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In April I posted a question to the list about juvenile fish using
tributary streams as a backwaters (nursery or rearing areas).
Determining how much of a tributary stream is used by juvenile fishes is a
study in itself. I was hoping someone on Fish-Ecology knew of a source
for this information. However, all my replies were from researchers with
a similar question.
I decided it was about time to post a reply for anyone with an
interest. The original question follows, along with my thoughts on the
subject.
>A decline in backwaters along the Lower Missouri River (a large
>floodplain river in Central United States) during the last
>century has been associated with a reduction in fish diversity and
>biomass. The lower reaches of tributary streams provide areas of reduced
>current where larval and juvenile life stages of riverine species can
>rear. These tributaries are the largest remaining source of backwaters
>on the Lower Missouri, but to my knowledge there has been no estimate
>of how much aquatic habitat they provide.
>Can anyone suggest defendable criteria for measuring the aquatic surface
>area associated with tributaries (with a reference if possible)? How far
>upstream is considered habitat for fishes from the mainstem river? Is
>this distance a function of tributary size? My best guess is to measure
>length of the tributary stream from river bank to floodplain edge off an
>air photo and multiply by mean stream width.
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The original query was in regards to a small question in my M.S. thesis.
Brown (1989) and Brown and Coon (1994) make the point that the largest
remaining source of backwaters on the Lower Missouri are tributary mouths.
My study focused on a new backwater source: scour holes created when
floodwaters breached levees during recent floods (1993, 1995). In the
thesis introduction I develop the tributary theme, then
discuss how scour holes are another source of backwaters.
Lacking a study on this subject, it would be defendable to draw a
line at the boundary between the Missouri River floodplain and the
uplands. I could then measure length of each tributary from the river to
the floodplain edge, and multiply this value by mean width of the segment
to estimate surface area provided by each tributary. However, the state
of Missouri is in the process of acquiring digital orthophotos for the
state. These have 1-meter resolution and will become available in 2
to 3 years. Because the new technology would greatly increase the
accuracy of the measurements, and because the area of tributaries is not
central to my thesis, I am not going to address this question at this
time.
The paragraph from my thesis reads as follows:
"The decline in backwater areas on the Lower Missouri River has
been associated with a reduction in fish diversity and biomass (Whitley
and Campbell 1974). Larval fish are highly concentrated in the lower
reaches of lower Missouri River tributaries, compared to adjacent main
channel areas (Brown and Coon 1994). Tributaries provide areas of reduced
current where larval and juvenile life stages of riverine species can
rear, probably functioning similar to the side channels and chutes of the
precontrol river. Although tributaries are the largest remaining source
of backwaters on the Lower Missouri River (Brown 1989), the area of
tributary water available is minuscule compared to backwater area lost due
to channelization. The number, area and volume of tributary waters has
remained relatively constant while other sources of quiet water have been
mostly eliminated. Thus, while tributaries may supply essential nursery
habitat for fish, they cannot mitigate more than a small fraction of the
lost backwater habitat in the lower Missouri River."
Brown, D. J. 1989. Larval fish abundance and assemblage structure in the
lower Missouri River and its tributaries. M. S. thesis, University of
Missouri, Columbia.
Brown, D. J. and T. G. Coon. 1994. Abundance and assemblage structure of
fish larvae in the lower Missouri River and its tributaries. Trans. Am.
Fish. Soc. 123:718-732.
Funk, J. L. and J. W. Robinson. 1974. Changes in the channel of the
lower Missouri River and effects on fish and wildlife. Aquatic Series 11,
Missouri Department of Conservation, Jefferson City, Missouri.
Galat, D. L., J. Kubisiak, J. B. Hooker and L. M. Sowa. (In press).
Geomorphology, distribution and connectivity of Lower Missouri River
floodplain waterbodies scoured by the flood of 1993. Verh. Internat.
Verein. Limnol. 26:
Kubisiak, J. (In preparation). Fish nursery use of Lower Missouri River
scour holes: the influence of connectivity. M. S. thesis, University of
Missouri, Columbia.
Whitley, J. R. and R. S. Campbell. 1974. Some aspects of water quality
and biology of the Missouri River. Trans. Missouri Acad. Sci. 7-8:60-72.
John Kubisiak
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