Effects of riparian canopy opening and salmon carcass addition on the abundance and growth of resident salmonids

We studied the concurrent effects of riparian canopy opening and salmon carcass addition on salmonid bio- mass, density and growth rates in small streams over 2 years. In each of six streams in the Smith and Klamath River basins in northern California, red alder (Alnus rubra) and other hardwoods were removed along both banks of a 100-m reach to increase incident radiation. A second 100-m reach, with an intact canopy, was established in each stream as a light control. Salmon carcasses were added each year to both cut and uncut riparian sections in three of the six streams. Differences in total density and biomass of cutthroat trout (Oncorhynchus clarki) and rainbow trout (Oncorhynchus mykiss) from pretreatment levels responded positively to canopy removal but were not detectably af- fected by carcass addition. Differences in specific growth rates of the fish between open and closed canopy reaches were greater in sites without carcasses than in sites with carcasses. In light-limited settings where temperature gains as- sociated with canopy opening are not problematic for aquatic resources, gains in salmonid production might be achieved by selective trimming of riparian hardwoods.