The Use of Passive Integrated Transponder Tags (PIT tags) in the Conservation and Management of Native Freshwater Mussels.
Teresa Newton, Steve Zigler and Patty Ries
USGS, Upper Midwest Environmental Sciences Center, La Crosse, WI.
Native freshwater mussels are one of the most imperiled group of animals nationwide, thus, research on their conservation and management is a priority concern for federal, state, and non-governmental organizations. Relative to other organisms, we know little about their ecology, especially rates of survival, movement, and reproduction. Part of our lack of knowledge comes from the difficulty in marking and recovering mussels, especially in large rivers. The development of PIT (passive integrated transponder) tag technology provides an opportunity for repeated identification of individual mussels without disturbance. PIT tags are glass-encased microchips that are passive until activated by a low frequency signal. When interrogated by a scanner antenna, the tag absorbs the electromagnetic signal, using it to transmit a unique identification code. Tag longevity is infinite, because an internal power source is not needed. Since 2009, we have used PIT tags on two mussel conservation projects. In the first project, we followed the fate of ~460 mussels (Lampsilis cardium and Amblema plicata), which were PIT-tagged and placed at 12 sites on the Upper Mississippi River (UMR) before and during a planned water level drawdown. Recovery of tagged mussels was >88% in both years. Mortality was similar and low (mean, ~5% in both species) among reference sites, but was variable and relatively high (means, ~27% in L. cardium and ~52% in A. plicata) among treatment sites. Weekly horizontal movements in both species were significantly correlated with changes in water elevation. In general, A. plicata responded to the drawdown by vertical movement into the substrate, whereas L. cardium responded by horizontal movement to deeper water. These data suggest that drawdowns can influence the mortality, movement, and behavior of mussels in the UMR. In the second study, we tagged ~578 mussels and are estimating survival of four species across two areas (in the core and periphery) of a dense and diverse mussel bed in the UMR. The first year after tagging, we recovered 49% of the tagged mussels. Annual survival of the recovered mussels averaged 90% and was similar among species. In the second year after tagging, we recovered 26% of the mussels that were recovered alive in 2013. Annual survival of the recovered mussels averaged 68% and was variable among species. Recovery and survival were generally greater in the core areas relative to areas around the periphery of the bed. Collectively, these data suggest that PIT tags are useful for assessing the survival, movement and behavior of mussels, but that the successful recapture of mussels depends on river hydrology and water depth.