464 
PACIFIC SCIENCE, Vol. XX, October 1966 
TABLE 2 
Results of Discrimination Tests with Blacktip (B) and Grey (G) Sharks 
( -\- = discrimination ; ? = probable discrimination; 0 = no discrimination; 
* - : simultaneous discrimination problems) 
SHARKS 
TARGETS (neutral vs. negative) Bl B2 B3 B4 B5 B6 B7 B8 Gl G2 
No target vs. white triangle 
White horizontal vs. white vertical rectangle 
White square vs. white triangle 
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 (N4/) square vs. grey (N6/) square 
Grey (N5/) square vs. grey (N8/) square 
+ 
p 
further training. This was shown by one or 
more kinds of overt responses, such as head- 
shaking, on seeing the negative target when 
displayed at either end. The criteria of dis- 
crimination have already been listed. 
It was expected that learning of the tar- 
get — punishment association would be fol- 
lowed, with further training, by learning to 
avoid the end zone in which the negative target 
was displayed (avoidance response). The avoid- 
ance response was learned reasonably well (with 
tests showing 0-10% of the total end-zone 
passes into the negative end) by only two 
sharks in apparently simple problems; Bl, no 
target vs. target; and B3, horizontal vs. vertical 
rectangles. It was not learned by other sharks 
trained to the rectangle orientation problem, 
nor by those exposed to discrimination prob- 
lems involving squares, circles, triangles, colors, 
and shades of grey. 
Prolonged training in attempts to induce the 
avoidance response sometimes produced be- 
havior which might be classed as negativistic or 
"'rebellious,” e.g., with B5. This blacktip had 
undergone extensive training to the circle vs. 
triangle problem with some signs of discrimi- 
nation. During rest periods, it would circle 
quietly in the center zone. At the start of a 
training period, it would make an initial shal- 
low pass into the end displaying the negative 
target, turn back and enter the neutral end, and 
then dash into the negative end with head 
shaking and body quivering. 
Some blacktips (but not grey sharks) had 
initially, or developed during training, a ten- 
dency to circle between the center zone and one 
end zone. This was called an "L-bias” or an 
”R-bias,” depending on which side was favored. 
Two sharks (Bl and B6) showed an L-bias 
during shape discrimination experiments; four 
(B3, B5, B7, and B8) developed a strong 
R-bias during color discrimination experiments. 
The end bias could not be overcome by per- 
sistent shocking nor, in the following instance, 
by offering food as a reward. B6 was being 
trained to distinguish between horizontal and 
vertical rectangles but showed persistent pene- 
tration of the L-end and avoidance of the R-end. 
At 1845 hours, during a rest period a piece of 
fish was put into the R-end, upstream of L, to 
induce the shark to enter. It approached the 
R-end with seeming interest but did not enter. 
At 2010 hours, while being consistently shocked 
at L as it entered against the negative target, 
it suddenly dashed into the R-end, took the 
fish, and then dashed back into the L-end to 
be shocked again as it entered. 
Some blacktips displayed behavior which 
