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Subject: Re: residualism in hatchery steelhead smolts
From: Geoff McMichael <[log in to unmask]>
Reply-To:Academic forum on fisheries ecology and related topics <[log in to unmask]>
Date:Wed, 24 Jul 1996 09:26:03 -0700

text/plain (53 lines)

>        I was wondering if there has been a high
>incidence of residualism occurring in the Snake
>River Basin within the last 10 years or so.  From
>what I've read it seems that residualism may occur
>under low flow conditions or if hatchery steelhead
>smolts are released at a 'larger-than-normal' size.
>        If residualism is occurring, is it a
>significant percentage of the hatchery releases
>during certain years, and if it is significant,
>what may be triggering it.
>        I would appreciate any thoughts on this, or
>direction toward steelhead field biologists who may
>have practical experience with such phenomena.
>        Thank you.
>                        Jon Firehammer
>                        [log in to unmask]
>        There has been a lot of work done in that area as well as other
areas in WA looking at incidence and effects, and to some extent, causes of
and ways to reduce  residualism in hatchery steelhead.  My average overall
guess for residualism in hatchery steelhead is about 15%. I have seen rates
closer to 40% with some regularity. Most research indicates fast growth
conditions in hatchery environments tend to produce many fish that make a
life history decision not to emigrate.  There are also systems where wild
steelhead produce predominantly age 2 and 3 smolts while wild broodstock
offspring are expected to smolt at age 1. The genetic component of age at
smolting rears its ugly head when wild broodstock from these systems are
used to try to produce age 1+ smolts. There is a lot of gray as well as
published literature on this subject, but as usual not all questions have
been answered.  Just a word of caution when reading through the literature
on the subject, as some report non-migrant rates while some report
residualism rates... many residualism estimates are derived by trapping
outmigrants, then subtracting the number of outmigrants from the known
release number.  In some cases the 'non-migrants' equate with residuals in
situations where mortality of non-migrants is low.  There are situations
where mortality of migrant and non-migrant hatchery steelhead is quite
high... and it is in these areas where non-migrants do not necessarily
result in residuals.  The ecological implications of large numbers of
residual hatchery steelhead in streams is great.  We have documented adverse
impacts on resident rainbow trout growth and abundance resulting from
residual hatchery steelhead presence.  To get our latest annual report call
BPA in portland (503) and ask for report number BP-99852-2.  Our next one
should be out within a few months and there are two publications concerning
this issue in review/press right now. Here are some other contacts:
        Art Viola, WDFW, Dayton, WA - work on Tucannon R. (509)382-4755
        Tim Whitesel, ODFW, Grande Ronde/Umatilla systems (541)962-3777
        myself, Geoff McMichael, WDFW, Yakima R. basin, WA (509)925-4467
        Jack Tipping, WDFW, Cowlitz and statewide, (360)978-4962

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