PEARLS AND PEARL FISHERIES. 
409 
an Illinois response, only that the shells are from 1 to 4 feet below the surface. One 
paper describes them as moving shoreward in the morning and back into deeper water 
later in the day (Illinois) ; another as feeding in the morning and evening (Iowa), and 
another as active at night and resting by day (Tennessee). In an Iowa paper they 
are reported as coming into shallow water to spawn in midsummer. 
Here, again, is evidence of much diversity, according to the species and to varying 
conditions. Hibernation, by burying themselves at the approach of winter, is an 
interesting feature that seems in some cases well attested, though a Kentucky paper 
states that no difference has been noticed between winter and summer. The younger 
shells are clearly somewhat migratory, but the tendency of the older ones is in many 
cases, where they have found a secure and favorable bedding-ground, to become 
closely massed together by gradual increase of size, so that dislodgment or moving 
becomes difficult. 
The responses to question 7, relating to the natural enemies of mussels, in 110 
papers, are varied and interesting, and in some respects quite contradictory. The chief 
natural enemy of the Unios seems to be the muskrat. Ninety- eight papers refer to it, 
40 reporting large destruction from this cause, 55 in some degree, and 3 denying any. 
Hogs come next, and are referred to in 67 papers. Of these, 9 hold them responsible 
for large destruction, 50 for some or a little, and 8 assert that there is none. Of other 
animals, raccoons are stated in 14 papers to destroy some shells; mink in 6 (New 
York, Iowa, and 'Wisconsin); mud turtles in 3 (Wisconsin); otter in 2 (New York and 
Iowa) ; crows in 3 (Tennessee) ; fish in 3 (Maryland, Ohio, and Texas) ; crayfish in 2 
(Maryland and New York); aquatic birds in 2 (Florida and Illinois); bears in 1 (New 
York), and cattle, by trampling, in 3 (Maryland, Indiana, and Iowa). 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 (Tennessee) that many pearls have been found 
where shells had been taken ashore by muskrats and left to open in the sun. 
With regard to physical causes of injury the most serious, no doubt, is found in 
freshets. Of 39 papers that refer to these, 18 report great destruction thereby, 18 say 
4< some” or “a little,” and 3 deny 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 washing down and caving in of banks in flood time 
or the stranding of great quantities of young shells, to perish 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 7 papers and drift ice in 4. Three papers allude to disease as a cause of 
injury and 3 to boring parasites. 
By far the most dangerous foe, however, is man, as his activity in pearl-hunting has 
nearly exterminated the shells at many points and greatly reduced them at nearly all. 
Twenty-six papers make mention of human agency as a destroyer, 14 of which regard 
it as the most serious and some as the only one of moment. Even where pearl-hunting 
has not yet extended, large numbers of Unios are used by fishermen for bait. 
Questions 8 and 9 were answered in a large majority of the papers, but in a manner 
so general and indefinite that little can be derived from them for a report. The 
answers to question 8 are chiefly unscientific statements as to sizes and colors that 
