measured about 3x5x1 cm, weighed only a few grams underwater, and produced 

 a 70KH signal detectable by directional hydrophone as far away as 300-400 m on 

 open bottom and remained detectable from 10-20 m when the lobster withdrew into 

 a crevice. Several sonic trackers were used (Smith-Root, Ametec-Straza, and a 

 unit custom built by the National Marine Fisheries Service Biological Laboratory 

 in Seattle, Washington (see Clifton, et al, 1970). 



Lobsters to be sonic-tagged were snared and hand carried back to the habitat. 

 There, the dorsal cephalothorax was dried with toweling and Eastman 910 adhe- 

 sive applied to both carapace and rubber "feet" on the tag. After several 

 seconds, the tag was firmly placed and the adhesive allowed to set for 10-12 

 minutes. Tags so attached seldom detached from a free moving lobster, even in 

 the den and on the reef. 



The rate of back tag loss was estimated from reexamining a randomly selected 

 sample of lobsters from Area 3 on or about September 15, 3 months after June 15, 

 the point in time at which half of the tagged lobsters in Area 3 had been 

 released. Ten percent of the lobsters examined with the secondary mark had 

 lost the back tag, indicating a rate of tag loss of 3.3 percent per month. 

 Assuming this rate to be constant with time, the number of tagged lobsters at 

 large (M^-) prior to the t^" day of sampling was adjusted accordingly. 



Multiple census population estimates were made of the lobster populations in the 

 four study areas from each day survey diving, excluding the initial day of tag- 

 ging. The Modified Schnabel formula from Ricker (1958) was used to calculate 

 population size (N) . Census dives produced the following information necessary 

 for computing N: 



Mj^ = total number of tagged lobsters at large 

 at the start of the t day. 



C = total number of lobsters seen on the t day. 



R^ = total number of tagged lobsters in the sample C|-. 



ER^ = total number of tagged lobsters seen up to and 

 including the t^ day. 



The formula used was, 



N = E(CtMt) 



ERj. + 1 



Tagging and sampling was sufficiently intensive in Area 3 to permit a single 

 census estimate, using Petersen's formula from Ricker (1958), of population size 

 during May and September. These estimates were based on releases and resight- 

 ings made during approximately one week periods in May and September. The 

 Petersen formula is: 



N = M (c-fl) 

 R+1 



VI-38 



