AQUICULTURE 287 



Helland's explanation of the high temperature of the Salter 

 deeper water in the pond is that the layer of fresh water 

 on the surface forms a cover, preventing the deeper water 

 below from coming to the surface and losing its heat. So 

 he considers that the heat of the lower water layers, derived 

 from the sun, constantly accumulates throughout the sum- 

 mer. From his observations he shows that only a few days 

 of sunshine are necessary to make a considerable difference 

 in the temperature ; he has observed a rise of two degrees in 

 one day. The ponds may be regarded as hot beds for oyster- 

 growth. The rocky sides are covered with masses of old 

 oysters, which are left undisturbed as a breeding stock, while 

 from wires stretched across the pond and supported at 

 intervals by empty barrels are hung bundles of birch branches 

 or fascines to serve as collectors of the spat. About 3,000 

 of these collectors are placed in the pond in early summer, 

 and the spat settles upon them between June and September ; 

 but the collectors are left in position until the following 

 April, when the young oysters are removed with shears and 

 sent either to another pond, where they are laid out in 

 galvanized wire ambulances, or to the oyster company's 

 grounds on the shore near Stavanger. 



An average harvest from the Espevig pond is about one 

 million young oysters, and it is said that in some years the 

 deposit of spat may be so large that one can hardly put a 

 needle's point between the individual young oysters, and 

 the whole of the collector looks as if it had been dipped 

 in mortar. In such a case, however, only a comparatively 

 small number of these young oysters has room to develop ; 

 the rest are sacrificed to overcrowding, but this loss might 

 be reduced by some alteration in the collectors. The whole 

 system is suggestive of possibiHties in scientific aquiculture 

 far beyond what is at present practised. 



The American oyster, which is a separate species (Ostrea 

 virginiana), is cultivated or fished at many places on the 

 Atlantic coast from New England down to Carolina, and 



