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Sin 40c/; E ?Jfl NOTES 0 A Critique of the Instream Flow Incremental Methodology Rl1C-`.fudd% Run. Ecological Labonrtor. 11.U Box 10, Drumore, PA t-; 1`1. t;SA William f L Bason Ln?7?-Ir? Delmarva Ecnfoeical Laboratory, Inc.. R 0 I M-x 286, Middletown. Of. "i-t'9. USA 'I P KNAf Edmund (. Purdy, Jr. Op, Phi!advIp.hi,I Electric Company, 2301 Vari.et 1?t-eet, Philadelphia, PA I(I10F. ( ISA and Carl A Silver Depardnent of Statistics, Drexel UnP,enit Philadelphia, PA 1911)1. (';:l Mathur, D., \•V. H. Bason, E. I. Purdy, Jr., and C. A. Silver. 1985, A critique of the Instream Flow Inc emental Methodology. Can. J. Fish. Aquat. Sci. 42: 825 831. A review and reanalysis of the published literature show that several assumptions are violated in the application of the Instream Flow Incremental Methodology (IFIM) without consideration of the implica- tions of so doing. The fundamental assumption of a positive linear relation hip between 'potential available habitat" MUM and biomass of fish has neither been documented riot- validated, partic. ularly in warmwater streams. Absence of correlation precludes prediction of changes in fist, populations. In some studies the test of this assumption appears to be equivalent to a calibration operation. The other assumption violated includes independent selection of habitat variables by fish. The presence of signi- ficant interaction among habitat variables can affect tht stream flow recommendations. mother problem exists in application of Physical Habitat Simulation (PHABSIM): one WUA unit should not be interpreted as being equal to another in biological production or habitat value unless sho,vn to be an exact replica. Several combinations of physical variables could give rise to the same amount of 1VUA, none of which may be correlated to the biomass of fish. The utilization, suitability, or preference cu,ves should not be treated as probability functions; a rating of 1.0 is not equivalent to probability of 1.0. Care should be taken to distinguish between real behavioral preferences of fishes based on distributional occurrence from abundance (relative or absolute size) in a stream. Lin examen et une anahse des ouvrages publics montrent que plusieurs hypoth6ses sont refutes Bans I'application de la misthode IFIM (u Instream Flow Incremental Methodology )) sans consideration des repercussions. Uhypothese fondamentale selon laquelle it existe une relation lineaire positive entre I'habitat potentiel disponible (WUA) et la biomasse des poissons n'a pas etc etudiee ni protrvee, en particulier clans les tours d'eau chaude. L'absence de correlation empeche la prediction de variations clans les populations de poisson. Dans certaines etudes, la verification de cette hypoth@se semble et; a equiva- lente A un exercice d'etalonnage. Le choix indepenclanl par les poissons des variables de I'habitat constitue tine autre refutation de Phypothese. La presence dime interaction importance entre les variables de I'habitat peut influer sur les recommandations en matiere de debit. II existe aLISSi Lin autre problenie dans I'applicalion fit- PI-IA1351M (« Physical Habitat Simulation u) : pour cc qui est de la production biologigUe et de la valetir de. I'hahitat, deLIX unites WUA no doivcnt i•tre considWes t'g ilvs oluc si Mlles sort des copies exacles. 1'lusirurs tomhinaisons de variables physirlue? pviivent produire Irti mt mcs val,,urs V1'tW dent our uric West Iwid-r•tre <:o c orr(Amion avec la bimnastiw des poissum. Les (%)ur ht •. dOxivanl I'utilisation, la convenance tint la preference ne devraient pas titre trait6es comme des frnu lions de probahilile : une evaluation s'elevant A 1,0 nest pas equivalente a une probability de 1,0. I.a distinction entre les vrait s prOdsrences comportement ales des poissons basees Stir la frequence de la reparlition et I'ahondance (relative ou absolue) clans on tours d'eau devra faire I'uhjet d'une attention parliculiere. Received luly.3, 1984 Resu /e 3 juillet 1984 Accepted December 31, 1984 Ar(ehte le 31 decemhre 1984 117857) d??31 Can. J. Fish. Aqurrt. Sri.. Vol. 12. 1985 825