5- 



3 

 < 



5 



Z 



z 



X 

 U 

 (— 

 < 



6 

 o 



3- 



1- 



50 



Figure 17. 



90 100 



CARAPACE LENGTH IN MILLIMETERS 



110 



120 



A simple catch curve calculated from the number of lobsters between consecutively numbered 

 probability modes starting- at 53-mm carapace length. 



"calculated this estimate from the arrangement 

 of probability modes as hypothesized in the 

 section on length frequencies. 



The estimates by year with probability modes 

 in parentheses are: 1967, 91.1% (numbers at 

 modes 85 and 97), 92.8% (numbers at modes 

 91 and 105); 1968, 91.6% (numbers at modes 

 85 and 97), 93.7% (numbers at modes 91 and 

 105); 1969, 44.0% (numbers at modes 85 and 

 94), 93.2% (numbers at modes 91 and 102); 

 1970, 60.3% numbers at modes 84 and 95), 

 96.6% (numbers at modes 91 and 106). 



These estimates are higher than those from 

 the consecutive probability modes and closer 

 to the estimates from some other methods of 

 estimating mortality. The two aberrancies 

 (1969 and 1970) for the first two modes could 

 be caused by using only the number of lobsters 

 at the specific modes. The high degree of con- 

 sistency of the estimates from the other modes 



strengthen the working hypothesis that we 

 developed in the section on length frequencies. 

 Estimates of the annual natural mortality 

 for the prerecruit sizes (modes from probability 

 paper) from sampling the prerecruit sizes with 

 wire traps are: 7.7% (»i//; 2 in 1968), this esti- 

 mate is identical with the natural mortality 

 estimate of 7.7% from the commercial sampling; 

 2.0% (ni/na for 1969); and 4.0% {n x \n 2 for 1970). 



(7) Silliman (1943) described a method that 

 requires a series of years at two different levels 

 of effort to separate natural from fishing mor- 

 tality. Because of the short series of years in 

 the present study on lobsters, we turned to 

 historical data in order to use the method. 

 The length frequencies for the available years 

 were separated by ¥2 -inch increments and the 

 effort was simply an estimate of the number 

 of traps by year as reported in "Maine Land- 



46 



