182 
PACIFIC SCIENCE, VoL XVII, April 1963 
TABLE 3 
Response of Sharks to Water Containing a Grouper Under Stress (Experiment IV) 
(All Sharks Came from a Downstream Direction) 
TRIAL 
TIDAL CURRENT 
NO. AND LENGTH OF 
SHARKS RESPONDING 
TIME TO 
INITIAL 
APPEARANCE 
TOTAL 
INTRODUCTION 
TIME 
1 
flood, moderate 
2 5 -ft greys 
15 min 
30 min 
2 
ebb, strong to slack 
3 4-ft whitetips 
5 min 
30 min 
3 
flood, moderate 
1 4-ft grey 
1 3 -ft whitetip 
10 min 
1 hr 
periment described below was designed to mini- 
mize these sources of error. 
Experiment IV 
This experiment was conducted to determine 
if these sharks are capable of detecting and 
tracking down, exclusively by olfaction, an un- 
injured fish under stress. 
The experiment was carried out using the 
procedure described for Experiment III, except 
that, in place of the extract solution, the large 
plastic container was filled with sea water and 
contained an uninjured grouper (1-10 lb) which 
was presumably under stress. In each case, the 
fish was caught by line with a barbless hook. 
During the experiment the fish was agitated 
intermittently with a pole, using care not to in- 
flict any damage, while the water was running 
from the container to the bottom as described 
for Experiment III. 
Three trials were conducted over a period of 
10 days, with at least 3 days between each trial. 
The results are given in Table 3. 
The response was essentially the same as that 
to the extracts in Experiment III. Greys and 
whitetips were involved in the experiment; no 
blacktips were seen. 
The captive grouper obviously emitted an ol- 
factory stimulus which attracted the sharks up- 
stream to the cave. Critics of this experiment 
may question whether a recently hooked fish can 
be considered uninjured. There is justification 
for pointing out the hook wound as well as the 
skin rubbed and mucus dislodged during han- 
dling. These factors offer a possible source of 
error. However, the results were consistent with 
findings in the laboratory tanks where it was 
possible to maintain considerably more control 
over experimental conditions. In the latter tests 
(Tester, 1963) the strength of the stimulating 
olfactory component varied with the degree of 
distress of the fish being used. It appeared that 
a maximum level was reached shortly after the 
death of the fish. 
It has been shown that the sharks were able 
to track down a distressed but apparently un- 
injured fish by olfaction alone in Experiment 
IV. Although they could also have made exclu- 
sive use of the olfactory sense in tracking down 
the hooked fish in Experiment II, it is highly 
unlikely that they did so. We shall see that, in 
all probability, other sensory modalities not only 
contributed to, but in fact dominated, certain 
phases of the approach. 
RESPONSE TO COMPRESSION WAVES 
Compression waves are regarded by many to 
have an important effect on the behavior of 
sharks, both as an attractant and as a repellent. 
Wright (1948) claims that attack patterns in 
sharks are released by sounds. Many investiga- 
tors (e.g., Eibl-Eibesfeldt and Hass, 1959) re- 
port that the vibrations and sounds made by a 
wounded fish will attract sharks. On the other 
hand, some sounds have been reported to have 
a repelling effect, as for example the underwater 
shouts of divers (Hass, 1951)- These reports 
are based on incidental encounters with sharks 
and are generally complicated somewhat by the 
presence of stimulating factors other than com- 
pression waves which might themselves have 
been influential in eliciting the observed re- 
sponse. For example, Wrights conclusion is 
based to a considerable degree on observations 
of sharks appearing just after an underwater 
explosion to feed on the dead and stunned fish. 
