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" 392 j, KORMAN, S, M, WIELE AND M, TORIZZO Table V. Effects of dam operations on the availability of suitable shoreline habitat for the seven study rel:l.cl'Ies. Plus and minus ~igns deoOlc whelher operatiol\':. have increas.ed or decreased suitable shoreline hiibitat 3\aitabi!ity relative to pre-dam condi- tions. The number of symbols denotes the signiJ1cance level of the operations effect3- RI R2 R3 R4 R5 ALe PAL JiJnuary Febnlary +++ March +++ ++ April +++ +++ + + May +++ +++ + +++ +++ +++ ++ June +++ +++ ++ +++ +++ +++ July August September Ocwber November ++ December No. positive effects 2 6 2 2 4 3 2 No. negative effects 8 2 8 8 4 8 3 A+. _, P ~ 0.05; ++. --, P ~ O.OI~ +++. -- -, p ~ 0.001. The large changes in the extent of daily variation in discharge under different operating periods (Figure 8) had a strong effect on the amount of suitable habitat ?rea that persisted across typical daily discharge ranges (Table VI). We used September as an index month for this analysis because the average daily discharge range was well represented by the discharges that we modelled in this study (Table II), and with discharge ranges seen in other months. During the pre-dam period. the daily range in discharge for September was minimal. increased to 226-566 m'/s during the 'no action' period, and was reduced to 425-566 m',s under the current operating regime (MLFF). Persistent suitable shoreline habitat was almost completely eliminated in the post-dam period under the 'no action' regime at all sites. The reduction in daily variation in discharge under the MLFF regime resulted in the persistence of small amounts of suitable habitat at all reaches except PAL, where the increase was much larger, The amount of persistent total suitable habitat in the pre-dam period was reduced by 60-90% under the 'no action' regime at all study reaches and by 50- 70% under the MLFF regime for all reaches except PAL, where the reduction was only 20%. EfJecls of discharge and calch per unil effort indexing The potential for discharge changes to increase variatio,n in ePE data was highly variable among reaches. The 190 electrofishing samples taken in 1993 between river km 99 and 107 were collected over a discharge range of 175 to 550m'/s. but more than 80% were collected over a narrower range of 200 and 4oom'Is (Figure 9). In the worst case (R4), the amount of suitable shoreline habitat area decreased fourfold over the 200-400 m',s range, Under the assumption of an inverse linear relationship between suitable habitat area and catchability (Equation I), this change implies thai ePE deosities taken at 400 m3 'S could be fourfold greater than those taken at 200 m'ls, Reaches RI and ALe showed potential for variations in ePE densities as high as Iwo- and 1.5.fold. respectively, over this same discharge range, whereas R3 and R5, where suitable shoreline habitat area was relatively insensitive to changes in discharge. showed little potential for increased variability even at the extreme ends of the discharge range where sampling was conducted. Reaches R2 and PAL showed a limited potential for ePE estimates to decrease at higher discharges because of increases in suitable shoreline habitat area. Dispersal The ability of a reach to retain particles tended to decline with increasing discharge, but the pattern varied con- siderably owing to differences in the morphology among reaches and the swimming behaviours that were modelled (Figure 10). In general, the more effective the behaviour at moving a particle to the low-velocity area near the banks, the higher the retention rate, Thus, a geotactic behaviour, where all the swimming velocity is focused in Copyright <<) 2004 John Wiley & Sons. lid. Ri\.tr Rtf. Applic. 20: 379-400 (2004)