154 
In I960, four blacktip and four grey sharks 
were starved under close supervision. Of the 
blacktips, a 20-inch male died after 36 days, a 
28-inch female died after 40 days, a 20-inch 
female died after 40 days and a 27-inch female 
survived for 43 days and was then fed. Of the 
greys, a 28-inch female died after 32 days and 
a 36-inch male died after 40 days. Two 30-inch 
females were starved respectively for 34 and 
46 days and were then fed. During starvation, 
the sharks became very thin. Those which died 
had difficulty in maintaining their equilibrium 
for several hours before death; they could not 
be revived by forced feeding. These experiments 
show that small blacktip and grey sharks can 
survive for more than a month without food 
but that some will die after 5 or 6 weeks. 
Using standard extract, tests were run at in- 
tervals to measure the response activity of both 
the starved blacktips and greys and, for com- 
parison, that of four blinded blacktips which 
were fed two or three times a week. Activity 
data are given in Table 2. 
The activity index for the fed sharks fluc- 
tuated from day to day but showed no trend. In 
contrast, the index for the starved sharks showed 
a more or less steady increase during both con- 
trol and test conditions, particularly in the case 
of the blacktips. For the latter, the decrease in 
index on the last day is due to the moribund 
condition of two of the four sharks. As starva- 
tion proceeded, the sharks seemed to become 
increasingly restless and to respond with in- 
creasing vigor to the standard extract. Tests on 
the greys were discontinued after August 5, 
1961 because of the death of one shark and the 
moribund condition of another (starvation be- 
PACIFIC SCIENCE, Vol. XVII, April 1963 
gan about 2 weeks earlier than with the black- 
tips). 
Normally the blinded blacktips were more 
sensitive to odorous substances than the black- 
tips with normal vision. This situation was re- 
versed when the latter sharks were starved. This 
is illustrated by one experiment (August 20, 
I960) when both the blind, fed and the normal, 
starved sharks were tested with a 1/1000 dilu- 
tion of standard extract (Fig. 6B). Using 0.003 
ml (rather than the usual 3.0 ml) the fed sharks 
showed a weak attraction response which did 
not differ greatly from mere sensing. The starved 
blacktips on the other hand gave a strong at- 
traction response which included the usual ex- 
cited circling and hunting activity. 
There is no doubt that hungry sharks are 
much more responsive than fed sharks to minute 
traces of odorous substances. 
RESPONSE TO HUMAN MATERIALS 
In this section are reported the results of tests 
on the response of normal and blinded blacktip 
sharks and normal grey sharks to human urine, 
blood and sweat, and to L-serine, a presumed 
component of human sweat. Other materials 
such as faeces and vomit were not investigated. 
Urine 
At Eniwetok, in both 1959 (eight tests) and 
I960 (three tests) blacktip sharks were pre- 
sented with human urine in quantities ranging 
from 3 to 80 ml of whole material. The urine 
was sensed, as indicated by a swirl or turn on 
encountering it, but there was no other con- 
sistent response. 
TABLE 2 
Activity Index of Fed (Blind) and Starved (Normal) Sharks to Standard Extract at 
Eniwetok Marine Biological Laboratory, I960 
DATE 
FED BLACKTIPS 
STARVED blacktips 
STARVED GREYS 
Controls 
Test 
Controls 
Test 
Controls 
Test 
7/20 
29.2 
41.2 
31.0 
40.4 
33.8 
60.4 
7/23 
21.2 
32.0 
31.8 
44.2 
23.8 
38.6 
7/29 
34.8 
37.6 
57.4 
76.8 
52.6 
74.2 
8/5 
29.6 
54.0 
50.6 
71.2 
86.3 
96.8 
8/18 
27.2 
36.2 
56.0 
97.0 
— 
— 
8/25 
23.4 
32.2 
36.4 
49.2 
— 
— 
