Relationship between chinook salmon (Oncorhynchus tshawytscha) redd densities and PHABSIM-predicted habitat in the Merced and Lower American rivers, California

Abstract

An index of chinook salmon (Oncorhynchus tshawytscha) spawning habitat predicted using the physical habitat simulation system (PHABSIM) component of the instream flow incremental methodology was compared with redd densities and locations for sites in the Merced River, California, during 1996 and with redd numbers in sites in the Merced and Lower American rivers, California, from 1989 through 1996. Predicted weighted useable area (WUA) was significantly correlated with chinook salmon spawning density and location at five of seven sites in the Merced River. At the microhabitat level, in the Merced River during 1996, there was a significant relationship between chinook salmon redd location and predicted WUA. Cells with more WUA in the Merced River tended to have more redds. At the mesohabitat level, there was a significant relationship between redd density and predicted WUA in both rivers. Transect areas in the Merced River with higher predicted WUA had more redds. Sites with higher numbers of redds had more predicted WUA. Significant correlations between predicted WUA and spawning locations increase confidence in the use of PHABSIM modeling results for fisheries management in the Merced and Lower American rivers as well as in other rivers.