Introduction
Fishers belong to the weasel family and are a Species at Risk and blue-listed in Canada. In British Columbia it is required for forest and range licensees to create stewardship plans to maintain habitats for Identified Wildlife. The Wildlife Habitat Decision Aid was created to help in the establishment of these stewardship plans.
Description
Fishers have a pointed face, long body, short legs and a long tail with chocolate-brown fur. The females and males have a few differences such as body length and mass, and they have larger bodies, darker fur and smaller ears than American martens.
Diet
Fishers belong to the carnivore family and eat anything they can catch and kill including snowshoe hares, red squirrels, northern flying squirrels, mice, voles, porcupines, grouse and ungulate carrion.
Distribution
Fishers are found in low and mid elevation forest areas including the Boreal White and Black Spruce zone, Montane Spruce zone, Sub-Boreal Pine- Spruce zone and Sub-Boreal Spruce zone. They inhabit areas with dry as well as wet climates and temperatures ranging from very cold to warm.
Habitat
Fisher habitats are forested areas with a home range of about 25km2 or bigger for females and 100km2 or bigger for males. They need forests to protect themselves from large raptors and other predators. Trees with large cavities, which are mostly found in areas like riparian forests, are of utmost importance to Fishers as they use them especially to protect themselves and their young from weather and predators. For their reproductive dens, fishers use large, usually veteran trees like black cottonwood, trembling aspen, balsam poplar, lodgepole pine or douglas-fir. The ecological process needed for a tree to become a den tree seems to be a rare occurrence. They are mostly live trees that have some form of rot on the inside, which will form a cavity. The cavity needs to be bigger than 30 cm in diameter, limiting the suitable trees to have a trunk greater than 40 cm in diameter. The same trees are used continuously for three months by the female fisher if she has kits and she might re-use it from year to year.
For resting, fishers use different types of sites depending on available structures and temperatures. If the temperature is above -10ºC they use cavities, rust brooms or exposed branches all found on trees, however, if the temperature falls below –10ºC they need to find shelter with thermal protection such as spaces under large logs, log piles or burrows dug by other animals.
If an area on Crown Land is identified as a Wildlife Habitat Area it can be protected to maintain fisher habitat such as denning sites, large-diameter trees and other important structures for fishers.
Forest Management Considerations
Fishers have very specific and rare habitat needs which must be maintained and promoted properly. For a short-term and long-term maintenance it is required to ensure habitat properties important to fishers are sustained such as conserving large declining trees and decreasing the suppression of disease, death and decay of trees. Another threat to fisher populations might be the accessibility to their habitat, increasing trapping mortality in these areas, as well as large-scale salvage logging of stands that were affected by the mountain pine beetle outbreak. However, fishers need habitat that is a mixture between early- and late-successional forests making balanced forest management planning critical to the population. Harvesting can increase the capacity of certain areas if it doesn’t cover too large of an area in too little time. For example, harvesting 250 ha in a 50 km2 area over a span of 12 years already reduces the chance of supporting fishers by 50%, therefore, it is critical to include the impact of the rate and extent of harvesting on the capacity of an area into management planning. Areas with suitable reproduction and resting features should be conserved as Old Growth Management Areas, Wildlife Tree Patches and/or Riparian Reserves. Other aspects that should be considered for management planning are the ever-changing habitat values of stands and the use of riparian forests as a connector between forests that are suitable to support fisher populations.
Methods to diminish the impact of forestry on fishers include leaving 25 m3/ha or more of elevated coarse woody debris throughout the cutblock to maintain foraging and resting areas, leaving shrub-layer cover for forage, avoiding the salvage logging of mountain pine beetle infected areas and protection of secondary structures with live overstory trees.
If fisher habitat needs are considered during the planning phase of cutblocks, the structures important to them can be maintained. Such planning would involve the inclusion of important tree species. Such Wildlife Tree Patches should be within 200 m of the edge of the cutblock linking it to unharvested forest and be at least 2 ha in size. Leaving large live trees can also help in the creation of more habitat as they might have or get heart-rot and form cavities useful to fishers.
When planning the machine operators can consider a few methods so that the area can be maintained as suitable habitat, for example by creating small and big cull piles of woody debris, leaving several single trees that will potentially form dens or rest sites and avoiding to disturb already suitable structures in the cutblock.
When a cutblock is regenerating it is important to plant several plant species in order to maintain a structure and prey diversity, avoid thinning or at least leave 25% of an area unthinned as this process would decrease snowshoe hares which are important food to fishers, conserve diseases that cause heart-rot in order for cavities to form and avoid burning of cutblock areas as it will destroy all the possible habitat structures like coarse woody debris.
These methods might result in longer regeneration times and other implications however, they will largely improve the suitability of areas to support fisher populations and are therefore essential to the conservation of this species.
Monitoring Recommendations
To monitor fishers it is critical to evaluate the use of reproductive denning trees and regenerating cutblocks. This will help to determine which conservation methods are mostly effective especially regarding regenerating cutblock areas.
Conclusion
Fishers are a species at risk belonging to the weasel family. They have very specific habitat needs with structures that only occur rarely. For reproduction and resting they need trees with heart-rot that formed cavities or larger log piles and other shelter with thermal protection when the temperature drops below -10ºC. Harvesting the forest can have huge impacts on fisher habitat, however with proper management and consideration it can improve the suitability of areas to support populations. Leaving several larger tree that might form cavities, coarse woody debris and cull piles in cutblock can already improve the area’s fisher habitat qualities.
Fisher in:
- Evergreen Stewardship Plan for Lillooet Sub Region
- Evergreen Stewardship Plan for South Chilcotin Sub Region
- Source Weir, R.D. and P.L. Almuedo. 2010. British Columbia’s Interior: Fisher Wildlife Habitat Decision Aid. BC Journal of Ecosystems and Management 10(3):35–41. www.forrex.org/publications/jem/ISS52/vol10_no3_art5.pdf