KROUSE: SIZE OF AMERICAN LOBSTERS 



SIZE AT MATURITY 



40 



50 



60 70 -^ 80 



CARAPACE LENGTH, MM 



90 



100 



Figure 5. — Annual length-frequency distributions of 

 lobsters sampled near Boothbay Harbor, 1968 through 

 1970. 



in the Boothbay Harbor area, SCUBA divers 

 have observed lobsters of less than 40-mm car- 

 apace length to be virtually inactive during noc- 

 turnal periods and apparently passing most of 

 their early life within subterranean burrows 

 (Richard A. Cooper, pers. comm.). 



Sharp reductions in the number of lobsters 

 above the minimum legal size (81-mm carapace 

 length) reflected the influence of commercial 

 exploitation. The legal-sized lobsters composed 

 only 6 to 99f by number of the three annual 

 catches. 



For each annual length-frequency distribution, 

 I attempted to select, on an objective basis, modes 

 representative of assumed age or molt groups by 

 analyzing the polymodal frequency distributions 

 graphically with probability paper (Harding, 

 1949). Unfortunately, I discovered that I could 

 not pick meaningful age or molt group modes 

 due primarily to the limited size range (70- to 

 80-mm carapace length) over which our samples 

 were considered to be representative of the nat- 

 ural lobster population. Since the increment 

 of a lobster's growth was assumed to be about 

 a 13 to 14 S^ increase in carapace length (Wilder, 

 1953), it became apparent that our represen- 

 tative size range of 70- to 80-mm carapace length 

 contained, at best, only one mode or possibly 

 more if an age class experienced diff"erential 

 growth. 



Males 



In the Boothbay Harbor area, 50 Sr of the male 

 lobsters sampled were sexually mature at about 

 44-mm carapace length (Figure 6). The smallest 

 mature male was 41-mm carapace length. Al- 

 though sample size was limited for lobsters 

 smaller than 45-mm carapace length, I do not 

 believe that this significantly aff"ected our con- 

 clusions. 



30 



40 



50 



5 60 5 70 T 60 

 CARAPACE LENGTH. MM 



90 



Figure 6. — Percentage frequency of mature male lobsters 

 by 5-mm size classes. 



In this study, maturity was solely based upon 

 the criterion of presence or absence of sperm 

 cells. Therefore, even though a lobster might 

 appear to be physically mature (possessed sperm 

 cells) , this particular individual might be incap- 

 able of successfully copulating with a female. 

 In mating experiments, Templeman (1934) ob- 

 served that male lobsters were unable to mate 

 with considerably larger females. In fact, the 

 success of mating was greatest when the males 

 were slightly larger than the females. As most 

 females in the Boothbay Harbor area mature 

 above the minimum legal size of 81-mm carapace 

 length (discussed in following section), it ap- 

 pears that prerecruit males seldom contribute 

 reproductively to the natural population. 



169 



