2003 AND 2004 FOLLOW-UPS ON A 2002 UNIONID TRANSLOCATION FROM 
MISSISSIPPI RIVER MILE 818.9, COTTAGE GROVE, MN  

Marian E. Havlik
Malacological Consultants, 1603 Mississippi Street, La Crosse, Wisconsin 54601-
4969

In 2003 and 2004 we conducted follow-ups of a 2002 mussel translocation from 
Mississippi River Mile 818.9, downstream from St. Paul, at Cottage Grove, 
Minnesota.  The 52258 m2 area (1500 X 375 feet) extended from the LDB to the 
Main Channel.  The translocation, done prior to burial of a wastewater disposal 
pipe, yielded a mean mussel density of 0.38/m2 among 19,630 live mussels (23 
live plus 4 sub-fossil species).  Of the 1439 (7.33%) mussels which represented 
two Minnesota endangered and five threatened species, at least 572 mussels were 
numbered, measured, and aged (1-17 years of age).  All other living mussels were 
hash-marked.  In May 2003, 609 live unionids (18 live plus 5 sub-fossil species) 
were recovered from the two Translocation Sites; 515 were numbered and hash-
marked mussels.  76 Arcidens confragosus had a 98.7% survival, while 232 
Quadrula nodulata had a 98.3% survival.  One each of Tritogonia verrucosa, 
Obovaria olivaria, and Ligumia recta were recovered alive.  The survival of 
numbered special status mussels was 98.36%; 12.6% of the numbered mussels had 
external growth ring disturbances.  About 3% of numbered mussels showed little 
growth.  The overall survival of all marked and numbered mussels was 97.2%.  The 
substratum throughout both translocation sites was mostly mud with woody debris, 
and up to 6 m deep.     

In June 2004, 183 numbered Quadrula nodulata (98.9% survival), 58 numbered 
Arcidens confragosus (96.7% survival), and 2 numbered Obovaria olivaria (100% 
survival) represented 54.2% of 448 mussels recovered (15 live plus 1 dead [hash-
marked] species).  Of the numbered mussels, 81 (33.3%) were new to the follow-up 
measuring and external aging process.  Nearly 98% of the numbered mussels 
survived in a muddy habitat, <1 meter deep.  About 12.7% of the numbered 
unionids showed little or no growth; however, most of these were older mussels 
that would be expected to have a slow growth rate.  At least 10.7% of the 
numbered mussels had external growth ring disturbances.  In 2004, the overall 
survival of all hash-marked and numbered mussels was nearly 95%.  Most numbers 
engraved on threatened and endangered mussels were still very legible.  A total 
of 392 of 572 (68.5%) numbered mussels were recovered three times with an 
overall survival of 97.95%, in spite of an increased mussel density.  Similar 
percentages of all age classes were recovered during each project year.  Two 
years after translocation, the overall survival of all numbered and hash-marked 
mussels was nearly 96%.  No numbered mussels ever moved into the sandy area 
upstream of Translocation Site 1.  Slightly more Dreissena were found in 2003 
than in 2002, but none were found dead or alive in 2004.  Since several PVC 
pipes remained in the original project area in 2004, construction impacts were 
unlikely to have extended beyond the marked project site.

Keywords: mussel translocation, external unionid aging, unionid substrata, 
Mississippi River, Threatened and Endangered mussels