FISHERY BULLETIN: VOL. 85, NO. 2 



Table 2.— The intensity of clam harvest treatments. All numbers and percents refer to legally harvested Mercenaha mercenaria >2.54 



cm in thickness. 



passes of the kicking boat and the minutes of clam 

 kicking applied (Table 2). All M. mercenaria col- 

 lected were returned to the laboratory for size- 

 frequency estimates. The cumulative removals from 

 the 2 clam harvesting applications produced relative 

 treatment intensities acceptably close to our initial 

 intentions (Table 2). For the hand raking treatment, 

 we used short-handled rakes with 6-10 prongs of =14 

 cm in length separated by 3.5 cm gaps (see descrip- 

 tion and photograph of "pea digger" in Peterson 

 et al. 1983a). We attempted to equalize the inten- 

 sities of the raking and light-kicking treatments by 

 removing equal percentages of the legally harvest- 

 able M. mercenaria from each of these two treat- 

 ment matrices (Table 2). We also recorded the length 

 of time actually spent raking as another indication 

 of treatment intensity (Table 2). 



RESULTS 



Initial Sampling and Estimation 

 of Shelliness 



Within each habitat (sand flat and seagrass bed), 

 one-way ANOVA was used on log {x + l)-trans- 

 formed data (which eliminated heteroscedacity in 

 Cochran's tests) to assess whether any response 

 variables differed significantly among the 6 matrices 

 in spring 1980 prior to application of harvest treat- 

 ments. There was no significant (a = 0.05) initial 



variation among sand-flat matrices in any param- 

 eter: average total density of hard clams, average 

 density of hard clam recruits (length <2.5 cm), aver- 

 age dry mass of seagrass, average density of all ben- 

 thic macroinvertebrates, and sediment size (0) (Table 

 3). Furthermore, the average percent organic con- 

 tent of sediments did not vary significantly among 

 sand-flat matrices (P > 0.05 in ANOVA on angular- 

 transformed proportions). Bay scallops were so rare 

 in this initial sampling that we do not even record 

 their densities in Table 3: bay scallops showed no 

 significant difference among matrices in either 

 habitat. The seagrass matrices exhibited significant 

 initial variation in all parameters except average 

 total density of hard clams and bay scallop density 

 (Table 3). Variation in the other 4 parameters was 

 not consistent across all seagrass matrices. A poste- 

 riori Duncan's tests, used to identify how specific 

 seagrass matrices differed, show that the control II 

 and raking matrices had significantly higher den- 

 sities of hard clam recruits than all other seagrass 

 matrices in spring 1980. Average seagrass biomass 

 was significantly greater in intense-kicking I and 

 significantly lower in control I than in all other sea- 

 grass matrices in the initial sampling. Control I also 

 initially possessed a significantly higher average 

 density of benthic macroinvertebrates, about 3 times 

 the levels in the other seagrass matrices (Table 3). 

 Duncan's test on mean 0s revealed that in seagrass 

 the raking and light-kicking matrices possessed 



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