A Geological and Ecological Reconnaissance off Western Oahu, Hawaii, 
Principally by Means of the Research Submarine "Asherah ” 1 
Vernon E. Brock and Theodore C. Chamberlain 2 
ABSTRACT: In November 1965 a combined geological and ecological reconnais- 
sance of the sea floor off western Oahu was undertaken using a variety of methods 
and techniques to maximize both the range and reliability of the information 
obtained. Bottom topography and fish concentrations were surveyed with a precision 
echo sound recorder for which the transducer was towed in a streamlined housing 
below the research ship. Photographic bottom surveys were also made with an auto- 
matic stereo-camera system, and some bottom dredging and trawling were under- 
taken to secure samples of the bottom and the biota. Direct visual observations were 
also made using a small research submarine largely in the depth range of 25-180 
meters. 
The dominant geological features were a series of submerged, wave cut, largely 
sand covered terraces separated by rocky escarpments. The major terraces were an 
upper one terminating seaward at approximately 60 meters, an intermediate one 
from 70 to 120 meters, and a deep one beginning from a shoreward depth of 180 
meters or deeper. 
Patterns of littoral sand movement were observed to be southerly in the region 
between Kaena Point and Kepuhi Point with a substantial movement offshore. It 
was estimated that approximately 10,000 cubic yards of calcareous sand move sea- 
ward and are deposited annually on the inner portions of the deep terrace. 
Associated with the escarpments were large and discontinuous aggregations of 
fish and, on the upper and intermediate terraces, extensive beds of the clam Pinna 
muricata. The observed patterns of distributions may be a response to the localized 
accumulation of food. Organisms which make nocturnal vertical migrations in 
adjacent deep water may be swept shoreward by surface currents and become 
trapped on the terraces. The collection of planktonic organic material in the 
thermocline where the water increases rapidly in density with depth may be a 
mechanism for the localized accumulation of particulate food of value to the clams. 
The simultaneous use of a variety of observational techniques in an area provided 
non-identical and independent observations of the same situations. This served to 
confirm the information obtained and to add new and significant detail. 
During November of 1965 a reconnaissance 
of the sea floor geology and of the marine 
ecology off western Oahu, Hawaii was made 
using a remotely operated stereo-camera system, 
a precision echo sounding recorder, biologic and 
geologic dredges, and, most importantly, a two- 
man deep-diving research submersible vehicle. 
1 Contribution 283, Hawaii Institute of Marine 
Biology. Manuscript received September 12, 1967. 
2 Department of Oceanography, Hawaii Institute 
of Geophysics, University of Hawaii, Honolulu, 
Hawaii 96822. 
Surface support was supplied by the University 
of Hawaii’s 90-ft research vessel, the "Teritu.” 
The intent of the investigation was to make a 
series of direct observations of the geomorphol- 
ogy and the biota by means of the submersible 
vehicle and to correlate with these observations 
data collected at the same time and in the same 
area by means of conventional, indirect data- 
gathering techniques (submarine photography, 
biologic and geologic dredging, etc.). The ex- 
periments were successful: 15 deep dives were 
made with the research submarine, most to 180 
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