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FISHER BIOJLOGY .fllND MANAGEMENT
IN 1CHE
WESTJ1:RN UNITED STATES
A l.iteratur1e Review and
·· Man31.gement Str:ategJ!
--~_:daptive
(VERSION 1.2)
Prepaired for
1tbe USDA Forest Sell'vice Northern Region
and
the bitier:itgency Forest Carnivore Working Group
lKIMBERLY S. HEINEMEYER!
J.EFFERY L. JONES2
National FS Library
USDA Forest Servi<;()
JUN 2 3 2009
March 1994
~l,I() W Pro•:p()(:I lid
Fort Collins CO 80526
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1P resent address: JEnvironmentall Studies, University of Califo1nia, Santa Cruz, CA 95064
2 Present address: USJ)A Foi:e.~t Service, Wisdom Ranger District, P.O. Box 238, Wisdom,
MT 59761
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PREFACE
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This document was prepared for the Interagency Forest Camivori~ Working Group
(Working Group) to synthesize information on fisher (Mlut_es pennanti) biology and to
provide an. initial direction for management of fishers in the western United States. We
consider this a working document (Version 1.1) requiring frequent updates and revisions
as more information becomes available, and .llll the assumption and hypotheses p~esented
are tested. We hope this effort will stimulate further discussion and research on the
management and conservation of fishers in western habitats. . .
. Part I reviews the biology of the-fisher. The literature review prior to 1989 was taken
priman1y fromBanei{1989), with permission from the British Colmnbia Ministry of the
Environment, Wildlife Branch and V. Banci. While the focus is on the: fisher occupying
western habitats, we often relied on the more extensive knowledge of e:astem populations
to lend insights into western populations of fishers.
Part Il presents a strategy for habitat and populatiori management in the western
Unit.ed States. As an adaptive management strategy, revisions should be made frequently
as more information becomes available on fishers in western habitats and for populations
within various physiographic regions. The strategy has a hierarchical :approach, with 6
scales, from continental to individual forest stand.
Parts ill and IV are an annotated bibliography and a set of reference papers,
respectively. The majority of the annotated bibliography prior to 1989 has been taken from
Banci (1989). Part IV contains published papers and unpublished rep1:>rts on fisher which
may provide additional information. No attempt was lllll.de to reprodui:e theses or
dissertations due to the length ·Of these docUillents.
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ACKNOWLEDGEMJB:NTS
The funding for the project was provided by the USDA, Forest Service. Northern
Region, under the direction of Bill Ruediger. The distribution maps were produr,ed by Oz
Garton of the University of Idaho and Mary Maj of the USDA, Forest Service, Northern
Region. V. Banci and the British Columbia Ministry of the Envi.ronml~t Wildlife Branch
generously allowed us to incorporate the literature review and anno~ bibliography from
Banci (1989) into this document.
.. , . V. Banci, R. Crabtree, B. Giddings, J. Mattison, J. Weaver, an1i B. Zielinski
rpviewed all or p~rtipns of the _docume1:1t and pr?vi~d helpful and !bought-provoking
comments. S. Minfa shared his expertise and his literature of carmvcre ecology.
Cite mi:
Heinemeyer, K.S. aµd J.L. Jones. 1994. Fisher biology and management: a literat11re
review aud adaptive management strategy. USDA Forest Service Noxthem Region,
Missoula., MT. 108 pp.
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Additional copies can be obtained from the USDA Forest Service No1rt:hem Region,
Threat.ened, Endangered, and Sensitive Species Program, Missoula, MT
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EXECUTIVE SUMMARY
Fishers historically occupled much of the forested habit':lts of Canada and the northern
United States, .P opulations declined in the i~a:dy twentieth century, probably due to habitat
loss from settlement a.lld loggjng, overttapping, and predator p(}isoning. Although many
eastern populations hiwe !l"..covered, westem population~: have rem;iined at low numbers or
are absent throughout most of their historic range in California, Oregon, W ashin~op.,
Idaho, Montana, and British Columbia.
Description
The fisher belongs to the Mustelidae family and shares the genus Martes with the
American lllllft!ln. Although 3 subspecies have been pmpo1;ed, additional analyses have
not.supported the designations. Fishers are: similar in body fotm to weasels, and are the
largest elongated tt:1trestrial mustellid, as well as the most sexually dimorphic. Males (3-6
kg) weigh approximately twice that of fem1lles (1.5-2.5 kg), and average 20% longer ip.
c:m
body length, with male's and females averaging 62 and 5l in length, respectively.
Reproduction
The fisher exhibits long-tt'rm (327-358 days) delayed implantation with an active
gestation of 30 to 215 days. Females may bn~ at 1 year of age, and have their first litter at
2 years of age. Whdping occurs from late. February to mi<j-April, and females breed 2-9
days later. Lil:ter sizes are sminll, usually with 2-3 kits, itbough litters have ranged from l to
4 kits. Kits achieve independence at f6-20 weeks of age, and disperse in the late sunup.er·
and early winter.
Ovulation frequently r.eported as 73-100%, may over-estimate actual fecundity,
ratl~,
as recent studies have shown denning rates. to be betw~:·1~n 34-54%. Reproductive success
may be dependent on'1the physical conditio111 of the females during the winter. There is
evidence suggesting the reproduclive potential offishe11~ in western habitats may be lower
than that in eastern populations. .
Food Habits
Fishers pmbably select prey on the. basiis of availabillity, and their diets are typically
diverse. Staples in western fishier diets have been reported as snowshoe hare, ungulate
carrion, sciurids, and voles. Prey presence ;ind abJU!J(lllllce may partially explain habitat use
of fishers, as they may switch to more available prey species in the winter.
Mortality
In eastern populations, fishers appear to h;ive few predators except man. Although
predation in most western populations also appears low, there are more reported incidences
of mortality due to predation. Intraspecifo:: strife, particlilarly in males, may contribµte to
natp.ral mortality. Altb.ough a vmiety of en.do-ancll ecto-parasites infest fishers, few have ill
effects. ·
. FiShers are susceptible to trapping, and are frequently c:aught in sets for other ..
furbearers. AdditionaJly, populations are vuhierable to trapping, as even light pressure
may cause loc:al e.xtinr,:tion. 'VV estem fisher popµJations :rnay have lower natality and higher
natural mortality rates as co11I1pared to eastern populations .. Consequently, western ·
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populations may be more sus<'-e>ptible to over-trapping. It has been suggested that incidental (.
captures may limit population growth in some an:as.
Home range
· :Males typically maintain larger )J.oxµe rangei;, which typically encompass 1 or more
smaller female home ranges. Home nmge estimates have rang·~d fro1n averages of 2. 7 to
40.8 Ian2 for females and averages of 15.0 to 85.2 km2 formaJes. Fishers in the northern
Rocky Mountains appear to roaiiltain larger home ranges tlian, fishers :in eastern habil:il.ts,
possibly due to a lower productivity of western habitatt;;. Generally,. fomales have shown
te1C11poral stability in home-range size, whereas males te)nporariU.y abandon their home ·
ra:nges .during breeding se!!So!! i.11. search of females. ·
· Movements and Activity
Fishers are active both day and night, with some tendency for inCJrease-,d activity during
crepuscular hours. A shifting of activity in response tQ envirc:mmental conditions, such as
smow conditions or prey availability mcy occux. Inactivity after large meals or during • ·
extreme weather has been noted.
Fishers· are capable of travelling relatively long distances iii short periods. Males in
particulair make long distance movements during the breeding season. Some of the longest
1-eported distances moved by fishers have been from translocated individuals.
Hl:lbit11t Use
Although fisher are selective in their use of habitat$, home :ranges typically encompass a <•
diversity ofp lant communities, In the west, fishers are generally found in conifer- .
dominated forests containing a diversity of habitat types and suci;essional stages. Jli,shers .
are closely associated with forested riparian areas which are used extensively for foragiµ.g,
f(:Sting, and as travel corridors. · .· ··
Although fishers have been found to prefer lnature and olcl-grow$ coniforous fo~
stands in most western studies, they also utilize a.variety of earlier successio111ll1 stages,
Most studies have reported that fishers prefer forests with cor1tinuous cover, though some
use of shrubby clearings can occur durilllg certailll seasons. A broader range ·~f habitats
may be used for hunting than for resting. Potential barriers to dispersal include large
rivers, mountain divides above timberline, and open-canopied habitats. . .
Fishers appear opportunistic in their use of resting sites, with hollow logs, tree cavities
aud canopies, snags, rocks, ground burrows, and brush piles freque11tly used. Witches
brooms in the cano.Py of ~ge diameter trees am commonly used by fishers. Natal dens are
most often in cavities of live or dead trees. The absence of hardwoods in western habitats
may limit the availaliility of suitable tree cavities for natal dens, .
Most studies have found fishers tolerant of moderate degrees of hwnan activity within
their habitats, including low densi1y housing, farms, roads, and small-scale logging
activities, In.directly, human activities may lead to negative impacts on fishc)rs through
removal or fragmentation of high quality habitat, and increas!)d trappinJl: apcc:ss.
l'opulation dynamics
Little is known about the composition of fisher populatiollf1 and the !temporal stability of
their spatial systems. Harvests reflect the abundance ilnc\ vubaerability of sex and age
classes and the effort expended by trappers. Males are more vuln<;:rable to trapping because
of their larger home ranges and movements. As trapping pressure incmases, harvest will ( ,
more closely reflect the true population composition. Males typically dominate the harvest . . .i
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when trapping pressure: is light, and the proportion of females increases with increasing
trapping pressure. J11vEmiles typically comprise the larg\lst segment of the harvest because
of their greater abunda11ce muli movements. . -
- Although data are few, densities estimated for western populations are much lower than
estim;ited densities for eastJ~m habitat5. Becausll of intra-sexually exdusive home ranges,
densities are a functlon of home range size. The large home ranges and low densities
found in western populations :may be a result of relatively lower productivity of the habitat,
as compared t0> eastern habitats.
Population and 1rnet11populatirn~ statt~~ in westem habitats
Jn.the westemJ.L.S .. flllJ~e!~ !l:\"e.J!µiired to_ the_peninsular mountain ranges of the Pacjfic
Coast and Rocky Mountains, forming the sonthem margins of a larger continental
distribution. The peninsular populations may be acurely susceptible to e~tinction becanse
of their location at the :mari>ins of their geographic distribution.
Fishers have been shown tco selectively use habitats; it is likely these habitats are .
patchily distributed in modem La11dscapes and extant populations of fiShers are widely"
spaced and fragmented. Littfo is known of the dispersal and colonization capabilities of
fishers, or the degree in which present populations are inter-relarecl
Management st1rategy
Planning for the 1011g-term 11iabillity of fishers in western habitats will require both
population andl habitat managem~nt, but data is lacking to develop an in-depth conservation
strategy, and it may be cost-prohibitive to acquire the neo;ded infonnation. A coarse-filtei;
or ecosysrem approach, acmss a hi~rarchy of landscape units, may be a more reasonable' -
alternative. The present guid(:lines are m(:<lllilt to provide in.rerim direction for fisher .:·,
management until an ecosystem approach can be developed alld effet-iively implemented .. :_
This management strdtegy inco:rporates multiple scales, from maintenance of genetic ' -
linkages between metapopulations to the management ofresting or foraging habitat within a
forest stand. The guidelines ~ire adaptive, meaning that information must be continually ·
collecred and used in an itera1ive process to improve the probability of successful
management. The overall goal is to maintain fisher populations with high persistence
probabilities across tlmir hiistoric range in western North America. This goal may be
achieved thro1J1gh m<'.eling several objectives: l) manage: for tbe continued distribution of
fishers throughout their c:1m:ent range; 2) manage habitats so that extant subpopulations
have the opportunity to dexXllograpl:1iically in.leract; 3) manage for the restoration of habitats
and populations within the: fillhers' histoi:ic range; md 4) inventory, monitor, lllld conduct
research to facilitate adaptive mmagement
At the largest, or continc~mtal landscape 11111it, the: overall goal of tbe management straregy
is to demographically ;md genetically link the Pacific am! Rocky Mountain populations to
the Canadian populllltion. 'Ihe historic alld current distribution of fishers in. southern British
Columbia and the 1r1o:rthem portion of the western U.S. :must be assessed prior to recovery
or man;tgement of populatioillS and linkage. . zones.
Withiri a physiographic region such as li:he Sien-as or the Northern Rockies, the overall
goal is to maii:1tain or recover the .fisher throughout its historic rang(~, and to maintain or
recover the suitability of potential habitat~. Objectives rnquired to meet this goal include
maintaining genetic diversity tlhrougb preservation or irestoiration of genetic :linkages
between metapopu!iltiom:, iden1tification of ;r>orential recoloniza1ion or augmentation areas to
funcµon as ste:pping-s1tone 1mpul.ations, rna'intenance of 11e11sitive-1inkage zones and
reduction of mortality and vulnerability fac1101:s within these critical corridors; and the
prevention of induced ecological barriers.
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I At the physiographic area landscape scale (e.g., nortllf:m Northern Rockies), the
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I overall goal is to :maintain or restore: metapoplllf!l:ion viability, as repl:(•se111ted by a group of
interacting subpopulations with finit1e lifetimes. To achieve this, it wiU be necessary to .
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maintain the viability of subpop111lations and e111sure the lilJ]kage of subpopulations ~ allow
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demographic exchange. Additioruill:y, it is recommended thalt a central suibpopulation be
I managed as a reservoir, co11taini111g a refuge to function as a source of dispersers for the
surrounding subpopulations. · · ·
At the major watershed landscape scale (approximately 500-1300 kJ.n2'), the overii.11 goal
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is to maintain the short-term viabilicy of the subpopulation. Objectives reqriin:d to meet this
goal include the maintenance or restoration of fisher habitat aci:oss thf• watershed and the
maintenance of connectivity between home ran~:s. · · · ·
At-the.subdrirlnagelevel (~prniQ~ly 25-250 km2) the overall! goal is tc• maintain
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functional home ranges. Tilis is achieved through the mainte1111mce of the: quality 8!).d .
connectivity of suitable habitats withln a subdrainage. ·
At the forest stand scii.Ie, the overall goals ar1~ to maintailll stand stroctll:fe imd .
composition suitable as resting and foraging habitat. These go~ are achieved throug\l,
managing of existing preferred and suitable habitats, desig111ing treatment of stands
managed for timber production to allow 1'apid recolonization of prey 1species, lUld
conservatively managing forested riparian areas.
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TABLE OF CONTENTS
PREFACE ........................................................................................... i
ACKNOWLEDGEMENTS ............................................... ....................... i
EXECUTIVE SUMMARY ..... , ................................... ; ............................ ii
LIST OF TABLES ................................................................................. iv
LIST OF FIGURES .. ......... ......................................... .......................... v
PART I: FISHER HIO:LOGY .AND MANAGEMENT
IN1RODUCTION ............................................................ , ........... 1
DESCR1P'I10N ........................................................................... 1
· · Taxonemy ............................... :. ....................................... .1
Evolution ...........................................................................2
Description ........................................................................2
DISTRmUTION ..........................................................................3
LIFE HISTORY ..........................................................................3
Reproduction ................................ :• ....................................3
Food Habits ........................................................................7
Energetics ..........................................................................9
Momility ............................................................................ l 0
Home range ....................................................................... 11
Movements and Activity ........................................................ 12
Habitat Use ... : .................................................................... 14
Population I~:stablishment and Reintroduction ..............•...•.•...•.•.. 19
POPULATION DYNA.JMICS ............ , ..............................................2 3
Poplllation Com]position ........................................................2 3
Harvests ................................................................... ·. .........2 3
Density .............................................................................2 4
Population mid Metapopulation Status in Western Habitats ................2 4
Federal and State Status ..........................................................2 5
PART II: ADAll'1'IVE MANAGEMENT STRATEGY
IN1RODUCTION ........................................................................2 6
MANAGEJivfE1"1'T S'IRATEGY .........................................................2 8
Co:n:dnemtal Ecofogi<:al Landscape Unit .......................................2 8
Physiojµ:aphi.c Region ...........................................................2 9
Physiographic Area ........................... , ..................................3 2
Milgor Wate:rshei:l .................................................................3 4
.................................................................... , .37
Subdrainag1~
Stand ..............................................................................3 9
LlTERAT URE CITED ..............................................................................4 2
PART III: BISJ[,IOGRAIP'HY
IN1RODUCTION ........................................................................ .46
Ll'I'ERAT!.JlUI ............................................................................4 6
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LIST O.F' TABLES
Table 1. Known litter sizes of fishers based on captive or wild animals or from
· in utero counts .............................................................................. 6
Table 2. Average numbers of corpora lutea countl'..d ip. the overaties of ;idu lt females .... 7
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T<tble 3. Annual home range sizes of male and fo!llille fisb~rs deter.mined iming
radiotelemetry ...................................................... ,...... .... ... ......... 13
Table 4. Maximum repoxted distances travelled by !'is.hers .................. ;............... 15
Table 5. Known fisher reintroduction attempts .................................................. 21
Table 6. Example of a heirarchical appoach to mana.g1~ment ..................................... 27
Table 7. Habitat structure recommended to maintain qualiW fisher habitat in the
Northern :Rocky physiographic region ................................................ 41
LIST OF FIGURES
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Figure l. Distribution of fishers in tbe w~~stem United States ........ ;. ...................... 4
