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 Cnios appears to be the 
muskrat; 65 papers refer to it, 26 reporling large destruction from this cause, 38 in some 
degree, and one denying any. Hogs come next, and are referred to in 47 papers. Of 
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 2;. 
and cattle, by trampling, in 3. All the animal depredators deal only or chiefly 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, aud 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 u covering with mud,” and by 
u change of bars.” On the other hand, low water and droughts are reported as 
seriously harmful in 5 papers, and drift ice in 3. Two papers allude to disease as a 
cause of injury, aud 3 to boring parasites. 
EXTERMINATION OF THE MOLLUSICS. 
The question as to exhaustion of the musSel-beds, its causes and its rapidity, has 
called forth a very suggestive body of replies in 57 papers; the remaining 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 59 papers, therefore, 
approximately three- fourths, the process of exhaustion is recorded, at times already 
