Assuming that dispersal and learned avoidance are the typical responses to 

 diver harassment, several implications consequential to population dynamics and 

 fisheries are suggested. First, such fishing pressure on a population by divers 

 using non-lethal capturing devices (hand, snare, etc), by which many lobsters 

 escape, would result in dispersal rather than total population decrease. The 

 effect would be to make subsequent location and capture more difficult. Second, 

 one might postulate that diver harassment mimics predator pressure. Thus, heavy 

 natural predation might be indicated by a dispersed population where individuals 

 frequently change dens. Last, field studies aimed at determining base level, 

 typical patterns of lobster behavioral ecology must control for the disruptive 

 effect of handling and repetitive capture in order to make valid conclusions. 



Predation 



Predation was observed only indirectly and infrequently. Known lobster predators, 

 primarily the nurse shark ( Ginglymos toma cirratum ) and the jewfish ( Epinephalus 

 itajara ) , were observed in the study area. Nurse sharks from 1.5 to 3 m in 

 length were particularly common and were observed with high frequency, by day, 

 in the area of dens 10 and 9 where they rested under the prominent ledges. One 

 large jewfish of several hundred pounds and a large (30-35 lbs.) snapper 

 ( Lutjanus sp.) were observed infrequently in this general area. 



The only apparent predation witnessed occurred during a night sonic tracking 

 study when the sonic signal abruptly began to move rapidly, at least 3 knots, 

 over a distance of several hundred meters and could not be overtaken by divers. 

 This rate and duration of movement negated the possibility of lobster locomotion, 

 and the area to which the signal was traced, off Cabritte Horn Point, suggests 

 either a nurse shark or a jewfish to be the predator. 



Although nurse sharks were not observed at night, it is known that this is an 

 active period of feeding for this species and it is assumed they prey primarily 

 at this time. 



Feeding 



No thorough attempt was made to determine the source of food for lobsters in 

 the study areas since this would have required sacrificing the specimens. 

 Occasional observations and indirect evidence from shell debris near dens indi- 

 cate lobster predation on mollusks. Large spiny lobsters are known to break 

 open and feed on conchs ( S trombus gigas ) . On 2-50, a lobster was observed 

 opening a milk conch and on 8-50 a lobster in a den was observed gnawing on a 

 freshly broken piece of conch shell. Conch shells, characteristically broken 

 about the whorl, were frequently found on the sand-algal plain where the live 

 conchs are abundant and lobsters are known to frequent. 



Gut contents from six lobsters collected early in the morning outside the study 

 areas in a region of similar habitat yielded the following: mollusk shell and 

 opercular, urchin spines (both Diadema and Eucidaris ) , exoskeleton fragments, 

 polychete (?) "teeth," sponge and holothurian spicules. The presence of urchin 

 spines suggests feeding occurs also on the reef itself as well as on the sand- 

 algal plain. 



VI-54 



