328 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



PRESENT ABUNDANCE OF FRESH- WATER MUSSELS. 



Out of 83 papers which respond to this inquiry 7 describe the shells as at present 

 very abundant: 36 as plentiful; 25 as scarce, and 3 as absolutely exterminated; 28 

 papers refer to the fact of diminished and diminishing numbers within a few years 

 past, some of them with great emphasis. Three of the Tennessee papers estimate the 

 numbers as reduced to about one-tenth of what they were ten years ago, and the same 

 general fact is stated, of former abundance and present rarity, and attributed to the 

 pearl-hunting destruction of a few years past. Several papers say that the shells 

 are now scarce in small streams and the shallower parts of larger ones, while still 

 abundant in deep water and where the currents are strong. 



NATURAL ENEMIES. 



In regard to natural enemies, 84 papers are varied and interesting, and in some 

 respects quite contradictory. The chief natural enemy of the Unios appears to be the 

 muskrat; 65 papers refer to it, 26 reporting large destruction from this cause, 38 in some 

 degree, and one denying any. Hogs come next, and are referred to in 47 papers. < >f 

 these, 7 hold them responsible for large destruction, 35 for some, or a little, and 5 

 assert that there is none. Of other animals, raccoons are stated, in 13 papers, to 

 destroy some shells; mink in 5; mud turtles in 3; crawfish in 2; aquatic birds in i'; 

 and cattle, by trampling, in 3. All the animal depredators deal only or chieily with 

 Unios that are either young, small-sized, or soft-shelled, and hence not largely pearl- 

 bearing. The only exception to this general rule is the statement in one paper that 

 many pearls have been found where shells had been taken ashore by muskrats and 

 left to open in the sun. 



INJURIES DUE TO PHYSICAL CAUSES. 



With regard to physical causes of injury, the most serious, no doubt, is found in 

 freshets. Of 31 papers that refer to these, 17 report great destruction thereby; 13 say 

 "some" or "a little," and 1 denies that there is any. Some papers say that their 

 injury is small, and that they only shift the beds and redistribute them; but a number 

 describe the burying of beds by the washing down and caving in of banks in flood- 

 time, or the stranding of great quantities of young shells when the water subsides. 

 Two papers that do not mention freshets should doubtless be included here, however, 

 as they speak of destruction caused to the shells by "covering with mud," and by 

 "change of bars." On the other hand, low water and droughts are reported as 

 seriously harmful in ."> papers, and drift ice in 3. Two papers allude to disease as a 

 ean^e of injury, and ."> to boring parasites. 



K\ TERMINATION OF THE MOLLUSKS. 



The question as to exhaustion of the mussel-beds, its causes and its rapidity, has 

 called forth a very surest! ve. body <>f replies in 57 papers; the ivmainiiii; third make 

 no response, or none that is at all definite; 9 papers report extermination of the shells, 

 either actual or imminent, within a very few years past ; 20 speak of rapid diminution 

 in their numbers; 16 of decrease as noticed and in progress; 8 are uncertain or report 

 little or no change; 6 describe them as abundant or "inexhaustible,'' and 4 refer to 

 partial recovery or replenishment after reduction. In 45 out of 5!> papers, therefore, 

 approximately three fourths, the process of exhaustion is recorded, at times already 



