WRRCTR No.171 Habitat modelling of Hawaiian streams

Abstract

An evaluation of the Instream Flow Incremental Methodology (IFIM) was carried out to assess the applicability of this technique to Hawaiian streams. Hydraulic simulations were made for two study reaches on Nanue Stream, Hawaii, and one study reach on Wainiha River, Kauai. Four simulations were carried out and compared: WSP used alone, IFG4 using several data sets, WSP and IFG4 in combination, and IFG4 using only a single data set. Habitat utilization and preference were determined for three stream gobies, Awaous stamineus, Sicyopterus stimpsoni, and Lentipes concolor. IFIM was used with habitat data for S. stimpsoni to determine weighted usable area and to carry out time series analyses for Wainiha River. Results of the hydraulic simulations indicate that IFG4 using several data sets yields the best simulation of stream hydraulics. The WSP simulation program does not appear to be suitable for many Hawaiian streams, particularly smaller streams or streams with complex channels. The habitat utilization studies indicated that the three species used available habitat in different ways giving rise to some microhabitat differentiation. Tests were also made to determine if habitat preference curves derived from fish in one stream could be transferred to another stream. Tests of transferability indicated that habitat utilization data collected from one stream could not be reliably transferred to another stream. Finally it was concluded that IFIM is suitable for certain Hawaiian conditions provided that appropriate precautions in project design, data collection, and simulation studies are taken.