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A Geological and Ecological Reconnaissance off Western Oahu, Hawaii, Principally by Means of the Research Submarine "Asherah"

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Title:A Geological and Ecological Reconnaissance off Western Oahu, Hawaii, Principally by Means of the Research Submarine "Asherah"
Authors:Brock, Vernon E.
Chamberlain, Theodore C.
Date Issued:Jul 1968
Publisher:University of Hawai'i Press
Citation:Brock VE, Chamberlain TC. 1968. A geological and ecological reconnaissance off western Oahu, Hawaii, principally by means of the research submarine "Asherah". Pac Sci 22(3): 373-394.
Abstract:In November 1965 a combined geological and ecological reconnaissance
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 automatic
stereo-camera system, and some bottom dredging and trawling were undertaken
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
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 seaward
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 . Th is served to
confirm the information obtained and to add new and significant detail.
Appears in Collections: Pacific Science Volume 22, Number 3, 1968

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