PETERSON ET AL.: IMPACT OF MECHANICAL CLAM HARVESTING 



mesh were then cleaned with freshwater, dried at 

 60 °C, and weighed to provide a quantitative indica- 

 tion of the relative degree of coarse shelliness in 

 each matrix. 



After our initial sampling in spring 1980, we ap- 

 plied harvest treatments on 2 occasions, 12-30 May 

 1980 and 19 December 1980-22 February 1981 with 

 a single sampling of response variables in between 

 (Table 1). We then sampled on 5 subsequent occa- 

 sions to test for the existence and persistence of any 

 treatment effects without applying any additional 

 harvest treatments (Table 1). Of the 6 matrices in 

 each habitat, 2 were left untouched as controls, 2 

 were given intense applications of "clam kicking", 

 and the remaining 2 were subjected to lower but 

 equal harvest intensities (judged by estimated per- 

 centage of spring 1980 M. mercenaria removed) of 

 different types ("clam kicking" in one and hand 



raking in the other). Clam kicking is a mechanical 

 form of clam harvest (described in detail in Guthrie 

 and Lewis 1982) practiced in North Carolina which 

 involves the modification of boat engines in such a 

 way as to direct the propeller wash downwards in- 

 stead of backwards. The propeller wash is sufficient- 

 ly powerful in shallow water to suspend bottom 

 sediments and clams into a plume in the water col- 

 umn, which allows M. mercenaria to be collected in 

 a trawl net towed behind the boat (see Figure 2). 

 To reproduce this process, we employed a commer- 

 cial clam kicker and his boat. We measured in a 

 crude way the relative intensity of the harvest treat- 

 ment by counting all legally marketable (>2.54 cm 

 in thickness in North Carolina) M. mercenaria 

 removed and then estimating the percent removed 

 of those available using the initial spring 1980 sam- 

 pling (Table 2). We also recorded the number of 



Figure 2.— Aerial photograph of a clam kicking boat in operation, showing the sediment plume in the wake and the tracks of previous 



kicking passes in the surrounding bottom. 



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