178 
PACIFIC SCIENCE, Vol. XII, April, 1958 
DISCUSSION 
Investigations of sound scattering of bio- 
logical origin are being pursued for their 
bearing on studies of animal behaviour, dis- 
tribution and ecology (Hersey and Moore, 
1949; Moore, 1950), physiology (Kampa and 
Boden, 1954^/ 1954^) and on fisheries biology 
(Richardson, 1952; Haffner, 1952). Not all of 
the physical characteristics of those inverte- 
brate organisms which cause scattering are 
understood as yet (Smith, 1951, 1954), but 
the air bladder in certain fish is regarded as 
an excellent scatterer of sound (Marshall, 
1951; Hersey and Backus, 1954). The princi- 
ples emerging from investigations into these 
various aspects of the subject may be gen- 
erally applicable, but such principles are only 
to be derived from specific, detailed observa- 
tions from many different localities. 
Scattering layer development may vary from 
one area to another. Some of the variation is 
attributable to the distributions of the differ- 
ent organisms which are able to effect the 
scattering. Moore (1950) has discussed such 
variations in scattering in relation to the dis- 
tributions of several species of euphausiids in 
the north Atlantic. On the other hand, strong 
development of layers could result from those 
high concentrations of animals which may be 
associated with areas in which intermixing of 
contiguous bodies of water of differing prop- 
erties is taking place. Thus localised scattering 
might well occur in the upwelling waters be- 
lieved to be present at several localities about 
New Zealand (Garner, 1953). On a larger 
scale, scattering could be associated with the 
—possible— extensive disruption of the water 
layering and the resultant mixing of the waters 
where north-south moving masses cross the 
Chatham Rise (Fig. 1). This topographic bar- 
rier to unrestricted flow rises from about 2800 
m. to within 450 m. of the surface and lies 
Fig. 8. Probable fish records combined with layers 
of plankton (on the left of the record). The latter are 
visible as three or four ascending layers cutting through 
the dense fish record; "Discovery II” record, D3. 
