Bottom samples and underwater photographs in the bullraked area 

 indicated fewer living forms than the control. Decrease in the number 

 of tube wormSj Cistenides ^ was especially noted. 



Bottom samples and underwater photographs in the dredged area showed 

 a decrease in living forms similar to that observed in the bullraked 

 area. On the basis of these observations no difference was noted in the 

 effect of the two fishing methods on bottom forms associated with the 

 hard clamSo 



Size Composition of Catch 



Figure 7 presents a comparison of the size composition of the catch 

 by raking and dredging. Maximum efficiency indicated by a catch effi- 

 ciency ratio of loOj is reached when clams are too large to pass between 

 the teeth of a rake or through the mesh of a dredge bag. Methods used 

 to determine "catch efficiency ratio" are described in Appendix B. 



Bullraking reaches its maximum efficiency for clams about 55 mm, 

 long, but catches a portion of the clams between 36 and 55 mm. Some of 

 these smaller clams represent those whose length is greater than the 

 space between the teeth of the rake but whose width is less than this 

 space. If these clams land on their sides they are retained, but if they 

 land on end they pass between the teeth of the rake, A few clams which 

 would normally pass between the teeth are retained among the larger clams 

 or by clumps of mud brought up by the rake. 



The dredge reached its full efficiency at about 70 mm. but caught 

 some of the clams between 35 and 70 mm. The zone of partial efficiency 

 is greater for the dredge than for the bullrake for two reasons. First, 

 more mud, shells and debris are retained in the bag of the dredge than 

 in a rake and these trap many small clams which otherwise would have 

 passed through the bag. This explains the large radius of the lower part 

 of the dredge efficiency curve in Figure 7= Second, the size at which 

 clams are retained is determined by the size of the rings in the bag and 

 also by the space between the rings. The space between the rings varies 

 "With the size of links used to fasten the rings together. Since a clam 

 may often go between the rings instead of through the rings the zone of 

 partial efficiency is extended. 



Size Composition of Clams Left in Plot 



Figures 8 and 9 show the size composition of the clam population 

 left in the dredged area after each year's fishing. The dotted line in 

 Figure 8 shows the original population in the dredged area as determined 

 by adding those removed by 19U9 fishing to the population shown by bottom 

 samples after the dredging had been completed. Figures 10 and 11 show 

 similar information for the bullraked area. 



15 



