The number of pigtoe mussels available to the fishery at the start 

 of the 1956 season was estimated by adding the total number harvested dur- 

 ing the 2-year period to the estimated escapement population at the end of 

 the 1957 season. This estimate is somewhat low since natural mortality 

 was not included in the estimate. The author believes that natviral mortal- 

 ity was slight, except in the youngest age groups, which comprised a small 

 percentage of the total population. 



The total population of all species and available sizes in Wheeler 

 Reservoir was also estimated from data gathered using SCUBA, gear. Length 

 data were recorded from all pigtoe mussels collected in the SCUBA, samples 

 to determine the size composition of the population on the Wheeler beds. 

 Measurements were taken to the nearest millimeter. 



Relation of abundance and catch . --The relation of population size 

 to catch success by crowfoot brail was studied on two 5^000 square yard 

 test areas in Wheeler and Chickamauga Reservoirs during August and Septem- 

 ber of 1957- One area was at mile 309 on Wheeler Reservoir, the other 

 at mile 515 on Chickamauga Reservoir. The population on the Wheeler beds 

 had been fished intensively for 12 years. In contrast, the beds on 

 Chickamauga were discovered in 1956 and had been fished for only 5 months. 



The sizes of the populations on these small areas were estimated 

 by taking 10 random SCUBA samples, covering 20 square yards of bottom 

 within each area. After the density of the respective populations was 

 determined, I6 brail samples were made in each area to measure the cor- 

 relation between population density and the mean catch per drag. 



Length frequency data for all pigtoe s collected by SCUBA sampling 

 in Wheeler and Chickamauga were compared with length data from brail sam- 

 ples taken in the same areas to determine the selectivity of the harvest 

 method on different size groups. The sample from Wheeler consisted of 313 

 mussels taken by SCUBA and 530 by brail, while Chickamauga was represented 

 by 212 collected using SCUBA and 262 collected by brail. 



Habitat conditions . --The correlation between population density 

 and the physical character of the bottom was determined by comparing bot- 

 tom conditions at the U8 sampling stations in Wheeler Reservoir with the 

 number of mussels found at each station. Distribution of the population 

 was determined with respect to the availability of three major bottom 

 types: rubble--gravel--sand, solid marl, and mud-gravel. 



Age and growth of the pigtoe . --A total of 236 pigtoes from Wheeler 

 Reservoir and 2^2 pigtoes from Chickamauga Reservoir, represented by all 

 available sizes in SCUBA and brail samples, were examined and their age de- 

 termined by a method described by Isely (l91^), Howard (l922), and Chamberlain 

 (1931) . The left valve of each specimen was cleaned with a wire brush, then 

 measured along the axis. Age was determined by the number of annuli and 

 growth by the increment distance between successive annuli. 



