190 
a shark in this situation immediately eliminated 
it from a chance at a bait. Fortunately the pres- 
ent tests, which required concentrated feeding, 
were concerned with probing questions which 
did not suffer from these effects. This change 
in behavior, along with the increase in numbers 
of the local sharks, was therefore viewed with 
interest rather than alarm. 
FOOD PREFERENCES 
Sharks have been popularly described in a 
general way as creatures with an exceptionally 
voracious appetite, feeding on such unlikely ob- 
jects as tin cans, bottles, and other trash (Linea- 
weaver, I960). Although considerable effort was 
brought to bear on the problem of food pref- 
erences during this study, the experiment de- 
scribed below was the only one, of many experi- 
ments conducted, which clearly indicated a pref- 
erence for one of two food materials presented. 
Experiment XI 
This experiment was an effort to determine 
whether or not these sharks show any preference 
between grouper flesh and the flesh of various 
species of mollusks, e. g., Tridacna sp., (10 
trials); Spondylus sp ., (5 trials); and Cassus 
sp., (3 trials). 
Mollusk flesh in 2 -inch cubes was paired with 
chunks of grouper flesh of the same size, with 
both baits thus offering an essentially identical 
visual appearance. Prior to the test, large pieces 
of grouper and mollusk flesh of the species to 
be tested were placed in the cage on the raft 
to attract sharks. When the introductions began, 
there were 10 grey sharks, 3 to 6 ft in length, 
present in the area. The method of introduction 
was as used in Experiments VIII, IX, and X, ex- 
cept that all trials were conducted during one 
session. Observations were made to detect any 
evidence of a preference which might be shown 
between the two baits. 
The fish baits were hit first 8 times, while the 
mollusks were hit first 9 times, indicating that 
there was no visual preference. However, al- 
though both the fish and mollusks were taken 
into the mouth with equal vigor, the fish were 
presumably swallowed while the mollusks were 
rejected almost immediately. The results were 
comparable to those of Experiment X, with the 
PACIFIC SCIENCE, Vol. XVII, April 1963 
response toward the mollusks similar to that 
shown toward the treated bait. On one occasion 
a single shark took the Tridacna and then the 
grouper. After a short period, with both baits 
in its mouth, the shark rejected one, presumably 
the Tridacna. These same rejected baits were 
subsequently taken by groupers and snappers 
which waited below the feeding sharks. Al- 
though the mollusks tested were unacceptable 
as food by these sharks, it is known that they 
will feed readily on squid. 
It was possible, therefore, to observe a pref- 
erence when one of the bait-choices offered was 
unacceptable to the sharks. However, when both 
bait-choices presented were acceptable, it be- 
came difficult to make this distinction, even 
though one might have been significantly more 
attractive than the other. Thus, most of our ex- 
periments concerning food preferences yielded 
inconclusive results. For example, a test might 
have been conducted to determine the compara- 
tive attractiveness of two baits, A and B, both 
motionless and presented on the lines within 
10 ft of each other. As indicated in Experiment 
VIII, although these sharks might have been 
drawn in by an olfactory stimulus produced by 
bait A, they would then have been quite likely 
to have hit B inasmuch as the final phase of the 
approach to the bait would have been visually 
directed. Once having taken bait B, this bait 
would be retained as long as it was not actually 
unacceptable. 
It has been noted (Tester, 1963) that some 
types of fish flesh appear to be more attractive 
to sharks than do others. In the ponds at Coco- 
nut Island the notably dry-fleshed snapper, Lu- 
tianus gib bus, appeared to be far less desirable 
to captive sharks as food than did the much 
juicier tuna, Katsuwonus pel amis. Springer 
(1958) also noted this preference for tuna. Is 
it possible that this apparent preference is ac- 
tually due to a higher concentration of some 
basic attractant which is common to the flesh 
of both fish? It has become increasingly appar- 
ent that some substance (or substances) in fish 
flesh is perceived by the sense of taste and/or 
smell of these sharks which is a powerful ele- 
ment in the release of a highly motivated feed- 
ing pattern. Furthermore, it was indicated in 
Experiment X and also in the work of Tester 
et al. (1955) that this substance could be ex- 
