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Predator-Prey Relationships, Other Lake Billy Chinook Issues Focus Of Bull Trout Study
Posted on Friday, March 04, 2011 (PST)

It’s a whole new world in central Oregon’s Lake Billy Chinook where a new water withdrawal-juvenile salmon collection “tower” is stirring the reservoir’s temperature-stratified waters and recreating historic seasonal temperature conditions below the Round Butte-Pelton dam hydro project in the Deschutes River.


The $108 million tower, which began operations late in 2009, is intended provide reliable downstream passage for salmon for the first time since the dams were built in the 1960s. It also allows the temperature-selective withdrawal of water to be sent downstream and serves to stir the reservoir, bringing more cold water from the bottom toward the top.


The tower is part of an effort by Portland General Electric, the Confederated Tribes of the Warm Springs Indian Reservation and the Oregon Department of Fish and Wildlife – with the help other groups and volunteers -- to reintroduce salmon above the dams by providing passage and restoring habitat upstream and downstream.


Into the mix comes the bull trout, a piscivorous (fish-eating) species that can consume fish up to half of their body length, including young salmon, steelhead and smaller bull trout. The bull trout spawn in headwater streams but spend much of their adult life in the lake.


PGE, in particular, has been concerned that at a blossomed bull trout population may eat up the foundation of the salmon restoration effort – young hatchery salmon outplanted in the three rivers and their tributaries that must swim downstream and across the lake on their journey toward the Pacific Ocean. The hope is that those fish will return as adults to spawn on their own in the wild.


The spring-fed Metolius River has always been a stronghold for bull trout because its cool waters and clean spawning are just what the fish-eating species likes.


The population has thrived so well that, when bull trout were listed under the Endangered Species Act as threatened in June 1998, the U.S. Fish and Wildlife Service judged that there were “sufficient populations to allow some fishing” in the Metolius “arm” of Lake Billy Chinook and elsewhere in the reservoir, according to Bianca Streif, Oregon bull trout coordinator for the USFWS. The Deschutes, Crooked and Metolius all drain into Lake Billy Chinook, which is backed up by PGE’s Round Butte Dam.


Fishing for bull trout is only allowed in Lake Billy Chinook “and a few places in Montana,” Strief said. A revised critical habitat designation created for the species under the ESA in September 2010 includes about 18,795 miles of streams and 488,252 acres of lakes and reservoirs in Idaho, Oregon, Washington, Montana and Nevada. In Washington, 754 miles of marine shoreline also were designated.


PGE requested that the predator-prey relationship in the lake be investigated to determine if some management action might be taken, such as a loosening of the fishing rules to allow the removal of more bull trout. The USFWS decided that it was time to launch an evaluation of predator-prey relationships in the lake, stock status and other issues in the changing Metolius River-Lake Billy Chinook system. The federal agency convened a panel of five experts to explore the issues.


“I’m pleased this federal agency is taking a hard look at the situation because juvenile salmon and steelhead are very vulnerable to predation during the spring when they pass through Lake Billy Chinook on their migration to the ocean,” said Don Ratliff, senior PGE biologist.


The panel was formed in early February. Its input and other data will be used by the USFWS to compile a final report for release in April or May, The results from the science panel are advisory to the USFWS, which has jurisdiction over any changes in bull trout management because of the species threatened status. Other fisheries resources in the basin are co-managed by the Oregon Department of Fish and Wildlife and the Warm Springs Tribes, Branch of Natural Resources.


When the bull trout listing determination was made, it included ESA 4d rules that adopted the existing Oregon and tribal angling regulations for bull trout in Lake Billy Chinook. Since then, anglers have been allowed to harvest one bull trout a day in Lake Billy Chinook, provided it is longer than 24 inches. Bull trout fishing is allowed in the Metolius arm for eight months each year: March 1 to Oct. 31. The Deschutes and Crooked River arms are open year-round for bull trout and other trout species. The Metolius River and tributaries are closed to the harvest of wild trout, including bull trout.


Bull trout are the top predator in the Metolius River-Lake Billy Chinook system. The slow-growing fish become piscivorous at about age 2. A 25 incher is likely about 5 years old and weighs about 4.5 pounds, Ratliff said.


He said adjustments to fishing regulations might be needed, such as allowing 16-24-inch fish to be harvested. That is the size range at which a bull trout are most likely to zero in on juvenile salmon sized prey.


The bigger fish are “less apt to eat the small salmon,” Ratliff said.


Changing the 4d rule, a prerequisite for a change in state regulations, is a considerable undertaking since it would require an assessment of the species across its four-state range, not just the Billy Chinook system. And since because the system is experiencing much change -- water temperatures, food production, fish behaviors, etc. -- it might be best to wait until things settle out, until more is known about how the fish and environment react to the changes, Streif said. The report will help the federal agency decide what sort of actions, if any, are needed.


The bull trout are not in many areas because they require very cold water, which is often in limited supply. The Metolius Basin has extremely cold water plus good habitat, and abundant bull trout, thanks also to strict angling limitations and habitat protection measures.


Since 2002, the number of bull trout spawning in the Metolius Basin has been significantly higher than the federal recovery goal of 800 adults on a five-year average, according to Ratliff. Annual spawner counts rose to nearly 2,500 in 2004 and the recent five-year average (through 2010) is just under 1,500, though it has been declining in each of the past four years.


Ratliff points out that PGE, the Warm Springs Tribes, ODFW, the U.S. Forest Service and other partners are working on a myriad of projects to improve flows and habitats for salmon and steelhead. In addition to the new passage facilities at Round Butte, efforts are under way to improve passage at the Opal Spring Hydro Project on the lower Crooked River and at other smaller dams and diversions in the three river tributaries to Lake Billy Chinook.


In the long run, a healthy bull trout population will benefit from restored steelhead and salmon runs because of the increased prey base they represent, Ratliff said.


For more information about the Deschutes Passage project see:


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