bottom unsuitable for oyster culture and there spread uniformly but leaving a 

 drill free zone around the periphery, This procedure adds a layer of material 

 over the mud bottom (1/2 foot thick over 4 5 acres in this case), which after the 

 drills are removed in Step 2 makes this area suitable for oyster culture. Suction 

 dredge samples taken around such drill dumping areas indicate that during the 

 summer drills move less than 150 feet from the concentration even when surrounded 

 by plantings of oysters from brackish water . While the suction dredge is in opera- 

 tion a constant check is maintained on the number of drills (those not washing 

 through a 1/4 inch mesh screen) brought up by the dredge so that trends in drill 

 density on the bottom may be followed closely. The screen is held under the stream 

 of sediment and water flowing from the conveyer belt screen for two seconds, and 

 the drills retained thereon are counted immediately. In ideal sampling it is im- 

 portant to relate the number of drills collected to a specific unit of the bottom; this 

 is not possible with this method, although it does give a rough indication of drill 

 population trends . A further error in sampling is introduced by the variable speeds 

 of the dredge over the bottom due to fluctuations in wind and tidal currents . 



Step 2 , A few weeks later the ground on which the drills were concentrated 

 in Step lis given a thorough suction dredging and these sediments (375 cubic yards 

 in this example) are transported to a third area of soft mud bottom where this time, 

 the drills and sand ar d shell are concentrated as much as possible in one large heap 



Step 3 . In another few weeks the drill heap accumulated in Step 2 is care- 

 fully suction dredged and the drills and sediments so obtained are concentrated on 

 a small piece of bottom located along the shore in an mtertidal area accessible to 

 the dredge boat during high tide but separated from deeper water by mud bottom . 



In the drill cleaning operation of the 50 acres described in the previous 

 three paragraphs, Flower estimates that a total of five million drills were removed. 

 This represents an approximate concentration of two to three drills per square foot 

 of oyster bottom before cleaning , The scanty data available on the capture of 

 drills by means of the suction dredge strongly suggests that the nozzle is not catch- 

 ing all the drills present on the bottom during the first, or even the subsequent few 

 dredgings. As F. B. Flower (pers com.) suggests, the efficiency of the nozzle 

 undoubtedly varies from boat to boat and from time to time on each boat depending 

 on the type of bottom, current, weather conditions, and the attention given by 

 captain and crew to the operation . 



Besides effecting satisfactory control of the drill for the Frank M. Flower 

 & Sons Co., this method, since its adoption, has contributed about 40 acres of new 

 hard oyster bottom . It is also instructive to analyze the method from a biological 

 point of view. The method takes advantage of (1) the partial barrier against 



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