Raymarine Marine GPS System User Manual page 125

RayTech Navigator User's Guide
Fish Indications
5-34
When the Fishfinder detects a fish, it displays an arch-shaped mark.
In general, a larger arch indicates a larger fish, though this is not
always true. For example, if there are two fish of the same size:
one is close to the surface, the other is near the bottom. The fish that
is close to the surface has a larger arch because, being closer, more
sound waves are returned to the Fishfinder.
The sound waves are actually reflected by an air sac near the center of
the fish, not by the body of the fish. The size of this air sac is different
for different kinds of fish and this can affect the size of fish arches on
the image. A fish with a large air sac produces a large fish arch, while a
fish with a small sac produces a small arch. Several arches together
show a school of fish. Figure 5-11 shows some example target images.
To display the depth of the fish:
1. Click
MENU
2. Click
TARGET DEPTH ID
Figure 5-11. Sonar Target Image Key
on the Pathfinder Panel
.