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<br />~
<br />
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<br />
<br />surface area changed signiricantly with the flow reductions.
<br />These physical variables are integral components of WUA.
<br />Kraft's results cannot be rejected lightly in face of the other
<br />supporting evidence on redistribution of fishes when stream
<br />flow is altered or significantly reduced (Clothier 1954: Rimmer
<br />1985). The major conclusion to be drawn is that. fishes do not
<br />respond as IFIM predicts.
<br />One source of confusion in the interpretation and application
<br />of IFlM is the method of manipulation of the data to satisfy
<br />assumptions. As indicated earlier it was originally assumed that
<br />WUA is approximately equivalent to carrying capacity and can
<br />be used as a surrogate for it. As such. relating biomass to WUA
<br />is actually equivalent of plotting "X" versus "X". Such a plot
<br />should yield a slope of I: this never occurs. However. when
<br />WUA is expressed as a percentage (a dimensionless number) of
<br />the total area. it has no physical meaning. It is puzzling to us
<br />why the relationship between percent WUA and biomass of fish
<br />(kilograms per hectare or kilograms per WUA) is tested to
<br />satisfy an IFIM assumption and then a flow recommendation is
<br />made from the relationship of actual stream flows versus
<br />WUA. If WUA is related to the stream flow and fish biomass,
<br />then why not ex'amine the relationship between natural river
<br />flows and fish biomass and get the desired result directly? We
<br />can only speculate on the possible reasons. Most correlations
<br />reported in the literature relating biomass or abundance of fish
<br />and natural river flows are negative. A negative relationship,
<br />although predictive in many cases, is not intuitively palatable
<br />to IFlM SUpporters because it implies reduced flows for greater
<br />fish biomass. '
<br />
<br />. ...... .eo .e,~sa;.~'II1i1'rd;~~TfO?
<br />!;laVa tdattonstu Y9fI~IM.l1~~~ ~y_,. .Iff~
<br />.J''YnPOSSI bre~tQ:Xafii:fatrlor"re~Qg!'gJy~n~~Jfi;'"E(M ath ur et al.
<br />1985).
<br />Since our original paper. recent publications provide evi-
<br />dence that the IFG-4 hydraulic s!mulation model (a component
<br />of IFlM) is not reliable for applications in many streams
<br />(Shirvell and Morantz 1983; Shirvell 1984; Loar et al. 1985).
<br />The errors or biases introduced via hydraulic simulations
<br />coupled with the unreliability of the WUA index in predicting
<br />fish biomass can only lead to compounding of errors and
<br />confusion.
<br />
<br />
<br />
<br />109.1
<br />
<br />a relationship (of potential habitat and population size) on
<br />blind faith. Orth and Maughan offer us nothing more - Dilip
<br />M:uhur, RMC Ellvironmeflllll Serv;c'cs, Mud(~\' RUII Ecologic-al
<br />Laboratory. 1921 River Road, P.O. Box 10, Drumore. PA
<br />17518, USA, William H. Bason, Delmarva Ecological Labora-
<br />tOry, Inc., R.D. I. Box 286, Middletown. DE 19709, USA,
<br />Edmund J. Purdy, Jr., Philadelphia Electric Company, 2301
<br />Market Street. Philadelphia, PA 19101, USA, and Carl A.
<br />Silver, Department of Statistics, Drexel University, Philadel-
<br />phia, PA 19/01, USA. (J844lb)
<br />
<br />References
<br />
<br />BAIN. M. B., J. T. FINN, L. J. GERARDI, JR., M. R. Ross, AND W. P.
<br />SAUNDERS, JR. 1982. An evaluation of methodologies for assessing the
<br />effects of flow fluctuations on stream fish. Mass. Coop. Fish. Res. Unit
<br />Contrib. No. 78. Univ. Mass.. Amherst, MA. FWS/OBS-82-63.
<br />CLOTHIER. W. D. 1954. Effect of waler reduclions on fish movement in
<br />irrigation diversions. J. Wild\. Manage. 18: 150-160.
<br />IRVINE, J. R. 1984. Effecls of varying discharge on stream invenebrales
<br />and underyearling salmon and trout. Ph.D. Ihesis. University of Otago,
<br />Dunedin, New Zealand. 254 p.
<br />KRAfT. M. E. 1972. Effects of conlrolled flow reduction on a trout stream.
<br />J. Fish. Res. Board Can. 29: 1405-1411.
<br />LARIMORE, R. W., AND D. D. GARRELS. 1985. Assessing habitats used by
<br />wannwaler stream fishes. Fisheries 10: 10-16.
<br />LOAR, J. M., M. J. SALE. G. F. CADA. D. K. Cox. R. M. CUSHMAN. G. K.
<br />EDDLEMON. J. L. ELMORE, A. J. GATZ, P. KANCIRUK. J. A. SOLOMON.
<br />AND D. S. VAUGHAN. 1985. Application of habilat evaluation models in
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<br />MATHUR. D.. W. H. BASON, E. J. PuRDY, JR., AND C. A. SILVER. 1985. A
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<br />Aquat. Sci. 42: 825-831.
<br />ORm, D. J., AND O. E. MAUGHAN. 1982. Evaluation of the Incremenlal
<br />Methodology for recommending inslream flows for fishes. Trans. Am.
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<br />RIMMER, D. M. 1985. Effects of reduced discharge on production and distribu-
<br />lion of age-O rainbow trout in seminatural channels. Trans. Am. Fish.
<br />Soc. 114: 388-396.
<br />SC01T. D.. AND C. S. SHIRVELl. 1986. A critique of Ihe Instream Flow
<br />Incremental Methodology and observalions on flow detennination in New
<br />Zealand. Proceedings Third International Symposium on Regulated
<br />Streams held on August 4-8, 1985, Edmonlon. Albena. (In press)
<br />SHIRVELL, C. S. 1984. Review of incremenlal flow type methodology for
<br />assessing the effects of reduced stream flows on fish populations. Can.
<br />Tech. Rep. Fish. Aquat. Sci. No. 1234: 83 p.
<br />SHIRVELL. C. S., AND D. L. MORAmz. 1983. Assessment of the Instream Flow
<br />Incremental Methodology for Atlantic salmon in Nova Scotia. Trans.
<br />Can_ EJecl. Assoc. Eng. Oper. Div. 22: 83-HJ.108: 22 p.
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<br />Can. 1.. Fish. Aqllal. SC'i.. Vol. 41.. 1986
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