Sari Sommarstrom sari at sisqtel.net
Fri Jul 25 14:35:39 PDT 2014

Any relevance to Klamath & Trinity PIT tagging efforts? Any evaluation
studies on coho tagging?

Study Suggests Sedating Chinook When Radio-Tagging Improves Returns To
Spawning Tributaries 
Posted on Friday, July 25, 2014 (PST) 

Sedating fish to implant radio tags, instead of collecting and restraining
them without sedation, significantly reduces the impacts of the procedure on
fish used throughout fishery research.


Radio-tagging fish for research, whether juvenile salmon and steelhead or
adults, results in unaccounted-for losses when conducting fish studies.


Yet, research is generally conducted assuming that there are no, or minimal,
impacts on the tagged fish and so seldom take losses into account.


A study of the radio-tagging procedure on both adult chinook salmon and
adult steelhead using both the collecting and restraining technique, and
sedating with Eugenol-based anesthesia on the Willamette River found that
sedated chinook reached their spawning tributaries 82 percent of the time,
while those that were restrained without sedation when inserting the radio
tag arrived at their spawning tributary 47 percent of the time.


In addition to the longer term impact (escaping to the spawning tributary),
the study found improvements in short term impacts: anesthetized fish were
less likely to head back downstream after the radio-tagging procedure,
according to lead author Chris Caudill, assistant professor in the
Department of Fish and Wildlife Sciences, College of Natural Resources at
the University of Idaho.


"Clearly, the results recommend that fish should be anesthetized whenever
possible, both for the sake of the fish and to minimize the potential for
tagging effects to bias study results," Caudill said.


The article, "A Field Test of Eugenol-Based Anesthesia versus Fish Restraint
in Migrating Adult Chinook Salmon and Steelhead," appeared in the July
Transactions of the American Fisheries Society,
7BresultBean.queryID%7D#.U9E_HvldVqV.  Its authors are Caudill; Michael A.
Jepson and George P. Naughton, research support scientists; Steven R. Lee
and Travis L. Dick, scientific aides; and Matthew L. Keefer, research
scientist. All are in the Department of Fish and Wildlife Sciences, College
of Natural Resources at the University of Idaho.


The study also included Willamette River winter steelhead. The researchers
found little difference in either fallback or escapement for steelhead
between restraint and sedation, apparently because some species are more
susceptible to handling effects than others.


"We don't have a good explanation for this result, but presumably it stems
from differences in physiology between the two species," Caudill said.
"Regardless, it does caution against extending results from one species to
another without confirming the effects are similar across species."


The study was conducted at the Willamette Falls Dam, a combined
hydroelectric project and natural falls near Oregon City, Ore. on the
Willamette River, one of the Columbia River's largest tributaries. Spring
chinook were collected at the dam every other week from April 16 to July 2,
2012, and winter steelhead were collected March 2 to June 16, 2012. All were
tagged: approximately half were restrained in a cradle during the insertion
of the tag and half were immersed in a bath of river water and the
Eugenol-based anesthesia.


Of the fixed-site radio receivers, ten were in the fishway or downstream,
while 34 were located in Willamette River tributaries (Clackamas, Tualatin,
Molalla, Yamhill, Santiam, Calapooia, McKenzie, Coast Fork of the
Willamette, and the Middle Fork of the Willamette rivers).


The short term component of the research tested whether fish lingered in the
dam's fishway or fell downstream after tagging. The long term component
tested escapement, whether the fish arrived at their spawning tributaries.


After release, 47 percent of the restrained chinook salmon and 20 percent of
the anesthetized salmon moved down the fishway and into the dam's tailrace.
There was no difference for steelhead between the restrained and
anesthetized fish: 17 percent of each fell back. 


Many of these fish eventually moved up to the spawning tributaries. Of the
restrained salmon, 60 percent re-ascended the fishway, while 89 percent of
the anesthetized salmon re-ascended the fishway.


Of the 17 percent of steelhead that fell below the dam, 88 percent to 90
percent re-ascended the fishway, and 79 percent to 83 percent of all
steelhead made it to the tributaries.


"The consistency across chinook Salmon studies suggest that manual restraint
may be particularly stressful for chinook Salmon," the study concludes,
going on to say that there is a "higher potential to compromise some types
of studies (e.g. survival estimation) than others (e.g. migration timing and


"These results might be applied to past tagging studies of unanesthetized
chinook salmon in the Willamette River, but I would only cautiously apply
them elsewhere," Caudill said of adjusting past research to these results.
"In either case, the results can be useful for speculating on the magnitude
of tagging effects in past studies, but it would be foolhardy to apply a
precise correction factor from our study."


Weekly Fish and Wildlife News


July 25, 2014

Issue No. 715


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