Estrella and Morrissey: Seasonal movement of Homarus americanus 
467 
The continued development of the offshore fishery 
has subjected American lobster in all remaining seg- 
ments of its range to intensive exploitation. Thus, 
stock identification and determination of any inter- 
relations between stocks of lobsters is of increasing 
importance to management of the lobster fishery 
(Pezzack 3 ). Earlier studies indicated that lobsters 
were relatively nonmigratory. Numerous tagging 
experiments conducted primarily in more northern 
inshore areas showed that most lobsters usually re- 
main within a radius of 3-5 km (Templeman, 1935, 
1940; Wilder and Murray, 1958; Wilder, 1963; Coo- 
per, 1970; Cooper et al., 1975; Krouse, 1980; Stasko, 
1980; Campbell, 1982; Lawton et al., 1984). Accord- 
ingly, management practices were based largely on 
the concept of discrete local stocks. Findings of ex- 
tensive lobster movement in tagging experiments 
conducted in offshore areas (Saila and Flowers, 1968; 
Cooper and Uzmann, 1971, 1980; Uzmann et al., 
1977; Fogarty et al., 1980; Campbell et al,. 1984) and 
in more southern inshore areas (Morrissey, 1971; 
Briggs and Muschacke, 1984) show significant move- 
ment of large, sexually mature lobsters which be- 
come intermixed with the inshore resource. Thus, the 
concept of discrete inshore stocks, characterized by 
a particular size range or maturity status (Camp- 
bell and Stasko, 1986; Campbell, 1989) becomes 
speculative. 
Intermingling of offshore lobsters with inshore 
stocks off southern New England is shown from re- 
captures of offshore-tagged lobsters in inshore areas. 
Cooper and Uzmann (1971, 1980) and Campbell 
(1986) hypothesized that seasonal depth-related 
movements are important to the biology of the spe- 
cies in providing optimal temperatures for mating, 
molting, egg extrusion, and egg development. 
In an effort to obtain information that would aug- 
ment offshore tagging studies off the Massachusetts 
coast, we undertook a three-year tagging experiment 
beginning in 1969 in the inshore waters of Cape Cod 
where previous work (Morrissey, 1971) showed the 
existence of a seasonal population of large, highly 
mobile lobsters. Additional lobster tagging in this 
area in 1984-85 also confirmed highly migratory 
behavior. 4 
Estrella and McKiernan (1989) described the ex- 
tensive size range of this segment of the lobster re- 
source, which is only seasonally available east of 
Cape Cod, as characteristic of an offshore migrant 
3 Pezzack, D. S. 1987. Lobster ( Homarus americanus) stock- 
structure in the Gulf of Maine. Int. Counc. Explor. Sea. Shell- 
fish Comm. Council Meeting 1987/K:17, 18 p. 
4 Estrella, B. T. 1997. American lobster tagging studies conducted 
in Massachusetts coastal waters. MA Div. Mar. Fish. In prep. 
group. This area exhibits the smallest percentage of 
sublegal-size lobsters in commercial trap catches of 
any other Massachusetts coastal region (10% com- 
pared with 89% in waters off Boston, MA, in 1995 5 ). 
Catch per trap haul of sublegal-size lobster off outer 
Cape Cod was four to eight times lower than that for 
other Massachusetts coastal regions sampled in 1994 
(Estrella and Armstrong 2 ). Outer Cape Cod habitat 
is not “classic” lobster habitat conducive to support- 
ing a resident (burrowed) resource; it is character- 
ized by expansive sandy bottom and is dynamic ow- 
ing to its exposure to strong easterly winds. Some 
local lobster production apparently occurs in the 
Nauset Marsh area of outer Cape Cod where limited 
numbers of early benthic-phase lobster have been 
found (Able et al., 1988). However, it is the larger, 
more common, offshore migrant lobster which sup- 
ports the commercial fishermen in this area and 
which shapes the style of fishing deployed there. Long 
strings of traps are set parallel to the shoreline to 
intercept incoming migrations each season. In late 
spring, traps are initially set by day-boat lobstermen 
approximately thirteen miles from shore. This gear 
is gradually fished shoalward as migrations proceed 
closer to land in warmer months, until declining au- 
tumn temperatures reverse the trend. 
It is informative that the intense outer Cape Cod 
lobster fishery has not been successful in reducing 
the size structure of this resource as definitively as 
in other inshore Massachusetts regions. A greater 
number of size-age groups are represented in outer 
Cape Cod catches. In most other inshore areas, lob- 
sters exhibit minimal migration and are exposed to 
fishing pressure throughout the year. New recruits 
(lobsters which, upon molting, become legal size) may 
represent as much as 95% of the legal catch, com- 
pared with only 55% in the outer Cape Cod area. The 
seasonal occurrence of these offshore lobsters in the 
outer Cape Cod area thus limits their exposure to 
intense fishing pressure. 
The size structure of this portion of the resource is 
similar to that from southern Georges Bank. Accord- 
ingly, the Sixteenth Northeast Regional Stock Assess- 
ment Workshop (16th SAW) of NMFS assigned this 
migratory group of lobsters to the Georges Bank- 
Southern Offshore stock unit (NEFSC, 1993). 
Estrella and McKiernan (1989) discussed the ge- 
ography as a potential factor in concentrating 
migrants. The outer Cape Cod area is adjacent to 
steeply sloping gradients which lead to a much 
greater depth range than that found in most other 
inshore regions. 
5 Estrella, B. T. 1997. Massachusetts Division of Marine Fisher- 
ies, 50 A Portside Drive, Pocasset, MA 02559. Unpubl. data. 
