Experiments with spat -catchers 



Experiments with screen "spat -catchers", similar to those described by Turner 

 (1949) also indicated large-scale movement of small clams. In 1950, some monofila- 

 ment plastic screen, called "Saran", with eighth-inch mesh was staked out on several 

 flats to collect or protect small clams. Nine strips, 8 to 10 feet long and 3 feet wide, 

 were staked down on five flats on May 10. One of these collected or protected nearly 

 2, 000 clams, 4 to 21 mm., per square foot by June 21, when a control sample of the 

 surrounding flat had only 6 clams 5 to 8 mm . Predation undoubtedly had cleaned out 

 the surrounding flat, but the dense population under the Saran was largely the result 

 of movement of small clams. These clams were too large and accumulated too early 

 in the year to have settled out of the plankton as larvae from the current year's spawn- 

 ing, and they were not abundant before the Saran was put down. Small clams were often 

 found on top of the Saran, sometimes about 1 or more per square foot where the Saran 

 was wrinkled „ The Saran was not successful as a collector that summer because the 

 clams were smothered by silt and detritus that collected under the Saran. 



In 1951 a strip of Saran was staked down at Hales Cove on April 12 when the immedi- 

 ate area had about 57 ciams, 3 to 16 mm. long, per square foot. On April 20, a square 

 foot under the Saran had 351 versus 74 beside it. On May 31, the "score" was 521 clams, 

 2 to 29 mm., compared to 10. fThis was after the predaceous green crabs and horse- 

 shoe crabs had started preying on clams in the unprotected flat.) On that date, the 

 Saran was replaced with 1-inch mesh chicken wire, which had proved so successful in 

 protecting an adjacent plot of transplanted clams and native 1949-year-class clams the 

 year before (Smith, Baptist and Chin, 1955). However, in 1951 the wire did not save the 

 1950-year -class clams collected in the spring. Only 25 clams per square foot were 

 found under this wire on October 26, and these ranged from 3 to 5 mm., so must have 

 belonged to the current 1951 year class. The 1950 year class, which was so abundant 

 in May, had completely disappeared, apparently by "voluntary movement" out of the area. 

 Predators may have removed some of the small clams, because green crabs, horseshoe 

 crabs, or birds are capable of reaching down througji the meshes of the chicken wire and 

 getting small clams near the surface. Also predaceous snails can go down through the 

 meshes or tunnel under the wire to devour the clams. However, it does not seem likely 

 that these predators could have gotten aH the clams since the same type of protection 

 was very effective on the same flat the year before. 



The above experiences showed that large numbers of small clams could be gathered 

 and protected by Saran, but did not solve the problem of bringing them up to market size 

 or even to the less motil sizes, such as 20 mm. and over. 



To try to bridge this gap, more Saran was put out in the spring of 1954. These 

 trials differed from previous ones m one important respect. The edges of the screens 



