April 29 and May 13, 

 1967. Lot 42 was treated again and two lots along- 

 side, lots 40 and 50, were treated for the first time. 

 Depths of water and current velocities are about 

 the same over these three lots. Lots 18 and 49 were 

 also treated for tlie first time. The depth of water 

 over these lots at low tide is about 2.5 m. and cur- 

 i-ent velocities do not exceed 0.9 km. per hour. Lot 

 19, adjacent to lot 18, was not treated and served 

 as a control. 



Effect on gastropods. — Divers made no observa- 

 tions during or immediately after these treatments. 



On lot 18 the treatment killed 52 percent of the 

 oyster drills (68 percent of the thick-lipped drills 

 and apparently none of the Atlantic oyster drills — 

 again, numbers of Atlantic oyster drills were too 

 low for significant comparisons) and reduced their 

 numbers from 8.4 to 4.0 per square meter (table 

 4). 



On lot 40 the treatment killed 78 percent of the 

 oyster drills (82.2 percent of the thick-lipped drills 

 and apparently 66.7 percent of the Atlantic oyster 

 drills — again, numbers of the latter species were 

 too low for accurate appraisal) and reduced their 

 numbers from 16.7 to 3.8 per square meter (table 



4). 



On lot 42 the treatment killed 44 percent of the 

 oyster drills (66.7 percent of the thick-lipped drills 

 and apparently no Atlantic oyster drills — numbers 

 of Atlantic oyster drills were too low for reliable 

 comparisons) and reduced their numbers from 3.3 

 to 1.9 per square meter (table 4). Because most 



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U.S. FISH AND WILDLIFE SERVICE 



