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S. Juhnke

Publications and source records attributed to S. Juhnke.

3 recordsLinked to original sources
USGS2011

Effect of dietary salt on migration and survival of yearling steelhead produced at Iron Gate Hatchery, Klamath River, 2009

We surgically implanted radio transmitters into 30 hatchery yearling steelhead (Oncorhynchus mykiss) released from Iron Gate Hatchery during the spring of 2009 to improve our understanding of the effect of dietary salt on their out-migration and survival. Steelhead yearlings were divided into two feed treatments to test the efficacy of a salt-enriched feed in promoting out-migration. Fish were fed either their regular diet (control treatment) or a salt-enriched diet (test treatment) for 38 d prior to their release. We implanted 15 fish of each treatment with radio transmitters for a total of 30 tagged individuals. Nine of the radio-tagged steelhead (four of the control treatment; five of the test treatment) completed their downstream migration to the estuary within the 60-d operational period of the tags. Tagged fish migrated from the hatchery release site to the estuary in an average of 45 d. Neither migration nor survival differed between diet treatments, but small sample size and the relatively short duration of this study limit the conclusiveness of our findings.

California↗
USGS2007

Effects of antenna length and material on output power and detection of miniature radio transmitters

The optimal antenna of transmitters used in small aquatic animals is often a compromise between efficient radio wave propagation and effects on animal behavior. Radio transmission efficiency generally increases with diameter and length of the conductor, but increased antenna length or weight can adversely affect animal behavior. We evaluated the effects of changing antenna length and material on the subsequent tag output power, reception, and detection of tagged fish. In a laboratory, we compared the relative signal strengths in water of 150 MHz transmitters over a range of antenna lengths (from 6 to 30 cm) and materials (one weighing about half of the other). The peak relative signal strengths were at 20 and 22 cm, which are approximately one wavelength underwater at the test frequency. The peak relative signal strengths at these lengths were approximately 50% greater than those of 30 cm antennas, a length commonly used in fisheries research. Few significant differences were present in distances for the operator to hear or the telemetry receiver to decode transmitters from a boat-mounted receiving system based on antenna length, but the percent of tagged fish detected passing a hydroelectric dam fitted with an array of receiving systems was significantly greater at the antenna length with peak output power in laboratory tests. This study indicates careful choice of antenna length and material of small transmitters can be used to reduce weight and possible antenna effects on animal behavior, to maximize tag output power and detection, or to balance these factors based on the needs of the application. ?? 2007 Springer Science+Business Media B.V.

Conference Paper↗