138 Mussel Beds; their Productivity and Maintenance 



more seaward (generally) situation of the seed areas may possibly be a 

 factor to be considered in attempting to account for the light weight of 

 their population. Remembering that the sea mussel is essentially a 

 brackish water animal, it is probably safe to say that its "condition" 

 varies with the difference of freshwater influence. 



Groivth-Rate of the Sea-Mussel. 



The growth-rate of Mytilus will be considered here mainly from the 

 economic standpoint, leaving points of more purely scientific interest 

 for another occasion. One point of general interest, and some import- 

 ance, must be noticed in this place, namely the amount of growth made 

 by Mytilus during the first year of its life, in its natural habitat. These 

 observations were made on a suitable portion of the foreshore, near the 

 fishing grounds, at Aberdovey, near low- water mark of spring tides, and 

 they extended over a considerable period. Certain stones were carefully 

 watched, as circumstances permitted, upon which mussel spat was likely 

 to settle (the spawning time probably commences at the end of April, 

 or during May). In due course, young Mytili were seen to have affixed 

 themselves thereon, and in July of the following year (1917) they had 

 attained a size varying from ^" to ^". 



During the course of transplantation work in Cardigan Bay, for two 

 successive years, it has been found that a large proportion of the seed 

 mussels measured about two inches in length. It was desired to ascer- 

 tain the growth made by these during the close season, which, at Aber- 

 dovey and Barmouth, extends from April 1 to October 81 inclusive, — 

 a period oL seven months. At Portmadoc, the close season begins a 

 month later, and ends a month earlier, than at the above named places. 



Various means were tried of marking large numbers of two-inch 

 mussels, as for instance, by the application of spots of specially prepared 

 paint. This pigment not only hardened under water, and is known to 

 have adhered for some considerable time to the shells, but it left the 

 mussel so marked quite uninjured. The attrition of water-borne sand, 

 however, removed all trace of it in the course of time, and to my disap- 

 pointment, not a single marked mussel has been recovered from any of 

 the beds. As a check experiment, some cages of galvanised iron wire 

 were constructed at the same time, and these were deposited in the river 

 at Barmouth. Some of them were recovered at the commencement of 

 the next fishing season, and the surviving mussels were carefully mea- 

 sured. As the cages would seem to have been affected by the shifting 

 sand that has lately covered portions of the Barmouth mussel beds, the 



