CH. IX] THE PRODUCTIVITY OF THE SEA 183 



Therefore we have a yield of 



10,860 kilogrammes per hectare per annum; 

 or 86 cwts. per acre per annum; 



and the money value is £14. Ws. per acre per year. 



In the case of the Conway mussel fishery the area exploited 

 is about 256 acres, or 103*6 hectares. In 1906 the total quantity 

 landed was 22,252 cwts., or 1,130,000 kilogrammes^ This gives 

 us a yield of 



10,900 kilogrammes per hectare per annum; 

 or 87 cwts. per acre per annum ; 



and the money value is £14. 18s. per acre^. 



In 1899 I estimated^ the total produce of the Lancashire 

 cockle fisheries as about 6685 tons for the year. This is probably 

 well above the average and the product varies greatly from year to 

 year. The total extent of cockle-bearing sands I placed at about 

 105 square nautical miles, or 35,900 hectares. All this extent of 

 sand does not always produce cockles. There is, in fact, a kind 

 of rotation in the fishery: at one time certain areas are densely 

 populated with the molluscs and the fishery is then very intense 

 on these restricted portions of the whole area. Soon, however, 

 these beds become exhausted of the larger, legal-size cockles and 

 the fishery ceases for a year or more until a fresh crop of 

 marketable shellfish grow up to maturity. The fishermen, in the 

 meantime, seek new grounds. So in the course of time the whole 

 area is exploited, though only a fraction of it is worked at any one 

 time. Nevertheless the whole extent of cockle-bearing sands 

 must be considered. But in considering our estimate it has to be 

 remembered that only cockles of a certain size are allowed to 

 be taken, and that if the legal size limit were greatly reduced 

 the yield would rise. The yield was in 1889 



189 kilogrammes per hectare per annum ; 

 or 166 lbs. per acre per annum. 



The value is about 19s. per acre. 



Now all these estimates of productivity are those of uncultivated 

 sea areas. If we consider a cultivated fishery the yield will be 



^ Lancashire and Western Sea Fisheries, SuperintendenV s Report, 31 December 

 1906. 



^ Conway mussels command the better price. 



^ In Ann. Rept. Lancashire Sea Fisheries Lahy., for 1899. 



