Feeding Behavior of Sharks — Hobson 
189 
were prepared. Half of these baits were soaked 
for 4 days in each of the following concentra- 
tions of ethyl alcohol: 35%, 75% and 95%, in 
that order. After the alcohol treatment the baits 
were soaked in sea water for 3 hr. It was hoped 
that the product of this process would be a 
bait which felt and looked like food, but did 
not taste or smell like food. In actuality, how- 
ever, the texture of the product was not identi- 
cal to that of normal flesh, being notably dry 
and leathery. The experiment was nevertheless 
continued, with each of the treated baits being 
paired with a normal bait. It was assumed that 
the normal bait would be taken. If the treated 
bait was also taken this would indicate that the 
wood in Experiment VIII had been rejected due 
to its tactile properties rather than its lack of 
acceptable olfactory or gustatory stimuli. If, 
however, the treated bait was not taken, Testers 
results would be confirmed and it would appear 
that gustation (and perhaps the tactile sense 
too) had been involved in the rejection of the 
wood. 
The test was carried out at the raft, in a mod- 
erate current, using essentially the same tech- 
nique described for Experiment IX, except that 
in this case all 15 trials of the experiment were 
conducted during a 30-min period of one after- 
noon and the response to both baits was noted. 
Only grey sharks were involved in the results. 
The treated bait was hit first 6 times, while the 
natural bait was hit first 9 times, indicating that 
the sharks did not make a distinction between 
the visual appearance of the two baits. All the 
baits were taken into the mouth, but although 
in all trials the natural bait was swallowed im- 
mediately, the treated bait was rejected within 
seconds. As this rejection took place after the 
bait had been taken into the mouth, it appeared 
to be based on gustatory stimulation (if we 
are correct in assuming that the bait offered ac- 
ceptable tactile stimulation). A snapper was 
seen taking, and apparently retaining, one of 
the treated baits rejected by the grey shark. 
Another effort to clarify the roles played by 
gustation and the tactile sense in feeding in- 
volved the use of sponges. It was thought that 
perhaps a sponge which had been soaked in an 
extract of fish flesh would be accepted by the 
sharks as food. If this were the case, then by 
pairing the soaked sponge with a normal sponge 
it would have been possible to present a choice 
of baits which posed the same problem to the 
sharks as did Experiment X. In order for the 
experiment to have been a success, however, it 
was necessary for the sharks to have accepted 
the soaked sponge as food, and this proved to 
be only temporarily true. Initially, the soaked 
sponge was carried off in the manner seen with 
a chunk of fish, while the plain sponge was re- 
jected as was the prepared bait in Experiment 
X. However, after 3 trials the sharks began to 
lose interest in the soaked sponges until they 
either dismissed them after an unenthusiastic 
nudge, or ignored them completely. Further- 
more, as the sharks learned that the soaked 
sponges were inedible, the extract no longer 
excited them. In this latter regard it is difficult 
to say whether the sharks actually learned that 
the extract did not indicate food or whether 
olfactory fatigue was the major factor. 
A definite change in general behavior of the 
grey sharks was first noted during Experiment 
IX and became very evident during Experiment 
X. As the sharks became conditioned to feeding 
about the raft they responded instantly to any 
object which was presented. In addition, there 
was a sharp increase in the number of sharks 
responding to our test situations. Where ini- 
tially a maximum of 5 or 6 grey sharks were in- 
volved in our experiments, the number steadily 
increased during this period of increased food 
supply until more than 20 were being drawn 
about the raft. The initial population had been 
relatively stable and through successive observa- 
tions involving experiments which utilized min- 
imum feeding, it had become possible to recog- 
nize a certain group of about 6 individuals that 
appeared day after day. These same individuals 
were seen after the population numbers in- 
creased, but apparently many other sharks which 
normally frequented other areas were drawn to 
this point of concentrated feeding. This change 
involved only grey sharks, which is understand- 
able as this species was completely monopoliz- 
ing the additional food. The increase in num- 
bers of sharks resulted in a markedly increased 
element of competition. When we witnessed 
the simultaneous rush at the baits by up to 10’ 
sharks, it was understandable that all baits were 
taken into the mouth before any discrimina- 
tions were made as the slightest hesitation by 
