348 REPORT OF COMMISSIONER OF FLSII AND FISHERIES. 



Eeceiit sunmier temperatures taken by authority of the United States 

 Fish Commissioner at the extreme soutlieni end of the bay, through the 

 cooperation of the Morgan Oyster Company, liave yiehled vahiable 

 information, the water of that part of the bay liaving been found to 

 have a summer Avarmth amply suflicient for tlie i)ropagation of the 

 oyster. TLe important table of temperatures from this locality is con- 

 densed to means often days fi^om a lengthy series of daily observations 

 at both high and low tide. 



Temperature at the oi/sttr heds, 1 viile from Dumharton Point, San Francisco Bai/, 

 July 12 to October 12, ISOl. 



Date. 



Jnlv ]2to 19 



July 20 to 29 



July :J0 to Aug. 8 . 



Aug. 9 to 18 



Aug. 19 to 28 



Aug. 29 to Sept. 7 . 



Sept. 8 to 17 



Sepf. 18 to 27 



Sept. 28 to Oct. 7 . . 

 Oct. 81o 12 



Surface-water 

 j^ ir temperature. 



teini)cr- 



ature. High Low 



°F. 

 C8. 

 C8.9 

 G7. y 

 68.4 

 72.3 

 66.8 

 6G.4 

 65.7 

 64.2 

 61.9 



tide. 



OF. 

 09. 6 

 70.9 



69. 5 



70. y 

 71.4 

 70.7 

 67.8 

 66.1 

 65.6 

 63.2 



tide. 



°F. 

 7l!9 

 71.9 

 69.7 

 70.7 

 72.0 

 69.1 

 68.0 

 67.3 

 62.9 

 64. 



Range of 



water 

 tempera- 



op 



67 to 73 

 C9 to 74 



68 to 72 

 68 to 72 

 09 to 74 

 67 to 72 

 64 to 71 

 64 to 70 

 58 to 70 

 62 to 65 



Peculiar situation of the oyster beds. — There are at present no eastern 

 oysters in San Francisco Bay that are not laid upon tide lands, or 

 so-called mudflats, completely exposed at the time of low tide. The 

 principal reason for the selection of such situations is that the beds may 

 be readily fenced in by closely set stakes to protect them from the dep- 

 redations of the stingray [MyUohatis californicus), which enters the bay 

 every spring and is tlie principal enemy of the oyster in these waters. 

 In this complete deix'iidence for oyster-growing upon tide lands, fre- 

 quently left dry, is doubtless to be found one exi)lanation of the slow 

 increase of the species. The California summer is absolutely dry and 

 rainless. It is a season of cloudless skies and regularly recurring heat 

 in the daytime j therefore an oyster bed at this season, when the tide 

 is out, is exposed not merely to the air, but to a heat suflicient to dry 

 the moisture off from all the oysters in sight, and perhaps injure the 

 majority of the spat that might have been attached to their shells. 

 If embryo oysters, set free on the beds, drift Avith the receding tides to 

 deeper Avaters outside the stake-protected area of the flats, they are 

 exi)osed to the stingrays A\iien they have attained suflicient size. 



Stingrays, and the stake protection employed against them. — The Cali- 

 fornia stingray {MyUohatis californictis) enters San Francisco Bay in 

 large numbers in the si)ring and remains until late in the fall. It is 

 said to be as destructive to oysters in these waters as the starfish is on 

 certain parts of the Atlantic coast. It has heavy flat teeth, arranged 

 in a sort of pavement in each jaAv, and is essentially a feeder on shell- 



