3oo 



BULLETIN OF THE BUREAU OP FISHERIES. 



females in shallow water during the maximum spawning season (March, April, and 

 May) and the increase in the number of large females in shallow water after the hatch- 

 ing season is over and the molting period of the females has begun (June, July, and 



August) . 



Table i.— Summary ok Catches of Spiny Lobster Taken in Three Traps, March to August, 



1919. 



Month. 



March 

 April. 

 May. . 



Females. 



Ratio of 

 females 

 to males. 



0.45 

 .26 

 •17 



The numbers of individuals involved in these data are small, butthecatches brought 

 into the markets at Key West were observed and the relative numbers of females to 

 males were approximately the same as given in the table. 



It is not evident that there are migrations parallel to the coast. Traps set offshore 

 at various depths always take spiny lobsters regardless of the directions of the openings. 

 Places known to be depleted from overfishing are not repopulated in a short time, which 

 it seems reasonable to suppose would be the case if migrations occurred parallel to the 

 coast. Migrations occur from deep to shallow water and back again to deep water. 



Large numbers of spiny lobsters come into shallow water at times, apparently for 

 the purpose of feeding. These constitute a type not usually found in such places, and 

 they can be distinguished by their size and color, since they are larger and darker than 

 those usually found in shallow water. The causes for this migration are obscure, but 

 the changes in the temperature of the water probably are a determining factor. 



INFLUENCE OF CHANGES IN TEMPERATURE. 



Changes in temperature of the shallow water about Key West are often great and 

 occur abruptly. The direction of the wind and condition of the weather account for 

 these changes, and their influence upon the sizes of the catches of spiny lobsters is marked. 



It is well known among the fishermen that the spiny lobsters are more abundant 

 in shallow water after gales than during long continued calm spells. Closer observation 

 has shown that when the wind blows from the sea more of them are taken in traps set 

 off a lee shore, or the shore upon which the wind is blowing, than in traps set in the 

 shelter of small islands or banks. It has also been observed that the catches are smaller 

 when the wind blows from the shore. 



The fluctuations in the abundance of spiny lobsters in shallow water at various times 

 can be explained as follows. Sea winds cause the water to move shoreward, and as this 

 water is generally cooler than that over the shallow banks it causes a temporary fall in 

 the temperature of the shallow water. Conditions in shallow water then approach the 

 conditions found in deeper water and spiny lobsters come into shallow water while 

 feeding. Continued offshore winds tend to drive the water from the shallow banks, 

 and thus prevent the cooling of the shallow water offshore. The spiny lobsters do not 

 come into shallow water, because the temperature is excessive. The temperature of 

 the shallow water rises rapidly during calm weather, and few spiny lobsters are caught. 



