OutdoorNebraska

7 Age and Longevity Simply figuring out how long freshwater mussels can live has been a major stumbling block. It had been assumed that the rings observed on the shell's exterior were annual growth rings. But we have found this to be partly false. Marked individuals that were periodically retrieved, measured and aged found that the rings consistently underestimated age. Cases of negative growth were actually observed. Ages from shell rings were consistently underestimated and that individuals in some populations could be over 100 years old. 2, 34 It has also been found that handling, especially repeated handling, reduced growth and further biased age estimates. 14, 15 The only consistently accurate method of aging freshwater mussels was by thin cross- sections of the shell. 15, 34 The points to note are that 1) mussels are very sensitive to handling and because of this, 2) freshwater mussel mark/recapture studies for age and growth are probably biased, and 3) external shell rings cannot be used to age mussels, which means that mussels may be considerably older than previously suspected. What is the significance? Many mussel populations are composed of very old individuals and they have a very low rate of recruitment. ["Recruitment" is the number of juveniles that actually survive to adulthood.] This means that impacts, like commercial harvest or a pollution event, will have long- lasting negative consequences. THREATS Threats. . . . just where do we start? Habitat alteration, siltation, drought and dewatering, chemical and organic pollutants, overharvest, physical damage, and exotic species. Mussels are sedentary organisms that cannot escape environmental threats. Furthermore, many are long-lived so that low-level chronic threats can take years to impact populations. They have low reproductive rates so their ability to recover these impacts is limited. Let's discuss these in turn. Impoundments While there are a variety of threats to freshwater mussels, the greatest has been habitat alteration. These animals evolved in streams, are immobile and depend on the mobility of fishes for their overall survival. Streams have a wide diversity of habitats including pools, riffles, runs, glides, rapids, and off-channel meanders. The negative impacts of impoundments on freshwater mussel faunas have been well-documented.

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