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Fish-ing Around – Discovering the Habitat Needs of the Pacific Fisher

  • Article
  • Middle School
  • 1 Classroom Period
  • Wildlife
  • Canopy Cover
  • Forest management
  • Habitat
  • Land Use
  • Pacific fisher
  • Species of conservation concern
Cover for the 'Fish-ing Around' article. The main image is a photo of a baby Pacific Fisher in its den.
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The scientists in this study were interested in figuring out which landscape characteristics were more abundant in the core areas of fisher habitat. They hypothesized that the core area would contain more late-successional forest, that there would be less tree mortality, less habitat disruption from humans, and less human presence in general.

 

Fish-ing Around – Discovering the Habitat Needs of the Pacific Fisher

Jump To

  • Meet the Scientists
  • Thinking About Science
  • Thinking About the Environment
  • Introduction
  • Methods
  • Findings
  • Discussion

Meet the Scientists

Eric Gese

Wildlife Biologist

I love having the opportunity to conduct research on a variety of carnivores for the past 40 years with my group of dedicated graduate students in incredible places on this... Read Full Bio

Jennifer Kordosky

Genomics Research Scientist

My favorite science experience was trapping mesocarnivores in the Sierra Nevada. Fishers make a faint chuckling noise while in the trap, so if you heard it when approaching, you knew... Read Full Bio

Kathryn Purcell

Wildlife Biologist

My best day in the field ever was when I climbed to a fisher den and extracted two kits to be measured and marked for future identification. My arm just... Read Full Bio

Craig Thompson

Wildlife Ecologist

I have worked with a variety of carnivores over the years, large and small, but one of my favorite research-related memories is being attacked by a northern grasshopper mouse. After... Read Full Bio

All the animals in these photos were unharmed and released back into the wild by trained scientists. Never approach or handle wildlife.

What Kind of Scientist Did This Research?

Genomics Research Scientist: A scientist who studies genes’ effects on physical traits and how multiple genes and their interrelationships influence the growth and development of an organism .

Wildlife Biologist: A scientist who studies wildlife, including what they eat, how they reproduce, and how they use their habitat.

Wildlife Ecologist: A scientist who studies the relationship of different kinds of wildlife with each other and with their living and nonliving environment.

Thinking About Science

Often in science research, scientists build and expand upon research that has already been done. When scientists begin researching a topic, they gather all previous research on the topic and review it. This process is called a literature review. The scientists use the information they have gathered to inform their research and help define the research question. In this article, the scientists had information from several previous studies that helped them narrow down their research question. Additionally, several of the scientists working on this research had worked on earlier research questions regarding this topic, so these scientists had a broad understanding of their research topic and could work together to learn even more about it.

 

Thinking About the Environment

Sometimes it is important to manage an area of land to help an animal or plant survive. When plants or animals are having difficulty surviving in their environment, they may be labeled a “species of concern” by local, State, or national agencies. Scientists then research ways to improve the situation for the plant or animal. Then, a management plan is designed to help support the plant or animal in its environment. The management plan can be used by land managers and others to help protect and improve the outcome for the plant or animal before it becomes endangered. In this research, scientists were interested in learning more about a particular animal that was listed as a species of concern. They wanted to learn specifically about its habitat needs so that they could help provide guidance and information about how to best help the animal. You will learn more about this animal and what the scientists found in the following article.

 

Introduction

The scientists in this study were interested in learning more about the habitat needs of the fisher (figure 1).

A fisher with fur of various shades of brown stands on a fallen log.
Figure 1. Fishers are sometimes called “fisher cats,” but they are not cats, nor do they fish. U.S. Fish and Wildlife Service photo.

The fisher is a rare mammal that lives in Canada and four areas of the United States: New England, the Great Lakes, the northern Rocky Mountains, and the Pacific States (figure 2).

A map of Canada (in blue), the United States (in green), and Mexico (in brown). The range of fishers is marked with a darker purple-blue. The range is predominantly in Canada with a few pockets in the northern U.S. and California.
Figure 2. Examine the map to see where fishers can be found. Are any of these areas close to where you live? FIND Outdoors map by Leslie Shaw Design.

Fun Facts!

Fishers are a medium-sized member of the weasel family. Contrary to its name, the fisher does not eat fish. Instead, it is a voracious hunter of other small animals. The fisher is considered a mesocarnivore, which means 50–70 percent of its diet is made up of meat from another animal. It has been known to prey upon porcupines. Very few animals are known to prey upon porcupines. One of the other known predators of porcupines is a cousin to the fisher—the wolverine.

A full grown fisher with fur in shades of brown and small ears, standing in a forest.

In California, the historic range of the fisher goes through the Sierra Nevada (figure 3). Since the 1940s, the fisher population in California has declined due to fur trapping, which almost brought the species to extinction. Trapping was banned in 1946 to help the population recover, and the fisher was listed a species of concern (see “Thinking About the Environment”).

 

A map of the western United States showing the range of West Coast fishers in a darker purple-blue. The range is mainly in southern coastal Oregon, northern California, and in the southern half of the Sierra Nevada.
Figure 3. The Sierra Nevada are a major mountain range in western North America . The Sierra Nevada run along the eastern edge of California. FIND Outdoors map by Leslie Shaw Design .

However, scientists note that the species has never fully recovered from that time. When this research was conducted, some populations of fishers, such as the West Coast Distinct Population Segment, were being reviewed for listing as an endangered species (see sidebar below). The West Coast Distinct Population Segment in the southern Sierra Nevada had less than 300 adults. In addition to fur trapping, the fisher population is declining due to habitat fragmentation, development, and climate change (figure 4).

 

A yellow digger and a bulldozer scoop dirt in a cleared lot of red clay. Other construction equipment is nearby, and a line of trees is visible in the distance.
Figure 4. As areas are developed, land is cleared for various purposes. In this photo, land is cleared for a shopping center . Courtesy photo by Babs McDonald .

Distinct Population Segment (DPS)

Sometimes a species may have several separate populations within its natural habitat. The fisher, for example, lives in several different areas of the United States (see figure 2). These fisher populations are geographically separate from one another and may have different genetic profiles, community behaviors, or challenges in their communities. The U.S. Fish and Wildlife Service calls these separate populations “distinct population segments,” or DPS. Sometimes one DPS of a species may have more difficulty surviving in its current habitat than other populations. That particular DPS can be protected under the Endangered Species Act while the other populations of the species are not protected. In the case of fishers and during the time period the research took place, the West Coast Distinct Population Segment was the population being considered for endangered species status. However, in 2020, the U.S. Fish and Wildlife Service broke the West Coast Distinct Population Segment into two parts. The southern Sierra part of the segment has been listed as endangered. The northern California/southern Oregon part has not been listed as endangered.

The fisher has a home range. This home range is an area where the fisher engages in its normal activities like eating, resting, and caring for its young. Within the home range, scientists have identified a core area. This core area may be used more frequently than the rest of the home range. The core area may contain more dependable resources such as food. Scientists think that core areas may serve as refugia (ri fyü jē yǝ). Refugia are locations that support an isolated population by sheltering it from unfavorable conditions. The fisher population is isolated due to habitat needs, human development and habitat fragmentation, and climate change.

 

The scientists in this study were interested in figuring out which landscape characteristics were more abundant in the core areas of fisher habitat. The scientists hypothesized that the core area would contain more late-successional forest. A late-successional forest is an older forest with more mature trees and undergrowth (figure 5). Additionally, scientists hypothesized that there would be less tree mortality, less habitat disruption from humans, and less human presence in general.

 

A black and white illustration of forest succession. Time progresses from left to right. On the left are rocks and bare earth, then lichens and mosses, then grasses and weeds. Around the middle of the progression, herbs and shrubs grow, then softwood trees. Finally, at the far right of the succession, hardwood trees grow.
Figure 5. Forest succession is the change from one plant community to another within a forest. Late- successional forests
are the forests at the end of the progression. Look at how the type of vegetation changes over time. What do you notice about late-successional forests? FIND Outdoors illustration by Stephanie Pfeiffer Rossow.

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Methods

The study was conducted in the Kings River Fisher Project area (KRFP) and the Sierra Nevada Adaptive Management Project area (SNAMP). Both areas are located in the Sierra Nevada in California. Specifically, the scientists gathered information from the Bass Lake and High Sierra Ranger Districts of the Sierra National Forest (figure 6).

 

A circular, enlarged map showing the two study areas in California. The SNAMP is south of Yosemite National Park and east of the city of Oakhurst. The KRFP is east of Fresno and Highway 168.
Figure 6. The project areas for this study (SNAMP and KRFP) are both located in the Sierra Nevada. FIND Outdoors map by Leslie Shaw Design.

 

During the summer months, very little precipitation fell in the area. The temperatures ranged from 9 degrees Celsius (°C) to 23 °C. Snow cover was typical from November to April with temperatures ranging from -4 °C to 7 °C. Both areas were impacted by a severe 4-year drought from 2012 to 2015. This drought is thought to be one of the most severe droughts in that region in the past 1,200 years. The drought, combined with a mountain pine beetle infestation, caused a significant loss of trees in the area.

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What is Mountain Pine Beetle Infestation?

Mountain pine beetles live for only 1 year. Most of the year is spent “chilling out” in a condition scientists call supercool. Because they live in high mountain environments where it is very cold, they spend most of their short life span being supercool. That does not give them much time to lay eggs and reproduce. When these beetles reproduce, they lay eggs in the phloem of pine trees. These eggs become the larvae that live in the phloem during the cold months. In late summer, pupa become adults and emerge from the pine trees. As adults, the beetles must bore holes in other pines trees so they can lay their eggs. When they bore holes in the trees and lay eggs, the beetles usually kill the tree. Pine trees produce resin to repel the beetles. To successfully lay their eggs, the beetles must work as a team. They bore holes in pine trees in large numbers. To learn more about mountain pine beetles, read the “Beetles Are Supercool!” monograph.

 

A black and white illustration of the life cycle of the mountain pine beetle. The beetle lays its eggs in the phloem of a tree. The eggs develop into larvae and then pupae emerge from the tree. The adult flies to the tree and bores into it to lay eggs in the phloem again.

The scientists trapped the fishers with live traps. They covered the traps with natural materials and baited the traps with chicken and bait lure. Fishers were handled with a canvas sleeve and a metal handling cone. The fishers were sedated, and dosages of the sedation medicine were based on the size, age, and whether it was a male or female fisher (figure 7). The scientists measured the following things:

  • Body length
  • Body mass
  • Tail length
  • Canine length (the canine is a type of tooth that is usually used for tearing food)
  • Reproductive status (scientists examined them for indications that they had reproduced)

 

A sedated fisher lies on a table with a fabric band over its snout. We can see the hands of two workers in blue surgical gloves examining the fisher and taking measurements.
Figure 7. Fishers are sedated and handled with care while scientists take measurements and record their observations. This photo was taken during another study of fishers’ ranges in Oregon conducted by the Forest Service and the Bureau of Land Management. Bureau of Land Management photo.

The fishers were fitted with a handmade, breakaway radio collar (figure 8). The fishers were also injected with a passive radio transmitter. The collar enabled the scientists to track the fishers’ movements within their home ranges. The passive transmitter allowed them to identify an animal later if it slipped out of the collar, like the way some people microchip their dogs and cats. All animals were captured and handled under authorization from the USDA Forest Service and local agencies. None of the animals were harmed, and all were released back into the wild.

Gloved hands hold a sedated fisher that is fitted with a breakaway radio collar that has a blue band and an antenna.

Figure 8. (A) The breakaway radio collar enables the scientists to track fisher movement. Bureau of Land Management photo.

A scientist sits on the ground in a forest. In front of him is a laptop and a large radio antenna.

Figure 8. (B) A scientist uses a computer and an antenna to track the fisher’s radio collar. These photos were taken during another study of fishers’ ranges in Oregon conducted by the Forest Service and the Bureau of Land Management. Bureau of Land Management photo.

The scientists collected information on home ranges for a year. They analyzed both male and female home ranges separately. The scientists also obtained data on where different silviculture treatments had occurred. Silviculture is the art and science of managing the establishment, growth, composition, health, and quality of forests and woodlands to meet the diverse needs and values of landowners and society. These needs and values could be wildlife habitat, timber, water resources, restoration, and recreation on a sustainable basis. Silviculture treatments include logging, thinning, burning, and regeneration (figure 9). The locations of buildings and roads were obtained from the Forest Service. This information was used to analyze the amount of human activity in these areas.

 

A large machine is picking up trees that have been cut down in a pine forest.
Figure 9. Thinning trees from a forest is a silviculture technique used to help manage forest fires. Photo by Cecilio Ricardo.

The scientists also collected information on habitat characteristics such as canopy cover and habitat type. They identified six habitats (figure 10):

 

  1. Conifer forests (forests composed largely
    of evergreen trees or cone-bearing, needle- leaved trees; in this study, mainly ponderosa pine, sugar pine, white fir, and incense cedar)
  2. Hardwood forests (forests that mainly have deciduous trees, which are trees that periodically shed their leaves; examples include California black oak and canyon live oak)
  3. Developed lands (lands with human development such as buildings and houses)
  4. Shrubland (areas dominated by shrubs such as manzanita (man zǝ nē tǝ), whitethorn ceanothus (sē ǝ nō thǝs), and bear clover/ mountain misery)
  5. Sparse cover (areas with granite or little shrub cover)
  6. Open water

Figure 10. Scientists categorized land into six habitat types for their study on fisher home ranges. These habitat types are: (1) conifer forest; (2) hardwood forest; (3) developed land; (4) shrubland; (5) sparse cover; and (6) open water.

Pine trees dusted with snow.

Figure 10. (1) Example of a conifer forest habitat. Photo by Molly Simonson.

Large hardwood trees in autumn.

Figure 10. (2) Example of a hardwood forest habitat. Adobe Stock photo.

A brown-sided service building in a clearing in a forest.

Figure 10. (3) Example of a developed land habitat. Adobe Stock photo.

A stream running through plants and shrubs.

Figure 10. (4) Example of a shrubland habitat. Photo by Jim Frazier.

A mountainous, rocky landscape with not much vegetation.

Figure 10. (5) Example of a sparse cover habitat. Photo by Paul Wade.

A lake with mountains in the background.

Figure 10. (6) Example of an open water habitat. USDA Forest Service photo.

The scientists noted that canopy cover or canopy density is the one characteristic that has been widely associated with the presence of fishers. Dense canopy is defined as greater than 60 percent cover and helps with foraging, rest site opportunities, and refuge from large predators (figure 11).

 

3 photos. A photo taken from the ground showing a dense tree canopy above; very little sky is visible. A photo taken from the ground showing a moderate tree canopy cover; sky and clouds are visible in the middle of the frame.A photo taken from the ground showing a low tree canopy cover; the image is mostly sky with tree canopy just around the outside edges.
Figure 11. The scientists in this study classified the tree canopy cover into three categories: dense cover, moderate cover, and low cover. This figure shows examples of (A) dense, (B) moderate, and (C) low tree canopy cover . Adobe Stock photos .

The scientists also obtained tree mortality data. Both an extensive drought that occurred from 2012 to 2015 and a mountain pine beetle infestation greatly increased the amount of tree mortality. There were many dead trees in all the home ranges of these fishers.

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Findings

From 2014 to 2016, scientists trapped 41 female fishers and 23 male fishers. Sixty-eight home ranges were identified for females. For the male fishers, the scientists had trouble distinguishing a home range because they did not appear to have regular spots that they visited frequently. Instead, they identified 32 “areas of use” for male fishers. Scientists used the term “area of use” to refer to all the areas that a male fisher used.

 

The main difference between males and females is that males use a larger space and do not use den sites. Den sites are used to raise the young (figure 12). Females raise the young independently.

 

A young fisher, all brown with dark eyes and small ears, looks out of its den in a hollowed-out tree.
Figure 12. A fisher kit looks out from its den. Adobe Stock photo.

For female fishers, building density and percentage of low canopy cover were significantly lower in their core areas (box 1). The percentage of hardwood habitat, percentage of sparse cover, and percentage of moderate canopy cover were also lower in the core area compared to the entire area. The percentage of dense canopy cover was significantly higher in core areas. Percentage of conifer forests was also higher in core areas.

 

A table that reads: Female core areas had more: Dense canopy cover, Conifer forest habitat.Female core areas had less: Building density, Low canopy cover, Moderate canopy cover, Hardwood habitat, Sparse cover habitat
Box 1. Characteristics of female fishers’ core areas.

 

For male fishers, the scientists found a significantly lower portion of developed land in their core areas compared to their whole area of use (box 2). Building density, percentage of shrubland, and percentage of low canopy cover were also lower in the core areas than in the entire area of use. Like female fishers, males’ core areas had a higher percentage of conifer forest habitat and dense canopy cover.

 

A table that reads: Male core areas had more: Dense canopy cover, Conifer forest habitat.Male core areas had less: Building density, Developed habitat, Shrubland habitat, Low canopy cover
Box 2. Characteristics of male fishers’ core areas.

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Discussion

Female home ranges had lower amounts of building density, percentage of hardwood forests, percentage of sparse cover, and percentage of low canopy within the core. The female home ranges also had a higher amount of conifer forests and dense canopy within the core.

 

Like the females, male fisher areas of use had lower building density, shrubland, developed areas, and areas with low canopy. Males also had higher amounts of conifer forests and dense canopy in their core areas. The scientists think that males may position their core areas to avoid developed habitat with low canopy cover.

 

Because fisher habitat is deteriorating due to development, wildfires, past logging, and other issues, the core area appears to provide a more suitable habitat for the fishers. Both male and female fishers seem to prefer being farther from human development and having the protection of denser canopy cover. This finding suggests that it may be important to help protect these core areas for species of concern such as the fisher.

 

The scientists also found evidence that fishers were able to adapt to small changes to the core habitat. Overall, the scientists recommended that managers conserve areas of dense canopy cover that are about 2 square kilometers (km2) in size. Ideally, the patches should contain conifers and have very few roads or buildings.

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Adapted from Kordosky, J.R.; Gese, E.M.; Thompson, C.M.; Terletzky, P.A.; Purcell, K.L.; Schneiderman, J.D. 2021. Landscape use by fishers (Pekania pennanti): core areas differ in habitat than the entire home range. Canadian Journal of Zoology. 99(4): 289–297. https://doi.org/10.1139/cjz-2020-0073.

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  • In this FACTivity, you will choose an animal to study that lives in the United States and create an Animal Fact File for that animal. If completing this FACTivity as...

    FACTivity – Fish-ing Around

    • Activity
    • Middle School
    • 2-3 Classroom Periods
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    In this FACTivity, you will choose an animal to study that lives in the United States and create an Animal Fact File for that animal. If completing this FACTivity as...
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    Explore Activity Download FACTivity (PDF)

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    Fish-ing Around - Discovering the Habitat Needs of the Pacific Fisher
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Glossary

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  • canopy

    (ka nə pē): A protective covering: such as, the uppermost spreading branchy layer of a forest.

  • cavity

    (ka vǝ tē): An unfilled space within a mass, especially a hollowed-out space.

  • evade

    (i vād or ē vād): To slip away or avoid capture.

  • forage

    (fȯr ij): (noun) Food for browsing or grazing animals.

    (verb) To wander in search of forage or food.

  • genetic

    (jə ne tik): Of, relating to, or involving genes or genetics.

  • genomics

    (jǝ nō miks): A branch of biotechnology concerned with genetics.

  • habitat fragmentation

    (ha bǝ tat frag men tā shǝn): When a place where an animal or plant naturally lives and grows is broken or separated into distinct parts.

  • hypothesize

    (hī pä thǝ sīz): To make an assumption or idea that is proposed for the sake of argument so that it can be tested to see if it might be true.

  • mortality

    (mȯr ta lǝ tē): The number of deaths in a given time or place.

  • phloem

    (flō em): A tissue in plants that contains sieve tubes that carry dissolved food material and that lies mostly outside the cambium.

  • regeneration

    (ri je nǝ rā shǝn): Renewal or restoration of a biological system (such as a forest) after injury or as a normal process.

  • sedated

    (si dā tǝd): Being in a calm, relaxed state resulting from the effect of a sedative drug.

  • Eric Gese kneels in the snow in front of a lake with his dog.

    Eric Gese

    Wildlife Biologist

    I love having the opportunity to conduct research on a variety of carnivores for the past 40 years with my group of dedicated graduate students in incredible places on this...
    View Profile
  • Jennifer Kordosky stands in a forest and holds a sedated fisher.

    Jennifer Kordosky

    Genomics Research Scientist

    My favorite science experience was trapping mesocarnivores in the Sierra Nevada. Fishers make a faint chuckling noise while in the trap, so if you heard it when approaching, you knew...
    View Profile
  • Kathryn Purcell stands in a forest and holds a sedated fisher.

    Kathryn Purcell

    Wildlife Biologist

    My best day in the field ever was when I climbed to a fisher den and extracted two kits to be measured and marked for future identification. My arm just...
    View Profile
  • Craig Thompson kneels in a forest and holds a sedated fisher.

    Craig Thompson

    Wildlife Ecologist

    I have worked with a variety of carnivores over the years, large and small, but one of my favorite research-related memories is being attacked by a northern grasshopper mouse. After...
    View Profile

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Standards addressed in this Article:

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Social Studies Standards are educational guidelines outlining the essential knowledge, skills, and concepts students should learn in subjects such as history, geography, civics, and economics, aiming to provide a comprehensive understanding of societal structures, historical events, and global perspectives.
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Natural Inquirer is a science education resource journal to be used by students in grade 6 and up. Natural Inquirer contains articles describing environmental and natural resource research conducted by Forest Service scientists and their cooperators. These scientific journal articles have been reformatted to meet the needs of middle school students. The articles are easy to understand, are aesthetically pleasing to the eye, contain glossaries, and include hands-on activities. The goal of Natural Inquirer is to stimulate critical reading and thinking about scientific inquiry and investigation while teaching about ecology, the natural environment, and natural resources.

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  • Meet the Scientists

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    Introduces the environmental topic being addressed in the research.

  • Introduction

    Introduces the problem or question that the research addresses.

  • Method

    Describes the method the scientists used to collect and analyze their data.

  • Findings & Discussion

    Describes the results of the analysis. Addresses the findings and places them into the context of the original problem or question.

  • Reflection Section

    Presents questions aimed at stimulating critical thinking about what has been read or predicting what might be presented in the next section. These questions are placed at the end of each of the main article sections.

  • Number Crunches

    Presents an easy math problem related to the research.

  • Glossary

    Defines potentially new scientific or other terms to students. The first occurrence of a glossary word is bold in the text.

  • Citation

    Gives the original article citation with an internet link to the original article.

  • FACTivity

    Presents a hands-on activity that emphasizes something presented in the article.

Science Education Standards

You will find a listing of education standards which are addressed by each article at the back of each publication and on our website.

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If you are a trained Project Learning Tree educator, you may use “Life on the Edge” as an additional resource.

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Additional Resources

  • USDA Forest Service: "The Fisher: Secret Phantom of Mature Forests"

    Fishers are a rare and secretive carnivore in the Rocky Mountains and along the West Coast. They are currently being considered for listing under the Endangered Species Act. They are also being considered as a Species of Conservation Concern on the Nez Perce-Clearwater National Forests. This study maps predicted habitat to help prioritize areas for conservation.

    Visit Website

  • Sequoia National Forest: The Pacific Fisher Fact Sheet

    Read a two-page fact sheet about the Pacific fisher.

    Visit Resource

  • Rocky Mountain Research Station, Science You Can Use: "Here today, here tomorrow: Managing forests for fisher habitat in the Northern Rockies"

    The fisher is a unique member of the weasel family and a sensitive species in the northern Rockies. Forest managers need information on fisher distribution and habitat needs to conserve this species while balancing multiple uses of forest lands and to maintain fisher populations under climate change.

    RMRS researchers matched DNA samples from fishers to habitat features at various scales and found that fishers require large trees and forests with a lot of cover and structure, all nested within a larger forested landscape. Models of fisher habitat in the future under a warming climate suggest that the amount of favorable area is likely to expand and move eastward into the Interior West, but it could become more fragmented. Now and in the future, fisher management will require retention and fostering of mature, complex, mesic forests with a high degree of habitat connectivity.

    Visit Resource
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