Empirically Derived Survival Rates of a Native Mussel, Amblema plicata, in the Mississippi and Otter Tail Rivers, Minnesota

Abstract

We used a mark-recapture method to measure survival of a native unionid mussel, Amblema plicata, at sites with low, moderate and high zebra mussel (Dreissena polymorpha) densities (mean values ± se equaled 0.4 ± 0.2, 50.5 ± 13 and 1750 ± 260 individuals/m2 respectively) in the Mississippi River, Minnesota, and at one site without D. polymorpha in the Otter Tail River, Minnesota. In 1996 240 A. plicata from each site were uniquely marked. In 1997, 1998, 1999 and 2000 marked mussels were recovered; identified; survival determined; and, if alive, they were returned to the substratum. Mean annual survival differed significantly among sites (χ2 = 4.08, df 3, P < 0.0001). Mean annual survival rates in the Mississippi River's low infestation population (LOW) were 99 ± 0.3%, and 89 ± 1.2% in the moderately infested population (MOD), while survival at the highly infested population (HIH) was 65 ± 7.8%. Mean annual survival for the Otter Tail River population (REF) of A. plicata was 98 ± 0.5%. Results demonstrated that A. plicata has high mean annual survival (>97%) in natural habitats that are not colonized by D. polymorpha and the survival rates decline significantly relative to increases in D. polymorpha densities.