9408 - Laserfiche WebLink

Home Browse Search

1 Discrete measurements of water velocity were not made; instead, visual assessments were made of the speed of water passing over the position of a located razorback sucker. Swift current was defined as being equal to the channel current. Slow current was defined as regions of no current or current that was visually estimated to be less than 2 km/hr. The category of moderate current was given to current other than swift or slow. The depth of the water where a razorback sucker was located was estimated by approaching as close to the fish as possible and lowering a 3-m-long, incremented oar into the water until it touched bottom or until the entire oar was beneath the surface. Water depth was placed into three categories: <1.2, 1.2 to 3, and >3 meters. Equipment Performance The ability of the ATS receiver to detect transmitter signals was affected by various factors. First, the effective range of the transmitter was more than doubled by efforts to eliminate static interference generated by the outboard engine. The receiver was placed into a large army-surplus rocket box. Next, the power supply was changed from running off of the boat's battery to a small motorcycle battery that was also placed inside of the rocket box. And finally, the whip antenna was mounted on the bow so as to maximize its distance from the outboard engine. After making these modif cations, shallow water detections improved from 100 to 250 m to an average of 700 to 1000 m, with maximum detection ranges often approaching 1.7 km. Even with the increase in receiver erformance dee si nals >5 m remained difficult to P ~ p g detect due to signal attenuation. Razorbacks in the deepest portion of the channel were usually detected at less than 300 m. Since the boat was operated at a constant speed of 350 m/minute, and the receiver was able to scan all of the tag frequencies in a single minute, it was unlikely that many tags were missed during the monitoring. Additionally, all surveys were "round-trip," so each portion of surveyed river was scanned for tagged razorbacks twice each trip. Very rarely were tagged razorbacks not detected on the initial leg and later detected on the return trip. Data Analysis The condition factor, a "plumpness" index, was calculated for each razorback sucker using the equation K = [weight(grams)* 100]/[length(mm)']. A regression analysis was performed on the condition factors to determine if there was a significant positive or negative relationship between K and either length or weight. This analysis was performed on Excel `97. Next, atwo-tailed t-test was utilized to determine if razorback suckers that utilized backwater habitat had significantly different condition factors than the suckers that were not observed to utilize backwaters. The t-test was performed on Excel `97. Finally, three separate 3-factor ANOVAs were performed to determine if the condition factor of a fish would influence its selection of a particular habitat type, current 7