We determined migration timing and abundance of juvenile spring chinook salmon from three populations in the Grande Ronde River basin. We estimated 6,716 juvenile chinook salmon left upper rearing areas of the Grande Ronde River from July 1997 to June 1998; approximately 6% of the migrants left in summer, 29% in fall, 2% in winter, and 63% in spring. We estimated 8,763 juvenile chinook salmon left upper rearing areas of Catherine Creek from July 1997 to June 1998; approximately 12% of the migrants left in summer, 37% in fall, 21% in winter, and 29% in spring. We estimated 8,859 juvenile chinook salmon left the Grande Ronde Valley, located below the upper rearing areas in Catherine Creek and the Grande Ronde River, from October 1997 to June 1998; approximately 99% of the migrants left in spring. We estimated 15,738 juvenile chinook salmon left upper rearing areas of the Lostine River from July 1997 to April 1998; approximately 3% of the migrants left in summer, 61% in fall, 2% in winter, and 34% in spring. We estimated 22,754 juvenile spring chinook salmon left the Wallowa Valley, located below the mouth of the Lostine River, from September 1997 to April 1998; approximately 55% of the migrants left in fall, 5% in winter, and 40% in spring. Juvenile chinook salmon PIT-tagged on the upper Grande Ronde River were detected at Lower Granite Dam from 4 April to 26 June 1998, with a median passage date of 1 May. PIT-tagged salmon from Catherine Creek were detected at Lower Granite Dam from 3 April to 26 June 1998, with a median passage date of 8 May. PIT-tagged salmon from the Lostine River were detected at Lower Granite Dam from 31 March through 26 May 1998, with a median passage date of 28 April. Juveniles tagged as they left the upper rearing areas of the Grande Ronde and Lostine rivers in fall and that overwintered in areas downstream were detected in the hydrosystem at a higher rate than fish tagged during winter in the upper rearing areas, indicating a higher overwinter survival in the downstream areas. Fish from Catherine Creek showed no difference in detection rates between the fall and winter tag groups, indicating similar overwinter survival in the upper and lower rearing areas. Chinook salmon parr were generally associated with low velocity habitat types during winter in Catherine Creek, and both winter and summer in the Lostine River. In summer 1997, we PIT-tagged parr on Catherine Creek and the Minam and Imnaha rivers in order to monitor their subsequent migration as smolts through the Snake and Columbia River hydrosystem. We found significant differences among populations in smolt migration timing at Lower Granite Dam in 1998. Fish from Catherine Creek and the Minam and Imnaha rivers were detected in the hydrosystem at rates of 16.4, 20.5, and 28.1%, respectively. In 1998, we estimated parr abundance and the number of parr produced per redd in Catherine Creek and the Lostine River. We estimated that 429 mature, age 1+ male parr and 13,222 immature, age 0+ parr were present in Catherine Creek in August. An average of 29 mature, age 1+ male parr and 287 immature, age 0+ parr were produced from each redd constructed in 1996 and 1997, respectively. We estimated that 75 mature, age 1+ male parr and 40,748 immature, age 0+ parr were present in the Lostine River in August. An average of 3 mature, age 1+ male parr and 832 immature, age 0+ parr were produced from each redd constructed in 1996 and 1997, respectively. For every anadromous female spawner in Catherine Creek and the Lostine River in 1998, there were an estimated 13 and 3 mature male parr, respectively.
