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PACIFIC SCIENCE, Vol XVII, April 1963 
Fig. 1 . The grey shark, Carcharhinus menisorrah. (Photo by E. Hobson.) 
2. A wire cage was suspended from a raft 
anchored on the slope at the edge of Deep 
Channel. An observer in this cage was located 
immediately below the surface. 
3. A canvas screen, anchored on the bottom, 
concealed an observer lying prone on the bottom 
wearing SCUBA equipment. 
4. A 16-ft glass-bottom boat, having the 
added advantage of mobility, provided for ob- 
servations of activity directly below. 
5. In many cases, the observations involved 
incidental encounters with sharks during the 
course of such routine underwater activity as 
installing apparatus, etc. 
Experimental procedures and apparatus will 
be further described as they pertain to the re- 
port. 
SPECIES STUDIED 
Identification of the sharks is based on Schultz 
et al (1953). All three species, Carcharhinus 
menisorrah , C. melanopterus , and Triaenodon 
obesus, reportedly have a wide Indo-Pacific dis- 
tribution. They are reported from the Red Sea 
as well as the Maidive Islands by Klausewitz 
(1958, 1959). Although positive identification 
of the two carcharinids awaits a revision of the 
family on a world-wide basis, all three species 
appear to be prominent in the shark popula- 
tions of most Pacific atolls. Harry (1953) re- 
ports them from the Tuamotus, as does Randall 
(1955) from the Gilbert group. The author 
found them abundant at Palmyra and they were 
the only species of sharks consistently seen in 
the lagoon at Eniwetok during the present in- 
vestigation. 
GENERAL OBSERVATIONS OF BEHAVIOR 
Often when we were engaged in various 
types of activity in the lagoon the resulting 
commotion, which commonly involved splash- 
ing on the surface or striking metal tools on 
hard objects underwater, was immediately fol- 
lowed by the rapid approach of an obviously 
alerted blacktip or grey shark. 
In spite of this initial attraction to many stim- 
uli, both species exhibited varying degrees of 
caution when encountering unfamiliar situa- 
tions. This was particularly apparent in the 
blacktip, a species which seemed especially sen- 
sitive to potential danger. When work was be- 
gun at Engebi, blacktips often circled at the 
limit of visibility in the baited area for as long 
as 2 or 3 hr before approaching the bait. Then, 
when an approach was made, it seemed to be 
done reluctantly and was often cut short by 
some stimulus, unnoted by the observer, which 
startled the shark as it neared the bait and 
caused it to swim rapidly away. Usually the 
shark repeated the approach, but in these early 
tests it was not until several sharks had become 
active in the area that a blacktip finally took 
the bait. We subsequently found that we were 
dealing with the same blacktips day after day 
at Engebi and that as the work progressed, their 
initial caution steadily declined. This was pre- 
sumably due to a growing familiarity with the 
situation. Nevertheless, a month of testing 
passed before the blacktips took the bait with- 
out hesitation. Once released, the attack of the 
blacktip was very fast and aggressive. 
The grey was a notably bolder species. Al- 
