30 



close together so the fish cannot get at the oysters, but not 

 close enough to keep the water from circulating freely. As soon 

 as the oysters are taken from the reef and culled they are put 

 inside this enclosure to be kept until they are to be sold. 



SKATES OR RAYS. 



In some parts of the State, espe'cially about the lower end 

 of the delta, the oyster men report that some of their beds have 

 been destr9yed by the depredations of some of the large rays, 

 which clean up an entire bed in a short time. So far as can be 

 learned, the attacks of these forms is limited to the delta region, 

 and there they are not very common. Unlike the "drum," these 

 fish attack the oysters on the natural beds so that to guard 

 against their destroying the beds it would be necessary to fence 

 in the whole area where the oysters were growing. 



BORING CLAMS. 



A boring clam (Martesia striata) is commonly found in the 

 shells of living oysters from many parts of the coast. This 

 form bores into the shell of the oyster when it is young, and 

 as it increases in size, enlarges its burrow, until in many cases 

 it breaks through into the mantle 'cavity of the oyster. While 

 these clams are not of sufficient abundance to be of very much 

 account, and do not of themselves destroy the oysters, their 

 presence in the shell tends to weaken it and thus make the 

 oyster more susceptible to the attacks of the enemies that crush 

 the shells. In the cases where the burrows of the clam reach 

 through the oyster shell into the mantle cavity, it becomes neces- 

 sary for the oyster to secrete a new layer of nacreous material 

 to cover up the opening, so that there is an extra drain on 

 its vitality. 



Besides those enemies which destroy the oyster directly for 

 their food, there are other destructive agents that do their dam- 

 age only indirectly; by cutting down the available supply of 

 food organisms, or by causing an increase in the deposition of 

 sediment over the oyster bed. 



MUSSELS. 



"Mussels are frequently found in abundance among the oys- 

 ters, both on the natural reefs and on the planted beds. The 

 mussels are attached to the oysters by means of a bundle of 



