tracked sonlcally often traveled westward unto the sand-algal plain up to 300 m 

 from their den and returned before dawn (Clifton, et al, 1970), Nearly half 

 (487o) of the lobsters observed to leave a den returned to either the original 

 den or one of the other monitored dens. The earliest return was at about 2300 

 hours, only two hours after the lobster left the den. Those moving out of the 

 den area returned between 0400 and 0700, augmenting the occasional observation 

 of eastward traveling lobsters in the immediately pre-dawn hours. 



Homing behavior, documented by successive day and night monitoring of dens, was 

 further characterized by sonic tracking using spontaneous and displacement 

 techniques. In spontaneous studies, a lobster was tagged during the day and 

 returned to its den, then monitored by tracking gun during the night period to 

 determine its typical nocturnal behavior (Clifton, et al, 1970). Most frequently 

 active lobsters, i.e., those that left a den, moved out onto the sand-algal flat 

 where they presumably fed, then returned to the reef. On TEKTITE I and 

 mission 2-50 of TEKTITE II, such lobsters were observed to return by direct 

 routs; at least one followed a similar path on several consecutive nights. This 

 suggests a formidable orientation mechanism and familiarity with the region. 



The latter hypothesis was further tested by displacement studies in which a 

 tagged lobster was carried to a point on the sand-algal plain about 200 m from 

 the den and some 70 m from the nearest portion of the reef. Eight lobsters 

 tested on 13 runs demonstrated homing ability as follows: 



1. Six of the eight returned to either the original den (3 lobsters on 



3 runs) or to a den proximal to one of the main dens (6 lobsters on 8 runs) by 

 the following morning. 



2. Two lobsters took up bearings in a beeline toward the site of capture 

 but one could not be located thereafter and the other proceeded past the main 

 den area and was subsequently found at Cabritte Horn Point. 



Typically, lobsters released during the day either headed directly to the reef 

 where they withdrew in a convenient crevice until dark or moved in a random 

 direction, becoming quiescent in a shallow depression. Resumption of movement 

 and actual homing occurred after dark for all those monitored during the appro- 

 priate periods. Hence, the orientation occurs during the period of lowest 

 visibility suggesting a non-visual mechanism. Indeed, two lobsters tested with 

 opaque tape over the entire eye and eyestalk showed direct orientation toward 

 the capture site and one was relocated the next morning within 30 m of the point 

 of capture. The other lobster was tracked to the reef edge but could not be 

 relocated later in the evening. 



Regardless of the mechanism(s) involved, the lobsters demonstrated a strong 

 preference for a home region, efficient orientation, and an apparent familiarity 

 of spatial reference throughout the study area. 



While some portion of the population apparently remained in the study area for 

 periods of a few days to several months, others were observed only once and 



VI-51 



