Olfaction and Sharks— Tester 
149 
they were confined in two-thirds of its length 
by a fence. Observations were conducted on the 
shark population from the 16-ft tower which 
had been moved to a central location along one 
side. Usually the sharks would swim back and 
forth along the length of the enclosure in a 
channel which averaged about 9 ft in depth. Oc- 
casionally the tiger shark and the hammerheads 
( but rarely the greys ) would traverse the length 
of the pond in shallows 1—4 ft in depth along 
the side of the pond opposite to the tower. Two 
testing techniques were employed which are 
henceforth referred to as "point” and "curtain- 
funnel” or "curtain-drum” introduction. In both, 
activity was recorded during the usual control 
and test periods in a test area 50 ft in length 
and extending across the width of the pond. 
The area, centrally located in front of the tower, 
was marked off by cords which stretched across 
the pond and were several inches above the 
water surface at high tide. 
In "point” introduction the material was con- 
tained in a 5 -gal funnel on top of the tower and 
was introduced at a point either just below the 
surface or at a depth by means of a rubber tube 
suspended from a boom (Fig. 5). In "curtain- 
funnel” introduction the material passed from 
the funnel to a perforated hose running trans- 
versely across the bottom of the pond at the 
center of the test area and extending part way 
into the shallows. In a modification, used in the 
spring and summer of 1961 and called "curtain- 
drum” introduction, a continuous stream of salt 
water was pumped into the hose before and 
during control conditions; the stream was then, 
switched to a 50' gal drum containing about 40- 
gal of sea water together with the test material 
After introduction, which usually consumed 
about three 3 -min test periods, the flow was 
again switched to salt water. With both methods 
care was taken to prevent the generation of air 
bubbles in the curtain for they produced a vari- 
able visual response. By using dye it was found 
that the curtain was fairly uniform and rela- 
FlG. 4. View of Pond 
E. S. Hobson.) 
5 at Hawaii Marine Laboratory showing the observation tower. (Photograph by 
