192 
greys, 3-6 ft long, were involved in the first two 
phases of this experiment. 
The response to the repellent clouds contain- 
ing the extract solutions was essentially the same 
in each case. After rapidly approaching the 
cloud, the sharks circled briefly about its edges 
and then moved slowly inside without notable 
excitement. Within 5 min of introduction, all 
sharks had lost interest in the introduction. 
Eight greys, 3-6 ft in length, were involved in 
these tests. 
It seems noteworthy that the extract elicited 
an unexcited pattern of exploratory behavior 
rather than the highly excited aggressive be- 
havior seen following the introduction of mac- 
erated goatfish. In any case, the most that can 
be said for the repelling qualities of the material 
used in this test is that the sharks did not swim 
into the cloud without incentive to do so. It 
may theoretically have served to conceal an 
otherwise attractive visual stimulus which might 
have been inside. 
Experiment XIV 
This experiment tested the effectiveness of 
an underwater light suspended on a line in 
protecting dead fish. 
The apparatus was designed so that the bait 
(dead goatfish) was suspended 2 ft below the 
light in a position where both could be viewed 
from the underwater chamber. Observations 
were then made of the response of the sharks 
to the bait, both in the presence and in the ab- 
sence of light. Tests were conducted during four 
different nights using both 110- and 300-watt 
bulbs. A steady light was used, as well as a light 
which flashed at rates of approximately 15, 35, 
and 50 flashes per min. Periods of light, 20 min 
long, were alternated with 20-min periods of 
darkness during both of which the baits were 
presented. Sharks had been drawn to the area 
by bait placed in a wire basket which was sus- 
pended in the water and then raised prior to 
each test. A strong current was flowing toward 
Deep Channel during each test. 
Initially the steady light was effective in pro- 
tecting the bait from the sharks for the entire 
20-min period, with the bait being taken soon 
after the light was extinguished. During the 
early periods of light the sharks milled about 
PACIFIC SCIENCE, Vol. XVII, April 1963 
at the edge of the field, consistently downstream 
of the bait and light. Upon continued contact 
with the light the sharks became progressively 
bolder until despite the light, flashing or steady, 
they showed little hesitation in taking the bait. 
This boldness seemed to increase notably with 
the number of sharks present. There were 
usually between 5 and 10 grey sharks present 
during these tests; no other species was seen. 
This test proved to be a good illustration of 
progressive loss of apprehension through grow- 
ing familiarity with an initially strange situa- 
tion, as well as the mutually stimulating effect 
of some species of sharks on one another in 
certain situations. 
CONCLUSIONS 
1. Three species of sharks are common in 
Eniwetok lagoon: the grey shark, Car char hinus 
menisorrah; the blacktip shark, C. melanopterus; 
and the whitetip shark, Triaenodon obesus. 
2. Each species inhabits a rather characteris- 
tic habitat within the lagoon: (a) the blacktip 
in relatively shallow water ( 1-40 ft approx. ) 
over sand and coral rubble flats which extend 
out from shore for distances ranging from a few 
yards to several miles; (b) the grey, along the 
outer slope of these flats, in deeper water and 
in the passages to the sea; and ( c ) the whitetip 
about rock-ledges and coral heads. 
3. The feeding behavior of these sharks shows 
differences which in many cases appears to be 
associated with their characteristic habitats. 
4. Blacktip and grey sharks show a marked 
increase in excitement when feeding in num- 
bers. This phenomenon, often referred to as a 
"feeding frenzy” in extreme cases, does not seem 
to occur in the whitetip. 
5. All three species are highly sensitive to 
stimuli emanating from or suggesting injured 
and/or distressed, as well as dead or moribund 
prey. 
6. These sharks can detect, by olfaction, both 
injured fish and uninjured fish in a state of 
stress. 
7. Olfaction is the most effective sense in 
detecting prey at a distance, providing the ol- 
factory stimulus has had sufficient time and 
means for effective dispersal. 
