The 1980 eruption of Mount St. Helens severely affected the North Fork Toutle River (hereafter Toutle River), Washington, and threatened anadromous salmon (Oncorhynchus spp.) populations in the basin. The Toutle River was further affected in 1989 when a sediment retention structure (SRS) was constructed to trap sediments in the upper basin. The SRS completely blocked upstream volitional passage, so a fish collection facility (FCF) was constructed to trap adult coho salmon (O. kisutch) and steelhead (O. mykiss) so they could be transported upstream of the SRS. The Washington Department of Fish and Wildlife (WDFW) has operated a trap-and-haul program since 1989 to transport coho salmon and steelhead into tributaries of the Toutle River, upstream of the SRS. Although this program has allowed wild coho salmon and steelhead populations to persist in the Toutle River basin, the trap-andhaul program has faced many challenges that may be limiting the effectiveness of the program. We conducted a multi-year evaluation during 2005–2009 to monitor tagged fish in the upper Toutle River to provide information on the movements and behavior of adult coho salmon and steelhead, and to evaluate the efficacy of the FCF. Radio-tagged coho salmon and steelhead were released: (1) in Toutle River tributaries to evaluate the behavior and movements of fish released as part of the trap-and-haul program; (2) between the FCF and SRS to determine if volitional upstream passage through the SRS spillway was possible; (3) in the sediment plain upstream of the SRS to determine if volitional passage through the sediment plain was possible; and (4) downstream of the FCF to evaluate the efficacy of the structure. We also deployed an acoustic camera in the FCF to monitor fish movements near the entrance to the FCF, and in the fish holding vault where coho salmon and steelhead are trapped.
A total of 20 radio-tagged coho salmon and 10 radio-tagged steelhead were released into Alder and Hoffstadt Creeks, the locations where trap-and-haul fish were released during 2005–2006. None of the tagged fish left the tributaries where they were released, but four radio tags were detected near the release sites, and it was not possible to determine if this was because the transmitters were regurgitated, or if some of the tagged fish had died. The results from this portion of the study indicated that trap-and-haul fish remain in the tributaries where they can spawn, but the trap-and-haul process is labor-intensive, and handling stress and mortality could occur.
Tagged-fish releases upstream of the FCF showed that the SRS spillway was a complete migration barrier for all coho salmon and most steelhead. We released a total of 20 radio-tagged coho salmon and 23 radio-tagged steelhead during 2005–2007. No tagged coho salmon passed upstream through the SRS spillway, whereas 13 percent of the radio-tagged steelhead did migrate upstream through the structure. Radio-tagged coho salmon and steelhead that did not pass upstream remained in the FCF–SRS reach for an average of 7.5 and 16.1 d, respectively, before moving downstream. These data show that trap-and-haul releases of fish immediately upstream of the FCF would not be beneficial to coho salmon and steelhead populations in the system.
Releasing tagged fish into the sediment plain was only moderately successful for coho salmon,
but a large percentage of tagged steelhead moved upstream through the sediment plain to areas where
spawning could presumably occur. During 2005–2009, we released 47 tagged coho salmon and 65
tagged steelhead into the sediment plain. Only 28 percent of the coho salmon were later detected
upstream of the sediment plain, and the highest percentage of the release group (62 percent) never left
the sediment plain. However, 69 percent of the steelhead moved upstream through the sediment plain
and entered Toutle River tributaries or remained in the mainstem Toutle River where spawning could
presumably occur. Adult steelhead can survive freshwater spawning, outmigrate to the ocean, and then
return to spawn in successive years; 12 percent of the tagged steelhead successfully moved downstream
of the FCF after the spawning period, and 5 percent of the tagged steelhead returned to the FCF a year
after they were originally tagged.
Evaluations at the FCF showed that the structure was not efficient at collecting adult salmon.
During 2008–2009, 9 radio-tagged coho salmon and 11 radio-tagged steelhead were released to observe
behavior near the facility and to estimate the recapture rate in the FCF. None of the tagged coho salmon
were recaptured and only 27 percent of the tagged steelhead were recaptured. Additionally, we observed
fish behavior at the FCF with an acoustic camera and found that relatively large numbers (>100
fish/sampling period) of adult salmon entered the FCF but similar numbers of fish exited during these
periods as well. This suggested that the efficacy of the FCF was low.
Our study was limited by the number of fish that could be handled each year and the number of
transmitters that could be purchased annually, but our evaluations provided the first empirical data on
adult salmon behavior and movement patterns in the Toutle River since the 1980 eruption of Mount St.
Helens. Since the completion of this work, the U.S. Army Corps of Engineers has altered the SRS
spillway and sediment plain; however, our results do provide information to assist fishery managers
tasked with the complex management of wild salmon populations in the Toutle River. Future
evaluations of juvenile and adult salmon behavior and movement likely will be required to effectively
manage these populations in this complex system.