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Fishery Bulletin 95(3), 1997 
port with their finding that through random or di- 
rected movements (or both), the offshore lobster popu- 
lation maintains itself within temperatures of 8°- 
14°C. Cooper and Uzmann (1971) hypothesized that 
seasonal shoalward migration to warmer water com- 
pensates for a lack of sufficiently high temperature 
during summer in the continental slope habitat to 
permit extrusion and hatching of eggs and subse- 
quent molting and mating. They found that offshore 
lobsters that demonstrated the most extensive on- 
shore migrations were predominately females and 
that the migration of offshore lobsters to inshore 
grounds is generally confined to areas south and west 
of Cape Cod (no recoveries were made north of Cape 
Cod in the Gulf of Maine proper). 
While diving to collect lobsters for tagging at sta- 
tion 1, we observed lobsters always to be concentrated 
in a narrow stratum where a thermocline intercepted 
the steeply sloping surfaces of a sandy escarpment 
paralleling the beach in that area, about 1.8 km from 
shore. Morrissey 7 conducted semiweekly SCUBA 
surveys throughout the summer of 1966 at Province- 
town, where station 1 is located, and found lobsters 
only in close proximity to the thermocline-sediment 
interface, which occurred at 24 m in late May and 
ranged between 9 and 19 m during June, July, and 
August. During a vertical transect along the bottom 
from the shoreline to a depth of 22 m, 14 July 1966, 
15 of 16 lobsters observed were within a stratum ( 11 
to 14 m) in which a bathythermograph cast showed 
a change of 12.8°C in water temperature. On the basis 
of observed activity of individual lobsters, he con- 
cluded that the lobsters were not concentrated by a 
thermal block but rather were attracted to the 
warmer epilimnion layer and used the reduced light 
intensity associated with the thermocline as cover. 
These observations support the conclusion of Coo- 
per and Uzmann (1971) and Uzmann et al. (1977) 
that offshore lobsters orient to optimum temperature. 
Our test results indicated that sublegal and legal- 
size females with no eggs moved significantly less 
than egg-bearing female groups. An explanation for 
why legal-size females without eggs move less than 
those with eggs may be that they tend to congregate 
in the warmer shoal water where egg extrusion oc- 
curs. During this study, three tagged females, which 
extruded eggs after tagging, moved only an average 
distance of 4.2 km before recovery. Although this 
sample size is small, the inference from it is sup- 
ported by fishing activity in this area. Fishermen 
7 Morrissey, T. D. 1970. Observations on behavior of the Ameri- 
can lobster, Homarus americanus, at Provincetown, Massachu- 
setts during the summer of 1966. MA Div. Mar. Fish., 50 A 
Portside Drive, Pocasset, MA 02559. 
report concentrations of females with immature eggs 
in the shoals east of Cape Cod during August and 
September. 
The fact that tagged inshore female lobsters with 
ripe external eggs moved greater distances than other 
classes of tagged lobsters may be a verification of 
the findings of Cooper and Uzmann (1971), that off- 
shore lobsters demonstrating the most extensive in- 
shore migrations are predominantly female. How- 
ever, unlike Cooper and Uzmann (1971), our recov- 
eries indicate that lobster migration occurs north of 
Cape Cod into at least the southwestern portion of 
the Gulf of Maine with one recovery made as far 
north as latitude 42°39'. Our subsequent tagging 
work in this study area (1984-85) yielded the return 
of a female after 362 days at large from even farther 
north, 43°33' (off Cape Elizabeth, Maine). 4 
None of our lobsters were recovered in the inshore 
grounds south and southwest of Cape Cod where 
most of the inshore recoveries were made by Cooper 
and Uzmann. The distribution of recapture points of 
the 58 lobsters recovered after their first season of 
release (Table 4) suggests that our inshore tagged 
lobsters returned to the shoal waters along eastern 
Massachusetts in successive summers. 
The movement described by the findings of Coo- 
per and Uzmann (1971) suggests that offshore lob- 
sters migrate to secure more suitable hydrographic 
conditions. The areas involved, i.e. the edge of the 
continental shelf and shoaler waters extending into 
inshore grounds south and west of Cape Cod, are 
quite generalized. The apparent return of our inshore 
tagged lobsters to the eastern shore of Massachu- 
setts in successive summers, and the greater move- 
ment shown by females with ripe eggs at tagging, 
suggest that the migration of offshore lobsters may 
be anastrophic or gametic (Heape, 1931; Wilkinson, 
1952) in character, i.e. nonrandom, stimulated by 
metabolic needs or reproductive cues. Campbell 
(1986) provided calculations that suggest ovigerous 
lobster need to make seasonal deep-shallow water 
migrations to obtain sufficient heat units for egg de- 
velopment within any 9-12 month period. Using a 
threshold temperature of 3.4°C, he determined that 
shallow water had more degree days than deeper 
water in summer months and that the reverse was 
true in winter months. 
Although significant American lobster migrations 
have been reported, Saila and Flowers (1968) pro- 
vided the first reference in the literature to long-dis- 
tance homing by this species. They found a pro- 
nounced directional tendency toward the original 
area of capture in the movements of berried female 
lobsters transplanted from Veatch Canyon on the 
edge of the continental shelf to Narragansestt Bay, 
