Visual Target Discrimination in Sharks — Tester and Kato 
465 
might be termed ''nervousness, 5 ’ particularly in 
problems involving grey vs. colored targets and, 
to a lesser extent, in problems involving 
squares, circles, and triangles. This was mani- 
fested by a hypersensitivity to incidental noises 
which normally did not seem to affect the sharks 
but which, with prolonged training, caused 
them to make sudden dashes and quick turns. 
Other signs of nervous activity were: (1) ap- 
parent agitation and rapid circling, (2) pro- 
longed figure-8 oscillations against the wall of 
the tank, or (3) rapid dashes from one end 
of the tank to the other during which the shark 
would turn on its back and rub the floor. This 
last behavior may have been related to irrita- 
tion from the tag or from copepod parasites on 
the back which was further aggravated by body- 
twitching induced by shocking. A similar be- 
havior was occasionally seen in sharks which 
were not being conditioned. 
In most discrimination problems, the black- 
tips circled with increased frequency in the 
safe center zone as training proceeded, thus 
avoiding shock at either end. This circling 
tendency slowed the training process and in a 
few cases caused us to abandon training tem- 
porarily or permanently. It did not occur with 
the grey sharks. 
There was no noticeable difference in re- 
sponse between sharks subject to successive and 
simultaneous training techniques. Each method 
was used in about half of the total number of 
test situations (Table 2). 
Despite the behavioral problems discussed 
above, some sharks did learn to discriminate 
between targets. The results are presented in 
the sections which follow. 
No Target versus Target 
The one shark (Bl) presented with this 
problem learned to associate the target (white 
triangle) with shock after 36 reinforcements 
TABLE 3 
Time (in minutes) of Training and Number of Training Sessions (in parentheses), 
for Blacktip (B) and Grey (G) Sharks 
targets (neutral vs. negative) Bl 
No target vs. white triangle 36 
( 2 ) 
White horizontal vs. white rectangle 
White square vs. white triangle 360 
(19) 
White circle vs. white triangle 
Grey (N5/) square vs. purple square 
Grey (N5/) square vs. blue square — 
Grey (N5/) square vs. green square — 
Grey (N5/) square vs. yellow square 
Grey (N5/) square vs. red square — 
Grey (N5/) square vs. grey (N6/) square 
Grey (N4/) square vs. grey (N8/) square — 
Grey (N5/) square vs. grey (N8/) square — 
SHARKS 
B2 B3 B4 B5 B6 B7 B8 Gl G2 
72 158 122 72 — — 54 — 
(4) (11) (10) (4) (3) 
320 — — —— — — — — 
(19) 
— — 78 486 — — — 180 — 
(5) (27) (10) 
( 10 ) 
— — — 108 — — 144 — — 
(6) (9) 
— 204 — — — — 255 198 — 
(15) (18) (11) 
— — — — — — 18 — 198 
(1) (ID 
— — — —— 360 89 — 210 
( 20 ) ( 5 ) ( 12 ) 
( 6 ) 
— 108 — — — — — — — 
( 6 ) 
— — — — — — 96 — 216 
(9) (12) 
