Fisher and Marten Status and Trend Monitoring

A fisher on a log next to a track plate box in the forest looking around before it enters the track plate box.

A fisher inspects the area before it enters the tunnel style track plate station.

Status and trend monitoring for fisher (Martes pennanti) and American marten (M. americana) began in 2002. The basic monitoring objective for each species is the same: to detect 20% declines in population abundance and habitat across the Sierra Nevada. Monitoring strategies for each species differ slightly due differences in current distribution of each species. Fishers are limited in distribution to the southern portion of the Sierra Nevada mountain range. Monitoring involves two components: intensive sampling on Sierra and Sequoia National Forests (NFs) designed to monitor population trend and less intensive sampling at sites in the central and northern Sierra (the area assumed to be unoccupied by fisher) focused on documenting population expansion.

Martens seem to be distributed throughout their historic range in the Sierra Nevada, and monitoring occurs on all forests throughout the Sierra Nevada though at slightly higher elevations than for fisher. For both species, population monitoring involves conducting presence/absence surveys throughout the region to estimate the proportion of sites (primary sample units) annually occupied by fisher and marten, and detect declines over the proposed ten year monitoring period. Each primary sample unit includes an array of six detection devices (track plates and cameras) offset from Forest Inventory and Analysis plots. Sample units are surveyed for ten consecutive days. Tracks and photographs of wildlife species visiting each sample unit are collected every two days. Each species is considered present at the primary sample unit if it is detected at one or more stations during the ten day survey. Habitat monitoring relies on tracking changes in habitat quality using a combination of remotely sensed vegetation data and plot data collected in conjunction with the on-going Forest Inventory and Analysis program.

Accomplishments

The Primary Sample Units had the following detection rates:

  • Fisher in 2002 was 0.268, in 2003 was 0.234, in 2004 was 0.238, in 2005 was 0.248
  • Marten in 2002 was 0.176, in 2003 was 0.167, in 2004 was 0.144, in 2005 was 0.084
  • Gray Fox in 2002 was 0.205, in 2003 was 0.162, in 2004 was 0.139, in 2005 was 0.175
  • Ringtail in 2002 was 0.087, in 2003 was 0.084, in 2004 was 0.089, in 2005 was 0.143
  • Spotted Skunk in 2002 was 0.199, in 2003 was 0.126, in 2004 was 0.178, in 2005 was 0.162

During the past four field seasons, 708 primary sample units have been completed (with more than 4,500 individual survey stations and over 45,000 survey nights). Sampling effort for both species has been greater on the Sequoia and Sierra NFs (510 sample units) than in the central and northern Sierra Nevada (198 sample units). In the southern Sierra Nevada, fishers were detected at 128 sample units.

Marten were detected at 84 sites throughout the region, 28 of which occurred in wilderness areas. The proportion of sample units with detections for fisher, marten and select associated carnivores during the first four years of the monitoring program is described in the table on page 3.

These preliminary proportions are estimated as number of sites with detections divided by the number of sites surveyed. In the future they will be adjusted based on species’ detectability, possibly resulting in annual estimates being higher than estimates reported here. Annual estimates ultimately will be used to monitor trend.

Fishers were consistently detected at lower elevations than martens. Fishers were detected as low as 3,110 feet and as high as 9,000 feet; martens detections ranged from 4,400 feet to 9,793 feet. Preliminary results indicate that fishers are well-distributed in portions of Sequoia and Sierra NFs, though annual occupancy rates are consistently higher on Sequoia NF (33.3% to 41.1% annual occupancy) than Sierra NF (14.5% to 22.7% annual occupancy). The spatial pattern of detections also appears to be more consistent from year to year on Sequoia NF than on Sierra NF. Fishers were not detected in the central and northern Sierra Nevada where more than 120 sites at historic fisher elevations were sampled. Martens were detected sporadically throughout the central and southern Sierra Nevada, including on the Inyo NF in the Mammoth Lakes area, though relatively few detections were recorded in the northern Sierra Nevada. The proportion of sites detecting martens during 2005 was lower than previous years. This probably reflects sampling emphasis rather than a population decline: during 2005 more sites were sampled in low and mid elevation habitats outside the typical marten range than previous years.

Continued monitoring will be critical not only to understand trends in the southern Sierra fisher population, but also to document fisher population expansion into the central and northern Sierra Nevada. Contingent on funding and meeting objectives of the fisher population monitoring program, sampling will continue in the central and northern Sierra Nevada to better understand regional variation in marten distribution. Program objectives for 2006 include:

  1. continued intensive sampling of the fisher population in the southern Sierra Nevada,
  2. sampling for fisher in the central and northern Sierra Nevada with emphasis on Stanislaus NF and Lassen NF,
  3. continued marten monitoring, and
  4. completing data migration to the Forest Service corporate databases,
  5. expansion of fisher monitoring onto National Park Service lands in the southern Sierra Nevada, and
  6. integration of hair snaring devices for genetic identification of individual fisher at all survey locations in the southern Sierra Nevada.

Forest Monitoring Summary for October 1, 2004 to September 30, 2005 (FY 2005)

Treatment in fisher den site buffers occurred on 37 acres on the Sequoia NF. Treatment within fisher den site buffers may occur if necessary to achieve fuel objectives in Wildland Urban Interface (WUI) zone (ROD page 61).

The ROD requires evaluation of CSO (California spotted owl) PACs after potentially stand replacing fires in order to replace PACs or PAC acres which may have become unsuitable (page 37). Three CSO PACs were affected by wildfire in FY 2004 and 4.5 acres became unsuitable as a result of the fire but suitable replacement acres were found. The fires occurred on the Sierra and Stanislaus NFs.

None of the Sierra Nevada NFs identified any vegetation management treatments in Great Grey Owl PACs, or marten den site buffers though the ROD allows some vegetation treatments (pages 61-62).