BOARD00438

• Board Meeting Date: 5/19/2003
• Description: EDO Director's Report
• Board Meetings - Doc Type: Memo

05/09r2003 16:09 FAX [phone]
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A/S FISH/WILDLIFE/PARK

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Aguatic Invertebrates: Aquatic invertebrates are the lifeblOod of the 10tic food web. Immature
and adult stages of most aquatic insects and other aquatic invertebrates are important links in the
food chain because they convert plant material into anili1al,tissue that is utilizable by carnivorous
fishes. Only recently have scientists discovered that many ,of these species occupy habitats
between the surface stream and the alluvial groundwater. rms underground ecosystem, tenned
the hyporheic zone, supports a vast array of aquatic insect~, bacteria, and algae.

In the Gunnison River; the relationship between stream fldws and the dynamics of the food web
is not well known. Stanford and Ward (2001) believe priinary food production (algal and
invertebrate) is cOlTelated with the geomorphic characteri$tics (e.g., substrate type and size,
channel morphology, stream gradient) of a reach. They found extensive hyporheic habitats and
aquatic biota (some of which may be new to science) witQin gravel bars in Black Canyon and
concluded that the formation and maintenance of gravel hars and interstitial flow are essential to
maintaining this forage base in the Gunnison River. They further concluded that spring flows are
necessary to flush and re-aerate gravel deposits, and occailionallarge flows are needed to
redistribute and build new gravel deposits and biotic hab{tats.

To protect aquatic invertebrate populations and habitats in the main stem channel and atijacent
alluvial deposits requires peakflows to redistribute sediment, and circulate water, oxygen, and
nutrients through the channel alluvium. Pealai between;2,500 cfs and 10,000 cft effectively
mobilize gravels and cobbles within the low flow channel, acijacent low flow balllai, and overflow
channels; thus serving to scour attached algae,flush entrained organic matter, re-oxygenate'
channel alluvium, and wet aquatic habitats within the active channel. Flows in excess of 10,000
cfs, which move gravels and cobbles on lateral gravel bi;lrs, are needed to rejuvenate and create
new aquatic insect habitat. Appropriate ramping rates (lssociated with the peak must allow,
ample time and opportunity for hyporheic and other aquatic insects to respond to changingflow
condition.,. Year-round minimum flows of at least 300 cfs (dependent on natural inflow) are
needed to maintain occupied habitats throughout the ydar. (Stanford and Ward, 2001)

Fish: Prior to consttuction of the Aspinall Unit, the riv~r reach within BLCA was a transition
zone between the upstream cold-water fishery and the q.ownstream warm water fishery (Kinnear
and Vincent, 1967). Brown and rainbow trout were present in the Monument at the time of
establishment. Both species were introduced into the upper Gunnison drainage during the late
1800's (Behnke, 1993). Presently, the reach through the Park (and downstream to the confluence
with the North Fork of the Gunnison River) is designa~ed Gold Medal Water and Wild Trout
Water by the Colorado Division of Wildlife (CDOW),:indicating a self-sustaining, high quality
rainbow and brown trout fishery. ;
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Analyses conducted by BOR (1990) in conjunction w~th the AB Lateral Hydropower Facility
suggest that flows of300 cfs provide 70-80% of opti~um summer and winter habitat conditions.
Rainbow and brown trout spawning habitat in these same areas is maximized at flows of 500 cfs;
yet 300 cm provides nearly 85-90% of optimum. BOR also found substantial habitat gains for all
life stages by increasing minimum base flows from 200 to 300 cfs. Flows below 300 efs cause

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