1 82 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" (749, p. 19), may be an error, as Appell6f 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 'traveUng 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 bott om- 

 feeding animal s 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, whgn^ 

 other conditions are favorable, growth is most rapid, and those dependent processes of 

 reproduction and exuviation most accelerated. The data available, howevejr, d^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 accotmt the following facts have been gathered. 

 The temperature of sea water at Woods Hole for May ranges from 50° to 60° 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°- 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°, 



o 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. 



