358 U.S. BUREAU OF FISHERIES 



OYSTER INVESTIGATIONS IN WASHINGTON 



Investigations on the spawning and setting of the native oj^ster 

 of the Pacific coast were continued at Olympia, Wash., under the 

 direction of Dr. A. E. Hopkins. Accurate records have been kept 

 during 3 seasons of the 2 most important oyster-prochicing bays 

 near Ol3''mpia, and in 1933 similar observations were made in 2 addi- 

 tional bays. The results already are being employed by oyster 

 growers to assist in determining the correct time to plant cultch 

 for the collection of seed. Owing to the short summer in 1933 the 

 setting season was only about half as long as in the 2 years preceding. 

 While in 1932 between IGO and 170 broods of larvae were produced 

 per 100 adults, showing that most of them spawned twice, in 1933 

 only about 75 percent produced broods during the entire season. The 

 number of larvae released in 1933 was less than half as great as in 

 the previous year, thus limiting the possible catch of seed. 



In Oyster Bay spawning started just after the middle of May, but 

 the larvae did not begin to set until July 3. As in the last 2 years, 

 definite periods of setting occurred, as shown by counts of spat caught 

 on shells planted at frequent intervals. Although there is consider- 

 able variation in the results for the 3 seasons studied, it appears that 

 there are characteristically, in this bay 2 distinct setting periods : The 

 first, at the beginning of the season, and the second, about 5 to 6 

 weeks later. In addition, secondary periods may occur either be- 

 tween or after these two. Results' from two other bays, Oakland 

 Bay and Little Skookum, studied in 1933, agree closely with Oyster 

 Bay in time of occurrence and relative intensity of the setting 

 periods. 



On the other hand, Mud Bay, which has been studied extensively, 

 appears to be entirely different with respect to spawning and setting, 

 although there is little dift'erence in the temperature and salinity of 

 the water. In 1933 there was only 1 setting period, beginning July 

 25 and continuing for about 3 weeks, after which no setting of any 

 importance could be observed. This appears to rei^resent the typical 

 season in this bay, for it is usually unsatisfactoi-y as a producer of 

 seed. 



The time required for setting of larvae after their release into 

 the open water appears to vary considerably from year to year 

 and in different bays. From the time of beginning of spawning 

 until the first spat were found there was in Oyster Bay in 1932 a 

 period of 39 days while in 1933 it was 47 days. In each year 4 days 

 longer were required in Mud Bay. Presumably this time depends 

 upon environmental factors as yet not thoroughly understood. 



The occurrence of periods of setting appears not to depend pri- 

 marily upon corresponding spawning but upon tidal cycles. Analy- 

 sis of the records of setting in all of the bays studied shows that 

 setting periods occur during runs of extreme tides. Preliminary 

 experiments were made to determine what factors favorable to 

 setting are controlled by the tidal cycles, but with inconclusive 

 results. 



Experiments on the effect of changes in salinity on the feeding 

 activity of the Pacific oyster Avere continued. It was found that if 

 the salinity is reduced from about 28 to about 15 per mille adapta- 



