F. S. Wright 129 



extent of the fishing grounds dealt with in the present paper, it will 

 be understood that these will soon become depleted unless restocked 

 from time to time. It is not legal to take mussels of a size less than 

 2| inches, except in certain places (see the Bye-Laws of the Lancashire 

 and Western Sea Fisheries District), and, from the time of the dis- 

 charge of the ovum, probably three years will elapse before this size 

 is attained, even under favourable conditions. The ova discharged 

 by a single female of Mytilus during the spring and summer months are 

 estimated to number from 10,000,000 to 15,000,000^, the vast majority 

 of which are destined to perish in various ways. So much so indeed, 

 that, in order that the beds may be fished from year to year, it is 

 necessary to restock them at the close of each fishing season — a matter 

 of comparative ease. 



Myticulture is practised in several different ways^, but the only one 

 that need be mentioned here is the system of bedding, as practised in 

 Britain. In a limited degree, transplantation has often been carried out 

 by the fishermen concerned, and others, and accounts descriptive of the 

 operations have appeared from time to time. Briefly, the shellfish are 

 removed in quantity, from certain beds (seed beds), where they do not 

 fatten, and redeposited in other situations where growth and fattening 

 proceed with rapidity. Beds of seed mussels are usually present in the 

 vicinity of the fishing grounds, and form nurseries or reservoirs from 

 which they may be restocked when necessary. 



The present paper is an attempt to discover the maximum produc- 

 tivity of mussel beds, — we might say the ideal productivity, and, like 

 most other ideals, the present one might perhaps be regarded as un- 

 attainable. Yet, even if this should prove to be the case in practice, 

 it is necessary to formulate a working hypothesis, and I venture to 

 believe that an output such as is described later is well within the range 

 of possibility. In its attainment, the chief factor to be taken into con- 

 sideration is that the population may secure a sufficiency of food material ^, 

 although there are other complicating factors to be considered. The 

 degree of restocking necessary to maintain a maximum yield from the 

 fishing grounds is also dealt with, etc. The data from which most of 

 the subject matter of the present paper has been written, was collected 



^ These figures apply to the American sea mussel, which is, however, of the same 

 species. See article by I. A. Field in The American Mvseum Journal, October, 1916. 



2 See article by Professor W. A. Herdman in the Beport for 1893 of the Lanes. Sea 

 Fisheries Laboratory. 



^ See article by I. A. Field in The American Museum Journal, October, 1916. 



•^ 



