Length measurements were recorded from 11,658 pigtoes taken 

 from Chickamauga, Wheeler, Guntersvllle, and Kentucky Reservoirs during 



1956 and 1957. The length was measured along the anteroposterior axis 

 of the left shell valve of each specimen. 



An estimate was made of the total fishing effort expended on 

 Wheeler Reservoir in 1956 and 1957^ as indicated by the total number 

 of drags made by fishermen. The total number of drags was estimated 

 by dividing the average catch of pigtoes per square yard per drag into 

 the total catch of pigtoes per square yard harvested from the available 

 fishing area. 



Population sampling. --Two methods were used to estimate the 

 size of the popiilation and the rate of exploitation of pigtoe mussels 

 in Wheeler Reservoir (mile 308 to 3l6) . The first method consisted in 

 a mark and recaptiire study carried on for a total of 9 months during 

 the fishing seasons of 1956 and 1957* The second method consisted in 

 taking randomized bottom counts of mussels in square yard plots within 

 the harvest area using SCUBA (self-contained underwater breathing apparatus) 

 diving gear. 



During May, 1956, 1,000 pigtoes were marked by drilling a small 

 hole through the umbo (beak) of one valve; a nickel pin was then inserted 

 through the hole to attach a plastic disk tag. The tagged mussels were 

 transplanted at random in the commercial fishing area. Tagged recaptures 

 were reported on a voluntary basis in 1956; fishermen were paid a 50-cent 

 reward per tag in 1957* An additional 100 mussels were marked for con- 

 trols and confined in a protected area to estimate mortality caused by 

 the tagging method. Data from tag recaptures and catch records of the 

 total number of unmarked pigtoes caught were used to calculate the size of 

 the population at the end of the 1957 harvest season using the Petersen 

 formula . 



SCUBA equipment was used to hand-collect all mussels found in 

 96 square yards of bottom area at 48 stations diiring June and July of 

 1957* A cluster of 2 square yard subsamples was taken per station, and 

 the mean number per square yard was determined by taking the combined 

 average from both samples. Eqiiipment consisted of a Scott Hydropac with 

 tanks of compressed air, a portable iron frame to form a quadrat of 

 1 square yard, a waterproof sealed beam light (6 volt), a boat, safety 

 line, and an anchor. Sampling was done in water varying from 20 to 29 

 feet in depth, with a current velocity averaging O.7 miles an hoiir. The 

 procedure used at each collecting station consisted in first fanning the 

 area free of silt, then probing into the soil to uncover all embedded 

 specimens. The size of the population was estimated by multiplying the 

 mean number per square yard of the sample by the total number of square 

 yards of fishing area (7, 480,000). The population at the end of the 



1957 harvest season was estimated by deducting the number harvested after 

 the population estimate was made. 



