Fisher Research and the Kings River 

Sustainable Forest Ecosystems Project: 

Current Results and Future Efforts 1 

Brian B. Boroski,2 Richard T. Golightly,

3 Amie K. 

Mazzoni,4 and Kimberly A. Sager5 

Abstract 

The Kings River Sustainable Forest Ecosystems Project was initiated on the Kings River 

Ranger District of the Sierra National Forest, California, in 1993, with fieldwork beginning 

in 1994. Knowledge of the ecology of the fisher (Martes pennanti) in the Project area, and 

in the Sierra Nevada of California in general, is insufficient to develop empirically based 

management strategies or to respond to the challenge of sustaining viable local 

populations concurrent with projected human population growth in the Sierra. Using a 

combination of track-plate surveys, snowtrack searches, and live-trapping, we 

documented a reproducing population of fishers between 1,067 and 2,438 m in elevation 

within much of the Project area. Whether survivorship and reproductive rate are sufficient 

to maintain the population within the Project area is unknown. Given current viability 

concerns for fishers in the Sierra Nevada, it would be prudent that, concurrent with 

future research, management activities in the areas occupied by fishers that are outside 

the forest carnivore network also conserve or promote habitat elements used by fishers. 

The Forest and Rangelands Renewable Resources Planning Act of 1974 and 

the National Forest Management Act of 1976 (NFMA) mandated additions to the 

process by which the USDA Forest Service manages its public lands (Dana and 

Fairfax 1980). A key section of the NFMA directed the Secretary of Agriculture to 

write regulations specifying guidelines that “provided for diversity of plant and 

animal communities based on the suitability and capability of the specific land 

area in order to meet overall multiple-use objectives.” The challenge to meet this 

provision is significant for National Forests in the Sierra Nevada. Land area 

developed for human settlement within the mountains could quadruple from 

1990 to 2040 as a result of a tripling in the human population within the region 

(Duane 1996). Ecological ramifications of the mosaic of forest ownership and 

differing owners’ objectives are many. 

Despite substantial efforts (Grenfell and Fasenfest 1979; Zielinski and others 

1995b, 1997, 1999), knowledge of the ecology of fishers (Martes pennanti) in the 

Sierra Nevada (fig. 1) is insufficient for development of empirically based 

management strategies that will ensure viable local populations in the face of 

increased demands on forest resources that will inevitably accompany the 

projected growth of the human population in the Sierra Nevada (Graber 1996, 

Ruggiero and others 1994). Ruggiero and others (1994) recommended a 

comprehensive, programmatic approach of research to acquire the information 

needed for developing conservation strategies. 

The Kings River Sustainable Forest Ecosystems Project (hereafter, the Project) 

was initiated in 1993 on the Kings River Ranger District of the Sierra National 

Forest, Fresno County, California, with fieldwork beginning in 1994 (Verner and 

Figure 1—Fisher in a pine tree on the 

study area in the Sierra National 

Forest. 

1 An abbreviated version of this paper 

was presented at the Symposium on 

the Kings River Sustainable Forest 

Ecosystems Project: Progress and 

Current Status, January 26, 1998, 

Clovis, California. 

2 	Senior Wildlife Ecologist, H. T. 

Harvey and Associates, 423 West 

Fallbrook, Suite 202, Fresno, CA 

93711. 

3 Professor, Department of Wildlife, 

Humboldt State University, Arcata, 

CA 95521. 

4 Graduate Student, Department of 

Biology, California State University, 

Fresno, CA 93710. 

5 	Student, Department of Wildlife, 

Humboldt State University, Arcata, 

CA 95521 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 143 
Boroski, Golightly, Mazzoni and Sager 

Figure 2—The Kings River 

administrative study area in the Sierra 

National Forest in central California 

includes the 64,000-acre Big Creek and 

Dinkey Creek watersheds (indicated by 

shading). 

Figure 3—Big Creek and Dinkey 

Creek units treated by the Kings 

River Sustainable Forest Ecosystems 

Project, Sierra National Forest, 

Fresno County, California. 

Fisher Research and the Kings River Sustainable Forest Ecosystems Project: Current Results and Future Efforts 

�

Sierra National Forest 

Sierra National Forest 

Study Area 

Dinkey Creek Watershed 

Big Creek Watershed 

Smith, this volume). The Project area of 26,000 ha encompasses about 13,000 ha 

in both the Big Creek and Dinkey Creek watersheds (figs. 2, 3). This was a 

collaborative Administrative Study among Forest Service managers and 

researchers to investigate whether forest ecosystems in the southern Sierra 

Nevada can be managed to maintain essential ecosystems components, 

processes, and interactions and still support a variety of other uses (Gill and 

others 1997). The Project is a unique opportunity to meet existing information 

needs for conservation planning for fishers because it is within a geographic area 

of concern, it is highly integrated with other disciplines, and it is committed to 

developing a comprehensive body of knowledge through a long-term, adaptivemanagement approach. 

This paper describes our general programmatic approach to understand use 

by fishers within the Project area, presents our current, preliminary results, and 

144 USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 
Fisher Research and the Kings River Sustainable Forest Ecosystems Project: Current Results and Future Efforts 

discusses the logical expansion of this research as the Project proceeds, with an 

ultimate goal of determining the fisher’s responses to landscape-level silvicultural 

treatments in the two watersheds. 

Study Area 

Forest management in the Big Creek watershed is applying uneven-aged, smallgroup selection with a 200-year rotation, which will result in 0.5 percent of the 

land area being harvested each year and half of the landbase supporting forests at 

least 100 years old. The primary goal is to maintain a continuous forest canopy, 

retain mature vegetation in riparian areas, retain large trees (crown diameter 

>12.2 m) on half of the landscape capable of growing them, and maintain and 

enhance riparian systems in streamside-management zones. 

In the adjoining Dinkey Creek watershed, a three-tiered forest landscape has 

been implemented—a riparian emphasis zone (20 percent of the landscape) at the 

bottom, a mid-slope zone of continuous forest cover (50 percent of the landscape) 

on side slopes, and a ridge-top zone managed as a shaded fuelbreak to provide a 

first line of defense against wildfires (30 percent of the landscape) (Smith and 

Exline, this volume). 

General Programmatic Approach 

Balancing multiple-use on lands managed by the Forest Service is a significant 

challenge for the National Forest System. Uses change, technologies evolve, and 

ecosystems respond concurrently, but at different rates. The approach chosen by 

managers must ensure timely responses to these issues. The approach must also 

involve direct participation among practicing resource planners, managers, and a 

variety of specialists studying diverse topics. The general programmatic approach 

of the research presented here emphasizes our commitment to respond to 

information needs. For the duration of the Project, we propose to conduct annual, 

systematic surveys of the fisher population within the Project area using base 

funding. These surveys will be augmented by studies to examine specific 

questions that emerge from management activities that cannot be addressed 

through survey results. 

Track-Plate Surveys 

Our initial survey of the Project area was designed to determine the occurrence 

and distribution of forest carnivores, especially fishers and martens (Martes 

americana). Over two consecutive field seasons in 1995 and 1996, we placed 

sooted aluminum track-plates (Fowler and Golightly 1994) at 160 stations along 8 

cross-elevation routes to cover all elevations in the Project area, based on 7-1/2 

minute series maps (1:24,000 scale, U.S. Geological Survey, Menlo Park, 

California). The routes followed roads or trails accessible during fall when snow 

was present. Stations included one track plate in a wooden box, systematically 

placed at 1-km intervals along the eight routes (fig. 4). Stations were placed as far 

as 70 m from the road, although most were within 50 m. The boxes housing the 

sooted plates were positioned in the field with one open end against a tree, rock, 

or log and then camouflaged with forest litter. Stations were often located in 

drainages with the boxes facing down slope to prevent rain and snow from 

falling on the plate and destroying the soot or track impressions. 

We conducted four (two each season) 22-day surveys because Fowler and 

Golightly (1994) reported that surveys at least this long maximized the probability 

of detecting martens. The first survey occurred from 17 October to 7 November 

1995 and included 81 high-elevation stations (1,275-2,592 m) divided among four 

routes. The second occurred from 17 November to 8 December 1995 and consisted 

Boroski, Golightly, Mazzoni and Sager 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 145 
Boroski, Golightly, Mazzoni and Sager Fisher Research and the Kings River Sustainable Forest Ecosystems Project: Current Results and Future Efforts 

Figure 4—Track plate stations and 

snowmobile routes used to determine 

the occurrence and distribution of 

fishers and martens within the south 

zone of the Sierra National Forest. 

of 79 stations divided among four routes at lower elevations (294-1,662 m). The 

same stations were surveyed again the following summer to measure potential 

seasonal variations in carnivore detection and increase our power to detect 

animals. The low-elevation stations were surveyed from 1 to 22 June 1996 and 

the high-elevation stations were surveyed from 7 to 28 July 1996. Each station 

was examined every other day. We replaced any track plate that contained tracks 

on either the soot or contact paper or if the soot had been disturbed so that it was 

no longer effective. Chicken wings were used as bait and replaced when 

desiccated or when rodents or insects removed meat. 

Detection ratios were calculated for fishers and martens by dividing the number 

of stations that had detected animals by the total number of available stations 

between the highest and lowest detection for each species, plus or minus 200 m. This 

allowed assessment within a range of realistically available habitat. No survey 

station was higher than the highest marten detection; therefore, we included stations 

from the highest to those as low as 200 m below the lowest detection. 

Results of Track-Plate Surveys 

Fishers occurred at elevations between 1,114 and 2,040 m, whereas martens were 

found at elevations between 1,992 and 2,520 m (fig. 5). The detection ratio for 

martens (0.38) was twice that for fishers (0.19). Martens were detected at 20 of 53 

stations, 15 in 1995 and 7 in 1996; 2 stations had detections both years. Fishers 

were detected at 14 of 72 stations, 8 in 1995, and 7 in 1996; only 1 station detected 

fishers in both years. 

Snow Track Searches and Camera Stations 

With confirmation of the occurrence of fishers and martens in the Project area, 

and preliminary assessments of their distribution, study priorities were focused 

on fishers, especially on the size and composition of the areas used and how the 

habitats within these areas have changed over time. Answers to these questions 

for martens would be equally interesting, but limited resources and the fact that 

the Project area encompassed habitats mainly within the range of fishers led us 

to focus on this species. 

These new objectives required live-trapping and radio-collaring fishers, 

which began in February 1999. Because it had been 2 1-

2 years since our last 

survey, we needed more current information on areas being used by fishers. By 

146 USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 
Fisher Research and the Kings River Sustainable Forest Ecosystems Project: Current Results and Future Efforts Boroski, Golightly, Mazzoni and Sager 

Figure 5—Locations where fishers 

and martens were detected in the 

Kings River Sustainable Forest 

Ecosystems Project Area, south zone 

of the Sierra National Forest, Fresno 

County, California. Occupied home 

ranges represent the aggregated 

minimum convex polygon home range 

estimates of nine animals. 

using snowmobiles to travel along roads within the Project area, we searched for 

fisher tracks (fig. 4). To help resolve uncertainties about the distinctions between 

tracks of fishers and martens, we placed Trail Master passive infrared monitoring 

setups (Model TM500 with TM 35-1 camera kit)6 at six locations above 1,830 m 

where we expected both species to occur. We used a combination of a scent call 

(Gusto by Caven Lures, Minnesota Trapline Products, Pennock, Minnesota) and 

approximately 5 kg of raw pork as attractants at each camera station. The pork 

was secured at least 2 m above the ground in trees with diameters exceeding 61 

cm at breast height. The dimensions of snow tracks left by animals photographed 

at the camera stations were compared to previously identified tracks to confirm 

that they had been classified correctly. 

Results of Snow Track Searches and Camera 

Stations 

We traveled 157 km of roads in 10 days between 3 February and 14 April 1999. 

Identifiable tracks of fishers and martens were found crossing these routes in 38 

locations, 28 by fishers and 10 by martens (fig. 5). Fishers or martens were 

detected at five of the six camera stations but never both species at a single 

station (fig. 5). Multiple pictures at each station confirmed fishers at 2,160 m and 

2,360 m and martens at 2,490 m and 2,550 m. The presence of two separate 

martens at the station located at 2,490 m was confirmed by an image with both 

animals in the same frame. Snow depths where tracks or images of fishers were 

recorded ranged from 5 to 124 cm. Marten tracks and images occurred at locations 

with snow depths ranging from 87 to 185 cm. 

Live-Trapping 

Capture and radio collaring began in August 1999. Live traps (Model 207


Tomahawk Live Trap Company, Tomahawk, Wisconsin) modified to include


wooden nest boxes (Seglund 1995) were placed in areas where track-plate surveys


and track searches had detected fishers (fig. 5). Traps were typically placed next 6 Mention of trade names or


to downed logs within 10 m of a stream and preferably where two or more products is for information


only and does not imply streams met. To attract fishers, the Gusto scent call was poured onto ProwickTM 

endorsement by the U.S.

scent dispensers (by Wildlife Research Center, Inc. available through Minnesota Department of Agriculture. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 147 
Boroski, Golightly, Mazzoni and Sager Fisher Research and the Kings River Sustainable Forest Ecosystems Project: Current Results and Future Efforts 

Table 1—Physical parameters measured on anesthetized fishers live-trapped within the Sierra National Forest, Fresno 

County, California 

Weight


Length (nose to end of vertebrae of tail, axis of body to vertebrae of tail)


Hind foot length (heel to end of longest claw)


Ear length (lateral notch to tip)


Neck circumference


Canine lengths (each tooth)


Canine diameters (base and tip of each tooth)


Dimensions of the testes (anterior to posterior and medial to lateral)


Diameter and height of each nipple


Trapline Products, Pennock, Minnesota) suspended above each trap. A chicken leg 

was securely tied within the trap on the side along the log and in the rear next to the 

wooden nest box. Traps were checked daily and re-baited or re-scented at least every 

fourth day depending on the condition of the bait and potency of the scent call. 

Captured animals were coaxed into a handling cone attached to the rear of 

the nest box following methods of Seglund (1995) and anesthetized with a 

mixture of ketamine and diazepam (1 mg of diazepam per 200 mg of ketamine) 

injected intramuscularly at a dosage of 11-24.2 mg/kg of body weight (California 

Department of Fish and Game 1996, Seglund 1995). Anesthetized fishers were 

removed from the handling cone, weighed, and examined. In addition to 

determining the sex of the animal and assessing overall condition, we assessed 

the development of the sagital crest, mammae, or testes and baculum. A series of 

measurements used by Zielinski and others (1999) were made to describe the 

morphological characteristics of each animal (table 1). 

We implanted subcutaneous, passive, integrated transponders (125 kHz, 

TX1405L, BiomarkTM, Boise, Idaho) in the nape of each fisher for permanent and 

unique identification. In addition, color-coded ear tags were fastened into each ear to 

outwardly identify animals recaptured or recorded at future camera stations. The 

small amounts of ear tissue displaced by the tags were preserved for genetic analysis. 

Each animal was also fitted with a radio transmitter with a 16-hour on- and 8-

hour off-duty cycling option to extend battery life (Models 080 for females, 205 

for males, Telonics, Mesa, Arizona) and a mortality sensor to alert biologists 

when an animal had died. Animals were placed back in the wooden nest box of 

the trap after being processed and then released after about an hour, when fully 

recovered from the anesthesia. 

Live-Trapping Results 

Three females and six males were caught on 11 occasions during 326 trap nights 

between 4 August and 15 November 1999—a capture rate of 0.0337 animals/ 

night. That is, 10 traps open for 10 nights were likely to capture fishers on about 

3 occasions. This capture rate was 2.8 times that reported by Zielinski and others 

(1999) for their work in the Sequoia National Forest from 26 May to 6 July 1999. 

The trap design, microhabitat placement, bait, and scent call were similar in the 

two studies. Trap latency (the mean number of nights that traps for fishers 

remained open before a fisher was captured) for the two studies provides 

evidence of this similarity. Our trap latency was 6.1 trap nights (n = 9, range 1 to 

15); that of Zielinski and others (1999) was 7.7. 

The sex ratio of captured fishers (6 males: 3 females) is probably not 

representative of the population in the Project area, as the sample is small and it 

148 USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 
Fisher Research and the Kings River Sustainable Forest Ecosystems Project: Current Results and Future Efforts Boroski, Golightly, Mazzoni and Sager 

Table 2—Physical measurements (weight in kg, lengths in cm) from anesthetized fishers captured on the Sierra National 

Forest, Fresno County, California 

Parameter Sex n Median SD Min. Max. 

Weight Male 6 3.6 0.5 3.3 4.5 

Female 3 2.1 0.1 2.0 2.2 

Total length Male 6 100.1 2.2 98.7 105.0 

Female 3 89.0 2.5 87.5 92.3 

Tail length Male 6 37.6 1.0 36.8 39.7 

Female 3 35.0 0.5 34.5 35.5 

Right hind foot length Male 6 12.7 0.4 12.0 13.0 

Female 3 10.9 0.6 10.0 11.2 

Left hind foot length Male 6 12.1 0.4 11.9 12.9 

Female 3 10.5 0.5 10.0 11.0 

Right ear length Male 5 10.5 0.7 3.5 5.1 

Female 3 4.3 0.8 3.0 4.4 

Left ear length Male 5 4.9 0.7 3.0 5.0 

Female 3 3.9 0.7 3.2 4.5 

Neck circumference Male 6 20.9 2.2 17.0 23.8 

Female 3 16.0 1.2 14.9 17.3 

is well known that both live-trapping and fur-trapping methods for mustelids 

are biased toward males (Buskirk and Lindstedt 1989, King 1975). 

The number of animals handled thus far is too small for multivariate analyses 

of body weight, length, or tooth measurements. Sexual dimorphism has been 

reported in the species elsewhere in California (Seglund 1995, Zielinski and 

others 1995a). Our male fishers were significantly larger than the females (MannWhitney U test, P < 0.05), based on every physical parameter measured except 

ear length (P = 0.09) (table 2). Preliminary tests also suggest that additional data 

will reject the hypothesis that canine lengths and diameters are the same for the 

two sexes (table 3). Given only tooth size, we found canine diameter at the base of 

the tooth most useful to distinguish between the sexes. The diameter at the tips of 

the canines appears to be similar between the sexes, and canine length is subject 

to more variability than diameter at the base due to breakage. 

Nipple dimension (length x width) in female fishers can provide information 

on their breeding status (Frost and others 1999, Zielinski and others 1999). Frost 

and others (1999) reported mean anterior nipple sizes of 45 mm2 for current 

breeders, 12 mm2 for former breeders; and 6 mm2 for nonbreeders, and Zielinski 

and others (1999) reported a mean anterior nipple size of 21 mm2 for a lactating 

female and values of 2 mm2 and 8 mm2 for nonlactating females. The nipple 

dimensions on two of the three females we captured suggest that they had 

previously produced offspring (fig. 6) and that the third female was a nonbreeder. 

Six of the animals had signs of past physical damage that included broken 

canines, torn ears, and scars, but all nine animals appeared healthy based on body 

weight, the relative amount of fat covering the ribs, coat condition, and external 

parasite loads. External parasites were rare on the nine animals trapped, agreeing 

with Powell (1993) that fishers exhibit a low incidence of parasites. Our assessment 

of their health at the time of capture was supported by the survivorship of the all 

individual animals through winter, at least to April 1, 2000. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 149 
Boroski, Golightly, Mazzoni and Sager Fisher Research and the Kings River Sustainable Forest Ecosystems Project: Current Results and Future Efforts 

Table 3—Median canine length (mm) and diameter (mm) for fishers captured on the Sierra National Forest, Fresno 

County, California. Three broken canines were removed from the length measures 

Characteristic Sex Right tooth length (n) Left tooth length (n) 

Upper canine 

Length 

Diameter of base 

Diameter of tip 

Lower canine 

Length 

Diameter of base 

Diameter of tip 

Male 14.73 (5) 15.68 (5)*1 

Female 11.44 (3) 11.62 (3)* 

Male 6.74 (5)* 6.75 (5)* 

Female 5.02 (3)* 4.81 (3)* 

Male 2.50 (5) 1.90 (5) 

Female 2.50 (5) 1.90 (5) 

Male 14.50 (5)* 15.32 (6)* 

Female 9.47 (3)* 9.57 (3)* 

Male 7.00 (5) 7.07 (5)* 

Female 5.47 (3) 5.59 (3)* 

Male 1.83 (5) 2.00 (5) 

Female 1.73 (3) 1.58 (3) 

1 Asterisks represent significant differences between the sexes, based on a Mann-Whitney U statistic an and alpha level of 0.05. 

Figure 6—Nipple dimensions 

(length x width) of three female 

fishers captured in autumn within 

three drainages on the Sierra 

National Forest, Fresno, County, 

California. 

Home-Range Size 

Locations used to estimate home-range size came from trap sites and radio 

telemetry locations between August 1999 and May 2000. Trap sites where animals 

were captured were treated as known locations. Relocations using radio 

telemetry relied on a scanner/programmer with a receiver (Models TS-1, TS-2, 

Telonics Inc., Mesa, Arizona) to detect radios. Receivers were attached to a 2- or 

3-element, hand-held antenna or a truck-mounted, manually rotated, Yagi 

direction-finding antenna array. Walking to the animal and identifying the 

physical structure it occupied was the preferred method of relocation, but 

locations in some instances were determined by a minimum of three azimuths 

from known locations. Azimuths were measured using a hand-held compass 

(Model Type 15T, Silva, Binghamton, New York). Locations of trap sites and 

physical structures occupied were determined using a global position system 

with real-time correction capability (Centurion, Trimble Navigation, Inc., 

Sunnyvale, California or PLGR, Rockwell International Corporation, Cedar 

Rapids, Iowa). 

150 USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 
Fisher Research and the Kings River Sustainable Forest Ecosystems Project: Current Results and Future Efforts 

We used the minimum convex polygon method (Mohr 1947) to estimate 

home-range size because of the small number of locations currently available for 

each animal, and all locations were used for each animal because outliers were 

difficult to identify with the small samples. 

Home-Range Results 

The cumulative area used by the three female and six male fishers with radio 

collars included much of the Project area within the elevations that fishers 

inhabit (fig. 5). Preliminary estimates of home-range size were derived from as 

few as 10 locations for males (n = 6, median = 13, range = 10-23) and 19 locations 

for females (n = 3, median = 26, range = 19-42). Median home range area for 

males (2,150 ha; sd = 1,873) was more than twice that for females (964 ha; sd = 

748). The lack of power to detect a significant difference (alpha level 0.05) 

between the areas used by males and females emphasizes the preliminary nature 

of these results (Mann-Whitney U = 3, P = 0.12, X2 = 2.4, 1 df). 

Changes in Habitat Within Home Ranges 

The distribution and numbers of fishers have decreased in California over the 

past few decades, despite their receiving protection from trapping. Because of 

this, Zielinski and others (1995b) suggest that the decline is attributable to a 

reduction in suitable habitat. In the summer of 2000, we began to examine 

changes in habitat composition and patterning within fisher home ranges in the 

Project area by comparing current conditions to those existing in 1958. Aerial 

photographs taken in 1996 were interpreted to produce a classification scheme 

similar to that produced by a timber stand-vegetation cover map completed in 

1958. Descriptions of habitat within each home range will be determined by 

using a geographic information system to intersect the boundaries of the home 

ranges with the 1996 aerial photo data and the 1958 vegetation cover map. 

Timber growth models, data on fire frequency and intensity, and timber harvest 

activities since 1966 will be used to explain changes in composition and 

patterning over the 38-year period. 

Monitoring Long-Term Trends 

Monitoring of fisher populations is difficult. Individuals are solitary outside the 

breeding season, densities are low, and sample sizes needed to detect change can 

be large (Zielinski and Stauffer 1996). In light of the fisher’s status (Lamberson 

and others 2000), the population of these animals within the 26,000-ha Project 

area must be monitored for both population numbers and demographic 

parameters. Baited track plates have been successful for monitoring local project 

areas (Fowler and Golightly 1994) and have been proposed for use to detect 

regional changes in an index of the occurrence and distribution of fishers 

throughout California (Zielinski and Stauffer 1996). Indeed, we have successfully 

used them to determine the occurrence and distribution of fishers within the 

Project area. Live trapping and telemetry will provide data on population 

parameters, including the number of individuals, age structure, survivorship, 

and possibly gene flow. Our preliminary results on nipple dimensions suggest 

that information on the past reproductive activity of females might also be 

obtained. Continuing research with radio-collared animals will also provide a 

marked population with a known distribution on which to assess biases 

associated with the live-trapping method. 

Systematic live-trapping is proposed to occur from July through October 

within a 168-cell grid that spans elevations from 1,067 m to 2,438 m across the 

Project area (fig. 7). This trap period was chosen because access is good, it is still 

Boroski, Golightly, Mazzoni and Sager 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 151 
Boroski, Golightly, Mazzoni and Sager Fisher Research and the Kings River Sustainable Forest Ecosystems Project: Current Results and Future Efforts 

Figure 7—Systematic trap grid 

proposed for use to monitor 

fishers within the Kings River 

Sustainable Forest Ecosystems 

Project Area, Sierra National 

Forest, Fresno County, California. 

possible to examine nipple enlargement to assess breeding status in females 

(Frost and others 1999), capture rates are good during this period, and it occurs 

after the nursing period. A single trap would be placed within suitable habitat 

for fishers within each 2.56-km2 cell and used to trap animals at that locale for 12 

days. Only once has it taken us longer than 12 days to capture a fisher at a trap 

site where one was eventually caught. On the basis of our preliminary estimates 

of home-range sizes, a grid cell size of 2.56 km2 will result in an average of three 

traps per female home range and eight traps per male home range. This design 

would enable three biologists to complete 2,016 trap nights in 4 months and 

handle fishers on 68 occasions, based on our previous trap success. Fewer 

captures than this are expected, however, because our previous efforts targeted 

the highly suitable habitat between 1,372 m and 1,829 m in elevation. 

Conclusions 

We found a reproducing population of fishers inhabiting much of the land base 

between 1,067 and 2,438 m in elevation within the Project area. Whether 

survivorship and reproductive rate within the Project area are sufficient to 

maintain the population is unknown. The fate of the population depends 

primarily upon the management direction taken by the Forest Service, which 

administers 85 percent of the land base within the Project area. A regional 

management directive has deferred activities that would significantly decrease 

the persistence of large-diameter live trees, snags, and downed logs in forest 

carnivore habitat networks not covered by standards set for the California 

spotted owl (Strix occidentalis occidentalis) (Verner and others 1992). The current 

forest carnivore network within the Sierra National Forest, however, 

encompasses only 18 percent of the Project area (fig. 5). Given current viability 

concerns for fishers in the Sierra Nevada, and because we still know too little 

about the survivorship and reproductive rate of fishers within the Project area, 

it would be prudent that, concurrent with future research, management 

activities in areas occupied by fishers that are outside the forest carnivore 

network also conserve or promote habitat elements used by fishers. 

152 USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 
Fisher Research and the Kings River Sustainable Forest Ecosystems Project: Current Results and Future Efforts 

Acknowledgments 

We are grateful to the many individuals who have contributed to our work. 

These include C. Caris, R. Schlexer, J. Schneiderman, and B. Zielinski of the 

Pacific Southwest Research Station, USDA Forest Service; R. Barrett and M. 

Jordan at the University of California, Berkeley; D. Grubbs at California State 

University, Fresno; K. Ballard, S. Burkindine, Y. Cougoulat, N. Fleenor, T. Frolli, 

and M. Smith with the Sierra National Forest, USDA Forest Service; E. Burkett 

and C. Cotter with the California Department of Fish and Game; and B. J. Boroski 

and T. Boyd, who volunteered. R. M. Castelli and J. S. Yaeger provided helpful 

comments on the manuscript. 

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