7979

• UCREFRP Catalog Number: 7979
• Author: Tyus, H. M.
• Title: Fish Radiotelemetry
• USFW Year: 1982.
• USFW - Doc Type: Theory And Application For High Conductivity Rivers.
• Copyright Material: NO

Results and Discussion
Figure 5. Insertion of AVM fish module into anesthetized Colorado
squawfish.
Figure 6. Suturing Colorado squawfish with surgically implanted
radio transmitter.
The equipment functioned satisfactorily in March. At this time, water
conductivities were about 500 pmho, and it was not difficult to locate fish.
(Table 4). The Larsen Kulrod whip antenna, coupled with the RF-40 receiver,
allowed workers to easily identify signals up to 200 m away from a fish. The
less effective loop antenna had a range of approximately 50 m. The Smith-Root
search receiver was ineffective and had to be returned to the manufacturer for
a tuning adjustment; after tuning, it performed satisfactorily.
On the day of its release (April 15), Fish No. 001 was monitored with the
Smith-Root RF-40 receiver and whip antenna while it was in the river holding
pen. The fish could be detected across the river, a distance of 150 m. The
maximum water depth in the pen was 1.5 m and water conductivity was 812 umho.
This conductivity severely limited the range of both antennas. The range of
the loop antenna was decreased from 50 m in March (conductivity of about
500 umho) to about 30 min April (conductivity of about 800 pmho). In addition
to the increasing conductivity affecting detection, another phenomenon was
noted. The received radio signal would alternately become stronger and weaker
and, occasionally, the signal could not be detected. Apparently this response
was attributed to movements of the fish in the pen which changed the position
of the transmitting antennas.
Fish No. 001 was released at the mouth of a small backwater (the initial
capture point) and its movements were monitored for approximately eight hours.
The fish moved into midstream and usually remained near a shallow (0.5 m) sand
bar. Radio reception was-good enough to .locate the fish across the river
(about 100 m) with the elevated whip antenna, but not with the loop antenna.
After location, the fish was approached by boat and its position pinpointed
with the loop antenna. Water depths in this portion of the river were less
than 1.5 m and conductivity was 810 pmho. The river was broad, with many
sandy bars and shoals, especially in midchanrtel.
On the morning of April 16, the fish moved downstream and contact was
maintained with the elevated whip antenna. River depth had increased in some
reaches to a midchannel depth of about 2 m. The maximum range from the boat
to the fish using the elevated whip antenna was about 150 m during the day
(water conductivity 780 pmho). It was difficult to obtain a good signal at
the end of the day. This was apparently caused by the fish moving into a
shallow backwater next to a relatively steep dropoff which probably blocked
the signal.
Early on April 17, fish No. 001 was relocated with the elevated whip
antenna at an approximate distance of 175 m in a shallow side channel. When
located, the boat was in the main channel opposite the mouth of the side
channel. The exact position of the fish (0.5 m deep) was located by using the
loop antenna on foot. At times, the fish was visible, and the loop antenna
could detect the signal to a distance of approximately 50 m.
During the afternoon, the fish moved down the side channel into an area
about 3 m deep. There were momentary losses of contact even with the elevated
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