SURVIVAL OF CHINOOK SALMON, ONCORHYNCHUS-TSHAWYTSCHA, FROM A SPAWNINGTRIBUTARY OF THE RAKAIA RIVER, NEW-ZEALAND, IN RELATION TO SPRING ANDSUMMER MAINSTEM FLOWS

To characterize the impact of spring floods on the survival of juvenil e chinook salmon in the unstable, braided rivers on the east coast of New Zealand's South Island, I examined correlations between spring and summer flows in the mainstem of the Rakaia River and fry-to-adult sur vival for chinook salmon spawning in a headwater tributary. Flow param eters that were investigated included mean flow, maximum now, and the ratio of mean to median flow (an index of flow variability), calculate d during peak down-river migration of ocean-type juveniles (August to January). Survival was uncorrelated with mean or maximum flow but was positively correlated with the ratio of mean to median flow during spr ing (October and November). The correlation suggests that pulses of fr eshwater entering the ocean during floods may buffer the transition of fingerlings from fresh to saline waters and thus partly compensate fo r the lack of an estuary on the Rakaia River. A positive correlation b etween spring flow variability and the proportion of ocean-type chinoo k. in relation to stream-type chinook is also consistent with this hyp othesis. All correlations were relatively weak, reinforcing earlier re sults that production is primarily controlled by marine influences. Th ese findings further demonstrate the considerable ability of chinook s almon to adapt to new habitats.