pie. differences in carapace length between size 

 groups in the recruit class and their corresponding size 

 groups in the next moult class are approximately 12.7 

 mm or 14 to 15 percent, indicating the average 

 carapace linear increase. 



The 4-yr measurements (1949-50 to 1952-53) corres- 

 pond to the size distribution for the 1947-56 period 

 (Table 5). Therefore, it is assumed the total sample 

 covers enough years to eliminate significant differ- 

 ences in year class abundance. It appears probable 

 that percentage differences between 79.375 mm and 

 82.55 mm sizes and between 82.55 mm and 85.725 mm 

 represent true differences on the basis of average age 

 and survival. Declines between 85.725 mm and 88.9 

 mm are not considered definitive because of the obvi- 

 ous scatter at the upper end of the recruit maximum 

 size. Since these lobsters have been protected as sub- 

 legal lobsters during their previous year, it is assumed 

 that differences in relative numbers represent natural 

 or trap-induced mortalities at the equivalent of 3-mo 

 intervals between the premoult sublegal and the post- 

 moult legal sizes. Increased catchability characterizes 

 increases in size to about 4 in. carapace (101.6 mm).^ 



When numbers are converted to percentages of the 

 sample, it is evident that there is a consistent percent- 

 age reduction in the sample at 3.175 mm intervals 

 from the minimum to the maximum legal size, with 

 major declines at approximately 12.7 mm intervals. It 

 is assumed that the major declines represent separa- 

 tion between moult classes and that there are approx- 

 imately three and one-third moult classes within the 

 legal size range. 



The percentage composition of the recruit class 

 under the former minimum legal size (2Vs in. or 89.4 

 mm) is shown in Table 6. 



Since the typical lobster during this high- 

 temperature period moulted once each year, any dif- 

 ference among the first three 3.175 mm groups of the 

 recruit class is indicative of the mortality rate within 

 the class from sublegal to legal size. While a 12.7-mm 

 carapace difference amounts to a year's growth, a 

 3.175-mm difference represents the equivalent of one- 

 quarter of the moult increase or one-quarter of a year's 

 growth. The 9 percent decrease between 79.375 mm 

 and 82.55 mm and 7 percent decrease between 82.55 

 mm and 85.725 mm (Table 7) probably represent 9 and 

 7 percent mortality for the two size classes for one- 

 quarter of a year. The relationship suggests that an- 

 nual natural mortality for this age and size of lobster 

 during the period covered ranged from about 28 per- 

 cent to about 36 percent. Moult increment overlap be- 

 tween 88.9 mm and 92.075 mm size classes, by mask- 

 ing the moult group boundary, precludes the use of 

 declines from 85.725 mm to 88.9 mm sizes for mortal- 

 ity estimates. 



The decline in size frequency by percent shown in 

 Table 7 suggests the probable mortality rate by size 

 increments for the recruit class. 



During this period (lobster years 1949-50 to 1952-53) 

 average seawater temperature at Boothbay Harbor 

 was about 10.4°C, nearly one-half degree higher than 

 what appears to be the upper limit of the optimum 

 range but more favorable than, for example, the 7.3°C 

 average in 1967. 



Mortalities among captive lobsters have generally 

 been associated with moulting, particularly when 

 moulting occurs coincidentally with higher tempera- 

 tures. Predation and cannibalism under natural or 

 seminatural conditions have also been observed to be 

 greater at this time and appear to be related to greater 

 activity by both lobsters and their predators. Discard- 



