The Rise And Decline Of The Olympia Oyster 



11. The free-swimming period is 30 or more days in 

 length and varies from year to year, probably according 

 to water temperature. 



12. Larvae set most frequently on an horizontal sur- 

 face, while fewest catch on upper horizontal surfaces. A 

 definite relationship exists between angle of surface 

 and number of spat caught. 



13. This setting beha^^ior of larvae is not due to a di- 

 rective influence of light but to the swimming position 

 whereby the larval foot projects upward. 



14. A special type of manufactured spat collector, de- 

 signed to take advantage of these habits, is now in use 

 commercially. 



15. In Oyster Bay the setting season consists of two 

 distinct periods, 6 to 8 weeks apart. Secondary periods of 

 setting may occur between these two or after the second. 



16. Setting seasons in Oakland Bay and Skookum Inlet 

 are similar to those in Oyster Bay. In Mud Bay seasons 

 are shorter and maxima occur at different times. 



17. Times of maximum frequency of setting fall with- 

 in periods of spring tides when tidal range is greatest. 



18. On cultch suspended from floats most spat are 

 caught at a distance of 1 to 2 feet from the surface. This 

 appears to be one reason why high grounds catch the 

 most seeds. Floats filled with cultch are now being em- 

 ployed commercially to take advantage of these results. 



19. Few spat are caught at low tide, most when the 

 tide is about half high. Frequency of setting appears to be 

 associated with swiftness of current. 



20. Setting of larvae begins in the third tidal period 

 following that during which spawning starts. Setting 



(90) 



