PACIFIC SCIENCE, Vol. XII, April, 1958 
proximately 1.5 m. per minute. The first 
begins to ascend at about 2130 hours, arriving 
at the surface around 2240; the second layer 
begins 15 min. later than the first and arrives 
at the surface at 2300 hours. Depth of water 
is between 102 and 124 m. The nighttime 
concentration of organisms at the surface is 
masked by the transmission signal. However, 
marked concentration in depth becomes ap- 
parent in the 15 to 20 minutes preceding the 
dawn descent (Fig. 3. This record is part of 
that shown in Fig. 2). This single layer begins 
to descend at 0645 hours. Downward migra- 
tion is approximately 2.1 m. per min. during 
the first 30 minutes, but over the next 45 
minutes the rate is slower, at approximately 
1.3 m. per min. The layer retains its entity for 
a short while after it has reached the bottom. 
Early stages in the descents of two separate 
layers are illustrated in Figure 4, a "Lachlan” 
trace from north of Cape Palliser (L4, in Fig. 
1). The first layer descends clear of the trans- 
mission signal at approximately 0430 hours 
and after a short descent appears to split into 
two layers. One of these two appears to join 
with a second, dense layer which begins to 
descend about 15 minutes later than the first. 
Rate of descent is at about 2 m. per min. In 
a "Galathea” record made over the Chatham 
Rise and shown in Figure 5 (G3, in Fig. 1), 
two separate layers, preceded by a dense sur- 
face concentration, are shown during the 
dawn descent. The downward migration com- 
mences about 0400 hours and is strongly in 
evidence by 0500 hours. Both layers appear 
to split into two. Rates of descent approxi- 
mate 1.3 and 0.6 m. per min. respectively for 
the first and second layers. The record rather 
abruptly fades out at 0515 hours. 
A second "Galathea” record, Figure 6, 
shows a scattering layer at its daytime level. 
At its deepest the layer is at about 183 m., 
but its depth varies considerably. This record 
was made between 1100 and 1230 hours in 
Fig. 2. The evening ascent of two separate layers in 
shallow coastal waters — the southern end of "Lachlan” 
record, L2, in Figure 1. 
