NATURAL HISTORY OF AMERICAN LOBSTER. 
183 
or about io° lower than the average at Woods Hole at a corresponding period. A station 
in that part of the sound which showed in August a bottom temperature of 55 0 (60.3° 
at surface) gave in March 36.7° (at the surface 37. 4 0 ). 
The temperature of the surface water of Winter Quarter Shoal, Virginia, ranges 
from 35 0 to 76° F. ; at Five Fathom Bank, New Jersey, the range is 37 0 to 76°. Dela- 
ware Breakwater, which at one time was practically the southern limit of the lobster, 
is situated between the lightships anchored upon these two shoals. In the Gulf of 
Maine the mean annual range is approximately 32 0 to 62°, while at some points the 
maximum is only 54 0 . ( 228 .) 
The average temperature on the north shore of Prince Edward Island has been given 
as 56.56° in June, 63.40° in July, and 62.27° i n August, the bottom temperature in 
6 to 8 fathoms being estimated at 55°. 
The temperature of the sea on the Labrador coast is said not to exceed 46.05° F. 
on the warmest summer days. The lobster thus seems to be debarred from this coast 
east of the straits of Belle Isle by the Arctic current and the lingering ice. 
From the facts given above we may infer that the optimum temperature of the 
lobster lies between 50° and 60° F. When the temperature of the sea water marks 
from 50° to 55° in spring large numbers of these animals have already begun to creep 
nearer the shores into shallower and warmer places, and again in fall, when the tempera- 
ture has fallen to this point, many have already been impelled to recede to greater 
depths. Many lobsters, however, remain in the relatively shallow water of harbors all 
winter, a fact already emphasized; so it is certain that temperature is not the only 
influence at work in directing these semiannual movements. The question of food 
or nature of the bottom may at times be of equal or of even greater importance. 
The lobster, like many other marine invertebrates, is very sensitive to the extremes of 
heat and cold. If exposed to direct sunlight out of the water, or to the nipping air of a 
winter’s day, it weakens or succumbs in a short time. On the other hand, if packed in 
seaweed with ice it will live for days or weeks, a fact daily illustrated in the transporta- 
tion of this crustacean alive to inland markets far from the coast. (See p. 176.) 
Lobsters which pass the winter in relatively shallow water often seek protection 
by burrowing in the mud, as usually happens when they are confined in pounds. In 
such cases a long period of severe cold may prove fatal. On March 10, 1882, a number 
of lobsters were taken through the ice by the scoop of a mud-digging machine off the 
coast of Prince Edward Island. They were said to be sluggish but not torpid. 
INFLUENCE OF LIGHT AND NOCTURNAL HABITS. 
The lobster is essentially an animal of the twilight, and in its semiadult and adult 
condition explores the bottom in quest of food mainly after sundown or at night, when 
it is generally far more active than by day. This may be proved by anyone who 
watches its behavior when confined in either lobster cars or pounds. These animals 
it is true on occasion move about by day, but at night they become exceptionally rest- 
less. It is probable that the eggs are laid and that pairing takes place as a rule under 
