Volume XXIV - 1993

Bull trout (Salvinus confluentus), and dolly varden (Salvelinus malma), were once considered to be the same species. They are now considered to be distinct species based on genetic, morphological and behavioral differences. In general, bull trout are an inland, freshwater form, whereas dolly varden spend much of their adult life history in the ocean before returning to freshwater to reproduce.

Although bull trout were once found in most major river systems in the Pacific Northwest and Canada, their distribution has been significantly reduced over the past 30 years, and many populations have become extinct. Habitat degradation and introduction of non-native and exotic fish species are believed to be the primary causes for the recent decline. The Klamath River Basin in Oregon is the southern limit of bull trout populations today. These populations are genetically distinct from other Pacific Northwest bull trout populations and qualify as a separate species for consideration under the Endangered Species Act. Bull trout are currently listed as a category 2 species (candidate species under the Endangered Species Act) by the U.S. Fish and Wildlife Service. The American Fisheries Society has petitioned the U.S. Fish and Wildlife Service to list the Klamath River Basin bull trout as an endangered species.

A 1947 stream survey in the park's Sun Creek drainage indicated that bull trout were well distributed in the headwater stream along with brook trout (Salvelinus fontinalis) that were stocked into the stream in the early pert of this century. A survey of the fish populations and instream habitat in Sun Creek in the summer of 1989 revealed that the bull trout population was reduced to 130 adult fish and restricted to a 1.9 km (1.2 mi) section of the stream (see map). Brook trout were distributed throughout the stream. Hybridization and competition with the introduced brook trout appeared to threaten the bull trout population with a high risk of extinction.

This alarming information led the park to draft a bull trout restoration plan in 1990. The objectives of the plan were to restore the remnant population of bull trout to historic numbers and distribution in Sun Creek, remove the introduced brook trout, and prevent the re-invasion of non-native species from waters outside of the park in the future. The plan called for additional research in 1990 and 1991 to verify the distribution and abundance of the bull trout, evaluate stream chemistry, temperature, flow, retention and travel time, and conduct surveys of amphibians and aquatic insects, with an emphasis on looking for rare, threatened and endangered taxa. Laboratory tests were conducted to determine the specific toxicity of the fish toxin Antimycin on trout in Sun Creek water. Alternative locations for a "back-up" population of bull trout were evaluated, including hatcheries and isolated creeks within Crater Lake National Park. Also evaluated were alternative methods for fish removal.

In October 1991, a peer panel and recovery team was assembled to evaluate the research to date and the recovery plan, as well as to offer recommendations on implementation of the plan. The peer panel included personnel from the National Park Service, U.S. Fish and Wildlife Service, U.S. Forest Service, Oregon Department of Fish and Wildlife, Oregon State University, and the Desert Fishes Council. Panel members had expertise in fish population restoration, fish toxins, electrofishing, fish barriers, genetics and fish and macroinvertebrate ecology.

The long-term goal of the plan was to eradicate brook bout from Sun Creek within the boundary of Crater Lake National Park. An immediate objective was to remove as many brook trout as possible from the portion of Sun Creek within the park. This would allow bull trout to increase in number and disperse downstream. The loss of any bull trout during the removal process was not an acceptable risk, as the viability of such a small population was already in question.

During the summer of 1992, a restoration program was initiated. Two log and rock fish migration barriers were constructed in Sun Creek near the park boundary to prevent the re-invasion of non-native fishes. The structures created an elevated stream channel and an artificial waterfall in a naturally constricted section of the stream. If the downstream barrier were to fail, the upstream barrier would prevent brook trout from immigrating further upstream into the park before the lower barrier could be repaired.

Brook trout were removed from Sun Creek with non-lethal electroshockers upstream of the bull trout population. Starting at the headwaters of Sun Creek, fifty meter sections of stream were blocked off with nets. Each section was electrofished until no fish were captured two out of three passes up the stream. This process was repeated two more times during the summer. Data were collected on fish weight, length, sex, abundance, biomass, and distribution.

Recent literature suggested that electroshocking may have higher injury and mortality rates on fish than previously believed. Therefore, electroshocking for brook trout in the bull trout section of the stream was tried with caution in 1992 and abandoned when the bull trout showed signs of stress. Alternative methods for removal of the brook trout in the bull trout section are now being evaluated. A special study was conducted in the fall of 1992 to evaluate rates of injury to brook trout from three different types of electroshockers. The data have not been evaluated at this time.

Non-lethal samples of fin tissue were removed from brook trout, bull trout, and brook trout-bull trout hybrids in 1992. These samples will be used for genetic analyses to evaluate hybridization and to compare the genetic make-up of Sun Creek bull trout with other populations located in the Klamath and Columbia basins. Results of the study are not yet available.

The recovery team agreed that electroshocking techniques would not be effective in fish removal downstream of the bull trout owing to increased stream flow and structural complexity of the stream channel. Therefore, brook trout were removed with Antimycin. This is an antibiotic that is extremely toxic to fish at dosages as low as 4 parts per billion. Antimycin is not toxic to mammals and birds, but is toxic to amphibians and to many species of aquatic insects. The Antimycin was successfully neutralized below the lower barrier and upstream of the boundary with potassium permanginate. Brook trout were collected at block net stations and by "dip-netters" along the stream. No amphibians were collected and preliminary observations suggested that insect mortality was low.

A sampling program will be initiated in 1993, supported by funding made available through the National Park Service. The objectives of the program are to monitor the recovery of insect and bull trout populations and to continue the removal of non-native brook trout.

Bull trout distribution in Sun Creek, Crater Lake National Park, Oregon