REHABILITATION OF THE MIDDLE FORK WILLAMETTE BULL TROUT POPULATION RISK ANALYSIS AND MONITORING PLAN Oregon Department of Fish and Wildlife USDA Forest Service/Rigdon Ranger District 1998 INTRODUCTION Bull trout populations have declined throughout their range in the western United States and Canada. Some of the factors that caused the decline were overharvest, water quality changes because of intensive land management practices, and removal of fish by chemical application. On June 11, 1997, USFWS proposed to list the Columbia River bull trout population segment (including the Willamette populations as Threatened. A public comment period ended August 12, 1997, and currently (November 1997) USFWS is determining how to proceed. The status of populations in the Willamette Basin is varied (Buchanan et al., 1997). Bull trout have been extirpated from Santiam systems and most likely the Clackamas. McKenzie bull trout have been fragmented into several populations by dams and their status varies from “Of Special Concern” to “High Risk.” The population in the Middle Fork Willamette basin is at an extremely low level with a low probability of persistence. Several specific factors are identified in the decline of bull trout in the Middle Fork Willamette. Rotenone poisoning in 1960 to remove undesirable fish above Hills Creek Dam killed bull trout. Subsequent to the Rotenone treatment, the river was heavily stocked with rainbow trout. A large number of anglers fished this area of the river and overharvest of the remaining bull trout undoubtedly occurred. In addition, timber harvest and road building practices damaged bull trout spawning and rearing habitat or precluded access to suitable habitat. Construction of Dexter, Lookout Point, and Hills Creek dams modified stream temperatures and restricted migrations to and from spawning areas. Table 1 displays the last reliable observations of bull trout in the Middle Fork Willamette basin. Table 1. Bull trout observations in the Middle Fork Willamette basin. WATERBODY LAST YEAR OBSERVED Middle Fork Willamette below Hills 1953 Creek Reservoir Middle Fork Willamette above Hills 1990 Creek Reservoir North Fork of Middle Fork 1962 Willamette Hills Creek Reservoir 1988 Salt Creek 1960 Bull trout habitat remains in spring-fed portions of the Middle Fork Willamette and tributaries. However, repeated electrofishing and snorkel surveys of the Middle Fork Willamette and tributaries have not detected bull trout. ODFW has electrofished margin areas of the Middle Fork Willamette and major portions of all tributaries from Chuckle Springs to Swift Creek, the areas with the most likely bull trout habitat on the Middle Fork Willamette. Most of the pools from Paddy’s Valley to Staley Creek, as well as much of Swift Creek, have been snorkeled by ODFW and/or USFS personnel. 2 Potential bull trout habitat remains in spring-fed portions of the MFW and tributaries above Hills Creek Reservoir (Rigdon Ranger District 1996). However, despite occasional angler reports, repeated electrofishing and snorkel surveys of the Middle Fork Willamette and tributaries have not detected bull trout presence. Therefore, the Upper Willamette Bull Trout Working Group believes that Middle Fork Willamette bull trout will not continue to persist in the subbasin without rehabilitation efforts. As you may recall at the SCCS meeting at McKenzie Bridge, Paul Spruell said the only way of holding on to the remaining genetic material was to provide a carrier for that material. Under the definition of Supplementation in the OAR's, 635-07-501 (53) we believe this is what we are doing. If we are not using this definition of supplementation, or if there are some non-policy rules that we don't have, please let us know (We're unsure if supplementation means an ongoing program. If that is the case, perhaps we are not supplementing because our plan is to go in for one life cycle and let the chips fall). We do have another alternative for you to consider. Under the Operating Principles for Wild Fish Management, OAR 635-07-527 (3) outlines special rehabilitation programs. We have always been very leery of calling this population extinct. If it was easy to call them extinct, we would probably have had this program going three years ago. If there is a chance that they are not extinct, our program fits into this category. This project is designed to comply with Wild Fish Management Policy (WFMP) Oregon Administrative Rules 635-07-527 (3), addressing rehabilitation of wild fish populations. PROJECT BACKGROUND In 1997, ODFW and USFS/Rigdon Ranger District began a cooperative effort to reintroduce bull trout to the Middle Fork Willamette basin. Release sites were chosen principally on criteria and information provided in Goetz (1994). In order to develop and evaluate rehabilitation procedures, ODFW transferred 178 bull trout fry (age 0+) from Anderson Creek on the McKenzie River, to three tributaries of the Middle Fork Willamette in June 1997. The release sites included Chuckle Springs, Indigo Springs and Skunk Creek. Of the three pilot program sites, only Chuckle Springs will be utilized in future restocking efforts. After further analysis, Skunk Creek was determined to be too warm to provide optimal rearing habitat for juvenile bull trout, and spawning and access were limited in Indigo Springs. Therefore, we chose new rehabilitation sites for 1998. Rehabilitation Sites The McKenzie basin contains the only verifiable populations of bull trout in western Oregon. These fish may have ranged occasionally into the mainstem Willamette and spawned with bull trout from the Middle Fork Willamette. However, warm water temperatures in the mainstem Willamette and the bull trout’s strong homing instinct probably precluded common genetic exchange between the populations. 3 Three streams have been selected as sites for rehabilitation of bull trout fry: Chuckle, Shadow, and Iko springs. These spring-fed streams emerge from rock on the north side of the Middle Fork Willamette between river miles 258 and 260.5 (Appendix A). The sites were chosen following surveys of several potential rehabilitation streams (see Appendix B). Once chosen, the food base and physical attributes of the rehabilitation sites were assessed (Appendix C). Cutthroat trout inhabit the lower reaches of each stream; there have been no brook trout sightings in the vicinity. Chuckle and Shadow springs contain minimal spawning habitat but are adjacent to good spawning habitat in the Middle Fork Willamette. For 1998, we propose to place 20% of the bull trout fry in Chuckle and 20% in Shadow springs. The remaining 60% will be placed in Iko Springs. Iko has the best combination of potential bull trout rearing and spawning habitat observed in the Middle Fork Willamette watershed. Spawning habitat could be improved dramatically at all three sites with gravel supplementation. Percentages may be adjusted as deemed appropriate in the future. We assume that fry released over the four-year period will disperse downstream and that adults will return to spawn in any suitable habitat. ACTIONS We plan to capture bull trout fry from Anderson Creek in the downstream migrant trap located below the OR Highway 126 culvert. We plan to remove 25% or 2,000 (whichever is less) of the potentially- trapped age 0+ bull trout fry (where potential assumes sampling 100% of the time, but does not account for trap efficiency) during the peak migration period in March and April. During the trapping week, the trap will be checked daily and captured fry will be held in mesh-lined plastic containers in the trap live box (Goetz 1989). Twice a week, we will combine all fry into one of the plastic containers, which will be suspended in a liberation tank. Ice will be added to the tank as needed along the route to the Middle Fork Willamette in order to maintain water temperatures at 4-6oC. The fry will be transported as close as possible to the release sites in a truck and carried the remaining distance in covered buckets. Because of the long-distance transport required to move fry to the Middle Fork Willamette, we propose transporting fry twice a week, every other week, through the months of March and April, with a goal of ten transfers per year from 1998-2001. RISK ANALYSIS Risks to the McKenzie River Bull Trout Population This project involves the risk of decreasing the size of the McKenzie River bull trout population by removing fry from Anderson Creek. The WFMP limits the number of fish that can be removed to 25% or less of the breeding population. Assuming the trap will operate an average of 50% of each week, removing all of the fry trapped in one week and not removing any fry the following week should result in removal of approximately 25% of the potentially trapped Anderson Creek fry over the migration period. Because some of the fry do not migrate during the trapping period and Anderson Creek trap efficiency 4 is estimated at 60-80 % (Pers. comm. Mark Wade, ODFW), we will actually remove far less than 25% of the migrating fry. Fry will be removed from Anderson Creek based upon fry migration totals for a single week. Therefore, we will need to monitor the number of fry removed from Anderson Creek to ensure that the number of fry removed never exceeds 25% of the potential fry totals at any point in the season. We believe that many of these migrating fry would not find adequate habitat in the lower reaches of Anderson Creek and would eventually enter the McKenzie River. We believe that fry migrating at this age rather than at age 1 or older have a lower survival rate because of a lack of fry habitat in the McKenzie and predation from other fish. We expect that a decrease in the density dependent mortality will somewhat compensate for removal of a portion of the fry population.