182 
BULLETIN OF THE BUREAU OF FISHERIES. 
under certain conditions not at present completely understood, movements of a somewhat 
different character may take place. The “traveling lobsters” of Sars probably belong 
to this category, and my former suggestion that they might represent “some large 
species of surface-feeding shrimp” (149, p. 19), may be an error, as Appellof asserts. 
Sars’s account, if correctly translated, is somewhat ambiguous; it is as follows: “The 
hard-shell and ponderous lobster must always make an extra exertion in moving about, 
and its movements can therefore not be of long duration. People certainly talk of 
the ‘traveling lobsters’ (‘Faerd-hummer’) which are said to come from the open sea 
in large schools, and some even say that they have seen such schools many miles from 
the coasts moving about rapidly near the surface of the sea. If this is really so, I con- 
sider it as absolutely certain that these schools come from no very great distance, possibly 
from some of the elevated bottoms off the coast.” (No. 244, p. 675.) We consider it 
highly probable that the “swarms” referred to represent only more concentrated move- 
ments of the usual inshore character, the animals coming from elevated areas not hitherto 
discovered and fished. 
In general we conclude that since lobsters as a rule spawn in warming water the 
migratory impulse must be regarded as primarily correlated with the development of the 
reproductive organs, which periodically respond to a rising temperature. Incidentally 
the carriage of eggs, the abundance of food, and molting which occurs in the female 
shortly after the eggs are hatched, tend to disturb the regularity of these movements. 
OPTIMUM TEMPERATURE. 
While the question of food supply must be of paramount importance to all bottom- 
feeding animals like the lobster, the temperature of the water can hardly fail to exert 
some influence upon their movements. Whether there is a direct reflex response in 
the lobster to the warming waters of the shores in spring or not, it is a fact that it shows 
a marked tendency, as we have seen, to move shoreward at this time. Further, without 
any doubt, there is a certain optimum temperature, under the influence of which, when 
other conditions are favorable, growth is most rapid, and those dependent processes of 
reproduction and exuviation most accelerated. The data available, however, do not 
enable us to determine this point with much accuracy. 
The physical conditions of Woods Hole region have been made the subject of 
special study by Sumner,® from whose account the following facts have been gathered. 
The temperature of sea water at Woods Hole for May ranges from 50° to 6o° F. The 
warmest period extends from approximately July 12 to August 24 (which corresponds 
with the height of the spawning period of the lobster at this point), with a temperature 
of 70° to 71 0 . The September range of 69° to 65° is about the same as that for the first 
half of July. In the latter part of October the water cools to about the same tempera- 
ture it had reached during the first half of May. The lowest daily temperature, of about 
30°,is recorded for mid-February. The bottom temperature at the western end of Vine- 
yard Sound, at the period of maximum summer heat, was found by Sumner to be 60.2°, 
a Sumner, Francis B. An intensive study of the fauna and flora of a restricted area of sea bottom. Proceedings of the 
Fourth International Fishery Congress, Bulletin of the Bureau of Fisheries, voL xxvm, p. 1223-1264. Washington, 1910. 
