52 



oyster being quite a match for any green crab. With 

 delicate-shelled brood oysters for months after detroquage 

 and also while these young are still attached to the 

 collectors, the case is different ; the crab has no difficulty 

 in breaking away the lip of the shell and picking out the 

 delicate morsel within. 



Of fishes quite a number occasionally feed upon 

 brood-oysters, but it is in regard to the maturing oysters 

 that the parkers fear fishes more particularly. Indeed 

 just as crabs may be considered the special enemies of 

 young oysters, so fishes hold this position towards the 

 adult generations. Large mollusc-eating relatives of the 

 rays are the special dread of the parker and against 

 these his most elaborate and expensive protective devices 

 are directed. The worst offenders are the tere (Trygon 

 pastinacd) and the epervier (Myliobatis aquila), whose 

 jaws are armed with a mosaic of strong milling teeth capa- 

 ble of crushing with ease even thick-shelled adult oysters. 

 Of the two species of oyster cultivated at Arcachon 

 the tere prefers the heavy shelled Portuguese for though 

 the shell be thicker than in the native species it is softer 

 and the contents are larger and presumably more satisfy- 

 ing to the depredator. It is interesting to note that the 

 inroads of large shoals of a related species of ray {Rhi- 

 noptcra javaiiica) axe, the frequent cause of the total dis- 

 appearance of extensive beds of pearl-oysters off the 

 coasts of India and Ceylon where instances are known of 

 millions of maturing oysters being cleared away during 

 the interval between examination in November of one 

 year and February of the next. Fishes undoubtedly are 

 the most dangerous enemies with which the Arcachon 

 cultivators of edible oysters and the owners of the pearl 

 banks in the East have to battle. 



Of passive enemies the list comprises practically all 

 sedentary marine organisms that flourish in shallow 

 waters and between tide-marks. Constant attention to 

 ensuring the cleanliness of the parks prevents the ma- 

 jority doing much harm ; it is the careless parker — a 

 man seldom met with at Arcachon — who suffers severely 



