Bottom 



type 



Percent of 

 total area 



Percent of 



all mussels 



Number of 

 species 



Rubble 



sand 

 Mud- gravel 

 Marl 



gravel - 



75.0 



6.0 



19.0 



97.^ 

 1.0 

 1.6 



18 

 2 

 1^ 



The importance of the rubble — gravel — sand bottom type is demon- 

 strated; practically all of the mussels occurred here. This type of 

 bottom best meets the requirements for most species. The mud-gravel type 

 was not extensive, found only on lateral areas close to shore. The marl 

 formation, extending across the stream to form an irregular pattern at 

 various locations, provides an impenetrable bottom unsuitable for mussels. 

 The few that were found here had embedded in isolated soil pockets where 

 the marl strata was broken or depressed. 



The deposition of silt on mussel beds ranged as high as 1 l/k 

 inches in depth on lateral areas close to shore where the current was 

 slow. Silt was about l/2 inch deep on central areas in the stream channel. 

 Silt deposits were especially deep on bottoms behind large boulders or 

 sunken logs where the stream flow was impeded. A relatively large number 

 of dead shells, of different species and sizes, were found under layers 

 of silt 1 inch or deeper at several stations. These shells were embedded 

 in a normal position with the valves closed; the shells showed little sign 

 of erosion, indicating that mortality had occurred within recent months. 



As previously reported, juvenile deertoe mussels, a noncommercial 

 species, were the most abundant of the small size classes found on the 

 areas sampled. According to Ellis (l93l) the deertoe is a mud-loving 

 species capable of surviving on bottoms that most other species cannot 

 tolerate . 



Bottom conditions on the limited area sampled in Chlckamauga 

 Reservoir were similar to conditions in Wheeler Reservoir except for 

 the absence of the marl type fonnation. The depth and extent of silt 

 layering on the beds was approximately the same as described for the 

 Wheeler beds. 



Age and growth of the pigtoe . — Age determinations of samples from 

 Wheeler and Chlckamauga beds showed that only a few specimens less than 

 1 year old were available fcr study from Wheeler and none less than 6 years 

 old from the study area in Chlckamauga Reservoir. The calculated annual 

 growth rate for the first 5-year period on the Wheeler beds was 7.O milli- 

 meters. The annual growth increment for the second 5-year period averaged 

 3.7 mm. on Wheeler and 2.8 mm. on Chlckama\:ga (table I6) . Growth was 

 slower and more variable on both reservoirs after the tenth year. Although 

 older specimens were present, age was indeterminate beyond 25 years. The 



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