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01195 1 HUMPBACK CHUB HABITAT MODELLING 389 aJ Total (<-0.25 mi.) 251 :! ~ 2.0 '" U ~ n.!t!. 15 e ~ ... t! "0 1.0 ~ N 'E ~ ~ 05 iil Study Reaches ...... -R1 -+-R2 '-'-'RJ - - R4 -R5 --It--ALC____PAL .. .. ~ ~ 00 o !>Xl 1000 1500 2000 Dlachu'gll(m"lsec) 2500 3000 b) 2,5 B 2,0 :;; . '" " . .l! 1,5 -e .. ... t! " 10 . . 'E ~ e 0,5 l! <n 0,0 0 Shoreline (<=0.25 mi. and <=1 m) Study Rea.ches ...... -R1 --+--R2 -+--R3 - - R4 -RS -.-AlC ______PAL ,. \', . \. \.... \.- :..: =_: .:.:: =-- .:. --= =-.-.:......:.. -...:. "'-= =..1'8."" &.... .:........ -...,:. ~ !>Xl 1000 1500 2000 D_1ll'l em'Me} 2500 3000 Figure 4. Effect of discharge on relative cr..ange in availability of suilahle IOtal (a) and shoreline (b) habitat. Units are standardized by reach- specific ..Ol1ue~ al 226m)/s (0 faciliate' comparison among study reaches Seasonal trends in the availabilit)' of shoreline habilal in the pre-dam em were highly variable among reaches (figure 6), There were large seasonal fluctuations among sensitive reaches (e.g, ALe, Rl, and R4) but relatively little fluctuation at insensitive ones (e,g. PAL, R2, R3, and R5). These differences were driven by the site-specific sensitivity of suitable shoreline habilat availability to discharge (Figure 4b). The alteration of the hydrograph caused by impoundment (Figure 5) resulted in considerable change in the seasonal pattern of shoreline habitat availability. but again, Ihis response was highly variable among reaches (Figure 6, Table V). In general, dam opera- tions have decreased the availability of suitable shoreline habilat relative 10 the pre-dam era during low-flow months (August-February) but have increased habitat availability in the spring (May-June), When averaged across sites, impoundment significantly (a .;; 0.05) decreased sui/able shoreline habitat for about six months of the year and increased it for three months. Significant differences between pre- and post-dam suitable habitat availability by month were more common at the sensitive sites. At R2. most of the significant impoundment effects were positive (Table V) because of the presence of a secondary peak in suitable habitat availability at 425-566 m)/s (Figure 4b), a discharge range that has become more prevalent since impoundment. Copyright ~ 2004 John Wiley & Sons. lid. River R~s. Appfic. 20: 379-400 (2004)