Olfaction and Sharks — Tester 
151 
Unfortunately the response to a given ma- 
terial varied considerably in repeated testing 
and was often difficult to classify. The problems 
of bioassay should not be minimized. The re- 
sponsiveness of the sharks both at Eniwetok 
and Hawaii seemed to vary from day to day 
for unknown reasons despite our attempts to 
maintain standard conditions of testing and 
feeding. Erratic behavior, frequently encoun- 
tered during both control and test conditions, in 
some cases could be traced to obvious sources 
of disturbance, such as noise, but in other cases 
could not be explained. Particularly exasperating 
was an occasionally exhibited tendency to circle 
at one or the other end of the pond or tank for 
long periods of time so that tests could not be 
conducted. Even though an attempt was made 
to conduct tests only after some reasonable uni- 
formity in swim pattern persisted throughout 
control periods, there was always the question 
of whether or not a subtle change in behavior 
pattern was related to the material being tested. 
In classifying a response, greater reliance was 
placed on overt signs such as sudden turns, cir- 
cling, gills flexing, and head shaking than on the 
quantitative data. Unfortunately the location and 
concentration of the material being tested was 
not known precisely during tests and could only 
be estimated from the use of dyes after an ex- 
periment had been completed. Thus even overt 
responses could be related to the test material 
only by inference. 
Our caution in interpretation is reflected in 
the large number of responses relegated to 
doubtful categories in the results which follow 
and the numerous tests which were conducted 
on materials of particular interest. 
RESPONSE TO EXTRACTS OF NATURAL FOODS 
Experiments were conducted on the response 
of the tiger shark to extracts of tuna flesh and 
decayed shark flesh and on the response of the 
blacktip and grey sharks to a wide variety of 
potential foods including tuna, eel, grouper, 
snapper, parrot fish, jack, giant clam, octopus, 
squid, lobster, fresh shark flesh and skin, and 
decomposed shark flesh and skin. In general, 
the extracts of all food substances tested could 
be classed as attractants, although because of 
variability in the response of the sharks some- 
times several tests of the same substance were 
necessary to establish this conclusion. Because 
of this variability it was not possible to make 
rigorous comparisons between the attractive- 
ness of extracts from equivalent quantities of 
the various foods. However, it seemed certain 
that extracts from moist- or oily-fleshed fish such 
as grouper, tuna, and eel generally resulted in 
greater activity than those from dry-fleshed fish 
such as snappers. In attempting to determine the 
response to nonfood substances, frequently 
standard extracts of grouper, tuna, or eel were 
used either before or after tests of the other 
substances to appraise the sharks’ responsive- 
ness. 
From Table 1, summarizing the results of 
169 tests, it will be noted that the response was 
classed as a strong attraction in 59, as a weak 
or doubtful attraction in 62, as nil or merely a 
sensing in 39, and as a weak or a doubtful re- 
pulsion in 9. The last, comprising 5% of the 
tests, warrants further comment. 
The five instances of apparent repulsion in 
the 1959 tests at Eniwetok involved extracts of 
little tunny ( Euthynnus yaito ) , yellowfin tuna 
( Neothunnus macropterus ) , and giant clam 
(Tridacna ) , and occurred early in the summer 
when testing techniques were being developed. 
Without doubt the response was related to either 
incipient pollution of the tanks or decomposi- 
tion of the test materials. Excessive quantities 
of extracts were being used and excess food was 
not being removed from the tanks; one or both 
of these factors resulted in the death of several 
sharks in one compartment before the condition 
was rectified. Our notes state that the tunny ex- 
tract, which had been kept for 9 days, smelt 
foul. 
The four instances of apparent repulsion in 
the I960 tests, involving standard extracts of 
eel, again took place early in the summer and 
involved not pollution of the tanks but decom- 
position of the extract even though it was held 
at ice-box temperature. The extract was pre- 
pared on July 7, I960. On that and the follow- 
ing day tests of both greys and blacktips showed 
strong attraction (Figure 6A). On July 13, in 
seven tests the responses were indicated as weak 
or questionable attraction, sensing only, or nil. 
On July 16, the material produced erratic re- 
