KREKORIAN, SOMMERVILLE, and FORD: LOBSTER BEHAVIORAL INTERACTIONS 



observed within 30 cm of the wall 13 times more 

 frequently than it was observed away from the 

 wall (Table 7). 



Table 7, — The total number ofPanulirus interruptus within 30 

 cm of the wall during the precontrol (Homarus absent), experi- 

 mental (Homarus present), and postcontrol (Homarus absent) 

 periods for the no shelter condition. The maximum number of 

 positions (wall + no wall) for each group during each period was 

 2,250. Values for the experimental period are one-half the 

 10-day total so that the totals shown for the three periods are 

 comparable. 



control observation periods for the number of 

 P. interruptus observed in shelters (P > 0.05, 

 Kruskal-Wallis One-Way Analysis of Variance by 

 Ranks). 



Table 8, — The total number ofPanulirus interruptus in shelters 

 or within 30 cm of the wall during the precontrol (Homarus 

 absent), experimental (Homarus present) and postcontrol 

 (Homarus absent) periods for the shelter condition. The max- 

 imum number of positions (shelter + wall -i- no wall) for each 

 group during each period was 2,250. Values for the experimental 

 period are one-half the 10-day total so that the totals shown for 



During the experimental observation period 

 (Homarus present) P. interruptus was usually 

 found in the center of the tank (no wall). 

 Four of the five groups were observed more fre- 

 quently in the center of the tank than within 30 

 cm from the wall. Only Group 5 was observed 

 near the wall more frequently than in the 

 center. However, Group 5 spent less time near the 

 wall during the experimental period than in the 

 precontrol period. 



During the postcontrol period, four out of five 

 groups were observed within 30 cm of the wall 

 more frequently than in the center (Table 7). 

 Group 2 spent approximately twice as much time 

 in the center than within 30 cm of the wall. 



The wall-no wall distribution of P. interruptus 

 during the three observation periods was signifi- 

 cantly different (P = 0.009, Kruskal-Wallis 

 One- Way Analysis of Variance by Ranks). The 

 sums of ranks for the three observation periods 

 were: precontrol 59, experimental 19, and post- 

 control 42. These sums of ranks indicate that the 

 differences are between the experimental and 

 control periods. There were no significant dif- 

 ferences between the precontrol and postcontrol 

 periods (P > 0.05, Mann-Whitney U test; Siegel, 

 1956). 



Homarus vs. Ponulirus with Shelter 



In the shelter condition individuals of all five 

 groups spent most of their time in the shelters 

 (Table 8). There were no significant differences 

 between the precontrol, experimental, and post- 



The wall-no wall distribution of P. interruptus 

 for the three observation periods also was not 

 significantly different (Table 8; P > 0.05, Kru- 

 skal-Wallis One-Way Analysis of Variance 

 by Ranks). The greatest number of P. inter- 

 ruptus found outside the shelters (wall and no 

 wall condition) occurred during the 1510-1700 

 h observation period. 



Fanulirus vs. Cancer with No Shelter 



During the precontrol, experimental, and post- 

 control periods, individuals of all five groups of 

 P. interruptus were observed within 30 cm of the 

 wall much more frequently than in positions 30 

 cm away from the wall (Table 6). The groups 

 were observed near the wall from approximately 

 3 (Group 2 postcontrol) to 332 (Group 1, post- 

 control) times more frequently than away from 

 the wall. Group 1 spent nearly all its time near 

 the wall during the postcontrol period. There 

 were no significant differences in the number of 

 lobsters found near the wall for the three periods 

 (P > 0.05, Kruskal-Wallis One-Way Analysis of 

 Variance by Ranks). 



Discussion of Lobster 

 Distribution and Locomotion 



The effect of the presence of H. americanus 

 on the distribution of P. interruptus in a tank 

 without shelter is quite evident. Homarus ameri- 

 canus displaced P. interruptus from its preferred 



1157 



