Page last modified
May 12, 2005
Research Activities and Results
sound to detect objects in water. Basically, it is like using
a sophisticated fish finder. In a River situation,however, we
the transducer sideways to look across the river, and track fish
travelling through the sound pulse. Every second, at least 3
pings of sound are produced by the transducer. Objects in the
reflect some of that sound back and the charactistics of the
sound received is used to determine an objects size, direction
Sound is measured in decibels. Scientists
use the "target strength" of an object to estimate its size.
will have a greater target strength than smaller objects. For
decibels (dB) and -15 dB. Small fish like a bass or perch may have
target strengths between -45 and -35 dB.
monitor adult migration, distribution, and timing in the Salmon
we installed a Simrad EY500
120 kHz split-beam hydroacoustic system at the Lighthouse Marina site, and recorded
data continuously from September 6 until November 1, 2004. A 7-degree conical
transducer was mounted on an aluminum pole, aimed horizontally across the river,
at a depth of 0.6 m. from the bottom. Data were downloaded daily from the site.
The Salmon River outlet
analyses and results
We used Sonar5 software for post-processing and analysis of
data (Balk and Lindem 2002). To determine diel and water column
distribution of adult salmon, we originally
planned to conduct snorkeling observations, but the turbidity of the river
precluded this method. Instead, we used our sonar data to determine
patterns. We selected data from September 15, 2004, in which 384 adult salmon-sized
targets passed through the beam. Only targets with a mean target-strength (TSc)
greater than –35 dB and a mean upstream velocity (mean Vx) greater than
0.1 m s-1 were counted (Figures 2a and 4). Data were stratified into six 4-hour
periods, and three 1/2-hour samples were randomly selected and analyzed from
each period. We are currently analyzing hydroacoustic data to estimate total
adult salmon migration and timing to compare with data obtained by other
Preliminary results show that
average length of migrating salmon on September 15th was 63 cm,
ranging from 31 to 121 cm (Figure 2b)
significantly more at night (Figure 3), with migrating
salmon totaling 368 at night compared to 16 fish during the
day (t-test, p=0.009). .
Figure 3. Diel distribution of tracked migrating adult Chinook
salmon in the Salmon River, New York, September 15, 2004
to swim in the mid-water column, slightly below the transducer’s
x-axis (mean Alo=-0.83o), equivalent to a mean depth of 2.3
meters (Figure 4).
Figure 4. Distribution of tracked migrating adult
Chinook salmon relative the transducer in the Salmon River, New
York, September 15, 2004.