Early life history study of Grande Ronde River Basin chinook salmon. Annual progress report, September 1, 1994--August 31, 1995

Abstract

The Grande Ronde River originates in the Blue Mountains in northeast Oregon and flows 334 kilometers to its confluence with the Snake River near Rogersburg, Washington. Historically, the Grande Ronde River produced an abundance of salmonids including stocks of spring, summer and fall chinook salmon, sockeye salmon, coho salmon, and summer steelhead. During the past century, numerous factors have caused the reduction of salmon stocks such that only stocks of spring chinook salmon and summer steelhead remain. The sizes of spring chinook salmon populations in the Grande Ronde basin also have been declining steadily and are substantially depressed from estimates of historic levels. It is estimated that prior to the construction of the Columbia and Snake River dams, more than 20,000 adult spring chinook salmon returned to spawn in the Grande Ronde River basin. A spawning escapement of 12,200 adults was estimated for the Grande Ronde River basin in 1957. Recent population estimates have been variable year to year, yet remain a degree of magnitude lower than historic estimates. In 1992, the escapement estimate for the basin was 1,022 adults (2.4 {times} number of redds observed). In addition to a decline in population abundance, a constriction of spring chinook salmon spawning distribution is evident in the Grande Ronde basin. Historically, 21 streams supported spawning chinook salmon, yet today the majority of production is limited to eight tributary streams and the mainstem upper Grande Ronde River. Numerous factors are thought to contribute to the decline of spring chinook salmon in the Snake River and its tributaries. These factors include passage problems and increased mortality of juvenile and adult migrants at mainstem Columbia and Snake river dams, overharvest, and habitat degradation associated with timber, agricultural, and land development practices. More than 80% of anadromous fish habitat in the upper Grande Ronde River is considered to be degraded.