They’re named for their size and brute strength – a bullish-looking head – and their penchant for piscivory. The bull trout (Salvelinus confluentus) is really a char, and oddly enough, most closely related to white-spotted char in Asia, genetics studies show. But it is kin enough to brook trout and Dolly Varden on the North American continent that they sometimes interbreed. That and other problems, like competition with its cousin the lake trout which was introduced into the Columbia River drainage from east of the Continental Divide, have made scientists bearish on its conservation status. The fish was listed as a threatened species in 1998.
With an eye toward trying to stay in front of conservation issues, Creston National Fish Hatchery initiated experiments in bull trout culture in 1993, to give fishery managers future options for refining fish culture techniques and possibly developing brood stock and augmenting wild populations. Mitigation planning for fisheries of the Flathead Basin had already identified bull trout as a potential species to mitigate fisheries lost to water projects. We built an isolation facility funded by the Montana Power Company to incubate wild bull trout eggs. Early on we collaborated with the Hill Creek Hatchery operated by the B.C. Ministry of the Environment, a mitigation hatchery near Upper Arrow Lake, British Columbia. Biologists there had a successful bull trout culture program since the late 1980’s, taking eggs from captively held wild adults and rearing and stocking in the wild.
In September 1993, we collected about 20,000 eggs from seven pairs of wild bull trout in Lion and Holland creeks of the Swan River drainage. An unexpectedly high 97 percent of the eggs hatched. The following year, we brought in another 12,000 eggs from three more pairs of wild fish.
We conducted a number of feeding and growth experiments using various light and temperatures regimes, plowing new ground in the field of what was known of bull trout aquaculture with these two captive age classes. We learned more about imprinting behavior evaluating thyroxine hormone levels. Because their growth in captivity was excellent, the bulls eventually outgrew their pen in the isolation facility. Some were sent outside to raceways and ultimately stocked in Duck Lake on the Blackfeet Indian Reservation in a recreational fishery. Others were transferred to Bozeman Fish Technology Center for additional studies.
The listing of bull trout as a threatened species began a new phase in the Creston National Fish Hatchery bull trout culture program. Our desires turned toward evaluating captive bull trout as broodstock and the production of eggs and fry for experimental research.
We learned that captive brood fish mature about two years sooner than is typical in the wild, due to the high growth rates achieved under hatchery conditions. Each year between 1997 and 2003, we collected between 70,000 and 210,000 eggs from the first known captive bull trout brood and incubated them in the isolation facility where we collected data on various aspects of development, fecundity and egg viability.
Year-round water temperatures at Creston NFH are appropriate for bull trout brood development. Broodstock performance was remarkably consistent for ages four through ten, and the rate of egg eye-up was consistently near 75 percent – a rate well within acceptable limits for other species where their culture is well understood. As the bulls aged, fecundity declined, as is typical. The last of the original brood fish were euthanized in 2006 and we presently maintain some of their younger progeny, continuing to supplying bull trout for research projects.
The listing of bull trout has underscored the need to have a reliable captive population given that the opportunity to use wild fish for research programs is curtailed. Over the course of our experimental program, eyed bull trout eggs and a few fry were sent to a wide variety of cooperating researchers, among them: Dr. Ronald Hedrick at UC Davis and MFWP both investigated the fish’s susceptibility to whirling disease; Oregon Department of Fish and Wildlife created field ID kits with preserved fish; Bozeman Fish Technology Center learned more about their thermal tolerance; the EPA and University of Wyoming studied dioxin and copper toxicities in bull trout; Dr. Eric Taylor at the University of British Columbia researched hybridization with Dolly Varden. Some adult specimens from the hatchery were carted off by visiting Russian scientists so that skull morphology could be compared to the bull trout’s close kin, Siberian char.
Scientists at the Abernathy Fish Technology Center in Washington, studied bull trout swimming behavior, fry entrainment, and the fish’s response to various screen configurations to better protect bull trout from water withdrawals in the wild. Here at Creston NFH we used larger bull trout to practice techniques for tagging – PIT tag, and surgical implants of radios and sonic tags – all for the express purpose to better arm field biologists who monitor the fish’s movements in the wild.
Bull trout from Creston NFH that were reared for experiments in facilities across the country have yielded basic, yet vital life history information on incubation, growth, thyroid hormone levels, smolting, diet and feeding behavior, thermal tolerance, and predator avoidance.
Some of the studies we’ve described have been or will be published in journals of science; other findings will remain in the grey literature. No matter where they reside, all the work will in some degree advance what we know about this wonderful fish and inform the future so the running of the bulls can continue in the Pacific Northwest. Creston National Fish Hatchery has been the fount for an impressive number and diversity of studies that in the end will contribute to the eventual recovery of the bull trout.
Wade Fredenberg is the Native Fish Coordinator for western Montana.
Mark Maskill is the manager of Creston National Fish Hatchery.By: Wade Fredenberg and Mark Maskill / USFWS
