46 Volume 24 – 1993


Volume 24, 1993

All material courtesy of the National Park Service.These publications can also be found at http://npshistory.com/
Nature Notes is produced by the National Park Service. © 1993



By Kent J. Taylor, Chief of Interpretation

Last year’s volume of Nature Notes from Crater Lake marked the first appearance of this publication in more than 30 years. The Crater Lake Natural History Association decided there was sufficient visitor interest for a 1993 edition because the limited number of copies in 1992 sold quickly. Contributors responded enthusiastically, so this volume is larger than last year’s effort.

Nature Notes share a common characteristic of being original research or observation relevant to the visitor experience at Crater Lake National Park. In most cases these articles have not been published previously. All of the authors are employees of the National Park Service, but their contributions were made primarily on a volunteer basis. Reprinting Nature Notes articles is encouraged, as long as credit is given to the authors and the Crater Lake Natural History Association.

This volume begins with an article on the park’s 1992 northern spotted owl survey. The results changed the way Crater Lake National Park has been viewed relative to the habitat it provides for the bird. Lori Stonum’s piece and the others that follow it serve to underscore the point made in last year’s lead article that Crater Lake National Park continues to be a vibrant field for scientific research.

The Crater Lake Natural History Association was established in 1942. Its purpose is to aid the National Park Service in educational, scientific, cultural, historical, and interpretive programs. Toward this end it sponsors this volume of Nature Notes from Crater Lake. The association operates three publication sales outlets, two at Crater Lake National Park and one at the Illinois Valley Visitor Center in Cave Junction, Oregon. Proceeds from sales items are used entirely to support the association’s goals. A list of items for sale can be obtained by writing to the Business Manager, Crater Lake Natural History Association, P.O. Box 157, Crater Lake OR 97604, or by calling (541)594-2211 ext. 499.

 Spotted Owl Survey

By Lori Stonum

The northern spotted owl (Strix occidentalis caurina) is one of three subspecies of spotted owls. It is a medium-sized forest owl distinguished by its large brown eyes and mottled brown and white breast. The spotted owl is a monogamous, long-lived species, that is mostly nocturnal. Ranging from southern British Columbia to northern California, it is found on the east and west slopes of the Cascade Range and on the Olympic Peninsula. Spotted owls live mostly in low elevation coniferous old growth forests and have a limited seasonal migration.

The first recorded observation of a spotted owl at Crater Lake National Park was in 1934. Between 1934 and 1978, there were several other sightings reported. The first surveys of the spotted owl at the park were conducted in 1978 in cooperation with the Oregon Department of Fish and Wildlife and the U.S. Forest Service. Sporadic studies have been conducted since then, but a complete census was never conducted. Until 1986, studies within the park concentrated on the west side of the Cascade Range. When the surveying resumed in 1990, the southern portion of the park was included. The 1990 and 1991 surveys, however, consisted only of two-day projects with limited coverage of the park’s spotted owl habitat.

A more comprehensive survey of the northern spotted owl at Crater Lake National Park commenced in May 1992. This was the first year that a study of spotted owls in the park was conducted according to standard protocol. Survey sites were determined based on historic spotted owl sites, areas of good habitat, and the location of proposed construction within the park. Since the survey was started late in the season compared to others in the region, we concentrated on historic owl sites and future construction zones, making them our priority. New sites were added as time became available.

Overall, the number of owls found at Crater Lake in 1992 was unexpected. We now know that the park holds greater significance for spotted owls than previously thought. During the 1990 and 1991 surveys, two pairs and one single male spotted owl were found each year. By the end of the 1992 field season, we had located seven pairs of spotted owls. Six of the seven pairs had two juveniles. Three single owls of unknown reproductive status were also found, making a total of 29 owls found in the park. Of these, 12 owls were banded with the help of the Oregon Department of Fish and Wildlife so that the owls can be identified in future studies.

The 1992 spotted owl survey produced two significant findings. One was the large number of owls located on the east side of the Cascade Range. Four pairs of spotted owls found in the park this year were on the east side of the Cascades, which was somewhat unexpected when considering that most spotted owls are found west of the mountains. The second finding was the relatively high elevation at which several owl pairs were living. For two years in a row, Crater Lake National Park has held the state record for the highest elevation at which a spotted owl pair was found. The Annie Creek site was the 1991 state record at 1829 meters (6000 ft.), and in 1992 it was the Crater Peak site at 1996 meters (6550 feet). In future studies we hope to be able to focus on these east side and high elevation sites to determine if there are factors influencing the owl’s range and reproductive status, as compared to west side and lower elevation sites.

There is still a lot of work to be done in the park on spotted owls. Less than 30 percent of the 50,000 acres of spotted owl habitat existing within Crater Lake National Park was surveyed. Considering the exciting results of the 1992 survey, the potential for even greater numbers of owls existing within the park is very high. If the spotted owl program at Crater Lake can continue to expand and survey more of the suitable habitat, perhaps the complete status of the spotted owls at Crater Lake could be better known.

Native Species Protection and Exotic Species Control: A Bull Trout Restoration Project in Sun Creek

By Mark Buktenica

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