various depths. The principal requirements for raft 

 culture are 1) shelter from storms, 2) sufficient 

 depth, and 3) permits from local zoning authorities 

 and Corps of Engineers for anchoring rafts. 



An anticipated development is a system of grow- 

 ing oysters on submerged rafts or racks. This system 

 will probably be necessary in areas where recrea- 

 tional use of the water surface for fishing, boating, 

 etc. would make it difficult to obtain permission for 

 raft culture. Engineering designs for structures 

 needed for this type of culture have not yet been 

 completed, but might be patterned after the sub- 

 merged racks which are used in French Polynesia for 

 pearl oyster culture to avoid storm damage and foul- 

 ing. 



Use of "Unattached" or "Cultchless" Seed 



Pacific Mariculture, Inc. near San Francisco, 

 Calif., has patented a process of producing indi- 

 vidual seed oysters which have several advantages. 

 This seed is readily available at any time of the year 

 and can be shipped economically by air freight. Sur- 

 vival during shipment and after planting has been 

 excellent and the individual oysters develop a un- 

 iform shape which makes a very attractive prod- 

 uct. 



Disadvantages of "unattached" seed are that it 

 requires special handling in screen trays, and this 

 requires a large amount of hand labor. Growth is 

 generally poor in trays unless there is adequate circu- 

 lation of water which contains adequate food sup- 

 plies. These individual oysters must be quite large 

 before they will stay in place on oyster beds which 

 are exposed to waves, currents, or storms. This 

 limits the use of this seed for traditional oyster farm- 

 ing and requires development of new aquacultural 

 systems. It appears that "unattached"" seed will be- 

 come an important factor during the next few years, 

 provided specialty markets can be developed for the 

 product. 



During March 1971, I made experimental plant- 

 ings of ""unattached"" Crassosrrea ^sii^cis seed from 

 the Pacific Mariculture hatchery at several locations 

 in the Fiji Islands. Survival ofthis seed was excellent 

 and growth was satisfactory after the spat were 

 cemented to fiberboard (Masonite or asbestos 

 board) squares strung on wire or rope and suspended 

 below rafts. It appears that this method v\ill be ap- 

 plicable any place where hydrographic conditions 

 permit the use of rafts or racks and where labor costs 

 are low. 



Air Shipment of Anesthetized Oyster Larvae 



Pacific Mariculture, Inc. has recently patented a 

 method for temporarily suspending activity of ma- 

 ture oyster larvae. With this method it is possible to 

 air ship large quantities of mature oyster larvae in 

 small containers from California to oyster culture 

 areas. At these locations larvae are placed in tanks of 

 warm water with suitable cultch materials. Attach- 

 ment is completed within 2 hr. This method avoids 

 the cost of shipping heavy "mother"" shells or other 

 cultch materials since one-half million larvae can be 

 shipped in a '/2-liter bottle. Oyster growers can then 

 "set"" the larvae on desired cultch materials and 

 plant them on their oyster beds. This method needs 

 further development to improve its reliability, but it 

 appears probable that this will be accomplished in 

 the near future and that this method will find applica- 

 tion in many places. 



Investigation of Causes of Oyster Mortality 

 on the Pacific Coast 



Mortalities of 10-70% during the second or third 

 summer after planting Pacific oyster seed has been 

 observed at several locations along the Pacific coast. 

 The most severe mortalities have occurred in south- 

 ern Puget Sound and part of Willapa Bay in Washing- 

 ton, and Humboldt Bay in northern California. 

 Negligible mortality levels have been observed in 

 British Columbia, northern Puget Sound and Hood 

 Canal in Washington, Oregon bays, and elsewhere 

 in California. 



Generally, heavy mortalities occur near the heads 

 of bays which are warm and muddy with high nutri- 

 ent levels, abundant phytoplankton, where oysters 

 grow rapidly and fatten well. Mortalities generally 

 occur during a few weeks in midsummer when the 

 oysters are in spawning condition. It has been ob- 

 served that mortalities have been more severe 

 during warmer years. 



Investigations during the past 5 yr by state 

 fisheries agencies of Washington, Oregon, and 

 California and by the laboratory of the National 

 Marine Fisheries Service in Oxford, Md., have 

 failed to detect a specific cause for this mortality. 

 Tests for Lcihyiintli(>niy-\(i marina which causes ex- 

 tensive losses of oysters in the Gulf of Mexico and 

 Minchinnia nelsoni which kills oysters in 

 Chesapeake and Delaware Bays have proved nega- 

 tive. Although numerous microorganisms have been 

 observed in the thousands of oysters examined from 



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