KROUSE: SIZE OF AMERICAN LOBSTERS 



Stage of 

 development 



immature 



developing 



mature 



Ovary color 



translucent white 

 yellow-orange 

 dark green 



Egg diameter 

 (mm,) 



^ 0.4 



0.5-0.7 

 ^ 0.8 



Two additional determinations were made for 

 each female: 1) width of the second abdominal 

 segment (distance between deepest part of 

 pleura on ventral surface) and 2) examination 

 of the seminal receptacle (structure where sperm 

 is stored upon copulation until egg extrusion) 

 for the presence of sperm. As a check on my 

 technique for detecting spermatophores, I ex- 

 amined 31 berried lobsters from Canada and 

 found sperm in all of them. 



In conjunction with the annual berried female 

 program, during which the State of Maine pur- 

 chases from the pound owners lobsters that have 

 become ovigerous while in captivity, carapace 

 lengths were recorded for 1,150 berried females. ° 

 These data were obtained during the period 1966 

 through 1970. 



RESULTS AND DISCUSSION 



SEX RATIOS 



Sex ratios were analyzed by assigning lobsters 

 from catches during the period 1968 through 

 1970 to 5-mm carapace length size groups by sex. 

 Midpoints of each size increment were then plot- 

 ted against the number of lobsters in each of the 

 respective size groups (Figure 3). Although 

 differences did exist between the proportion of 

 males to females within various size classes, these 

 differences were not consistent from year to year, 

 suggesting that they may have been artifacts 

 of sampling. In 1969 and 1970 when the catches 

 were relatively large (greater than 1,000 lob- 

 sters), the overall percentages of females were 

 48.1 and 50.3, respectively. While the sex ratio 

 approached 1: 1 in 1969 and 1970, in 1968, when 

 the sample size was half that of the other two 

 years, the proportion of females was 56.4%. 

 This disparity may best be attributed to the 

 smaller sample size in 1968. 



30 40 



60 70 80 90 100 

 CARAPACE LENGTH, MM 



110 



° Maine law prohibits the possession or sale of egg- 

 bearing female lobsters. 



Figure 3. — Number of male and female lobsters grouped 

 by 5-mm size classes from Boothbay Harbor, 1968 through 

 1970. 



As the samples were predominantly composed 

 of sublegal lobsters, our estimate of approxi- 

 mately a 1:1 sex ratio suggests that immature 

 female and mature male lobsters have similar 

 molting frequencies and increments of growth. 

 In contrast to this, Herrick (1911), Templeman 

 (1939), and Wilder (1953) have demonstrated 

 that most sexually mature males molt annually 

 and mature females every other year. In a 

 tagging study conducted off Monhegan Island, 

 Maine, Cooper (1970) found no significant dif- 

 ferences in growth increments of male and 

 female lobsters (average carapace length of 

 90 mm). Unlike the Maine findings, studies by 

 Wilder (1963) in Egmont Bay, Prince Edward 

 Island, and Squires (1970) and Ennis (1972) 

 off Newfoundland revealed larger increments 

 of gro\\i:h for males than females for sizes above 

 about 65-mm carapace length. Based on the 

 maturity work of Templeman (1944), female 

 lobsters from the aforementioned Canadian 



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