MOVEME^^^s of small soft-shell clams, 



(MYA ARENARIA) 



The fact that small soft -shell clams can come up out of the soil, can move voluntarily, 

 and can be carried about by current or wave action was fully described by Kellogg in 

 1901 and 1905; but the extent of their movements has not been investigated. The 

 general assumption since then seems to have been that clams ordinarily move little 

 after they have dug into the fiat. Clams that are attached by their byssi to floating 

 objects or are washed about at the water's edge usually are thought to have been washed 

 out accidentally. 



The important question, of course, is not whetliier clams can move Jjut how many move 

 about and how important this movement may be in determining the final distribution of 

 the adults on any flat. If most of them move about until they are itiearly half an inch 

 long (12 - 13 mm.) then we must try to attract them up to this size and induce them to 

 stay if we are trying to increase a natural set. Also, any population estimates based 

 on clams less than half an inch long will be of little or no value in estimating future 

 production . For the same reasons, transplanting the very small clams would be of 

 doubtful benefit. 



In order to learn more about the importance of clam movements, an experiment was 

 carried on from May 1951 to November 1952 to determine how many moved into a 

 square foot area in a given time . Trays 1 foot square with screened bottoms were 

 filled with clam -free mud, set down flush with the flat. The sides of the tray were 

 wood, 2-1/2 inches hi^. The bottom was plastic fly screen with 15 meshes per inch 

 one way and 17 the other. Each trayful of clam-free mud was left in the flat for about 

 2 weeks, and then taken up and replaced by another. Thus each "movement tray" 

 contained only those clams that had moved in durlTigthe previous 2 weeks, while square- 

 foot samples of the adjoining flats indicated the density of clams of all sizes where there 

 was no time limit on the period over which they might have accumulated. A few move- 

 ment trays were left down for shorter and longer periods . The mud in the biweekly 

 collecting trays was flush with the sides, and the whole thing was down flush with the 

 surrounding flat . In fact, after they had been in place a day, they were hard to find, 

 so they did not offer an unusual barrier or eddy to collect water-borne clams faster than 

 the surrounding flat. 



The trays were set out on flats at Hales Cove and at Ordways in the Town of Newbury, 

 Massachusetts . The Hales Cove flat was a relatively soft mixture of fine sand and silt; 

 Ordways was similar, but firmer, with more shell fragments. Clams over an inch 

 long were practically absent on both flats, but "various clam -farming experiments 

 carried on nearby showed that physical conditions were suitable for clams . 



