REPRODUCTION AND ARTIFICIAL PROPAGATION OF FRESH -WATER MUSSELS. 1 89 



enables them to move out into deeper water when the deposit of silt becomes a menace. 

 The result of our study of the conditions obtaining in sloughs like the west channel 

 at La Crosse, which are closed by dams at their heads, proves conclusively that such 

 waters afford a very unfavorable habitat for mussels, and that therefore they are not 

 adapted to experimental uses. 



VIII. ECONOMIC APPLICATIONS. 



It may not be inadvisable to discuss briefly certain applications of the results 

 obtained in the foregoing investigations to the practical work of artificially propagating 

 fresh-water mussels on a commercial basis. It must be emphasized at the outset that 

 the ultimate object of the investigations — the restocking of depleted waters with com- 

 mercial species of mussels — is not dependent for its realization solely upon the success 

 of rearing mussels artificially from the glochidia, but that other methods of attaining the 

 same end may be employed which are of equal, if not greater, importance. 



PROTECTIVE LAWS. 



Much can undoubtedly be done by securing the passage of laws by State legislatures 

 for the closing of certain streams or sections of streams against all clamming for a period 

 of years of sufficient length to allow of a natural increase of the mussels; by laws pro- 

 hibiting the use of the ordinary "crow-foot" dredge, which takes immature and adult 

 individuals indiscriminately," and by laws prohibiting the discharge of sewage and 

 factory refuse in the neighborhood of mussel beds. By these and other protective 

 measures of a legal nature, a great deal might be accomplished in the way of conserving 

 the supply of mussels in the more important waters, but, since in the case of many rivers 

 the control is in the hands of two or more States, the passage of such laws would require, 

 to be effective, similar action on the part of several legislatures, and such cooperation 

 might not be obtained without the greatest difficulty. 



The utter futility of laws which would establish a closed season of the year against 

 clamming is apparent in the light of our knowledge of the breeding seasons of the 

 Unionidae. We have already seen that there is no month in the year whexi some species 

 are not bearing embryos or glochidia, and as species of commercial value are found in 

 both groups — those with the long and those with the short period of gravidity — a 

 closed season at any time would be of little or no avail. Several species of Lampsilis, 

 for example, which bear embryos or glochidia from August to July, furnish valuable 

 shells for the pearl-button industry, while the species of Qiiadrula and other summer 

 breeders, gravid from May to August, supply shells of the best quality. Any law then, 

 designed to relieve the situation, which prohibits the taking of mussels during a sup- 

 posed breeding season is based on ignorance of the facts, for the entire year is the breed- 



oMussels caught on a hook of the "crow-foot" are generally so badly injured internally in the process that, even if they arc 

 afterwards thrown back into the river, the majority probably die. A special form of hook has been devised by Mr. J. F. 

 Bocpplc which is so constructed that small mussels can not be caught by it. The use of some such selective apparatus should 

 be retiuired by law. 



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