156 
PACIFIC SCIENCE, Vol XVII, April 1963 
that the sharks were attracted to human blood 
at a concentration of about 0.1 to 0.01 parts 
per million of sea water. 
A blood suspension held under refrigeration 
for 4 days or longer usually underwent hemoly- 
sis and acquired a faint to strong putrid odor. 
The aged blood produced erratic results with 
blacktip sharks as had been suspected in the 
1959 tests. At times there was only a sensing 
of the material, an avoidance of the area, or 
possibly a slight attraction. At other times there 
seemed to be a "startled” or 'alarm” reaction 
with speeding from the area such as had been 
noticed the previous year. This was classed as 
repulsion. With grey sharks, on the other hand, 
the hemolyzed blood seemed more consistently 
attractive. 
Our results prove that fresh blood excites 
blacktip and grey sharks and promotes a strong 
hunting response. They suggest that decomposed 
human blood contains a component which is 
repellent to blacktips. 
Sweat 
A large number of experiments were con- 
ducted at both the Eniwetok and the Hawaii 
laboratories on the response of sharks to human 
sweat. They were stimulated by the observation 
of Brett and McKinnon (1954) that water in 
which human hands had been rinsed retarded 
the upstream migration of salmon and induced 
an "alarm” response. 
Sweat was collected initially by sponging the 
body and wringing the sponge in 500 ml of 
sea water. Later, at Eniwetok it was collected 
directly from the body as it ran down arms, 
chest and abdomen in the hot, humid atmos- 
phere of the shark house, and at Hawaii it was 
collected in the same way by exercising and 
subjecting the body to heat lamps. The material 
was tested according to the standard procedures 
already described. Each sweat test was usually 
followed or preceded by standard extract to ap- 
praise the sharks’ responsiveness to a known 
attractant. 
The results of 29 tests conducted on normal 
and blinded blacktip sharks at Eniwetok are 
included in summary form in Table 4 and are 
given in detail in Table 8. The majority of the 
tests yielded results which were classed as re- 
pulsion. A weak repellent effect (R) was com- 
prised of an initial sensing, followed by a slow- 
ing of swimming speed, an apparent wariness, 
TABLE 4 
Response of Sharks to Human Sweat at Eniwetok Marine Biological Laboratory (embl) 
and Hawaii Marine Laboratory (hml) 
RESPONSE* 
YEAR 
LABORATORY AND SHARKS 
RR 
R-R? 
o-s 
A-A? 
AA 
Total 
1959 
EMBL, Normal blacktips 
1 
6 
3 
1 
— 
11 
Blinded blacktips 
8 
9 
1 
- 
- 
18 
Total 
9 
15 
4 
1 
- 
29 
I960 
EMBL, Normal blacktips 
5 
7 
1 
1 
_ 
14 
Blinded blacktips 
2 
4 
1 
- 
- 
7 
EMBL, Normal greys 
- 
9 
6 
- 
- 
15 
Total 
7 
20 
8 
1 
- 
36 
1959-60 
HML, tiger, Pond 2 
HML, tiger, grey, 
1 
3 
2 
- 
- 
6 
hammerhead, Pond 5 
- 
8 
7 
- 
- 
15 
Total 
1 
11 
9 
- 
- 
21 
1960-61 
HML, tiger, greys, Pond 5 
- 
3 
2 
- 
- 
5 
Total 
17 
49 
23 
2 
- 
91 
* RR, strong repulsion; R-R?, weak or doubtful repulsion; O-S, no apparent response or sensing; A-A?, weak or doubtful 
attraction; AA, strong attraction. 
