LENTIC SESTON ENHANCEMENT OF

TAILWATER FISHERIES

John S. Sproul1, Kent A. Hatch2, Dennis K. Shiozawa3

 

1Biology Program, Brigham Young University, Provo, Utah 84602 USA; 2Long Island University, C.W. Post Campus, Brookville, NY 11548 USA; 3Department of Biology, Brigham Young University, Provo, Utah 84602 USA

 

What makes tailwater fisheries so productive?

Thermal Hypothesis - High productivity seen in tailwaters may be largely attributed to the thermal effects of the impoundment.

• Impoundments act as temperature buffers to tailwaters• Hypolimnetic releases create cooler summer highs and warmer winter lows in tailwaters

• These buffered temperature conditions provide more degree-days for invertebrate growth and optimal conditions for growth and development of fish

Thermal Hypothesis

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Green River prior to FG Dam 1958-1959 (USGS Greendale Gage 09234500)

Green River below FG Dam 2004-2005 (USGS Greendale Gage 09234500)

Thermal Hypothesis

Is temperature the only factor affecting productivity?

• The sources of the energy generating the increase in productivity are not fully defined in the thermal hypothesis. • The emphasis on moderated temperatures alone implies that autochthonous primary production is also enhanced during the extended growing season and that it results in the increased secondary production in the tailwater system. • Yet many investigators have measured significant densities of zooplankton rich reservoir seston in tailwaters.• We attempted to quantify the subsidy of reservoir seston (zooplankton) on tailwater food-webs.

Alloctonous Carbon Source

Autocthonous Carbon Source

Additioinal Allocthonous Carbon Source (animal protein)

*Organisms expanding their diet to include reservoir zooplankton are likely to show an upward shift in trophic position.

Methods

-We collected invertebrates below impoundments of three reservoirs-We compared their stable C and N isotope ratios to invertebrates above the respective reservoirs. -We also analyzed stable isotope ratios in drift, as well as zooplankton netted from the reservoirs.

-We performed MANOVA’s to test for significant differences between sites.

Results

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Hunt A and Hunt B

Hunt A

Hunt B

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Sco A and Sco B

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Carbon

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Straw A and Straw B

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Straw B

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D. Fork and 6th Water

D. Fork

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Results

Results

Results

Results

ResultsNitrogen

Location Species Mean Below Mean Above Mean Diff. DF t-Value p-Value

Electric lake Drift 4.106 3.211 0.896 32 -3.157 0.0035

  Baetis 7.375 5.808 1.556 23 -11.326 <0.0001

  Cynigmula 6.74 5.6548 1.085 9 -4.484 0.0015

  Drunella g. 7.709 5.627 2.036 21 -5.705 <0.0001

  Rhyacophila 9.314 7.503 1.882 18 -4.208 0.0005

  Simuliidae 7.561 5.327 2.234 10 -3.247 0.0088

Strawberry Dam Drift 7.519 3.084 4.435 31 -3.885 0.0005

  Baetis 11.226 6.084 5.141 24 -5.646 <0.0001

  Epeorus 10.808 5.845 4.963 9 -1.717 0.1201

  Simuliidae 10.315 6.005 4.309 17 -3.783 0.0015

Strawberry Tunnel Drift 7.645 1.26 6.385 32 -13.802 <0.0001

  Baetis 8.646 6.097 2.549 19 -4.56 0.0002

  Brachycentrus 9.974 5.597 4.376 9 -7.205 <0.0001

  Drunella g. 11.522 6.334 5.187 10 -9.098 <0.0001

  Hydropsyche 11.139 7.322 3.818 18 -10.948 <0.0001

  Pteronarcella 9.753 4.816 4.937 12 -6.551 <0.0001

  Rhyacophila 11.66 6.938 4.722 12 -4.436 0.0008

  Simuliidae 10.74 4.623 6.118 10 -28.999 <0.0001

Scofield Drift 5.25 1.097 3.334 32 -3.48 0.0015

  Asellus 7.409 7.679 -0.27 15 0.456 0.655

  Leech 10.456 11.09 -0.634 9 0.8 0.4444

  Simuliidae 7.56 5.685 1.875 18 -3.37 0.0034

Conclusions

• Lentic seston can provide a significant subsidy to the food base in tailwater food-webs.

-The importance of this subsidy likely varies with factors like reservoir trophy, volume of discharge, etc.

• Future studies could investigate the distance downstream that the isotopic signal of the reservoir persists.

• An understanding of these dynamics can influence management decisions as agencies consider the impact of restoring natural flow/temperature regimes to impounded rivers.

Acknowledgements

-Keith Tanner, Heather Stutz, Michelle Barney, and Chris Hansen for field and laboratory work.  

-Funding came from a grant from the Roger and Victoria Sant Educational Endowment for a Sustainable Environment, to Dennis K. Shiozawa.