THE OYSTER A]S;D THE OYSTER IIS^^DUSTRY. 31 



means of examinations of samples of water of definite volume taken 

 in various places from day to day. '^ 



Tills method consisted essentialh^ in noting the number and size 

 of free-swimming larva? 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 

 larvre could be ascertained and the setting time predicted several 

 davs ahead. ^ As the larvte 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 rendei-s them readily dis- 

 tinguishable from other bivalve larvtr, 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 commissions 

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

 train one of their own members to do the work. The deveh)]unent 

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

 places in the watei-s of the State and exact information relative to 

 setting time ascertained and imj>arted to the oyster planters. After 

 a few yeai-s 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 dillercnt 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 gi'ound 

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

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

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

 o\'sters. 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 larvfc are carried about by the tides and 

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

 movements of the larvje 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 dejiend on the contour of the bottoms 

 and coasts, they are the same frcjm 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 frec- 

 swiniming larvx were carried on in 1919 by the United States Bureau 

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



1 Churchill, E. P. Jr., and Ciufell, J. S. Reports on Inve'ftigation of Oyster I>arv?rin Longlsland 

 Soiinfl, IDlHand 19l!», nnd InvestiKation of Oyster Larva- of (ireat South Hay. (Contains nii-thods.) 

 ForthcoiiiinK reports, U. S. Uuroaii of Fisheries. 



'' Dr. T. C. Nelson (iOltl), in his study of the occurrence of frce-swimminc oyster larvic in I-ittle KpK 

 Harhor, .M. J., was able to ascertain the relative abundance of the lar\'y; in different areas and to predict 

 the setting date about 10 days in advance. 



