84 BULLETIN OF THE -UNITE1> STATES FISH COMMISSION. 



being very severe. On December 3, 1880, I found the same. The win- 

 ters of 1S79-'S0 and 188CM81 were exceptionally cold, so that it appears 

 they are not dependent on "heat and tranquillity n for their proper de- 

 velopment. 



On May 25, 1879, after a very severe winter of abont nine weeks' con- 

 tinuous frost, I found on one of the beds under my charge several acres 

 of brood mussels, about the tenth of an inch in length. In the spring 

 of the year 1879 and the spring of 1880 overwhelming quantities of brood 

 were found on the scalps on the east coast of England, which might be 

 measured by hundreds and thousands of acres. 



Where mussels are found in thick and dense masses, they will be 

 three years before they are what is called "sizable," that is, two inches 

 in length j but instances are found near low- water mark where a few 

 have become isolated, and have grown much more rapidly. 



I do not think that mussels will spat, or rather that the spat will ma- 

 ture, in partially salt water. The only places where I have ever seen 

 any young brood is where the water has the same degree of saltness as 

 the outside sea, which, on the east coast of England, has a density of 

 about 1026.J, distilled water being 1000. Although it appears that salt 

 water is necessary at their birth, brackish water is better adapted for 

 fattening and growing, provided they are covered with the tide at high 

 water. I find by experience that the most suitable degree of saltness 

 of the water for fattening purposes is where the density of the water is 

 about 1014. This likewise applies to the fattening of oysters. 



To save the bulk of the spat when free is the great object of mussel 

 culture, therefore it is imperative to have the ground of the natural sea 

 bed as free from sand, weeds, and mud as possible, so that the young 

 may have some clean hard substance to which it can attach itself. 

 Aseidians and sponges are very destructive to the young mussel, as 

 they cover the culch, which would otherwise be favorable for their at- 

 tachment. 



Mussels have a great many natural enemies, amongst which may be 

 mentioned the star-fish or five-finger, the dog-whelk {Purpura lapillus), 

 the sea-urchin or echinus, sea birds, Danish crows, and sometimes rats; 

 but star- fish deal the most wholesale destruction. I have known ten 

 acres of a thickly covered scalp to be almost denuded in a fortnight. 

 Last summer I had carted from beds under my control between two 

 and three hundred tons of this fish. The star-fish will always attack 

 small mussels in preference to those of larger growth. It first grasps 

 the mussel with its five fingers, and when the mussel opens slightly to 

 breathe and feed, it inserts its stomach, or part of it, into the body of 

 the mussel, when, I believe, digestion commences, and the mussel dies 

 and opens its shell, and the star-fish withdraws its stomach with the 

 meat of the mussel. This operation I have seen performed, in all its 

 stages, thousands of times, upon oysters, mussels, and cockles. 



The dog-whelk bores a hole in the shell of the mussel about the size 

 of a small pin-head, and destroys it. 



