Investigations into the Early Life-history of Naturally Produced Spring Chinook Salmon and Summer Steelhead in the Grande Ronde River Basin, Annual Report 2001.

Abstract

We determined migration timing and abundance of juvenile spring chinook salmon Oncorhynchus tshawytscha and juvenile steelhead/rainbow trout Oncorhynchus mykiss using rotary screw traps on four streams in the Grande Ronde River basin during the 2001 migratory year (MY 2001) from 1 July 2000 through 30 June 2001. Based on migration timing and abundance, two distinct life-history strategies of juvenile spring chinook and O. mykiss could be distinguished. An 'early' migrant group left upper rearing areas from 1 July 2000 through 29 January 2001 with a peak in the fall. A 'late' migrant group descended from upper rearing areas from 30 January 2001 through 30 June 2001 with a peak in the spring. The migrant population of juvenile spring chinook salmon in the upper Grande Ronde River in MY 2001 was very low in comparison to previous migratory years. We estimated 51 juvenile spring chinook migrated out of upper rearing areas with approximately 12% of the migrant population leaving as early migrants to overwinter downstream. In the same migratory year, we estimated 16,067 O. mykiss migrants left upper rearing areas with approximately 4% of these fish descending the upper Grande Ronde River as early migrants. At the Catherine Creek trap, we estimated 21,937 juvenile spring chinook migrants in MY 2001. Of these migrants, 87% left upper rearing areas early to overwinter downstream. We also estimated 20,586 O. mykiss migrants in Catherine Creek with 44% leaving upper rearing areas early to overwinter downstream. At the Lostine River trap, we estimated 13,610 juvenile spring chinook migrated out of upper rearing areas with approximately 77% migrating early. We estimated 16,690 O. mykiss migrated out of the Lostine River with approximately 46% descending the river as early migrants. At the Minam River trap, we estimated 28,209 juvenile spring chinook migrated out of the river with 36% migrating early. During the same period, we estimated 28,113 O. mykiss with approximately 14% of these fish leaving as early migrants. Juvenile spring chinook salmon PIT-tagged at trap sites in the fall and in upper rearing areas during winter were used to compare migration timing and survival to Lower Granite Dam of the early and late migrant groups. Juvenile spring chinook tagged on the upper Grande Ronde River were detected at Lower Granite Dam from 4 May to 20 May 2001, with a median passage date of 17 May. Too few fish were collected and tagged to conduct detection rate and survival comparisons between migrant groups. PIT-tagged salmon from Catherine Creek trap were detected at Lower Granite Dam from 27 April to 13 July 2001. Early migrants were detected significantly earlier (median = 10 May) than late migrants (median = 1 June). Also, early migrants from Catherine Creek were detected at a significantly higher rate than fish tagged in upper rearing areas in the winter, suggesting better survival for fish that migrated out of upper rearing areas in the fall. Juvenile spring chinook salmon from the Lostine River were detected at Lower Granite Dam from 2 April through 4 July 2001. Early migrants were detected significantly earlier (median = 27 April) than late migrants (median = 14 May). However, there was no difference in detection rates between early and late migrants. Survival probabilities showed similar patterns as dam detection rates. Juvenile spring chinook salmon from the Minam River were detected at Lower Granite Dam from 8 April through 18 August 2001. Early migrants were detected significantly earlier (median = 28 April) than late migrants (median = 14 May). Late migrants from the Minam River were tagged at the trap in the spring. Spring chinook salmon parr PIT-tagged in summer 2000 on Catherine Creek and the Imnaha, Lostine, and Minam rivers were detected at Lower Granite Dam over an 87 d period from 8 April to 3 July 2001. The migratory period of individual populations ranged from 51 d (Imnaha River) to 67 d (Catherine Creek) in length. Median dates of migration ranged from 30 April (Imnaha River) to 17 May (Catherine Creek). Detection rates differed between populations with Catherine Creek spring chinook salmon detected at the lowest rate (8.2%). Imnaha, Lostine, and Minam detection rates were not significantly different from each other. A similar pattern was seen for survival probabilities. Using mark-and-recapture and scale-aging techniques, we determined the population size and age-structure of spring chinook salmon parr in Catherine Creek and the Lostine River during the summer of 2001. In Catherine Creek, we estimated that 986 mature age-1 parr (precocious males) and 15,032 immature age-0 parr were present during August 2001. We estimated there were 7.5 mature male parr for every anadromous female spawner in Catherine Creek in 2001. We estimated 33,086 immature, age-0 parr inhabited the Lostine River in August 2001.