Migration and Dispersion of 



Tagged American Lobsters, Homarus americanus, on 



the Southern New England Continental Shelf 



JOSEPH R. UZMANN, RICHARD A. COOPER, and KENNETH J. PECCI ' 



ABSTRACT 



An apparently contiguous stock of American lobsters, Homarus americanus, is concentrated 

 along the outer continental shelf margin and slope from Corsair Canyon westward and southward to 

 the region of Baltimore Canyon. Between April 1968 and May 1971 we captured, tagged, and released a 

 total of 7,326 lobsters at 52 localities between Corsair Canyon and Baltimore Canyon. As of December 

 1972, 945 recaptures (12.9% recovery) had been reported, providing a basis for interpretation of 

 seasonal and long-term movements, as well as measurements of growth rate and moult frequency. A 

 classification scheme is developed and applied to distinguish between apparently directed seasonal 

 movements (migrations), localized movements of less than 10 nautical miles (18.5 km), and long- 

 period (>120 days) dispersions of 10 miles or more. This last category includes point to point tracks 

 that cannot be objectively resolved in terms of directionality and may represent random dispersal, a 

 summation of seasonally directed tracks, or both. 



We conclude from the track analyses that at least 20% of the offshore lobsters annually engage in 

 directed shoalward migrations in spring and summer with return to the shelf margin and slope in fall 

 and winter. This conclusion is reinforced by independent analysis of the time/depth/temperature 

 associations of tagged lobsters at recapture which, of itself, suggests that an even larger proportion of 

 the offshore lobsters annually effect directed migrations in response to seasonal temperature 

 variations. 



INTRODUCTION 



Commercial concentrations of American lobsters, 

 Homarus americanus, inhabit the outer continental shelf 

 and slope off southern New England and the Middle 

 Atlantic states southward to Virginia. The history, 

 development, and recent status of this resource have 

 been summarized in the collective studies of Firth 

 (1940), Schroeder (1955, 1959), McRae (1960), Hughes 

 (1963), Saila and Flowers (1968), Skud and Perkins 

 (1969), Uzmann (1970), and Cooper and Uzmann (1971). 

 This report is an extension of the last mentioned paper 

 and deals further with findings and implications of 

 seasonal and long-term movements derived from an ex- 

 tensive tagging program conducted over the period 1968- 

 72. 



Schroeder (1959) defined the offshore lobster popula- 

 tion as "a population of lobsters, large enough to support 

 commercial fishing off the east coast of the United States 

 along the outer shelf and upper slope between the eastern 

 part of Georges Bank and the offing of Delaware Bay. 

 This area at depths of roughly 60-250 fm (110-450 m) is 

 about 400 miles long and 5-10 miles wide. Lobsters are 

 more plentiful along the eastern half of this stretch than 

 to the west and south." 



The offshore lobster fishery, so-called, has rapidly 

 assumed a role of prominence among the major offshore 



'Northeast Fisheries Center, National Marine Fisheries Service, 

 NOAA, Woods Hole, MA 02543. 



fisheries of the northwest Atlantic. A brief review of its 

 growth over the past two decades will place it in perspec- 

 tive relative to the long established coastal fishery and 

 indicate its future trend. 



Like the coastal stocks from Maine to New Jersey, the 

 offshore stock has sustained a steadily increasing rate of 

 exploitation since the mid-fifties prior to which time it 

 ranked as a minor fishery with the majority of catches 

 taken incidental to trawling for groundfish species. 

 Following World War II, the coastal fishery expanded 

 rapidly to a peak yield in 1960 of 29 million pounds (13.2 

 million kg) and has since declined measurably despite 

 increased fishing effort; meanwhile, offshore lobster 

 catches increased from nearly 2 million pounds (0.9 

 million kg) in 1960 to over 8 million pounds (3.6 million 

 kg) in 1970. Ungrouped landings statistics indicate that 

 U.S. lobster production is relatively stable at some 30 

 million pounds (13.6 million kg) annually, but the fact of 

 the matter is that offshore production has annually offset 

 the decline of coastal landings. From 1968 to 1970 

 offshore lobster landings averaged over 20% of the U.S. 

 catch. 



MATERIALS AND METHODS 



The tagging program reported here was conducted as 

 part of the work plan of 14 research cruises over the 

 period 1968-71 during which time a total of 7,326 lobsters 

 were tagged and released at 52 localities along the outer 

 edge of the continental shelf from Corsair Canyon west 



