172 MARINE FISHERIES OF NORTH CAROLINA 



to swim, it is doubtful that this ability is used to any great extent among the 

 adult animals or that distinct migrations occur. As a result of the swimming 

 habit, the adductor muscle develops to a large size, thus rendering economi- 

 cally feasible the practice of utilizing only the muscle. 



Another unique character of the scallop is the possession of eyes of deep 

 blue color, located on short stalks among the tentacles of the mantle. The 

 eyes have been the object of much study and discussion. Each eye contains a 

 cornea, lens, iris, retina, and optic nerve, and is capable of perceiving motion 

 of objects. To see the metallic glitter of the eyes in a bright light is a striking 

 sight. 



ECOLOGY 



DEPTH OF WATER. Scallops are found at various depths and are apparently 

 not influenced by the depth. Deep water affords a protection in northern 

 areas during severe winters, for freezing often causes considerable mortality 

 among populations found in shoal water and areas that are exposed during 

 the ebb tide. Deeper water also protects scallops from such enemies as the 

 herring gull. 



CURRENTS. The water currents are of importance in the dispersal of the 

 larvae. In the adults, which are filter feeders, the currents may play an im- 

 portant role in the food supply. In concentration of large numbers of scallops 

 in a localized area, the exchange of the water replenishes the oxygen and 

 carries away the metabolic wastes. 



SALINITY. Scallops are confined to more saline water than oysters and 

 clams. Outsell discusses the minimum salinity, indicating a salinity of 20 

 parts per thousand as the minimum tolerated by scallops over prolonged 

 periods, but adult scallops are able to endure salinities as low as 13 parts per 

 thousand for brief periods. 



TEMPERATURE. On exposcd flats and in shoal water extreme winter 

 weather often causes considerable destruction of scallops. Freezing weather 

 is probably of greater significance in the northern states than in North Caro- 

 lina, although Outsell reports that the chilling of water in North Carolina 

 below freezing was responsible for the mortality of many scallops in 1928. 

 Temperature also influences feeding, growing, and spawning. Belding states 

 that the minimum temperature for growth is 45° F. 



BOTTOM. The type of bottom on which scallops are found varies from mud 

 to hard sand. A grassy bottom is generally considered necessary for the 

 growth of scallops. The bay scallop is confined largely to areas where an 

 abundance of eelgrass (Zostera) occurs. In the early 1930's when a 

 wasting epidemic disease killed off the eelgrass, scallops disappeared from 



