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",. - \hfllIlR. I).. W. H, I"~ll~. E. J. PLIRIJ\':JR.. ,\NIl c. A. SII.VER. 191\5. A ,'ritiqu.: .,1' Ih.: In.(r.:am Fh,\\' Incren":nlal ;>'klhllJlllol:\'. em. J. Fi~h. "\'Iual. S,'i. -I~: S~5 - KJ I. .. diifll. I) J.. R. N, Jlll<l~.\~n 0 I!. M\lI(ill,\N, II)M~. Cllll~iJi!filtioll~ ill thl! J.:wl"pmcnl "I' ,um:~ for habilal ~uitability CrihJria. 1'. 1 ~-I-I.\.'. III N. ll. Armantn.ut [cd.] Symp.. Acquisilion anJ utilizalion of aquatic habilat in\'Cnlory inf..rmatilln. American Fi~hcric~ Socicty. Bclhc~Ja. ;\10. OHII. D. J.. .\:-;0 O. E. ;\hl'I.IIAN. 19K~. Evalu'lli'lII of the Incrcmental i\kth..J"h,t:y f\'r rc.-"mmenJing instrcam Ilow~ for fishc~. Tran~. Am. Fi~h. S"c. III: -1(,\--1-15. Reply to "In Defense of the Instream Flow Incre- mental Methodology" by D. J. Orth and O. E. Maughan .,.-,."".,...........p.--....--. -," -, __s_~_"-~-""'"!'___" '_._ '0'.-'..---'..,:..- ~ ,- -,- " Orth)nrl ..~taii_gh~iI~,fcommentS.~.ourpiiper '(Maih-uret"aI' I~,~lp~d,t~!!hc:r .evi<ience!bat appli~.~!igt1~QfJb:~).~~~rea~" ~Iow) !1.~,f,~mel1tal,M,~.thod.!?lp~.t.. (In.~}J.n_ jts presetlt ~()rm;' shqt!l<!t>eabandQI1~!i. As stressed in our paper, the requirement for a positive linear correlation between weighted usable area (WUA) and fish biomass is essential. Their comments still fail to address this and other central issues. The original assumption of IFlM is that usable habitat ex- pressed in WUA (absolute units) is linearly and positively related to fish biomass (absolute weight). WUA is roughly equated to the carrying capacity of a stream. Therefore. the only relevant test of that assumption is the correlation between the biomass of each life stage of fish and its calculated WUA. In defense of IFI~1. Orth and Maughan selectively cited the results of Loar et al. (1985). Of the 160 possible correlations for the rainbow trout. Salma gairdneri. only 14 (9%) were significant. None of the significant correlations were between WUA and fish biomass. Negative correlations were also obtained by Loar et aI. (1985). It is puzzling that Orth and Maughan highlight a minor- ity of significant positive relationships (even though irrelevant to the basic assumption) and avoid even mentioning the over- whelming number of nonsignificant or negative relationships reported by Loar et al. (1985). Negative and weak correlations were also reported by Shirvell and Morantz (1983) for four years of IFlM data on juvenile Atlantic salmon, Salma salar. A flow diversion study using IFIM by Irvine (1984) provided similar results. Recently. Scott and Shirvell (1986) examined all the statis- tical correlations between usable habitat and fish biomass re- ported in the literature. Of the 517 correlations, 82% were nonsignificant; of the remainder, some were positive and some negative. Because a positive linear relationship is found so rarely, it is reasonable to conclude that such relationships are really due to chance and WUA can not be considered a predic- tor of fish biomass. In light of these analyses it is hard to conceive how Orth and Maughan can continue to have faith inWUA. Orth and Maughan commented on the presence of cor- relation between biomass of three riffle dwelling species and their respective percent WUA during the summertime in Glov- er Creek. We interpreted their data (Mathur et al. 1985) to indicate merely seasonal variations in biomass independent of changes in WUA. We again do so. We believe their argument that limited recruitment of young fish occurred in summer is illogical with respect to the data and contradictory to their statements. Examination of their data in tables 5 and 6 in the time sequence they were collected. i.e. beginning Cull. J. Fish. .'\"'Illl. Sci.. \',,1.43. IlJ8fJ in fall (November- December) 1977 to summer (August- September) 1979, reveals that the biomass of all the riffle dwellill~ species WAs hi~hcr in sprin~ i!n~ summer 1979 follow- Ing th6 ndQr :zero nowll el(Pcrll!nced In lIummlu-roll 1978. Where did these fish come from if the population was being limited or recruitment was restricted in summer-fall? WUA provides no explanation. The failure of proponents of IFlM to distinguish between changes in distribution of fishes and abundance continues to lead.,hmisinterpretati()nof the available ~ta. Nos~4Y~ ~qi11Rg~S}j,~m1~tl?n]f~~11:r~['4!21ion'"'ay~'e a~ .51 !t11.']:.'!yJ;9<fyof "vate~';Jfthere IS always a "decline (redIS- tribution) in fishes from summer to winter at a given location. The fact is that distribution of stream fishes changes through seasons. Such was the case in Glover Creek. Orth and Maughan believed that it was unreasonable for us to plot their pooled data in tables 5 and 6 (two pools plus two riffles over seasons and sites). This is a tenuous and strange contention. Data plotted in our fig. 3 and 4 were simply those given by Orth and Maughan in their tables 5 and 6. Presentation of identical data in different format should not logically lead to different conclusions. They used those pooled data as a basis for concluding whether or not usable habitat was limiting abun- dance of fishes in Glover Creek (Orth and Maughan 1982. p. 427, 429-431). The seasonal statistical correlations between percent WUA and fish biomass (kilograms per hectare) presented by them were based on analysis of pooled data (rif- fles, pools. and years) from two years. Our reanalysis showed those correlations were spurious. Their reported relationships were also based on suitability curves obtained for one season and one year and applied to the entire data set from two years and all seasons. No evidence exists in the literature which supports the view that such a generalized curve is sufficient to describe microhabitats of fishes. particularly when the seasonal arid daily changes in behavior of fishes are considered. Orth and Maughan's comment that the "suitability" curves developed after adjustments for habitat availability are un- biased shows only that they did not critically evaluate the implications of the curves presented by Mathur et al. (1985). First. no evidence in the primary literature demonstrates that adjustment in suitability curves for the availability of the three physical habitat attributes (as measured in IFlM) will improve the prediction of biomass of fishes. Second, we showed that such curves will differ with streams. size. stream flow. and seasons and also over a 24-h period. thus causing large biases in calculation of WUA. Larimore and Garrels (1985) provided examples of large diurnal differences in suitability curves for the northern hogsucker. Hypentilill1n nigricans. in the same stream. Bain et al. (1982) cited the differences in suitability curves for the small mouth bass. Micropterus dolomielli (both juvenile and adults), at different discharges and seasons within the same river. Third. no uniform criteria exists on where to measure the distribution of depths and velocities at different flows to obtain information on availability and utilization of physical variables. An investigator can get any number of WUA estimates he wishes depending upon which curves (day. night. or season, etc.) he selects for the calculations. Orth and Maughan reject our interpretation of Kraft's (1972) study as showing that biomass and flow are unrelated because the study stream had a well-defined channel and the reductions in available habitat were not in proportion to flow reductions (the summer flow was reduced by 90%). This contention is absurd because Kraft (1972) noted that depth, velocity, and 1093