184 
sensory capacity for stimuli of this sort is prob- 
ably best approached with conditioned response 
experiments on captive sharks under controlled 
conditions before attempting to establish their 
role in feeding behavior under natural con- 
ditions. 
Although the work of Parker (1903, 1911), 
Kritzler and Wood (1961), and others has 
demonstrated that at least some sharks are sensi- 
tive to compression waves of a relatively wide 
range of frequencies, it has yet to be proven 
experimentally that such stimuli normally re- 
lease feeding behavior. Nevertheless, incidental 
observations at Eniwetok indicated they do play 
an integral role in feeding activity. These ob- 
servations are of a nature similar to those men- 
tioned at the beginning of this section and are 
subject to the same reservations. One such ob- 
servation is quoted from the field notebook: 
... A 30 lb. grouper was speared on the slope border- 
ing Deep Channel . . . the grouper fled, dragging the 
spear, into a small cave. . . . Within seconds, 5 greys 
4—7 ft. in length swam excitedly into the area from 
downstream. As soon as they were in the area, how- 
ever, their excited state diminished. They swam about 
in the area for several minutes, appearing to steadily 
lose interest, before slowly drifting off downstream 
and out of sight. After a few minutes ... 5 greys made 
another approach which seemed as highly motivated 
as the preceding one. Immediately I looked below to 
see a small puff of sediment emerge from the cave — 
the grouper was obviously thrashing about inside. 
Almost as soon as the sharks were in the area, all be- 
came quiet in the cave, whereupon the sharks imme- 
diately lost their excited state and settled down to 
cruising about as before. Two 4-ft. whitetips joined 
them before they all again drifted off downstream. 
After a few minutes . . . another small puff of sedi- 
ment was visible at the mouth of the cave — the 
grouper was struggling again. I quickly looked down- 
stream to see the greys on their way in as before. The 
pattern previously described was repeated, but this 
time there were 4 whitetips (3—5 ft.) in addition to 
the 5 greys. Several minutes after the sharks disap- 
peared downstream for the third time the grouper 
scrambled out of the hole and, dragging the spear, 
struggled along the bottom toward the bigger, more 
protective caves farther up the slope. The 5 greys 
charged into the area from downstream before it had 
gone 20 ft. At this point, the grouper stopped, and 
ceased all movement. Although the grouper was in a 
completely exposed position, the excited state of the 
onrushing greys diminished almost as soon as the 
grouper stopped moving. Instead of attacking the com- 
pletely vulnerable grouper as I expected, the greys 
settled down to swimming slowly and randomly about 
the area. Often they came within inches of the mo 
PACIFIC SCIENCE, Vol. XVII, April 1963 
tionless grouper, and on at least one occasion grazed 
it. The 4 whitetips rejoined the group, along with 2 
blacktips (3 and 4 ft.) making a total of 12 sharks, 
all obviously interested, but offering no show of ex- 
citement or indication that they regarded the wounded 
grouper as prey. Nevertheless, the sharks did not 
gradually drift off downstream as they had previously, 
but continued to swim about in the area. Thirty min- 
utes later, when we had to leave, the situation was 
unchanged — the grouper was still sitting motionless in 
the same spot, while the 12 sharks swam slowly about. 
Most of this random swimming about the area, both 
at this point and earlier, had occurred downstream of 
the grouper. 
It was significant that all approaches and de- 
partures, as well as most of the random swim- 
ming in the area, occurred downstream of the 
grouper. This indicated that olfaction was in- 
volved throughout the incident. Although the 
excited approach of the greys during this inci- 
dent appeared to coincide with the periods when 
the grouper was struggling, it is possible that 
they had first been conditioned by an olfactory 
cue. In this case, the olfactory cue may have had 
a threshold lowering effect for the postulated 
compression wave stimuli. At least one author 
(Wright, 1948) doubts that olfaction alone will 
release attack patterns in sharks. In this latter 
regard, blinded sharks in the tanks fed avidly on 
chunks of fish flesh which were lying on the 
bottom, thus offering little other than olfactory 
stimuli before the sharks came into contact with 
them. The question here is whether or not the 
behavior of these blinded sharks can be con- 
sidered normal. 
While the sharks in the latter phase of the 
incident did not attack the wounded grouper, 
they did not drift off downstream as they had 
done when this same fish was concealed in the 
cave. We are probably safe in assuming that the 
behavior pattern demonstrated in swimming 
slowly about in the area was appetitive in nature. 
This suggests that an additional stimulus was 
required to release the actual attack. This is to 
say that a combination of stimuli, e.g., an olfac- 
tory element and erratic motion might have been 
necessary to release the attack in this case. The 
olfactory cue may have simply released an ex- 
ploratory behavior pattern which drew the 
sharks to the area. Once there, the release of 
the attack may then have required a specific 
stimulus not presented by the quiet, natural 
looking grouper, the coloration of which blended 
