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<br />178
<br />
<br />D. J. ORTH
<br />
<br />instream flow-habitat model. The following suggestions are offered for future instream flow assessments
<br />and research:
<br />
<br />1. Microhabitat availability is not the only factor limiting fish populations and does not operate
<br />continuously. Therefore, persons using IFIM must identify the time(s) when microhabitat is most
<br />critically limited and avoid the mistake of assuming that WUA is positively related to fish abundance
<br />at all levels of WUA at all times.
<br />2. Because food availability may limit abundance, habitat suitability criteria for invertebrates must be
<br />developed and used in PHABSIM applications. New approaches for assessing instream flow needs for
<br />invertebrate production must be developed and tested.
<br />3. Habitat suitability criteria can vary with body size, season, time of day, activity, predators, and
<br />competitors. Therefore, the applicability of habitat suitability criteria is limited to sites with similar fish
<br />assemblages and thermal regimes. Furthermore, seasonal (or size-related) differences in habitat needs
<br />and limiting factors must be identified and incorporated in assessments.
<br />4. Structural complexity plays a major role in position choice by stream fishes through the need to feed
<br />efficiently and avoid predators. Greater emphasis must be placed on developing reliable criteria for
<br />defining suitable habitat for fishes and invertebrates.
<br />5. Assessments must address the needs of a wider array of target species, especially non-game fishes and
<br />invertebrates in order to recommend flows to maintain ecological integrity of steam ecosystems.
<br />6. Temperature and water quality limitations on fish and invertebrate populations are potentially severe
<br />and should be evaluated in instream flow assessments.
<br />
<br />Although the need for more research is obvious and the complicating factors which I have discussed
<br />may seem to make the problem intractable, the benefits of improved stream management are undeniable.
<br />In the near future, assessments can be greatly improved by applyin.,g.o.I,l,!:Q!'esent knowledge of stream fish
<br />ecology. The IFIM is not intended to be a panacea~owever, IFIMhas.the potential to identify limiting
<br />habitat events and avoid them in developing flow regimes in regulated rivers._l'he IFIM is a process, not a
<br />model, and the process allows the consideration of the other ecological factors that I have discussed. As
<br />new models are developed and tested they can be incorporated into ~he IFIM process. However, it is still
<br />not possible, with our current knowledge base, to accurately predicHish population sizes under various
<br />flow regulation scenarios - this remains as a goal fer:research. The additional cost for studying all the
<br />factors that I have discussed may not be feasible for all agencies to consider, ex~ept in a research mode;
<br />the pressure to take short cuts in assessments will continue. More detailed, cOmprehensive studies of
<br />stream fish and invertebrate responses to altered flow_ regimes will be needed before simpler and less
<br />costly methods evolve. In the meantime, flow recommendations developed on the basis of incomplete
<br />assessments should, by necessity, be overly conservative to protect stream resources.
<br />
<br />ACKNOWLEDGMENTS
<br />
<br />1-.
<br />
<br />I thank P. L. Angermeier, C. J. Goudreau, P. M. Leonar~l,~a;d M. D. Lobb for their reviews and
<br />discussions of this paper. Two anonymous reviewers also made important suggestions for this paper.
<br />
<br />REFERENCES
<br />
<br />Allan, J. D. 1982. 'The effects of reduction in trout density on the invertebrate community of a mountain stream', Ecology, 63,
<br />1444-1455. . '0"-" ';' ...,' .
<br />Angermeier, P. L. 1985. 'Spatio-temporal patterns. of foraging success f~r. ~shes in, an Illinois stream', Am. Midl. Not.., 114,
<br />'342"';359. .' .'.'..___, ,.- '_.', '. ': ,
<br />Angermeier, P. L. and Karr, J. R. 1984. 'Relatio~shipsbetween woody debris 'and fish habitat in a small warm water str.earn', Trans.
<br />:;Am:FiI'h.Soc., 113,716-726.'1::::"": ~." .; ") ..,... ".J ,:..,;J....,.;..~ ;,":i F) ~.::.,:...::, ... .-'.:.." '. ... -."."--<
<br />
<br />'AnderSon, C. S. 1985. 'The structure of sculpin populations along a stream size gradient', Environ. Bioi. FiI'h.;13, 93-102. ~';b- .
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