184 THE PRODUCTIVITY OF THE SEA [PART II 



much greater. There are, however, few cultivated fisheries which 

 can supply us with this information. Here and there in Great 

 Britain oysters are imported from America and elsewhere and laid 

 down to be fattened, and in France and Holland the " succulent 

 bivalves" are actually bred and reared. But I do not know of any 

 published figures for the yield of these oyster layings or farms. 

 We have, however, figures for the yield of the German carp-ponds. 



German carp fisheries. In Germany the cultivation of the 

 carp is carried on extensively. In many places large ponds are 

 stocked with the fish and the fishery is worked as a commercial 

 affair, while in most small villages smaller fish ponds are to be 

 found. The ponds are regularly stocked with young fish and the 

 latter are fattened. Sewage is deliberately led into these ponds, 

 and the resulting addition of nitrogenous inorganic food stuff sets 

 up an abundant microscopic fauna and flora, which is the ultimate 

 food of the fishes. Whether a carp- pond is situated badly or well, 

 the addition of sewage always makes it better. There is quite 

 a literature relating to the practical culture of carp, and the details 

 of carp metabolism have been studied in much the same kind 

 of way as in the breeding and raising of live stock on the farm. 

 Many estimations of the yield of these carp-ponds have been made. 

 I quote a few. Hensen^ estimates the yield of certain ponds 

 as 76*5 kilogrammes of caip flesh per hectare ; Brandt^ estimates 

 the least yield of some ponds at Stettin as 6 5 '5, the average 

 as 106*5, and the maximum yield as 164 kilogrammes per hectare. 

 Von Steman^ gives the yield of some carp-ponds in Schleswig- 

 Holstein as 112"2 kilogrammes per hectare and year. Thus we 

 have a productivity for a fresh-water cultivated area of 65*5 to 164 

 kilogrammes per hectare, or 58 to 141 lbs. per acre; and a value* 

 varying from £6. lis. to £16. 9^. per hectare and year. 



Productivity of a cultivated mussel fishery. Since the yield 

 of an inshore fishing area is greater than that of an open sea 

 one we should also expect to find that a cultivated shell fishery 



1 "Resultate stat. Beobacht. Fisch. deutschen Kiisten," 3 Ber. Komm. Untersuch. 

 deutschen Meeres, Kiel, 1878. 



2 " u. d. Stettiner Haflf," Wiss. MeeresunL Kiel Komm. Bd. i. Heft 2, 1896. 



3 Allgemeine Fischerei-Zeitung, Berlin, 1895. 



■* One pound of carp is worth about Is. in Germany. 



