have barges fleeted there a greater percentage of the time. When 

 we sampled the piling plot in October, the diver could not get 

 under the barge to the corrals, and the Naples Terminal Company 

 moved the barge for us. As previously mentioned, it appeared 

 that a barge had settled on top of the corrals and mussels, and 

 mussels may have suffocated. No fragile-shelled mussels 

 ( Leptodea fragilis or Proptera laevissima ) were recaptured at the 

 grounded plot. 



In the downstream control plot, only three recaptured 

 experimental mussels, one Leptodea fragilis and two Proptera 

 laevissima , had died between June and October. We have noticed 

 these two species suffer higher mortality in handling and in 

 aquaria at our laboratory than Amblema plicata , so they may be more 

 sensitive to handling stress or water quality factors. As 

 previously mentioned, comparatively low mortality rates in the 

 fleeted plots could be an artifact of displacement of dead fragile- 

 shelled species. 



GROWTH 



Growth rates are usually greater in younger mussels of a 

 given species. To adequately compare growth rates of individuals 

 from different treatment plots, it is necessary to collect enough 

 individuals of different ages from each plot to construct growth 

 curves. At present we do not have enough data to delineate these 



37 



