Size Composition, Sex Ratio, and Size 

 at Maturity of Offshore Northern Lobsters 



By 



BERNARD E. SKUD and HERBERT C. PERKINS, Fishery Biologists 



Bureau of Commercial Fisheries Biological Laboratory 

 W. Boothbay Harbor, Maine 04575 



ABSTRACT 



The fishery for northern lobsters, Homarus americanus , in the offshore waters 

 of the North Atlantic is developing rapidly and is expected to alter certain biological 

 characteristics of the stocks. Samples of lobsters have been taken during research 

 cruises and from commercial catches to document the existing size composition, 

 sex ratio, and size at maturity. These records will provide useful indices of popula- 

 tion changes as fishing effort increases. 



The data in this report are from five of the major fishing areas-- 

 Hudson, Veatch, Oceanographer, Lydonia, and Corsair Canyons. Lobsters from 

 canyons 200 km. from shore were substantially smaller than those from areas 

 farther offshore. The size of lobsters generally increased with depth and the propor- 

 tion of females generally increased with increasing size. Females dominated the 

 samples and sometimes were 70 percent of the catch. The numbers of egg -bearing 

 females are reported. The smallest female with external eggs was 8.0 cm. in car- 

 apace length. 



INTRODUCTION 



Landings of northern lobsters ( Homarus 

 americanus ) from the offshore trawl fishery 

 of the North Atlantic have been increasing 

 rapidly during the past 10 years. Otter trawls 

 took 484 metric tons of lobsters in 1958 and 

 over 2,500 metric tons in 1968. As the fishery 

 develops, it is important to document the 

 changes in the size composition and sex ratio 

 of the stocks. These data, together with catch 

 and effort statistics, will be needed to assess 

 the effect of fishing on the abundance of off- 

 shore lobsters. Sampling of the catch was too 

 limited in earlier years to detect changes in 

 population structure. During the past 3 years, 

 however, sampling of commercial landings 

 and of catches from research cruises has been 

 more extensive and has provided information 

 by fishing area that will be a base for future 

 comparison. 



The early history of the offshore fishery was 

 described by Firth(1940) andSchroeder (1959). 

 The first reports of lobsters caught by trawling 

 date back to the early 1900's, when beam and 

 otter trawls were introduced to American 

 waters. These lobsters were incidental catches 

 in the fisheries for various groundfish. Inci- 

 dental catches continue but usually are not 



included in the catch statistics of the lobster 

 fishery. The earliest otter trawl catch of 

 lobsters that is recorded was 4 metric tons 

 landed in New York in 1921; the exact location 

 of the catch is unknown. Even through I960, 

 little information was gathered on the location 

 of the offshore catches. 



Statistics of the Bureau of Commercial 

 Fisheries do not separate inshore and off- 

 shore catches of lobsters; however, practically 

 all of the fishing inshore is done with pots 

 whereas otter trawls are used offshore. Trawl 

 catches from the New England region to the 

 Chesapeake date back to the late 1920's; and 

 though a few inshore catches are included, 

 these data serve to document the increase in 

 offshore landings that has occurred over the 

 years and show that these catches remained 

 less than 45 metric tons annually through 1 946. 

 Skud (in press) described the increased catches 

 of recent years. From 1947, the landings 

 increased steadily and approached 500 metric 

 tons for the first time in 1955 (table 1). This 

 growth continued and the peak offshore land- 

 ing--2,500 metric tons in 1968--accounted 

 for 16.9 percent of the total U.S. catch of 

 lobsters. Landings from the offshore fishery 

 contribute substantially to the total landings in 

 Massachusetts, Rhode Island, New York, and 



