MATURITY, SEX RATIO, AND SIZE COMPOSITION OF THE NATURAL 

 POPULATION OF AMERICAN LOBSTER, HOMARUS AMERICANUS, 



ALONG THE MAINE COAST' 



Jay S. Krouse^ 



ABSTRACT 



From 1968 through 1970, American lobsters, Homarus americanus, were collected in 

 coastal water near Boothbav Harbor, Maine. Length-frequency histograms graphically 

 displayed the marked effects of high commercial exploitation on the natural lobster 

 population. Sex ratios approximated a 1:1 relationship for sublegal lobsters (Maine 

 minimum size is 81-mm carapace length). Length-weight relationship was determined 

 for 454 lobsters. Shedding was observed to begin in spring and then peak in late summer. 

 On the basis of ovarian classification, presence of spermatophores in seminal recep- 

 tacles, length-frequency distribution of berried females, and morphometric measurements, 

 nearly all females above 100-mm carapace length were assumed to be mature, whereas 

 only a few females between 81- to 90-mm carapace length were mature. Examination 

 of male gonads suggested that male lobsters began maturing at relatively small sizes 

 (50% mature at about 44-mm carapace length). 



The American lobster, Homarus americanus 

 Milne Edwards, is one of the most valuable and 

 heavily exploited commercial species occurring 

 along the Maine coast. Recognizing the urgent 

 need for biological management of this inshore 

 fishery, the Maine Department of Sea and Shore 

 Fisheries initiated the Lobster Research Pro- 

 gram in April 1966. The two primary phases 

 of this program have encompassed: 1) proba- 

 bility sampling of the commercial lobster fishery 

 along the entire Maine coast and 2) collection 

 of prerecruit and legal-sized lobsters (minimum 

 size in Maine is now 81-mm carapace length) 

 near Boothbay Harbor, Maine (this phase began 

 in March 1968). With data from these two in- 

 dependent sampling schemes, various popula- 

 tion parameters have been calculated and then 

 ultimately employed to estimate the minimum 



' This study was conducted in cooperation with the 

 U.S. Department of Commerce, National Marine Fish- 

 eries Service, under Public Law 88-309, as amended. 

 Commercial Fisheries Research and Development Act, 

 Project 3-14-R. 



* Maine Department of Sea and Shore Fisheries, West 

 Boothbay Harbor, ME 04575. 



size limit for maximum sustainable yield (Thom- 

 as, 1971).'' 



The objectives of this paper, which are based 

 upon data collections of the natural lobster pop- 

 ulation from Boothbay Harbor, are concerned 

 with: 1) sex ratios; 2) incidence of molting; 

 3) length-weight relationship; 4) size compo- 

 sition of catch; and 5) the size at first sexual 

 maturity for both sexes. 



METHODS AND MATERIALS 



Lobsters v/ere collected in coastal waters near 

 Boothbay Harbor, Maine, from April 1968 

 through December 1970. The following types 

 of gear were used : ( 1 ) rectangular vinyl-coated 

 lobster traps (1- X 2-inch and 1- X 1-inch 

 mesh) ; (2) elliptical polyethylene lobster traps; 

 (3) conventional wooden lobster traps; (4) a 



Manuscript accepted July 1972. 



FISHERY BULLETIN: VOL. 71. NO. 1, 1973. 



" Thomas, J. C. 1971. An analysis of the commercial 

 lobster (Homarus americanus) fishery along the coast 

 of Maine, August 1966 through December 1970. Un- 

 published manuscript, 73 p. Maine Department of Sea 

 and Shore Fisheries, Completion Report. 



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