Monitoring the Migrations of Wild Snake River Spring/Summer Chinook Salmon Juveniles, 2007-2008 Report of Research.

Abstract

This report provides results from an ongoing project to monitor the migration behavior and survival of wild juvenile spring/summer Chinook salmon in the Snake River Basin. Data reported is from detections of PIT tagged fish during late summer 2007 through mid-2008. Fish were tagged in summer 2007 by the National Marine Fisheries Service (NMFS) in Idaho and by the Oregon Department of Fish and Wildlife (ODFW) in Oregon. Our analyses include migration behavior and estimated survival of fish at instream PIT-tag monitors and arrival timing and estimated survival to Lower Granite Dam. Principal results from tagging and interrogation during 2007-2008 are listed below: (1) In July and August 2007, we PIT tagged and released 7,390 wild Chinook salmon parr in 12 Idaho streams or sample areas. (2) Overall observed mortality from collection, handling, tagging, and after a 24-hour holding period was 1.4%. (3) Of the 2,524 Chinook salmon parr PIT tagged and released in Valley Creek in summer 2007, 218 (8.6%) were detected at two instream PIT-tag monitoring systems in lower Valley Creek from late summer 2007 to the following spring 2008. Of these, 71.6% were detected in late summer/fall, 11.9% in winter, and 16.5% in spring. Estimated parr-to-smolt survivalmore » to Lower Granite Dam was 15.5% for the late summer/fall group, 48.0% for the winter group, and 58.5% for the spring group. Based on detections at downstream dams, the overall efficiency of VC1 (upper) or VC2 (lower) Valley Creek monitors for detecting these fish was 21.1%. Using this VC1 or VC2 efficiency, an estimated 40.8% of all summer-tagged parr survived to move out of Valley Creek, and their estimated survival from that point to Lower Granite Dam was 26.5%. Overall estimated parr-to-smolt survival for all summer-tagged parr from this stream at the dam was 12.1%. Development and improvement of instream PIT-tag monitoring systems continued throughout 2007 and 2008. (4) Testing of PIT-tag antennas in lower Big Creek during 2007-2008 showed these antennas (and anchoring method) are not adequate to withstand high spring flows in this drainage. Future plans involve removing these antennas before high spring flows. (5) At Little Goose Dam in 2008, length and/or weight were taken on 505 recaptured fish from 12 Idaho stream populations. Fish had grown an average of 40.1 mm in length and 10.6 g in weight over an average of 288 d. Their mean condition factor declined from 1.25 at release (parr) to 1.05 at recapture (smolt). (6) Mean release lengths for detected fish were significantly larger than for fish not detected the following spring and summer (P < 0.0001). (7) Fish that migrated through Lower Granite Dam in April and May were significantly larger at release than fish that migrated after May (P < 0.0001) (only 12 fish migrated after May). (8) In 2008, peak detections at Lower Granite Dam of parr tagged during summer 2007 (from the 12 stream populations in Idaho and 4 streams in Oregon) occurred during moderate flows of 87.5 kcfs on 7 May and high flows of 197.3 kcfs on 20 May. The 10th, 50th, and 90th percentile passage occurred on 30 April, 11 May, and 23 May, respectively. (9) In 2007-2008, estimated parr-to-smolt survival to Lower Granite Dam for Idaho and Oregon streams (combined) averaged 19.4% (range 6.2-38.4% depending on stream of origin). In Idaho streams the estimated parr-to-smolt survival averaged 21.0%. This survival was the second highest since 1993 for Idaho streams. Relative parr densities were lower in 2007 (2.4 parr/100 m{sup 2}) than in all previous years since 2000. In 2008, we observed low-to-moderate flows prior to mid-May and relatively cold weather conditions throughout the spring migration season. These conditions moved half of the fish through Lower Granite Dam prior to mid-May; then high flows moved 50 to 90% of the fish through the dam in only 12 days. Clearly, complex interrelationships of several factors drive the annual migrational timing of the stocks.« less