Of 18 species in SCUBA samples from Wheeler Reservoir, 11 occvirred 

 in "brail samples; I7 species in SCUBA samples from Chickamauga, 16 occur- 

 red in brail samples (table 1^). The data show the rate of exploitation 

 was highly variable for the different species. This indicates that the 

 brail method of fishing is selective, tending to catch certain species 

 more frequently than others. The pigtoe appears to be especially vulner- 

 able since the rate of depletion per drag for this species was higher 

 than the average depletion rate for all other species combined on each 

 test area. 



Length frequency data acquired by SCUBA and brail samples provided 

 a comparison between the size composition of the population and the size 

 composition of the catch for two different areas (table I5). The length 

 frequency distribution for the SCUBA samples in Wheeler Reservoir ranged 

 from 15 to 104 mm.j the length range for the brail samples was 30 to 

 10i^ mm. Sizes less than 50 mm. made up 6 percent of the population and 

 1.8 percent of the catch. In Chickamauga Reservoir the length range was 

 30 to 119 mm., in both SCUBA and brail samples. Size frequencies less 

 than 50 mm. in length comprised 1 percent of the SCUBA samples and 0.6 

 percent of brail samples. To test the homogeneity between SCUBA and 

 brail samples at each location, the length data were analyzed by chi- 

 square: 



( Length data grouped at 10 mm. intervals ) 

 Wheeler Chickamauga 



SCUBA samples - X^= 15.0^^ SCUBA samples - X = 3.64 



brail samples - x^- 7.51 brail samples - X = 2.12 



S^-- x"^- 22. 5S - ^^^'- X^TTTf^ 



6 d.f.; P : 0:005 5 d.f.; P = 0.30 



The size frequency differential between SCUBA and brail samples 

 in Wheeler Reservoir was highly significant, whereas the difference 

 between SCUBA and brail samples from Chickamauga Reservoir was not 

 significant. These tests indicate that the brail method of fishing 

 tends to catch pigtoe mussels larger than 50 mm. in length more suc- 

 cessfully than it does the smaller sizes. Since a greater number of 

 the smaller sizes (less than 50 mm.) were available on the Wheeler beds, 

 the size composition of the catch was not in agreement with that of the 

 population. In contrast, the size composition of the catch in Chicka- 

 mauga Reservoir was very similar to that of the population because of 

 the lesser availability of small mussels on beds at this latter location 

 (figure 6). 



Habitat conditions , — Comparison of bottom characteristics at the 

 48 SCUBA sampling station in Wheeler Reservoir with the number of mussels 

 taken at each station showed the following relation: 



24 



