472 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1960 



that was acceptable to the commercial market, providing a period of 

 prosperity for the Quincy clam diggers. A similar occurrence on 

 another beach a few years later was studied in more minute detail by a 

 graduate student at Harvard. His doctoral dissertation confirmed our 

 own findings and proved so many of our assmnptions that the principle 

 of "hydrographic concentration" became firmly established as one of 

 the mechanisms of the formation of aggregations of certain bottom 

 animals. 



These studies also contributed significantly to an understanding of 

 the enormous magnitude of natural mortality in the marine environ- 

 ment. Biologists concerned with marine fisheries have speculated 

 from time to time as to how many individuals of a generation of any 

 given species survive to maturity, and, for practical purposes have 

 pulled numbers out of a hat ranging from 10 to 90 percent. The 

 mortality rate of the clams in the particular generation under study 

 was well over 95 percent during the first year of their lives, and by the 

 time they were ready for market only a fraction of 1 percent of the 

 original number were still alive. It would be a mistake to claim that 

 these numbers apply to all the creatures that live in the sea, but they 

 may well be applicable to the clams and codfish. Each mature female 

 of these species produces 1 or more million eggs. If all their offspring 

 sui-vived for only a few generations, the ocean level might rise con- 

 siderably and there would not be room for any other fish I 



FURTHER STUDIES 



Now after more than 10 years of intensive research it has become 

 clear that the problems associated with the development of clam farm- 

 ing are many and complicated. We have come to the conclusion that 

 these problems cannot be solved by limiting the investigations just to 

 the biology of the clam and some of the obvious predators. Instead, 

 it appears necessary to build up a large background of basic knowl- 

 edge on the ecology of marine bottom communities. Consequently 

 we have discontinued our investigation of the clam for the time being 

 and with generous support from the National Science Foundation 

 have undertaken a study of environmental influences on the repro- 

 ductive cycle of a variety of bottom-dwelling organisms. 



