THE OYSTER AND. THE OYSTER INDUSTRY. 31 



means of examinations of samples of water of definite volume taken 

 in various places from day to day.'* 



This method consisted essentially in noting the number and size 

 of free-swimming larvae found in samples of water taken daily over 

 the oyster beds by pumping 50 gallons through a net or bag of 

 No. 20 bolting silk. By the study of a considerable number of 

 samples taken each day the general abundance and size of the 

 larvae could be ascertained and the setting time ju-edicted several 

 days ahead. ^ As the larvae approach setting time, with the accom- 

 panying increase in size, the left valve of the shell becomes very 

 prominent, as stated on page 13. This renders them readily dis- 

 tinguishable from other bivalve larvae, and it is easy, after a little 

 practice, to recognize them under the microscope. 



It would seem that the advent and development of the larvae 

 could be noted by this means each season. The State comniissions 

 could hire a biologist for a month to make the examinations or 

 train one of their own members to do the work. The development 

 and movement of the larvas could be followed in a few representative 

 places in the waters of the State and exact information relative to 

 setting time ascertained and imparted to the oyster planters. After 

 a few years it would be found that the time varied within certain 

 fixed limits, and examinations would need to be made only to learn 

 the variation within that period for the particular year. 



Location of cultch beds. — The different oyster planters have deter- 

 mined by experience the locations at which beds of cultch are placed. 

 After a term of years each man has found the portion of his ground 

 on which cultch may be placed with what seems the most likelihood 

 of getting a set. Individual planters have their own views as to 

 the proper position of the cultch in relation to the beds of spawning 

 oysters. Sometimes beds of cultch and of oysters are placed side 

 by side; sometimes several are located alternately. Some planters 

 place a certain number of spawning or "mother oysters" about in 

 groups on the cultch bed. 



Since the free-swimming larvae are carried about by the tides and 

 currents, it becomes of unportance to follow in each locality the 

 movements of the larvae in order to ascertain as nearly as possible 

 the place in which they will set. This involves a study of the tides 

 and currents and the directions in which and the distance to which 

 they carry the larvae in any particular bay, cove, or river mouth. 

 Accurate knowledge of these facts would enable one to state where 

 the cultch should be placed in relation to the spawning oysters. 

 Since the tides and currents depend on the contour of the bottoms. 

 and coasts, they are the same from year to year, unless disturbed 

 by storm. The data, once accumulated by perhaps two or three 

 years' study, would have permanent value. 



Investigations calculated to ascertain the advantages of such 

 knowledge of the movements and points of aggregation of the free- 

 swimming larvae were carried on in 1919 by the United States Bureau 

 of Fisheries, using Great South Bay, Long Island, as a testing 



a Churchill, E. P. Jr., and Outsell, J. S. Reports on Investigation of Oyster Larvse in Long Island 

 Sound, 1918 and 1919, and Investigation of Oyster Larvse of Great South Bay. (Contains methods.) 

 Forthcoming reports, U.S. Bureau of Fisheries. 



b Dr. T. C. Nelson (191(5), in liis study of the occurrence of free-swimming oyster larva; in Little Egg 

 Harbor, N. J., was able to ascertain the relative abundance of the larvse in different areas and to predict 

 the setting date about 10 days in advance. 



