462 
PACIFIC SCIENCE, Vol. XX, October 1966 
TABLE 1 
Code Number, Total Length, and Sex of 
Blacktip (B) and Grey (G) Sharks 
NO. 
LENGTH 
(inches) 
LENGTH 
(cm) 
SEX 
Bl 
201/2 
52 
F 
B2 
21 
53 
F 
B3 
23 
58 
M 
B4 
211/4 
54 
M 
B5 
321/2 
82 
M 
B6 
301/2 
77 
F 
B7 
221/2 
57 
F 
B8 
19 
48 
F 
Gl 
31 
79 
M 
G2 
33 
84 
F 
of the bottom. Shocking was accomplished by 
capacitor discharge. A coupling transformer 
isolated the system from the 115 volt AC line. 
Voltage was controlled by a Variac transformer. 
A fullwave selenium rectifier produced DC 
which charged a bank of capacitors. The charge 
was released by a toggle switch controlling a 
solenoid switch, the latter with heavy contact 
points. A double-pole, double-throw knife 
switch enabled the selection of electrode pairs 
at either end of the tank. The best field was 
produced at a charge of 90 volts, the maximum 
rating of the capacitors. 
Visual cues were made of Munsell color 
standards 4 on high gloss paper, possessing 
known values of hue (color), value (bright- 
ness), and chroma (saturation), based on the 
human eye in air. 5 
All targets had an area of 9 sq inches, and 
consisted of white (N9/) squares, circles, 
equilateral triangles, and rectangles (1.8 X 5 
inches), grey squares with values ranging from 
white (N9/) to black (Nl/), and colored 
squares with the following characteristics: red 
(5R5/14), yellow (5Y5/6), green (5G5/8), 
blue (5B5/6), and purple (5P5/9.2). All 
colored targets were equal to medium grey 
(N5/) in subjective brightness for the average 
human eye. The targets were glued to panels 
4 Munsell Color Company, Inc., 2441 North Cal- 
vert Street, Baltimore 18, Maryland, U.S.A. 
5 A complete description of the system of specify- 
ing color, with graphs for conversion to other 
systems, is given by the American Society for Testing 
Materials (astm Standards, Part 8, 1958). 
of vinyl floor tile which had been painted dull 
black. 
Continuous illumination was provided by a 
fluorescent light fixture, located about 6 ft 
above the center of the tank with its long axis 
parallel to that of the tank. Similar fixtures 
elsewhere in the shark house contributed only 
slightly to the illumination, which was mea- 
sured with a Weston Illumination Meter 
(Model 756) with Viscor filter. The remote- 
measurement paddle was housed in a water- 
proof plexiglass covering. Incident light, 
measured 1 inch above the water surface at 
various points of the tank (Figure 1 ,B), ranged 
from 27 to 42 ft-c. At any point, the values 
varied only about 1 ft-c between day and night 
readings. Measurements taken below the sur- 
face of the water (1, 10, and 18 inches) 
showed vertical gradients from 37 to 30 ft-c 
in the center of the middle sections, and from 
24 to 22 ft-c in the center of the end sections. 
At the level of the targets and immediately 
adjacent to them, the illumination was 11 ft-c. 
The light and water clarity were sufficient to 
allow a submerged diver with a face plate to 
distinguish all shapes and colors of targets 
from one end of the tank to the other. 
Training and Testing Procedure 
Sharks were trained to associate selected 
targets with electric shock. This was accom- 
plished by the following procedure: 
A 
B 
^Overhead Lights 
28 ! ( 39 . 35 
28 28 3'2 3 
40 
Fig. 1. A, Experimental tank, B, incident illu- 
mination one inch above the surface of the water, 
in foot-candles. 
