methods of propagating certain species of mussels. Coker (l91^), Coker, 

 Shira, Clark^ and Howard (l92l), and Howard (l922), have described the 

 early industry and the results from these studies. 



Since 19^2 the Tennessee River has become the nation's most impor- 

 tant source of fresh-water shell. This stream was intensively developed 

 by the Tennessee Valley Authority between 1936 and 19^^- for hydroelectric 

 power, flood control, and navigation. The development program included 

 the construction of seven dams which impounded 58O miles of stream. Two 

 other dams completed earlier (l913 and 1925) impounded 55 miles of stream. 

 Development of the mussel fishery began on the lower section of the river, 

 gradually extending upstream as new productive beds were found. During 

 1956 and 1957, the bulk of the catch was taken at foior locations: Kentucky 

 Reservoir (mile I90 to I96), Wheeler Reservoir (mile 308 to 3l6) , Gunters- 

 ville Reservoir (mile 379 to 389)^ and Chickamauga Reservoir (mile h98 to 

 519) . (See figure 1.) 



The importance of fishing areas depends on the abundance and 

 quality of the shells produced. Shells of good quality have thick valves 

 of pearly white and lustrous nacre, free from spots or stains and of a 

 firm but not brittle texture. The pigtoe mussel, Pleurobema cordatum , 

 and the niggerhead mussel, Fusconaia ebena, meet these requirements. 



Method of harvest. --Mussels are harvested commercially in the 

 Tennessee River by crowfoot brail. This device was first used in I897 

 on the Mississippi River and has become the usual method of harvest on 

 many large streams. Coker, Shira, Clark, and Howard (1921) described 

 this device in detail, along with other types of shell-fishing equipment. 

 The brail assembly used on areas where most of the present studies were 

 carried out has been modified to some extent and warrants a brief descrip- 

 tion. 



The brail consists of a wooden bar I8 to 21 feet long to which 

 chains are attached at i4-inch intervals; each chain is approximately I8 

 inches long and bears a cluster of several multipronged hooks linked to 

 its free end. The prongs of the hooks are straight instead of curved, 

 and each prong has a small knob on the tip. The hooks are made of heavy- 

 gauge wire, and the niimber used may vary up to 720 for brails 21 feet 

 long. A rope bridle is attached for towing the brail downstream. 



The brails are fished from flat-bottomed "john" boats 20 to 25 

 feet long. Most of the larger boats fish two brails at a time, keeping 

 a spare for replacement when one of the other brails is lifted to remove 

 the catch. Power is provided by an underwater sail, made of canvas, called 

 a "mule." The rate of speed can be adjusted to some extent by changing 

 the pitch of the sail in the ciirrent (figure 2). 



When one of the trailing hooks of the brail passes between the 

 slightly gaping valves of a feeding mussel, reflex action causes the 



