The Spotlight on Fishers By Kerry Coleman

Do we have fishers in eastern Ontario? Yes, we definitely do! As I told my neighbour recently, I found a large male fisher dead on the road last winter less than a kilometre from her house. “Oh,” she whispered. She sounded very concerned. I assured her that fishers are no threat to her or her family and she had no pets or livestock to be worried about either. Still, I could sense a high level of anxiety and couldn’t help but be reminded of the myths and unfounded fears that seem to go hand-in-hand with fishers, especially in areas where they are found in southern Ontario.

The fisher (Martes pennanti) is a member of the weasel family (Mustelidae). Members of this family include in ascending order of size, based on the average weights of males, the least weasel (Mustela nivalis) at 43.7 grams (1.4 oz.), ermine (Mustela erminea) at 80 grams (2.57 oz.), long-tailed weasel (Mustela frenata) at 225 grams (7.23 oz.), American martin (Martes Americana) at 995 grams (2.18 lbs.), mink (Mustela vison) at 2.07 kg (4.55 lbs.), fisher at 3.7 kg (8.14 lb), river otter (Lentra canadenis) at 7.75 kg (17.05 lbs.) and the wolverine (Gulo gulo) at 14.8 kg (32.56 lbs.) (Banfield, 1974). Although male fishers average 3.6 to 4.5 kg (8 to 10 lbs.), very large males can exceed 9.0 kg (20 lbs.).

There is no doubt that pound for pound the fisher is a formidable predator. There are records of fishers attacking and killing young fawns, but stories of fishers attacking adult deer or jumping out of a tree onto the back of an adult moose are unrealistic. It is doubtful that fishers are even a significant predator of fawns. If the right situation presented itself, such as the doe being absent, they might attack a fawn; however, most fishers would not risk the hooves of a protective doe. Small mammals typically make up about 80% of the fisher’s diet. Carrion (dead animals) is also an important part of the fisher’s diet and it is not unusual to find deer, moose and beaver showing up in diet studies. Perhaps somewhat unexpectedly, vegetation is a common food item for fishers. In summer, they eat a variety of fruits and mast including: berries, apples, cherries and beechnuts. In more southerly areas they will take advantage of crops such as corn.

Fishers are renowned for their ability to prey on porcupines, a prey for which they have almost no competition (Powell, 1981, 82). They will bite at the porcupine’s face until they are weakened or succumb to the bites. Eventually the fisher will attack and feed on the porcupines unprotected underbelly. They seem to be somewhat immune to the effects of the porcupine quills.

In January 2000, the Ontario Ministry of Natural Resources (OMNR) in Kemptville undertook a study to examine the stomach contents of fishers caught by trappers (Bland and others, 2001). The stomach contents of 68 fishers trapped between November 15 and January 15 revealed that 25 fishers (37%) had at least some vegetation in their stomachs. Winter berry was the vegetation type most often found. Small mammals and deer carrion made up the greatest volume of food found. Raccoons were found in 18% of the fisher stomachs and 40% had fisher in their stomachs. This might represent predation on other fishers or more likely feeding on fishers caught in traps or carcasses thrown out by trappers. Interestingly, 23% of the fishers had reptiles, mostly snakes, in their stomachs. It would appear as though some fishers had access to snake hibernacula. Also of interest, not one fisher had porcupine in its stomach – and there were no cats!

Fisher population levels are probably determined to a large extent by food availability, as it is with most predators. In central and northern Ontario, snowshoe hare cycles have a strong influence on fisher population cycles (Bulmer, 1975; Powell, 1982). However, even in areas south of the Canadian Shield, where the soils are more productive and there is a greater diversity of food available, fisher population cycles still appear to be influenced by snowshoe hare and cottontail rabbit population cycles. For several years, trappers for the OMNR’s rabies unit have trapped, vaccinated and released (TVR) raccoons in eastern Ontario to prevent the spread of raccoon rabies. Other animals also get caught in the traps, including hares, rabbits and fishers. The incidental catches in the TVR program showed a classic predator-prey relationship between fishers and hares and rabbits. Fisher abundance in the live traps would follow the highs and lows of the hare and rabbit catches, with a two-year delay (Bowman and others, 2006).

Like most predators, fishers are opportunistic. If they find an abundant or an easy-to-obtain food source, they will take advantage of it. This can put them on a collision course with people. Fishers will certainly prey on house cats and on small livestock such as chickens and rabbits if they can get easy access to them. If they have made a kill, they will most likely return. This can happen any time of year, but the probability is higher in the late winter. Winter can be a lean time for predators. Snowshoe hares don’t have young until late April or May, and even the prolific meadow vole stops reproducing from mid-to-late November until April, depending on temperatures. A dwindling food supply, higher energy demands (especially for pregnant females) and deepening snow, can make travel for the short-legged fisher difficult, and can result in fishers gravitating to where people live in search of food. Some might say that when house cats are roaming in the outdoors they become part of the food chain. Cats prey on small birds and mammals but they in turn can be prey. This is little consolation to someone who has lost a beloved family pet. The OMNR advises people to keep their house cats indoors.

Fishers, like many members of the weasel family can be very curious and bold. Many of us have had a mink, otter or fisher approach within a few feet curiously staring at us trying to determine what we are. Although fishers pose little danger to people, to have a fisher approach you or come up onto your deck and stare through your patio door can be a little unnerving to say the least. If a fisher is protecting its den or food cache, or if its escape route is blocked, it will stand its ground and can act very aggressively. There are a few reports of people being bitten under these circumstances.

The Mammals of Canada (Banfield, 1974) describes the fisher as “a denizen of the climax forest. Unlike the martin it will venture into sub climax deciduous groves and old burns.” In Wild Furbearer Management and Conservation in North America, (1987), Douglas and Strickland cite literature describing the fisher as a forest-dwelling species utilizing mixed deciduous-coniferous forests most often with a 50–75% closed canopy. These descriptions generally refer to fishers living in central and northern Ontario. Since the mid-1990s, they have expanded their range to a number of areas south of the Shield. This has been very evident in eastern Ontario. In most cases, the habitat they are using would be described as a mix of forest, forested swamps and agriculture lands, quite different from the habitat described above for central and northern Ontario. Why and how did fishers expand their range into southern Ontario? Where did they come from? How do their habitat preferences and home-range sizes compare to those in central and northern Ontario?

In a study area covering 4,600 km² in eastern Ontario, it was determined that the proportion of the area that was forested had increased from 29 to 40% from 1934 to 1995. Census data from the same area showed a decline in the amount of land being farmed over the past 50 years (Lancaster and others, 2008). Fur harvest data shows that Fur Management Units (FMUs) reporting a harvest of fishers all had 40% or greater of the unit in forest cover. Not all FMUs south of the Shield have harvest quotas for fishers, and fishers will show up from time to time in areas with less than 40% forest cover. However, it seems pretty clear that the presence of fishers south of what was considered traditional fisher range on the Shield is most likely due to an increase in the amount of forest cover in these areas. Somewhat like the 1989 movie “Field of Dreams,” if the habitat is there, they will come.

Fishers were once common in southern Ontario, but were extirpated from much of their historic range during the 1920s and ‘30s, likely as a result of habitat loss (loss of forest cover), intensive fur trapping and possibly incidental poisoning from predator control efforts (de Vos, 1951; Aubry and Lewis, 2003). A small remnant population remained in Algonquin Park. There was also a small remnant population that remained in the Adirondacks of New York state. Many people believe fishers were introduced into southern Ontario by the OMNR. Although the OMNR did re-introduce fishers to the Parry Sound area (1957–63) and to Manitoulin Island and the Bruce Peninsula (1979–82), the OMNR did not release any fishers in southern Ontario. The movement of fishers into central and the northern parts of southwestern Ontario probably originated from the remnant population in Algonquin Park. Interestingly, that was not the case for eastern Ontario. DNA analysis of trapper-caught fisher determined that they are migrants from the Adirondacks (Carr and others, 2005), likely crossing the St. Lawrence River in the Thousand Islands area. Of further interest, it has been determined that this migration of fishers into eastern Ontario from the U.S. is still occurring. Therefore, eastern Ontario can be considered an “ecological sink” for fishers.

In an another research study in eastern Ontario, 61 fishers were radio collared and tracked for two years, to determine home range size, population density and survival (Koen and others, 2007).

The average home-range size for male fishers in Koen’s study area was 11 km² and 2.1 km² for females. These home ranges are considerably smaller than those reported from studies on the Shield. For example, Tully (2006) reported an average home-range size of 38.7 km² for males and 29.9 km² for females in Algonquin Park. If fishers occupy smaller home ranges in the south, it would make sense they would have the potential to reach higher densities as well. Koen (2007) estimated a population density of 32.7 fishers per 100 km² of suitable habitat within her eastern Ontario study area. Similar studies have estimated densities of 12 fisher per 100 km² in Maine (Arthur and others, 1989); and 19 to 25 per 100 km² in Massachusetts (Fuller and other, 2001). It should be kept in mind that these population densities were estimates at the time the studies were conducted. Fisher populations will fluctuate depending on food supply and mortality rates.

Over a two-year period (2003–2005), Koen determined that the combined average fisher survival rate was 35%. Of the 28 collared fishers that died during her study, 12 (42.8%) died from human causes such as fur trapping, nuisance animal control and road kill. Eight died from natural causes including natural injuries, starvation and canine distemper. Eight died from unknown causes. Fishers in southern Ontario enjoy the benefits of a more productive landscape and have the potential to reach higher population densities than their cousins on the Canadian Shield; however, they also face more hazards. With an average home range size of 11 km², male fishers cross a lot of roads in their travels. In addition, average home-range sizes do not consider annual dispersal, which can take fishers (mostly young males) considerable distances. The high populations of coyotes, foxes and raccoons in southern Ontario can result in high exposure rates to diseases such as canine distemper. Southern Ontario has a high human population, and when there is conflict between fishers and people, the fishers usually lose.

The curious nature of fishers makes them easy to trap compared to other predators such as foxes and coyotes. Quotas have traditionally been used by the OMNR to control the harvest of fishers and prevent overtrapping. Adult females have small home ranges and are the least likely to be trapped. When they start showing up in high numbers in the harvest, there is generally reason for concern. Douglas and Strickland (1987) determined that on the Shield a harvest of less than three juveniles per adult female would result in a population decline. No studies have been conducted south of the Shield to determine the impact of trapping on fisher populations, if quotas are necessary or if the Douglas and Strickland index of three juveniles per adult female is applicable. Starting in June 2005, the Kemptville District of the OMNR, which makes up the majority of eastern Ontario, initiated an experiment to remove fisher quotas. The study was contingent on the cooperation of local trappers who were asked to submit the skulls of trapped fishers so that ages and sex ratios could be determined.

Although the study is not complete, after four years, it appears as though the open trapping quotas for fisher have not resulted in a major population decline in eastern Ontario (S. Smithers, per comm.) This is not surprising when one considers the number of trappers in eastern Ontario and the area of land being trapped compared to the total area of suitable fisher habitat. The relatively small home-range sizes in southern Ontario, (e.g. 2.1 km² for adult females) ensure that many fishers are not exposed to trapping.

One unknown is the level of fisher harvest taken under the protection of property legislation. Animals caught under Section 2.1 of the Fish and Wildlife Conservation Act, which deals with the protection of property, are only required to be reported if the animal is being processed and kept to be sold as fur. The OMNR does not want to see any natural resource wasted and all licensed fur trappers are encouraged to skin and sell any fur they catch. A landowner and/or his or her immediate family members have the right to destroy fishers under the authority of the protection of property legislation, if they believe the animal has or is about to destroy their property (e.g. livestock). They do not have to report the kill or sell the fur. The legislation is quite specific about who is authorized to act as an agent on the landowner’s behalf. In most cases licensed fur trappers are used as agents. Although the number of fishers trapped or shot and not reported is unknown, the OMNR does not think it makes up a significant proportion of the total harvest (S. Smithers per comm.). Fur harvests can fluctuate based on the price of fur. Recently, fisher pelts were selling for $30 to $40 each. However, OMNR fur harvest data did not show a significant increase in the fisher harvest three years ago when fisher pelts were selling for $80 to $90 per pelt. (S. Smithers, pers comm.). The open quota project is scheduled to continue for at least one more year. All of these studies are critical for the long-term management and sustainability of the fisher population in southern Ontario.

Love them or hate them, the fisher has returned to stay in parts of southern Ontario. Their return reflects an increase in the amount of forest cover on the landscape. In a report prepared for Environment Canada in 2001, entitled How Much Habitat is Enough?, many ecological values are identified for landscapes having greater than 30% forest cover. We also know that forests have and will continue to play a key role in sequestering carbon and helping to mitigate the effects of global warming. The fisher might well be considered an indicator species for a healthy environment – but keep your cats indoors.

Literature Cited

Arthur, S. M. , W.B. Krohn, and J.R. Gilbert.1989. Home range characteristics of adult fishers. J. of Wildlife Management 53: 674-679

Aubry, K.B. Lewis, J.C. 2003. Extirpation and reintroduction of fishers (Martes pennanti) in Oregon: implications for their conservation in the Pacific states. Biological Conservation: 114: 79-90

Banfield, A.W.F. 1974.The Mammals of Canada. University of Toronto Press. Toronto. 438 pgs

Bland , D.S. 2001. Unpublished report. OMNR Kemptville District

Bowman, J., D. Donovan and R.C. Rosatte. 2006. Numerical response of fishers to synchronous prey dynamics. J. of Mammology 87: 480-484

Bulmer, M.G. 1975. Phase relations in the ten year cycle. J. Animal Ecol. 44:609-621

Carr, D. 2005. Genetic structure of a recolonizing population of fishers (Martes pennanti) Thesis Trent Univ., Peterborough Ont.

De Vos, A. 1951. Recent findings in fisher and marten ecology and management. Transactions of the N. American Wildlife Conf. 16: 498-507

Douglas CW and Strickland MA. 1987. Fisher: In: Novak, M, Baker, JA, Obbard, ME, Malloch B (eds) Wild Furbearer Management and Conservation in North America, OMNR, Toronto pp 511-529

Fuller, T.K., E.C. York, S.M. S.M. Powell, T.A. Decker and R.M. DeGraff. 2001. An evaluation of territory mapping to estimate fisher density. Canadian J. of Zoology. 79: 1691-1696

Koen, E.L., J. Bowman, and C.S. Findlay. 2007. Fisher survival in eastern Ontario. J. of Wildlife Management: 71: 1214-1219

Koen, E.L., J. Bowman, C.S. Findlay, and L. Zeng. 2007. Home range and population density of fishers in eastern Ontario. J. of Wildlife Management. 71: 1484-1493

Lancaster, P.A. , J. Bowman, and B.A. Pond. 2008. Fishers, farms and forests in eastern North America. Evolutionary Applications 1: 620-630

Powell, R.A. 1982. The fisher: life history, ecology and behaviour. Univ. of Minnesota Press, Minneapolis. 217 pgs

Tully, S. M. 2006. Habitat selection of fishers (Martes pennanti) in an untrapped refugium: Algonquin Park. Thesis Trent Univ., Peterborough, ON

This article was featured in a past edition of the S&W Report, the newsletter of the Ontario Woodlot Association. 

© Ontario Woodlot Association, 2010