CLAM FARMS — TURNER 469 



material from the old fisherman's marsh bank had just the right prop- 

 erties to resist erosion so that the entire plot remained practically 

 intact. 



We thought that we had solved the problem of establishing a clam 

 farm and waited for our crop to grow. The clams were still there 

 the following spring and showed such growth that we had hopes for 

 the future. Then we were beset by an invasion of predators. Horse- 

 shoe crabs wallowed through the area, cleaning it out at a rate as high 

 as a square foot per crab per day. Boring snails invaded from all 

 sides, each eating as many as three clams per week. To top it all, the 

 green crab population exploded along the New England coast, appear- 

 ing in such large numbers that they not only worked over our areas 

 but also migrated northeastward through New Hampshire and Maine 

 inflicting serious damage on extensive natural clam beds as far as the 

 Canadian Maritime Provinces. Before the middle of the summer 

 our experimental farm was entirely cleaned out. 



12 MILLION HORSESHOE CRABS 



We then expanded our investigation to include studies of the life 

 histories of certain predators which were poorly understood at the 

 time. A complete account of our activities in this direction would 

 be much too long for this article, but the results are of scientific 

 interest. We determined that the horseshoe crab takes at least 12 

 years to mature. Tagging experiments indicated that the horseshoe 

 crabs of Barnstable Harbor traveled many miles and were part of a 

 motile population in Cape Cod Bay containing over a million adults. 

 When the immature members entered the calculation, the total popula- 

 tion was determined to run well over 12 million individuals. This 

 clearly indicated the futility of killing a few thousand horseshoe 

 crabs in a single locality such as Barnstable Harbor because of the 

 continuous immigration of others from Cape Cod Bay. The life 

 history of the boring snail was worked out, and it was determined that 

 their swimming larvae remained suspended in the water for as much 

 as a month before settlement. Consequently all efforts to reduce the 

 population in a single locality by attacking the breed stock would be 

 a futile venture. No practical means of handling the predator prob- 

 lem was discovered, but an extensive investigation of the possibility 

 of using toxic substances is now in progress by the U.S. Fish and 

 Wildlife Service and there are indications of promise. 



We also continued our studies of the settlement of clams in an 

 attempt to determine the factors that apparently induced the meta- 

 morphosing larvae to choose our resurfaced areas. We were puzzled 

 by the fact that marsh-bank materials other than those from the fisher- 

 man's favorite bank accomplished this even though their assortment 



