284 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



T.\BLE 2. — Mean growth of clams in five test areas, based on 

 selected samples 



ANALYSIS OF RESULTS 



SURVIVAL 



Survival of planted clams at Bedroom Cove and 

 Sagadahoc Bay was high enough that sufficient 

 clams remained after the 1951 growing season to 

 provide reliable growth data. The proportion 

 recovered from plots dug in December 1951 and in 

 January, February, and March, 1952, ranged from 

 24.7 to 67.3 percent, as shown in table 1. The 

 survival at Robinhood Cove was very poor; only 

 3.2 to 7.6 percent of the planted clams were re- 

 covered after the 1951 growing season. Green 

 crabs, Carcinides maenas, wliich are serious pre- 

 dators of clams, were very abundant in Robinhood 

 Cove and are believed to have been responsible 

 for the poor survival of planted clams. It was 

 necessary to use clams from the supplementary 

 plots to provide enough measurements for analysis 

 of the growth. 



Clams from Meetinghouse Cove survived satis- 

 factorily when planted at Falls Cove, as indicated 

 by a recovery of 66.7 percent after the 1951 grow- 

 ing season. Of the Western Beach clams planted 

 at Falls Cove, 31.3 percent were recovered during 

 the winter of 1951 and 1952, but survival of native 

 Falls Cove clams replanted in the experimental 

 area was extremely poor. On November 16, 1951, 

 all of the monthly plots and the supplementary 

 plot were dug, and only 13 live clams were re- 

 covered. The poor survival of Falls Cove clams 

 is believed due to their small size, which made 

 them more susceptible to injury from the marking 

 ink used on their shells. If Volger's opaque ink 

 touches the mantle or siphon of the clam it will 

 injui-e the tissues. Since these clams were smaller 

 than those in any other group, the cliances of 

 injury from this source were greater. The growth 

 of Falls Cove clams that survived was intermediate 

 between that of the Western Beach clams and that 

 of the Meetinghouse Cove clams planted at Falls 



Cove, which had a much higher rate of survival. 

 If the marking ink was the cause of the mortality, 

 it appears that it did not affect the growth rate of 

 the clams that survived. 



It is likely that the initial size of 21.3 mm. given 

 in table 1 for native clams replanted at Falls Cove 

 is somewhat higli because it is based on shell 

 measurements of the 13 clams recovered at tlie 

 end of the experiment. Many of the clams 

 planted in the spring of 1951 were 12 to 16 mm. 

 long and had the thin shells characteristic of clams 

 of this size. It therefore appears likely that the 

 marking ink was the cause of the poor survival. 

 It was unfortunate that clams closer to the desired 

 planted size of 25 mm. were not available at this 

 location. 



Each group of clams planted at Plum Island 

 Sound had a mortality of 100 percent during the 

 late summer and autumn of 1951. Before this 

 time, however, these clams had grown at an 

 extremely rapid rate, as shown in table 1. If we 

 can assume that there was no differential mortality 

 among the three groups, the measurement of 

 growth from the shells of dead clams can be used 

 in the analysis. Since the total mortalities of the 

 three groups were identical and since growth rates 

 were nearly identical, varying only from 19.03 to 

 19.69 mm., it is likely that inclusion of these data 

 will not cause any significant error in the analysis. 

 In fact, the conclusions are the same whether or 

 not this group is included in the analysis. 



The percentage recovery after the 1951 growing 

 season shown in table 1 is a rough indication of 

 survival, and is based on the number of clams dug 

 from plots during the winter of 1951-52. It is 

 not a true measure of survival, since it does not 

 take into account the clams that moved, or were 

 moved by hydrographic forces, away from the 

 planting location. Frequently, clams planted in 

 one row were recovered in other rows. Sample 

 digging in the vicinity of the test plots also 

 showed that the marked clams had spread over 

 a considerable area. Therefore, the percentage 

 recovery listed in table 1 might be considered as 

 a minimum percentage survival. 



INITIAL SIZE 



All clams obtained from each source for use in 

 this experiment were dug at the same time and 

 had a common mean length, regardless of the area 

 to which they were transplanted. At the time of 



