Setting and First Season Survival 

 of the American Oyster, Crassostrea virginica , 

 Near Oxford, Maryland, 1961-62 



By 



J. R. WEBSTERi and W. N. SHAW, Fishery Biologists 



Bureau of Commercial Biological Laboratory 

 Oxford, Maryland 21654 



ABSTRACT 



The setting of oysters in Broad Creek and Tred Avon River, on the eastern 

 shore of Chesapeake Bay, was monitored during 1961 and 1962. Setting was sub- 

 stantially greater both years in Broad Creek, and the highest number of spat 

 were found on shells suspended from 0.3 to 9 meters below the surface. Three times 

 more spat were caught on shells in bags than on shells broadcast on the bottonn. 



In Tred Avon River setting was very light in 1961 and light in 1962, except 

 during the week of 30 July to 6 August. In Broad Creek setting was heaviest dur- 

 ing the week of 1 7 to 24 July 1961 and during each week from 25 June to 1 3 August 

 1962. 



First- season survival rates were 1 to 27 percent. There was some indi- 

 cation, especially in Broad Creek during 1962, that the greater the setting rates 

 the lower the first- season survival rates. 



INTRODUCTION 



The Tred Avon River and Broad Creek are 

 tributaries of the lower Choptank River on the 

 eastern shore of Chesapeake Bay, Talbot 

 County, Md. Both waterways receive relatively 

 small amounts of fresh-water drainage and 

 are characterized by similar salinities ranging 

 from 8 to 16 p.p.t. (parts per thousand) and 

 tennperatures fluctuating from 0° to about 30 

 C. Each has natural oyster grounds that are 

 tonged commercially from September to April. 

 Past surveys have shown the Tred Avon River 

 to be low or erratic in oyster setting (Beaven, 

 1954). In contrast, oyster setting in Broad 

 Creek has been high enough to justify shell 

 planting on a small reservation of bottom 

 (2.0 to 2.8 hectares) by the Maryland Depart- 

 ment of Chesapeake Bay Affairs in a program 

 of annual oyster propagation. 



In 1961 the Bureau of Commercial Fisheries 

 Biological Laboratory, newly located near the 

 mouth of the Tred Avon River, at Oxford, Md., 

 began studying the oyster- setting potential of 

 adjacent waters. These studies included esti- 

 mates of oyster setting rates and survival 

 in the Tred Avon River and Broad Creek. 

 The information obtained could be used in 



^Present address is RpD #1, Sanbornville, N.H. 03872. 



planning specific projects of research related 

 to or dependent upon setting potential. 



METHODS 



Oyster shells (cultch), obtained from a local 

 shucking house, were placed in bags of 2.54 cm. 

 mesh galvanized poultry wire, (New bags were 

 kept submerged for several weeks before add- 

 ing oyster shells, to oxidize the galvanized 

 wire and reduce active ionization which might 

 deter setting.) The shell contents (8.8 liters 

 or about 90 shells) of each bag formed a 

 mass about 23.1 cm. high, 38.5 cm. wide, 

 and 12.8 cm. thick. In this report, bags 

 put in the water for 7 days and then replaced 

 are called weekly bags and those which re- 

 mained in place throughout the setting season, 

 20 June to 3 October 1961 and 18 June to 

 10 September 1962, are called seasonal bags. 



Ten stations were established in 1961 at 

 intervals along 1 3 km. of the Tred Avon 

 River, from near the headwaters to near 

 the mouth, in water depths of 2.2 to 2.4 m. 

 Four stations in Broad Creek were at similar 

 water depths (fig. 1). Two seasonal bags and 

 single weekly bags were placed just touching 

 bottom at stations 1 to 9 in the Tred Avon 

 River and at stations 1 to 3 in Broad Creek. 



