OYSTER RESOURCES OF THE PACIFIC COAST. 349 



fish. Its presence requires the feucing iu of all the oyster beds in the 

 bay with closely set stakes about 13 feet long, which are driven about 4 

 feet into the ground. Plates 8 and 9 show the nature of these fences. 

 When a broken stake allows a school of stingrays to raid an oyster bed, 

 the surface, after the tide has gone out, presents much the appearance 

 of a field that has been rooted by hogs. Sometimes the oystermen, 

 discovering their presence, manage to entrap them inside the line of 

 stakes, and thus destroy many of them during one low tide. 



Fencing oyster beds against stingrays constitutes another heavy 

 expense to the California oystermen, in addition to the annual outlay 

 for seed oysters from the Atlantic coast. The fences must be looked 

 after constantly and kept in repair. The heavy winds that sometimes 

 during the winter season cause vessels in San Francisco Bay to drag 

 their anchors do great damage to the fences of the oystermen, which 

 they must manage to have in good condition by the time the stingrays 

 reappear in the bay. 



I do not know how late in the fall stingrays continue to menace the 

 oysters, but I netted a few small specimens in San Pablo Bay as late 

 as jSTovembev 7, 1S90. They first appear in April. 



The danger from stingrays is probably overestimated, in view of 

 the natural increase of oysters upon wide tracts unprotected by stakes. 



Other enemies of the oyster. — The drill ( Urosalpinx cinerea) has not 

 become troublesome upon the oj^ster l)eds of San Francisco Bay until 

 very recently, and even now is abundant only in the southern part of 

 the bay. The oystermen showed me heaps of shells, all more or less 

 drilled with small holes, iu evidence of its ravages. At the Belmont 

 beds I had no difficulty in gathering a quart of these mollusks in less 

 than ten minutes by merely turning over the large oysters when the 

 water had receded from the beds. Sometimes half a dozen were to be 

 found on a single oyster. With its minute "tongue-file" this creature 

 drills a hole through the oyster's shell, and inserting its proboscis into 

 the opening, barely large enough to admit a pin, it feeds directly upon 

 the soft parts. 



This destructive animal may have been introduced much earlier than 

 the oystermen suppose, as a few individuals accidentally imported 

 among the original oysters would require several years to increase to 

 the present numbers. Mr. Moraghan informed me that there were no 

 drills upon his beds at Millbr ae, which, as stated above, are much nearer 

 the sea than tlie Belmont beds. If they are restricted to the Bel- 

 mont beds, as seems to be the case, it would i^ay tlie oyster-growers to 

 pick them off" as far as possible. Any gathering of drills that would 

 Iceep them in check is important, as their increase will cause great loss 

 in the future. 



Two species of crabs are found upon the San Fi-ancisco oyster beds, 

 one of which is exceedingly abundant, but their presence has probably 

 no effect upon the oysters. 



