tted by ships is
id weak forward
mining the three-
nderwater noise
hool distribution
Jated.
Ó—À—M—
a
í snmmsendenmees
Starboa
100m
of fish school
Jance.
teristics of fish
ul to identify the
the school (Weill
and Simmonds,
ervation using
> range because
sawater (Pitcher
ine that moving
with the convex
ovement. In this
' were classified
or to test the
nd species or
-Crosswise ratio
nsion, and fish
. characteristic
matrix of three
pth, elongation,
value). The
ters show that
leep water, and
Port
i Forwarding dire con >
T
Forwarding direction
Figure 6 Perspective image of plate type fish
school by surface rendering.
Viewpoint, lighting angle, shading, cropping, cutout
can all be controlled to produce the best expression.
Fish schools, observed and analyzed by three-
dimensional shape analysis were classified into three
types: plate type. stick type. and mixture type.
The plate type fish schools were thin vertically, but
covered large areas (Figure 6). The scale of the fish
schools in the horizontal plane was 139m x 152m.
Such fish schools were abundant at 10-30 m depth.
The mixture type fish schools (Figure 7) were
composed of several small schools. The shape of
perspective image changed drastically with changing
viewpoint. The mixture type fish schools frequently
occurred between 30-m depth and the sea bottom.
The stick type fish schools were long and narrow, and
parallel to the sea surface (Figure 8). The shape of the
perspective image also changed deepening on the
viewpoint angle. These fish schools measured 556 m
long and 30 m long in diameter, and occurred at all
depths.
4. DISCUSSION
4.1 Three-Dimensional Distribution of Fish School
and Avoidance Behavior to the Ship
733
ee ries a -
ism wi
Starboard
«pee dam ———»!
Figure 7 Perspective image of mixture type fish
school by surface rendering.
i ue
e
1
I
Starboard
C
Figure 8 Perspective image of stick type fish
school by surface rendering.
In general acoustic fish resource surveys, fish school
echoes are sampled with a vertical echo-sounder that
has about a 10-degree beam width. However, as
shown in Figure 5, the echogram only scans a vertical
cross section under the ship's course. So when