density of fishers in the sub-boreal spruce biogeoclimatic zone of

118

NORTHWESTERN NATURALIST 87:118–127 AUTUMN 2006

DENSITY OF FISHERS IN THE SUB-BOREAL SPRUCEBIOGEOCLIMATIC ZONE OF BRITISH COLUMBIA

RICHARD D WEIR

Artemis Wildlife Consultants, 4515 Hullcar Road, Armstrong, British Columbia V0E 1B4;[email protected]

FRASER B CORBOULD

Peace/Williston Fish and Wildlife Compensation Program, 1011 Fourth Avenue (3rd Floor),Prince George, British Columbia, V2L 3H9

ABSTRACT—Information on fisher (Martes pennanti) densities is needed for the managementand conservation of this mid-sized carnivore in British Columbia. To address this knowledgegap, we estimated the density of fishers in an industrial forest in north-central British Columbiabetween 1996 and 2000 using a minimum number alive estimate derived from live-trapping andradio-telemetry data. Density estimates averaged (� s) 11.2 � 2.1 fishers/1000 km2 (n � 4 cap-ture sessions) on 31 October and 8.8 � 1.1 fishers/1000 km2 (n � 4 capture sessions) on 31March. In comparison, the densities of fisher populations in eastern regions of North Americawere documented to be 6 to 49 times higher than our estimate for north-central British Colum-bia. The density of fishers in north-central British Columbia may be lower due to larger homerange sizes and more widely dispersed individuals than elsewhere. Low-density fisher popu-lations, such as in our study area, will require more conservative management strategies bytrappers and wildlife agencies to ensure population persistence in these areas.

Key words: fishers, Martes pennanti, density, inventory, live-trapping, radio-telemetry, Sub-Boreal Spruce biogeoclimatic zone, British Columbia

Whether for conservation of vulnerable spe-cies or management of harvested wildlife, pop-ulation management often necessitates an ap-proximation of the density at which a speciesoccurs. Density estimates and vital rate dataare necessary information for modelling pop-ulation changes under various managementscenarios. Density estimates are also useful towildlife and habitat managers because theyprovide benchmarks from which habitats canbe ranked at both regional and landscapescales. Additionally, habitat-based density es-timates and their resultant population esti-mates for identified areas are often integral in-puts for analyses of population viability.

Fishers (Martes pennanti) are medium-sizedcarnivores of the family Mustelidae that arefound in boreal and temperate coniferous anddeciduous-coniferous forests across NorthAmerica (Proulx and others 2004). Fishers aredifficult to inventory because effective methodsare generally labour-intensive and costly (Pow-ell 1993). As a result, no universal method ex-

ists for estimating the density of fisher popu-lations. In the past, fisher densities have beenestimated using snow-track counts (de Vos1952), fur-harvest returns (Douglas and Strick-land 1987), live-capture and radio-telemetrydata (Kelly 1977; Arthur and others 1989), andtrack plate surveys (Zielinski and Kucera 1995).Recently, Fuller and others (2001) estimated thedensity of fishers in Massachusetts by usingmark-recapture information and territory map-ping.

Fisher density estimates for eastern NorthAmerica range from 50 to 385 fishers/1000 km2

(Powell and Zielinski 1994; Fuller and others2001), but Banci (1989) suggested that fisherdensities were considerably lower in westernNorth America. She cited only 2 studies thathad quantitative data for this portion of thespecies’ range; both provided rough estimatesof �5 fishers/1000 km2. One of these estimateswas from northeastern British Columbiawhere, due to differential habitat quality acrossthe landscape, substantial areas of land were

AUTUMN 2006 119WEIR AND CORBOULD: DENSITY OF FISHERS IN BC

not thought to be occupied by fishers (Quick1953). Similarly, Jones (1991) surmised that thelow densities of fishers in the west were the re-sult of generally poorer quality habitats.

Fishers in British Columbia are currentlymanaged as a furbearer that can be legally har-vested by trappers on registered traplines be-tween 1 November and 15 February. However,harvests of fishers have declined considerablyin British Columbia over the past 30 y, whichhas contributed to its current status as ‘‘vul-nerable’’ in the province (Weir 2003). Due to thelack of relevant density estimates for fisherpopulations in western North American, andparticularly in north-central British Columbia,harvest management may be incorrectly basedon estimates from other jurisdictions. We esti-mated the density of fishers in an industrial for-est landscape in north-central British Columbiato provide wildlife managers and trapperswith data to better regulate harvest levels andhelp facilitate population persistence.

METHODS

Study Area

Our study area covered approximately 1930km2 and was centred 70 km NW of Mackenzie,British Columbia (55�19�16�N, 123�6�42�W; Fig.1). The topography was characterized by agently rolling plateau rising from the WillistonReservoir in the east to the lower slopes of theWolverine and Swannell mountain ranges inthe west. Our study area represented a rela-tively closed fisher population because it wasbounded to the east and south by a large waterbody (Williston Reservoir) and to the west bya mountain range comprised of generally low-suitability habitats (for example, alpine). Theboundary of the study area was defined by theextent of the Sub-Boreal Spruce (SBS) biogeo-climatic zone (BCMF 2004).

The study area lies at the northern extent ofthe SBS zone at elevations between 670 m (val-ley bottom) and 1100 m. Mean annual temper-ature during the study period was 2�C andranged between �52�C and 36�C. Snow coverin the study area generally lasts from mid-No-vember until mid-April, with average depths ofapproximately 40 to 50 cm throughout most ofthe winter. Annual precipitation averages be-tween 690 mm and 905 mm with total snowfallaveraging between 335 cm/y and 1075 cm/y(MacKinnon and others 1990).

Forests were dominated by hybrid spruce(Picea glauca � engelmannii), lodgepole pine (Pi-nus contorta), black spruce (Picea mariana), andsubalpine fir (Abies lasiocarpa), with tremblingaspen (Populus tremuloides) and paper birch(Betula papyrifera) also present. Black cotton-woods (Populus balsamifera trichocarpa) occurredas notable elements in riparian-type ecosys-tems and occasionally in other areas with sub-hygric or wetter ecological moisture regimes.

The study area included portions of 5 regis-tered fur-harvesting traplines. Trapping oc-curred to varying degrees during the study, asevidenced by the harvest of between 28 and 154American martens (M. americana) per year oneach trapline, totalling 352 between November1996 and February 2000 (Provincial Wild FurHarvest Database, Ministry of Environment,Victoria, British Columbia, Canada). Between 1and 3 fishers were harvested each year amongthese traplines, with a total of 8 fishers har-vested during the 4 y of our study; 3 of these 8fishers, however, were taken on portions of thetraplines outside of our study area.

Live-trapping and Tagging

We captured and radiotagged fishers duringthe fall and winter to determine the minimumnumber of fishers that were alive in the studyarea by the end of winter (late March) eachyear. We attempted to capture and radiotagfishers in 4 annual intensive capture sessionsconducted during the late-fall and winters of1996–1997 to 1999–2000. We set live traps sothat they were continuously operational for be-tween 12 to 22 d for 2 to 6 time-periods duringeach of these annual capture sessions.

We used 3 types of live trap sets to capturefishers: wire-cage, log-cabin, and metal-barreltraps. The majority of live traps that we setwere wire-cage traps, which were approxi-mately 24.5 � 31 � 81 cm (Havahart Models1081 and 1089). The log-cabin sets (approxi-mately 1.2 � 0.8 � 2.4 m) were made of inter-meshing logs, with a trigger mechanism thatreleased a log door when bait was pulled frominside the trap (Copeland and others 1995).Barrel traps, used relatively infrequently, con-sisted of a 30-gal metal drum with a slidingdoor cut into one end (Banci 1987), similar indesign to culvert traps used to capture bears.

We took several actions to enhance the effi-cacy of the traps. We selected trap locations

120 NORTHWESTERN NATURALIST 87(2)

FIGURE 1. Location of the study area in north-central British Columbia. Delineation of the study area wasbased upon the extent of the Sub-Boreal Spruce (SBS) biogeoclimatic zone in the area. Inset map shows dis-tribution of the SBS (in grey) within British Columbia.

within patches that had microsite attributes,such as coarse woody debris or clusters of im-mature trees, that fishers have been reported touse (Weir and Harestad 2003). We baited eachwire-cage trap with approximately 500 g ofsalmon, moose carcass, or grouse carcass. Log-cabin and barrel traps were baited with wholesalmon (1 to 4 kg) or pieces of moose carcass(1.5 to 3 kg). At each trap location, several near-by trees were scented with a combination ofcommercial fisher, marten, and skunk oil lure.

We checked live traps daily and assessed thefunctioning of each trap every 2 to 3 d.

Fishers were immobilized using either a 10:1 mixture of ketamine HCl:xylazine HCl, a 5:1mixture of ketamine HCl:meditomadine HCl,or a 1:1 mixture of tiletamine HCl:zolazepamHCl (Telazol�) prior to radiotagging. Frommost fishers, we removed a premolar 1 for ce-mentum annuli analysis (Strickland and others1982) to determine age. For individuals fromwhich we could not extract a tooth, we classed


fishers as adult or juvenile by palpating thesaggital crest and examining the level of toothwear (Powell 1993). We considered fishers thatwere �1 y old as juveniles, between 1 and 2 yold as subadults, and those �2 y old as adults.We applied unique marks to each fisher by us-ing inguinal tattoos and, during the first cap-ture session, 3.4 � 1.0-cm nylon ear tags.

We used 2 methods to radiotag the fishers.During the first 2 y of the study, we tagged fish-ers with radiocollars (Holohill MI-2M [1996–97] or Telonics MOD-080 [1997–98]). In subse-quent years, we surgically implanted fisherswith intraperitoneal transmitters (TelonicsIMP/200L or IMP/300L). All capture, han-dling, and tagging protocols were reviewedand approved by the provincial government’swildlife veterinarian.

Density Estimate

We calculated the density of fishers at thestart and end of each annual capture session.We estimated a late-winter (31 March) densityby dividing the area that was effectively sam-pled during the annual capture session (see be-low) by the number of fishers known to be aliveat the end of that capture session (minimumnumber alive, MNA; Krebs 1966). We also es-timated a fall (31 October) density using thesame effectively sampled area and the fallMNA, which was derived by tallying all of thefishers known to be alive at the start of each an-nual capture session. This latter number in-cluded animals captured during the subse-quent capture session plus those fishers thatwere previously tagged and still alive based onradio-telemetry data. Thus, the late-winter es-timate was based on the fall estimate minusknown mortalities.

The fall density estimate relied upon the as-sumption that juvenile and subadult fishersthat were caught during the subsequent cap-ture session were present in the sampled areaon 31 October. Although juvenile and subadultfishers are generally believed to be transient(Powell 1993), our data for transient radio-tagged individuals (2F, 1M) showed that the netdispersal distance (that is, the distance be-tween the centres of each fisher’s maternalhome range and their respective establishedhome ranges) was between 0.7 km and 41.3 km(x � 20.2 km, s � 20.4 km, n � 3). Based on thislow dispersal distance and the very low suit-

ability of habitats surrounding much of thestudy area (alpine tundra to the west, large res-ervoir to the east), it is unlikely that many an-imals dispersed into or out of the project area.Also, our data and that of Weir (1995) suggest-ed that fishers establish their home ranges, andthus become resident, by the end of March, sowe likely would have captured transient indi-viduals within the study area by the end of thecapture session (31 March).

We estimated the area that we sampled dur-ing each capture session by considering the ‘‘ef-fective area’’ that each live trap sampled. As a1st step in delineating the sampled area, weidentified live traps that were operational for asufficient time to capture a fisher based on thelatency to 1st detection (LFD; Zielinski andStauffer 1996). Derived from empirical data,the LFD was 13.7 d for resident fishers that wecaptured (s � 12.3 d until capture, n � 18 fish-ers). We did not include captures of 3 fishers inour LFD calculation because these animals laterproved to be transient and may not have beenexposed to live traps as consistently as fisherswith established home ranges. For our estimateof area sampled, we only included live trapsthat were operational for �16 d during eachcapture session to ensure that only traps thathad surpassed the LFD criteria were used.

Second, we determined the effective areasampled by each live trap. We assumed that afisher would have a reasonable likelihood of en-countering traps on its day-to-day travelsthroughout its home range. We considered the75% isopleth of the animal’s utilization distri-bution (UD) during the winter (that is, a cap-ture session) as the smallest area that a fisherwas likely to use consistently during our sam-pling. Based on our calculated 75% isopleths(range � 18.8 to 34.9 km2, n � 5 females), weselected the smallest 75% isopleth (18.8 km2) torepresent the area that was effectively live-trapped. Consequently, a 4.89-km buffer, whichcircumscribed an area that was equivalent toour smallest 75% isopleth, was placed aroundeach live trap that was active during the cap-ture session. Portions of the buffer that over-lapped the inundation area of the WillistonReservoir were excluded from the area sam-pled. In addition, because we were attemptingto produce a density estimate for the SBS zoneand because we live-trapped exclusively withinthis zone, we excluded any areas that fell out-


TAB

LE

1.Fa

ll(3

1O

ctob

er)

and

late

-win

ter

(31

Mar

ch)

den

sity

esti

mat

esd

eriv

edfr

omth

em

inim

um

nu

mb

eral

ive

(MN

A)

esti

mat

efo

rar

eas

sam

ple

dd

uri

ng

each

ann

ual

cap

ture

sess

ion

inn

orth

-cen

tral

Bri

tish

Col

um

bia,

1996

–200

0.

Cap

ture

sess

ion

aT

rap

-n

igh

tsb

#of

trap

s

MN

A

31O

ctob

er

adsu

bju

v

31M

arch

adsu

bju

v

Are

asa

mp

led

c

(km

2 )

Den

sity

(fish

ers/

1000

km

2 )

31O

ctob

er31

Mar

ch

1996

–199

719

97–1

998

1998

–199

919

99–2

000

3255

3033

2088

1348

77 110

101 79

7 5 6 8

3 0 6 0

1 9 1 0

11 14 13 8

5 5 4 8

3 0 4 0

1 6 0 0

9 11 8 8

1135

1069

1009 87

3

9.7

13.1

12.9 9.2

7.9

10.3 7.9

9.2

aN

ovem

ber

toM

arch

,bu

tin

clu

din

gSe

pte

mb

eran

dO

ctob

erin

1997

–98.

b1

trap

-nig

ht

�1

live

trap

set

for

one

24-h

per

iod

.c

Est

imat

edu

sin

ga

4.89

-km

dia

met

erbu

ffer

arou

nd

each

live

trap

that

was

oper

atio

nal

for

�16

trap

-nig

hts

and

the

95%

isop

leth

sof

resi

den

ttag

ged

anim

als

that

wer

eal

ive

du

rin

gth

eca

ptu

rese

ssio

n,e

xclu

din

gth

eW

illi

ston

Res

ervo

iran

dar

eas

outs

ide

the

Sub

-Bor

eal

Spru

cebi

og

eocl

imat

iczo

ne.

FIGURE 2. Intensity of live-trapping effort (trap-nights per site) for fishers during each capture ses-sion in north-central British Columbia, 1996–2000.Sites for which �16 trap-nights were conducted persession (to right of vertical line) were included in thecalculation of sampled area. n � 9724 trap-nights.

side this zone, including other forested areas.We felt confident in excluding these other areasbecause �7% of the amalgamated home rangesof all fishers included these outlying areas.

Lastly, to delineate the entire area that we ef-fectively sampled, we also included all portionswithin the SBS of the home ranges (that is, 95%isopleths of the annual UD) for radio-taggedfishers that were alive during the annual cap-ture session that fell outside of the livetrappedarea as defined above. This resulted in small ar-eas outside the livetrapped area (6% to 8% ofthe total area) being included in the effectivearea that, although unlikely, may have includedportions of the home ranges of untagged resi-dent animals.

RESULTS

We had 281 different live trap sets operation-al for 9724 trap-nights (1 trap operational forone 24-h period) over the 4 annual capture ses-sions (Table 1). On average, sites were active for42 trap-nights during 1996–97 (range: 3 to 98,n � 77), 28 trap-nights during 1997–98 (range:1 to 75, n � 110), 21 trap-nights during 1998–99 (range: 4 to 45, n � 101), and 17 trap-nightsduring 1999–2000 (range: 2 to 37, n � 79). Mosttrap sites were operational for �16 d duringeach capture session (Fig. 2). We sampled alarger area in the early stages of the project andfocused sampling efforts in later years (Table 1,Fig. 3). Trap-night density was higher in thefirst 2 capture sessions (2.87 and 2.84 trap-nights/km2, respectively) than in the 1998–99


FIGURE 3. Spatial distribution of live-trapping effort and effective area sampled for fishers during each of4 capture sessions conducted in north-central British Columbia, 1996–2000. Grey shading represents portionsof the effective area that were livetrapped; cross-hatched shading were portions of home ranges of residentfishers that occurred outside of the livetrapped areas.

and 1999–2000 sessions (2.07 and 1.54 trap-nights/km2, respectively).

We captured 21 fishers (15 F, 6 M) during the4 annual capture sessions. At first capture, 7were adults, 8 were subadults, and 6 were ju-veniles. Additionally, 1 untagged adult male

fisher was kill-trapped by a trapper within oursampling area during the 1996–97 capture ses-sion.

We assumed that we either captured or hadpreviously tagged all of the fishers within oursampled areas by the end of each capture ses-


sion. Many areas that we livetrapped appearedto be unoccupied by fishers. Conversely, smallportions of several fisher home ranges occurredoutside of the livetrapped area. In only one in-stance after the 1st capture session did we cap-ture a previously untagged adult fisher (3-y-old male) in the study area. Data from 2 othermales that we radiotagged suggested that sub-adult males were transient until at least 2 y ofage. Thus, we assumed that this male was pre-sent in the sampled area during the 1998–99capture session (that is, as an adult), but notprior to this.

The average (� s) density for the 4 y of sam-pling was 11.2 � 2.1 fishers/1000 km2 on 31October and 8.8 � 1.1 fishers/1000 km2 on 31March (Table 1). The estimated density variedamong years, ranging from 7.9 to 13.1 fishers/1000 km2.

DISCUSSION

Although our estimates were greater thanthe only other reported density estimate forBritish Columbia (4.8 fishers/1000 km2; Quick1953), the density of fishers in our study areawas still substantially lower than that reportedfrom elsewhere within the species’ range. Bycomparison, populations from eastern NorthAmerica were 6 to 49 times denser than ourstudy area (Douglas and Strickland 1987; Pow-ell and Zielinski 1994; Garant and Crete 1997;Fuller and others 2001). In fact, the densitiesthat we calculated were among the lowest thatwe encountered in the literature.

For species that have intrasexually exclusivehome ranges and polygamous males, such asfishers (Powell 1994), density will largely bedependent upon the home range sizes of eachsex and the distances among home ranges. Themagnitude of both these variables is likely afunction of the quality and spatial distributionof habitats. Given similar mortality parametersamong areas, areas with homogeneous, high-quality habitat, which supplies all of an ani-mal’s life requisites in a small space, will gen-erally have smaller, closer-spaced home ranges(Harestad and Bunnell 1979), and thus a higherdensity of individuals, than areas with patchy,high-quality habitat.

Indeed, the low density that we observedmay be related to the home range size andspacing of individuals within our study area.Powell (1994) summarized the size of fisher

home ranges from across North America andderived a mean home range size of 38 km2 formales and 15 km2 for females. In comparison,fishers in our study area and a site elsewherein the SBS zone of central British Columbia hadhome ranges that averaged (� s) 162 � 105 km2

for males (n � 3) and 38 � 18.6 km2 for females(n � 11) (Weir 1995; Peace/Williston Fish andWildlife Compensation Program, unpubl.data). Consequently, based on home range sizealone, we would expect that fishers in the SBSzone would occur at ½ to ⅓ of the density ofother fisher populations. In addition, our live-trapping and radio-telemetry data indicatedthat not all of the sampled area was inhabitedby fishers (Peace/Williston Fish and WildlifeCompensation Program, unpubl. data), likelycausing greater disparity with other fisher pop-ulations where the habitat is more spatiallyuniform and of higher quality (Arthur and oth-ers 1989; Garant and Crete 1997; Fuller andothers 2001).

Fisher densities fluctuate temporally, some-times in excess of an order of magnitude (Pow-ell 1994), as populations respond to various fac-tors. Changes in prey abundance and vulnera-bility, such as that caused by the 10-y snowshoehare (Lepus americanus) cycle, can have a dra-matic effect on fisher populations (Powell 1993;Powell and Zielinski 1994), although Bulmer(1974) did not detect significant cycling of fish-er populations in British Columbia. Kill-trap-ping for fur harvest can also affect the localdensity and spatial organization of fisher pop-ulations (Arthur and others 1989) because har-vest pressure is usually spatially and tempo-rally uneven (Powell and Zielinski 1994). Al-though fur harvesting affected the density offishers in our study area (5 of the 22 fishers thatwere detected in our sampled area were laterkilled by trappers) and this was included in ourdensity estimates, we do not feel that it overtlyaffected our estimate compared to othertrapped populations that did not account forlosses due to kill-trapped animals. Our dataindicated that density varied during our 4-ymonitoring period, but the confounding fac-tors of different sampling areas, fur harvest,unknown prey abundance, and low samplesize limited what we could conclude aboutthese differences.

Enumeration indices that rely on capturingindividuals, such as our MNA technique, pro-


duce an underestimate of the population ordensity (Jolly and Dickson 1983; Tuyttens 2000;McKelvey and Pearson 2001). An alternative tothe enumeration approach is to use estimatorsthat involve marking captured individuals andevaluating proportions of marked to unmarkedindividuals in subsequent sampling (mark-re-capture; Krebs 1989:15). Mark-recapture esti-mates have been shown to have low bias andrelatively high precision in their estimates ofpopulation size and are often preferred to enu-meration techniques (Jolly and Dickson 1983;Tuyttens 2000). However, mark-recapture es-timators were not appropriate for our data be-cause 2 assumptions required for these meth-ods were violated: not every individual had thesame probability of being caught and it was un-likely that marked individuals in our popula-tion had the same probability of survivalamong sampling periods.

We chose to use MNA enumeration methodsto estimate population size in our study areafor 2 additional reasons. In their review of pop-ulation estimators, McKelvey and Pearson(2001) suggested that, for populations of �50individuals, the number of unique individualscaptured (that is, MNA) was the populationmeasure with the lowest variance and sensitiv-ity to sources of variation. Also, they found thatthe MNA performed better than estimators,such as mark-recapture methods, when popu-lation attributes (for example, capture proba-bilities that vary across time, individuals andcapture history) were unknown and the varia-tion in capture probabilities was very differentfrom null expectations. In light of these factors,we chose the known negatively biased MNAtechnique to best estimate our population size.

Several aspects of our sampling regime likelyminimized the negative bias of our populationand density estimate. Adult male and juvenilefishers are reported to be the most susceptiblesegments of the population to capture, whereasadult female fishers are believed to be the mostdifficult to catch (Douglas and Strickland 1987;Powell 1994). Therefore in a biased sample, onewould expect juveniles and adult males todominate captures, and adult females to bemuch less common. However, 46% of our cap-tures (29 of 63) were of adult females, whereaswe captured adult males 11 times and juveniles7 times during the term of the project. Animalsthat are in poor body condition may also be

more susceptible to capture because theywould likely be more desperate for food (trapbait) than healthy animals. Although we hadno quantitative measure of health (for example,fat levels), all adult fishers that we caught ap-peared to be in good physical health based onexternal and, where possible, internal exami-nation (M McAdie, DVM, and R Weir; pers.obs.). Thus, the intensive effort expended tocapture fishers in the study area, the relativelyhigh frequency with which we caught adult fe-males relative to other age-sex classes, the ap-parent good health of fishers and, as well, theanecdotal observation that fisher tracks werenot observed during the winter period in anyarea that did not have a captured animal, sug-gests that the negative bias in our estimate waslikely minimal.

Although the MNA estimate may have beenslightly negatively biased, the area effectivelysampled was also, if anything, negatively bi-ased. This is because our estimate of the areathat an individual trap was assumed to samplewas based on the 75% UD of the smallest win-ter home range for our adult females. We oc-casionally caught radiotagged fishers at trapsoutside of their winter 75% UD, which suggeststhat the effective area sampled by each trapmay have been larger than the 4.89-km bufferthat we used. Consequently, the negative biasof the sampled area may have somewhat ame-liorated the MNA bias.

Minimum number alive estimates, eventhough they are negatively biased to some ex-tent and require an intensive capture effort toget reasonably accurate population indices, arelikely the most appropriate method to censusthe small population of fishers in our studyarea. Lower-intensity capture methods, such asnon-invasive molecular tagging (Mowat andPaetkau 2002), may be a more cost-effectiveway of estimating population size and densityof fishers in north-central British Columbia.

Although our study area has undergone in-tensive forest harvesting since 1972, we believeit is representative of the current state of theSBS zone because of similarities in forest har-vesting and fur-trapping pressure among are-as. Because the SBS zone is typically comprisedof productive conifer-dominated forests locat-ed on rolling terrain at lower elevations of Brit-ish Columbia’s interior region (Meidinger andPojar 1991), this area is a large and integral


component of the forest-harvesting landbaseand has among the most suitable habitat forfishers in the province (Weir 2003). Thus, ourdensity estimate should be representative ofsimilar landscapes elsewhere in the SBS zone.

Until new data demonstrates otherwise,wildlife managers in British Columbia can usethe density of between 7.9 and 13.1 fishers/1000 km2 to help them manage populations offishers in the SBS zone and possibly elsewherein the province. Specifically, wildlife managersand trappers may use these data to estimatesustainable harvest rates on traplines of inter-est within the SBS. This density estimate mayalso be applied to habitat suitability data to es-timate population sizes in other areas of BritishColumbia. Further studies are required to ex-pand on our results and describe fisher popu-lation demographics in other biogeoclimaticzones in British Columbia and other westernlandscapes. Information is also needed on therelationships among densities, population dy-namics, habitat, and prey to help guide themanagement and conservation of fisher popu-lations in the dynamic and industrialized forestlandscapes of British Columbia.

ACKNOWLEDGMENTS

This project was funded by Forest Renewal BritishColumbia and the Peace/Williston Fish and WildlifeCompensation Program, which is a joint venture be-tween BC Hydro and British Columbia’s provincialfish and wildlife agencies. Partners in this projectwere the Peace/Williston Fish and Wildlife Compen-sation Program, the British Columbia Ministry ofWater, Land and Air Protection, Slocan Group Mac-kenzie Operations, and Abitibi Consolidated. ABowser, G Carlson, H Davis, A Hahn, V Hawkes, JMcCormick, J Perreault, and D Wellwood tirelesslymonitored traps, radio-tagged fishers, conducted ra-dio-telemetry monitoring, and entered data. MMcAdie, DVM, performed surgeries in the field to tagfishers with intraperitoneal transmitters. Our projectwas conducted co-operatively with the NorthernWolverine Study, whose personnel generously as-sisted in the live-capture of fishers for this study:many thanks to E Lofroth, D Reid, W Harrower, VHawkes, C Hoodicoff, V Larsen, J Proche, E Rafuse,D Wellwood, and many volunteers from this project.H Davis, D Heard, J Lewis, E Lofroth, J Krebs, and GMowat provided helpful comments on earlier draftsof this paper.

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Submitted 15 November 2004, accepted 1 December2005. Corresponding Editor: CD Apps.

density of fishers in the sub-boreal spruce biogeoclimatic zone of

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