LIFE-HISTORY PATTERNS OF FINGERNAIL CLAMS (MUSCULIUM TRANSVERSUM) OF BIG LAKE, 
POOL 9, UPPER MISSISSIPPI RIVER

Jim Eckblad, Karl Swenson, David Schultz, Melissa Howie, Trish Young, Nick 
Leslein, Bret Powell, Leah Doerr, Katie McVey
Biology Department, Luther College, Decorah, Iowa 52101

In order to build realistic models of a benthic population like Musculium it is 
essential to have realistic estimates of its life-history characteristics.   We 
have been participating in a two-year study, May to October 2003 and 2004, in 
which monthly samples were taken of these fingernail clams.  During 2003 we 
dissected 1808 adult Musculium to establish pregnancy rates and numbers of 
shelled-embryos per adult.  Pregnancy rate ranged from 80 to 40 percent, with a 
decline noted from June to October.  The number of shelled-embryos per pregnant 
adult also declined from over 10 to less than 5 per adult.  With this 
information, and population size, we calculate that the reproductive 
contribution to the next generation is spread out over this six-month period, 
but it is three times greater in July and August than it is in September and 
October.    Upon completion of these life-history characteristics we will be 
much more confident of our ability to build a realistic model of this dynamic 
population.

Keywords:  fingernail clam, Musculium transversum,  modeling, life-history, 
Mississippi River