25 Oct 1999

     Freshwater drum (sheepshead), A. grunniens, eat freshwater mussels; they
have a pharyngeal teeth arch to do this (I'm not a fish person).  In so
doing, they crunch up the shells.  We've found small shells (~25 mm long),
particularly the deertoe, Truncilla truncata, crunched up and apparently spit
out by the fish (nothing else could have crunched up shells like this, and
shells were not in a place afftected by pleasure boats, swimmers etc).
     Muskrats and raccoons (these 2 particularly) as well as mink and otter,
only leave claw/scratch marks on shells (I've see thousands of those).
Occasionally one of the small mammal's eyes are bigger than their teeth and
they can't open a good sized shell, so they'll leave the shell stranded (top
of a muskrat house, or on a log are favorite places), and then eat them after
the mussel starts to die and opens it's valves. We've found live/dying
mussels with claw marks so we know small mammals have tried to make a meal of
them.
Marian E Havlik
Malacological Consultants
1603 Mississippi Street
La Crosse, WI 54601-4969
[log in to unmask]
P/F: 608.782.7958