Olfaction and Sharks — -TESTER 
159 
A different technique was employed in tests 
with the hammerhead which was particularly 
responsive to attractants. The introduction hose 
running from the funnel on top of the tower 
was submerged just below the surface at the 
center of a bullseye target area 32 ft in diameter, 
the boundaries of which were judged by eye 
from reference points on the bottom. During 
control conditions, sea water was introduced 
from the funnel. During test conditions the fol- 
lowing materials were used in varied sequence: 
( 1 ) an attractant consisting of water from the 
funnel in which fish ( Tilapia ) were swimming, 
(2) 50 ml of sweat mixed with sea water in 
the funnel, and ( 3 ) a mixture of the attractant 
and sweat in sea water. Activity data on one 
test are given in Table 5. Based on records of 
the time spent and the path followed by the 
shark in the target area, activity was calculated 
as the distance- swum in each of four rings of 
the target per unit of time. It is apparent that, 
in general, activity was greatest with the attrac- 
tant, intermediate with the mixture of sweat 
and attractant, and least (less than controls) 
with sweat alone. The sweat depressed but did 
not eliminate the response to the attractant. 
By tracing the spread of materials in the pond 
with the use of dye and calculating the volume 
of sea water involved, it was concluded that the 
actual sea water concentration of sweat in the 
pond experiments at the Hawaii laboratory were 
still considerably less than those used in the 
tank experiments at Eniwetok. Additional ex- 
periments were undertaken during the early 
summer of 1961 using much larger quantities 
of sweat (100-400 ml per test) and the im- 
proved "curtain-drum” method of introduction. 
The results are summarized in Table 4. Despite 
the larger quantities of sweat which were used 
no strong repulsion was noted. In the five tests, 
there was weak or doubtful repulsion in three 
and sensing only in two. In those tests indicat- 
ing repulsion, all three species of sharks, espe- 
cially the tiger, showed definite signs of aversion 
including veering from the curtain and gill 
flexing. The sweat of one donor (sk) seemed 
to be more active than that of the other (blo) . 
From the above experiments on blacktip, 
grey, tiger, and hammerhead sharks one cannot 
conclude' that human sweat, per se, is an active 
shark repellent. On the other hand, it is certain 
that human sweat does contain, at least at times, 
a component which is aversive to sharks. Oc- 
casionally this induces overt signs of repulsion 
such as head shaking, gill flexing, veering, and 
rapid retreat; more frequently it induces only 
a subtle wariness manifested chiefly by avoid- 
ance of the area of introduction. The response 
is highly variable. This is unfortunate but almost 
inevitable when one considers the uncontrolled 
environmental conditions and the many factors 
which could contribute to both the variability 
of shark behavior and variability of sweat com- 
position. 
Steinberg (1961) found no evidence of re- 
pellent properties in either human sweat or pure 
compounds forming constituents of human 
sweat in tests with a captive lemon shark at the 
Lerner Marine Laboratory. Unfortunately he 
gives no information on the concentrations of 
material used. Moreover, he reports that the 
lemon shark was not responsive to solutions of 
dried beef blood nor would it eat chunks of 
fresh shark liver which, at other times, had been 
particularly attractive to captive sharks. His 
negative results are understandable. It has been 
our experience that sharks which have not yet 
fed in captivity do not respond to either highly 
attractive substances such as eel extract or fresh 
human blood, nor do they respond to subtle 
repellent substances such as human sweat. 
In view of the results of this series of tests, it 
seems safe to assume that shark attack on hu- 
mans is not motivated by the smell of human 
sweat. 
L-serine 
Following the discovery by Brett and Mc- 
Kinnon ( 1954) that human hand rinse retarded 
the migration of salmon, Idler, Fagerlund, and 
Mayoh (1956) undertook an analysis of hand 
rinse to determine the repellent component ( s ) . 
By employing various fractionation techniques 
and testing the fractions on migrating salmon, 
they were able to identify the active fractions as 
amino acids of which serine was a major com- 
ponent. In further tests, the L-isomer of serine 
was found to induce the alarm response whereas 
D-isomer did not. They stated "L-serine defi- 
nitely elicited a typical alarm reaction but the 
effects were neither so dramatic nor so long a 
duration as the response obtained by hand 
