INVESTIGATION OF THE PHYSICAL CONDITIONS CON- 

 TROLLING SPAWNING OF OYSTERS AND THE OCCUR- 

 RENCE, DISTRIBUTION, AND SETTING OF OYSTER LARVi€ 

 IN MILFORD HARBOR, CONNECTICUT 



By HERBERT F. PRYTHERCH 

 Assistant Aquatic Biologist, U. S. Bureau of Fisheries 



CONTENTS 



Page 



Introduction 429 



Methods and equipment 430 



Topography 432 



Physical conditions 433 



Temperature 435 



Tide and current 450 



Salinity 467 



Hydrogen-ion concentration 472 



River discharge 472 



Pae« 



Biological observations 474 



Condition of the gonads of the oyster. 474 



Time of spawning 478 



Occurrence and distribution of larvae. 481 



Setting 488 



Predicting the intensity and time of oyster 



setting 495 



Summary 497 



Bibliography 499 



INTRODUCTION 



The primary purpose of this investigation is to show the close relationship that 

 exists between physical conditions and the success or failure of oyster production in 

 inshore waters. It is hoped that the analysis of conditions in Connecticut waters 

 and the determination of the predominating factors that control oyster propagation 

 there may serve as the basis for the development of scientific oyster culture in our 

 extensive coastal waters. To accomplish this, it is essential that we have a thorough 

 knowledge of the oyster in every stage of its development and a greater under- 

 standing of the influence of each physical and biological factor on the egg, embryo, 

 larvae, spat, and adult. In the cultivation or control of an aquatic animal such as 

 the oyster, the response of the organism to changes that occur in its environment is 

 not only of scientific interest but may be of great practical importance. The plan 

 of the investigations carried out at Milford, Conn., during the summers of 1925 and 

 1926 was to study the effect of the physical conditions on the oyster and oyster 

 larviB in this typical location, the results of which would serve as the basis for analyzing 

 and understanding the conditions found in other oyster-growing regions. 



The most important problem that presented itself was the analysis of the causes 

 of the great variations that occur in the annual production of seed oysters on an 

 entire natural bed as well as on the cultivated oyster beds. A good example of 

 this is the Bridgeport natural bed, which, according to Collins (1889), produced 

 115,000 bushels of oysters in 1887, 31,000 in 1888, and 3,500 in 1889, most of which 



429 



