150 
PACIFIC SCIENCE, Vol. XVII, April 1963 
Fig. 5. Diagram of the arrangement of test apparatus in Pond 5 at Hawaii Marine Laboratory. 
tively stable during periods at or near slack 
water. When there was a tidal current the cur- 
tain lacked uniformity in concentration and was 
irregular in shape; it slowly spread to one end 
or the other of the test area; sometimes it spread 
in one direction at the surface and in the op- 
posite direction at or near the bottom. Normally 
the sharks would encounter the curtain of ma- 
terial during their passage along the deep chan- 
nel. They could avoid it by swimming in the 
shallows. 
Interpretation of a response 
Based partly on quantitative data averaged as 
an index of activity or plotted in graphic form, 
partly on notes of overt responses, and, in the 
case of pond experiments, partly on diagrams of 
the swimming paths of the sharks in, out, or 
through the test area, the result of each experi- 
ment was classified as no noticeable response 
(O), sensing only (S), weak attraction (A), 
strong attraction (AA), weak repulsion (R), 
or strong repulsion (RR). Occasionally these 
were supplemented by other descriptions such 
as "startled reaction,” "alarm reaction,” "agita- 
tion,” etc. 
The category "no noticeable response” needs 
no further explanation. The category "sensing” 
was reserved for a response which consisted of 
a sudden start or turn on the part of the shark 
on first encountering the test material but with 
no other noticeable component suggestive of 
either attraction or repulsion. Sensing responses 
were obtained with a variety of materials in- 
cluding weak acids, bases, and salts. The re- 
sponse was interpreted merely as an awareness 
of any change in the composition of an other- 
wise uniform environment. An "attraction” re- 
sponse included an initial sensing followed by a 
more or less prolonged hunting response, usually 
with rapid swimming, circling at or near the 
surface, and occasionally with a "gulping” or 
flexing of the jaws as when feeding. The shark 
would usually make several excited circles in the 
test area on encountering the material, and 
would then dash down the tank, returning to 
the test area for further circling. Almost in- 
variably the average index of activity during 
test conditions was higher than during control 
conditions. A "repulsion” response included an 
initial sensing, but this was followed usually 
by rapid departure from the test area, a slowing 
of swimming speed, and a "cautious” re-ap- 
proach to the test area. Often in subsequent 
passes the sharks would turn short of the test 
area. A strong repulsion was often accompanied 
by shaking of the head or flexing of the gill 
slits. Almost invariably the average index of 
activity during test conditions was lower than 
during control conditions. 
