EXPERIMENTAL OBSERVATIONS ON SPAWNING, LARVAL 
DEVELOPMENT, AND SETTING IN THE OLYMPIA 
OYSTER, OSTREA LURID A 1 
By A. E. Hopkins, Aquatic Biologist, United States Bureau of Fisheries 
CONTENTS 
Page 
Introduction 4-39 
Method of cultivation 441 
Enemies of the oyster 441 
Aims of investigation 443 
Hydrographical observations 443 
General description of region 443 
Temperature 444 
Salinity and pH 448 
Spawning 456 
Size of broods 458 
Relation of temperature to spawning- 460 
Spawning season 464 
Development of larvae 467 
Setting 471 
Effect of angle of surface 472 
Method of determining frequency of 
setting 475 
Setting seasons, Oyster Bay 477 
Season of 1931 477 
Page 
Setting — Continued. 
Setting seasons, Oyster Bay — Continued. 
Season of 1932 479 
Season of 1933 480 
Season of 1934 481 
Season of 1935 483 
Setting seasons, Mud Bay 483 
Season of 1931 484 
Season of 1932 484 
Season of 1933 484 
Season of 1934 486 
Season of 1935 486 
Periodicity of setting 487 
Stages of tide and setting 489 
Depth of setting 493 
Correlation between spawning and setting. 495 
Discussion 497 
Summary 500 
Literature cited 502 
INTRODUCTION 
The native oyster of the Pacific coast has never been produced in great enough 
abundance to reach markets all over the country. Toward the end of the nineteenth 
century extensive commercial use was made of the crops growing naturally on tide 
lands of Puget Sound and Willapa (Shoalwater) Bay, in the State of Washington, 
resulting in almost complete depletion in most of the favorable localities. In 1902, 
according to Galtsoff (1929), 154,000 bushels of oysters were produced; in 1904, 
170,000 bushels reached the market; while in 1926 only about 58,000 bushels were 
grown. Since this time production has been at an even lower level. The native 
Willapa Bay oyster has been almost completely destroyed so that it is now difficult 
to find in the local markets. The native 03 ^ster is unique in the United States in that 
it never attains a shell length much greater than about 5 centimeters (2 inches), and 
for this reason is used primarily for special dishes such as cocktails and pan roasts. 
It is too small to serve on the half shell. 
Oyster growers commonly market them in 2-bushel sacks, containing about 5,000 
oysters, or about 2,500 to the bushel. Most of the native oysters now grown on the 
1 Bulletin No. 23. Approved for publication Oct. 14, 1936. 
439 
