The status of Fisher (Martes pennanti) at the northwestern edge of their range: are they increasing and expanding in the Yukon?
Key words: abundance, distribution, Fisher, Martes pennanti, range expansion, Yukon
Fisher (Martes pennanti) are distributed widely across the boreal and mixed coniferous-deciduous forests of northcentral North America, including southerly projections of those forests in the cordillera of the eastern and western United States (Proulx and others 2004). The status and distribution of the Fisher has been examined extensively at the range-level (Rand 1944; Hagmeier 1956), as well as for several states, provinces, and territories (for example, Coulter 1960; Dilworth 1974; Aubry and Houston 1992; Zielinski and others 1995; Weir 2003). Although Fisher are relatively common in the eastern portion of their range, they appear to be somewhat rare in the western portion (for example, British Columbia, Alberta, Washington, Oregon, California, etc.; Rand 1944; Hagmeier 1956; Powell 1993; Aubry and Lewis 2003; Weir and Courbould 2006). Fisher reach the northwestern edge of their distributional range in the Yukon, Canada (Hagmeier 1956; Banfield 1974), but their abundance and distribution has been poorly documented there (Rand 1944; Youngman 1975).
The Fisher is listed as a species of Least Concern on the IUCN Red List due to its widespread distribution and abundance (Reid and Helgen 2008); however sub-national rankings in various states, provinces, and territories vary. For example, the NatureServe status ranking for Fisher in the Yukon is S2S3-Vulnerable, due to a small population, limited range, and perceived threats to populations (for example, trapping) and habitat (for example, logging). Carroll and others (1999, 2001) identified Fisher as a focal species to monitor in the mountains of western North America.
The first scientific evidence of Fisher in the Yukon is from 2 specimens collected in 1956 near Francis Lake (UTM: Zone 09V, 466227E, 6808707N, WGS84). The distribution of Fisher in the Yukon was reported by Youngman (1975). Based on 4 museum specimens, he concluded that they were rare and restricted to the southeastern part of the Yukon. The Fisher's range in the Yukon was similarly mapped by others to include only southeastern Yukon (for example, Banfield 1974; Powell and others 2003; NatureServe 2009). There have been no scientific surveys of Fisher in the Yukon to aid in improving upon the distributional range mapped by Youngman (1975). Proulx and others (2004) recently provided a revised distribution of Fisher, but changes to the Yukon range in their review were based solely on a personal communication.
Additional data are now available to reassess Fisher distribution and status in the Yukon (Slough and Jung 2007). Given their conservation status as Vulnerable in the Yukon, we sought to better understand their abundance and distribution within the Yukon. We investigated the distribution and relative abundance of Fisher in the Yukon, at the northwestern edge of their distributional range.
No systematic field surveys have been undertaken to document Fisher occurrence in the Yukon. Because of this, we used all available information and datasets including fur harvest records, museum specimens, and anecdotal observations, to complete our analysis.
We used harvest records (Yukon Department of Environment, unpubl, data) to examine Fisher distribution and relative abundance over a 30-y period (1980 through 2009). Although Fisher can be legally harvested in the Yukon by fur trappers, trappers likely do not target Fisher, given their low densities and low pelt prices (H Jessup, Yukon Department of Environment, pers. comm.). Most Fisher harvested in the Yukon are likely taken incidental to a targeted harvest of American Marten (Martes americana; hereafter Marten), and it is not mandatory to report Fisher harvested in the Yukon for personal use. Records, however, are kept of all pelts sold, exported, or processed by taxidermy. The use of harvest records to infer population sizes is problematic; however, we believe that they provide a useful index of broad trends in abundance of Fisher in the Yukon. Harvest data has been collected in the Yukon since 1920, but fur harvest data collected before 1980 is fraught with clerical errors and is not reliable (H Slama, Yukon Department of Environment, pers. comm.). Data collection and management had improved considerably by 1980, and an estimated >97% of pelts of all furbearers harvested were recorded and assigned to an area-specific registered trapping concession, making the data from 1980 onward reliable (Slough and others 1987). Furthermore, given the rarity of Fisher in the fur harvest in the Yukon, many fur trappers had brought their incidental captures of Fisher to our attention. To detect differences in the number of Fisher harvested over the past 3 decades, we statistically compared the number of Fisher harvested in each decade (n = 3) using a Kruskal-Wallis analysis of variance. Because most Fisher harvested in the Yukon are incidental to harvest of Marten, we also examined the trend in Marten harvest over the same time period.
We searched the literature (for example, Youngman 1975) and North American museum collections to locate specimens of Fisher from the Yukon held in museums. Once located, we contacted museum collection managers to obtain the collection date and location for each specimen, and created a database of this information.
Incidental sightings have contributed substantially to understanding the distribution of other elusive carnivores in areas where they are particularly rare, for example: Long-tailed Weasel (Mustela frenata; Proulx and Drescher 1993; Richter and Schauber 2006); Wolverine (Gulo gulo; Groves 1988); and Cougar (Puma concolor; Gerson 1988). We used ancedotal sighting information of Fisher in the Yukon to aid in delineating their distributional range, primarily through an annual questionnaire sent to all registered Yukon fur trappers. The questionnaire, developed by one of the authors (BGS), was designed to ask trappers about the trends in perceived abundance of common furbearing species or their prey within the trapper's concession. In 1986, a small series of questions were added to the annual questionnaire to solicit information from fur trappers about Fisher occurrences on their traplines. Additionally, in 2005, we requested local biologists, conservation officers, select fur trappers, and naturalists to submit any recent observations of Fisher. Additional incidental sightings were contributed by local residents via personal contact with the co-authors. In most instances after 1980, we contacted fur trappers and others to discern their knowledge of Fisher and the details of their observation, in order to assess the reliability of their observation. We concur with Aubry and Houston (1992) that data of this nature should be interpreted with caution, and we ranked each record as to its reliability using the rating scheme they developed for Fisher records in Washington State, specifically: (1) museum specimen or photo; (2) harvest report (with no specimen available for confirmation); (3) detailed sighting by an experienced observer (for example, resident trapper or naturalist); (4) sighting by an observer with undetermined or limited qualifications; (5) tracks only reported; and (6) a record containing insufficient or questionable description or locality data. Reliability ratings of 1 were considered the most reliable and those of 6 being the least reliable.
To place the Yukon records into context, we entered the distributional range of Fisher into a geographic information system (ArcView GIS 3.3, ESRI, Redlands, California), as mapped by Banfield (1974), Powell and others (2003), Proulx and others (2004), and NatureServe (2009). The records we collated were then overlaid on these distribution maps. We also overlaid known locations of Fisher harvested by fur trappers in adjacent southeast Alaska (MacDonald and Cook 2009) and northwestern British Columbia (E Lofroth, British Columbia Ministry of Environment, unpubl, data) to provide additional context.
We compiled 100 records of Fisher in the Yukon between 1956 to 2009 (Table 1), including: 73 Fisher harvested by licensed fur trappers between 1980 and 2009; 8 museum specimens collected between 1956 and 1989 (see Appendix); 7 observations of Fisher or their tracks reported by trappers in the 1986 questionnaire to trappers; and 11 incidental observations of Fisher reported by local trappers and naturalists between 1999 and 2009. Most (88%) of the Fisher records had high reliability ratings (ranks 1-3; Table 1), and 81% of all records were based on trapped specimens. All museum collections of Fisher from the Yukon were legally obtained as incidental by-catch by licensed fur trappers.
Fisher harvests in the Yukon have been increasing in the past decade (Fig. 1). The mean number of Fisher harvested in the 1990s and 2000s was about twice that of the number harvested in the 1980s. This difference, however, was not statistically significant (P = 0.078), likely because of low sample sizes and the similarity in harvest numbers in the last 2 decades (Fig. 1). While harvest of Fisher appeared to increase over the past 30 y, their pelt price decreased substantially (Fig. 1). As well, harvest of Marten (the species targeted by trappers) decreased in the 1990s and 2000s to about 50% of what it was in the 1980s, and the pelt prices remained fairly stable (Fig. 1).
Fisher appeared to have significantly expanded their range westward in the Yukon and adjacent British Columbia and Alaska, based on earlier published distribution maps (Fig. 2). Prior to the early 1990s, almost all Fisher reported in the Yukon were from east of the village of Teslin (UTM: Zone 08V, 626703E, 6672412N, WGS84), with most specimens coming from the vicinity of the town of Watson Lake (UTM: Zone 09V, 516097E, 6658459N, WGS84; Fig. 2). This coincided with the distribution of virtually all incidentally trapped Fisher. Since 1998, there have been sightings of Fisher west of Teslin, including a very reliable sighting in 2008 as far west as near Kluane Lake (UTM: Zone 07V, 637512E, 6771390, WGS84; Fig. 2). Additionally, between 1992 and 2006, 3 Fisher have been incidentally trapped by fur trappers [greater than or equal to]200 km west of Teslin. Fur harvest data from adjacent Alaska (MacDonald and Cook 2009) and northern British Columbia (E Lofroth, British Columbia Ministry of Environment, unpubl, data), further suggest that Fisher do occur west of their previously mapped distributional range (Fig. 2).
[FIGURE 1 OMITTED]
Harvest records suggest that Fisher abundance in the Yukon may be increasing. Observed increases in Fisher harvest have occurred despite a downturn in the trapping industry caused by a combination of low pelt prices, high expenses, and alternative employment opportunities. We-recognize that harvest data are difficult to interpret without corresponding data on trapping effort; however, circumstantial evidence suggests that Fisher harvest data may be as useful as a rough index of population growth (but perhaps not population decline). Fisher harvest increased during the 1990s and 2000s despite average pelt prices being about 25% that of the 1980s. Trapper effort and the number of Fisher harvested should have decreased over this time period if trappers were targeting Fishers. Most Fisher, however, are likely trapped incidental to Marten harvest. Therefore, if Fisher populations remained stable we would have expected that the number of Fisher harvested would have decreased as the Marten harvest decreased. Conversely, we observed an increase in Fisher harvest and a decrease in Marten harvest. We have no reason to believe that Marten populations have recently decreased in the Yukon, but suspect that the decrease in Marten harvest is directly related to reduced trapping effort in recent decades. Thus, the increase in number of Fisher harvested during a time when trapping effort for Marten is reduced by 50% suggests that the increase in Fisher harvest is a result of more Fisher being available to be harvested.
[FIGURE 2 OMITTED]
Frey (2009) correctly asserted that it is important to distinguish between extra-limital records that are a result of apparent range expansion, versus those that simply reflect previously undocumented occurrences, particularly for small or cryptic species. To declare that a species has expanded its range, there must have been ample opportunity to detect occurrence prior to the observation of extra-limital records. Fisher are a medium-sized mammal (2.0 to 5.5 kg; Powell 1981), that are relatively easily trapped and are easily distinguished by fur trappers from other furbearers, including American Marten. Additionally, southwestern Yukon has been the most surveyed region of the Yukon by mammalogists and other naturalists, and is home to >85% of the Yukon's human population. We believe that had Fisher been present in southwestern Yukon historically, then trappers, mammalogists, or other naturalists and residents would have reported such observations, but none were reported.
Recent fur harvest records for Fisher, additional museum specimens, credible track sightings by experienced trappers and naturalists, and unverified sightings by others, confirm that the core range of the Fisher in the Yukon has expanded since the 1980s, and now includes southwestern Yukon. Available records suggest that Fishers may be expanding their range in recent decades as suggested by Proulx and others (2004) and Slough and Jung (2007).
It is important to note that sighting data is inherently inconclusive and can lead to false positives for rare and elusive species, such as Fisher (Aubry and Lewis 2003; McKelvey and others 2008). Several of our key observations of Fisher from west of Teslin, however, were made under ideal conditions by knowledgeable field biologists and fur trappers. In addition, several harvested Fisher from an area outside the range mapped by Proulx and others (2004) provided substantive records of apparent range expansion. Moreover, harvest records of Fisher in nearby Alaska and British Columbia from the same time period lend further credence to the observation that Fisher have expanded the northwestern edge of their range.
Much of southwestern Yukon is regulated as a Marten Conservation Area, where Marten harvest is limited by quota and few fur trappers target Marten (Slough 1989). Most fur trappers in southwestern Yukon target Canada Lynx (Lynx canadensis) and Wolverine, whereas those in southeastern Yukon typically focus on Marten. We suspect that the limited harvest of Marten west of Teslin is partially responsible for the lack of Fisher specimens from that region, given that most Fisher in the Yukon are trapped incidental to Marten harvest.
The apparent population increase and range expansion of Fisher west of Teslin was largely based on sightings, not specimens (Fig. 2), and may be related to similar observations for Marten. Marten were historically rare in southwestern Yukon (Slough 1989), and their populations have apparently been increasing in recent years in southwestern Yukon, based on incidental captures by trappers. The observations of trappers are supported by data collected from recent snow track transects north of Haines Junction, which indicated a marked increase in Marten activity from essentially no Marten tracks in the years 1987 to 2001 to 8 to 16 tracks per track night/100 km from 2001 onward (CJ Krebs and EJ Hofer, University of British Columbia, unpubl, data). Low-density Marten populations in the Marten Conservation Area were augmented in the 1980s with the transplant of 171 Marten from the Teslin and Watson Lake areas (Slough 1989). Whether the apparent increase in Marten populations in southwestern Yukon is a result of the earlier transplants or not, is unknown. Natural factors such as changes in habitat or prey availability may also be responsible for the apparent Marten increase in southwestern Yukon, and the apparent increase in Fisher abundance and distribution in the region.
Fisher habitat in southwestern Yukon appears to be limited compared to the southeastern part of the territory. Dense conifer forests in the southwest are limited to low elevation river valleys and lakeshores, and connectivity of populations among watersheds may be limited in northern British Columbia (Weir and Courbould 2006) and southern Yukon. Fisher occurrence in southwestern Yukon may be confined to suitable low elevation forested habitats, and range expansion may be facilitated by these linear corridors.
Potential prey, however, are likely more abundant in southwestern Yukon than in southeastern Yukon. Depending on where they are in their 10-y cycle, Snowshoe Hare (Lepus americanus), a frequent prey item of Fisher in adjacent British Columbia (Weir and others 2005), are typically abundant in southwestern Yukon, but are relatively uncommon in southeastern Yukon (CJ Krebs and others, unpubl. data). Additionally, local knowledge suggests that the abundance of North American Porcupine (Erethizon dorsatum) in southwestern Yukon, another typical prey item of Fisher (Powell 1981, 1993), appears to have been increasing steadily in recent years, since their last local population peak in the early 1980s.
The abundance and range of several mammal species in the Yukon also appears to be increasing. For example, Cougar (Puma concolor; Jung and Merchant 2005) and Mule Deer (Odocoileus hemionus; Hoefs 2001) are relatively new members of the mammalian fauna of the Yukon. Fisher may also be a relatively new colonizer in southwestern Yukon. We suggest that while suitable coniferous forest habitat may be limiting in southwestern Yukon, once Fisher colonize the region, available habitat could support a low-density Fisher population based on prey availability, moderate winter temperatures, low snow depths, and limited Marten trapping. As demonstrated by Aubry and Lewis (2003) for Fisher in the Pacific Northwest, focused survey effort would aid in determining the status and distribution of Fisher in the Yukon. We concur with Carroll and others (2001) and Weir and Courbould (2006) that low-density Fisher populations in northwestern North America will require conservative management strategies to ensure population persistence.
APPENDIX: MUSEUM SPECIMENS OF MARTES PENNANTI FROM THE YUKON TERRITORY:
1. Canadian Museum of Nature, Ottawa, Ontario: CMNMA 34487, north end of Morley Lake, 10 Jan. 1964, F. Sidney; CMNMA 33351, north end of Morley Lake, 10 Jan. 1964, F. Sidney; CMNMA 33352, 36 mi (58 km) west of Watson Lake, 1 Dec. 1964, D. Morris; CMNMA 33353, 35 mi (56 km) northwest of Liard Crossing, 12 Jan. 1965, H. Jimmy.
2. University of Alaska Museum of the North, Fairbanks, Alaska: UAM 51272, upstream of confluence of Larsen Creek and Beaver River, date unknown (1988/1989 trapping season), L. Lee.
3. University of Alberta Museum of Zoology, Edmonton, Alberta: UAMZ M2572, Francis Lake, Jan. 1956, A. Oeming; UAMZ M2573, Francis Lake, Jan. 1956, A. Oeming; UAMZ M2574, Smith River, Jan. 1956, A. Oeming.
We thank the many Yukon trappers, biologists, and naturalists who reported their sightings and other records of Fisher in the Yukon. H Slama and T Fox managed and kindly provided access to the Yukon fur harvest and trapper questionnaire data. E Lofroth provided location data for Fisher harvested in northern British Columbia. We thank 2 anonymous reviewers for providing thoughtful comments that improved the manuscript.
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Submitted 24 March 2010, accepted 1 October 2010. Corresponding Editor: RL Hoffman.
THOMAS S JUNG
Yukon Department of Environment, PO Box 2703, Whitehorse, YT, YIA 2C6; email@example.com
BRIAN G SLOUGH
35 Cronkhite Road, Whitehorse, YT, Y1A 5S9, Canada; firstname.lastname@example.org
TABLE 1. Number and percent (%) of records of Fisher (Mantes pennanti) by reliability rating for the Yukon Territory, 1956-2009. Reliability rating (a) Number Period of years 1 2 3 4 5 6 Total 1956-1979 (b) 24 7 -- -- -- -- 1 8 1980-1989 10 1 14 0 0 7 0 22 1990-1999 10 0 34 2 0 0 0 36 2000-2009 10 0 25 5 3 1 0 34 Total 54 8 73 7 3 8 1 100 (a) (1) Museum specimen or photo; (2) Harvest report (typically no specimen is available for confirmation); (3) Detailed sighting by experienced observer (e.g., local trapper or naturalist); (4) Sighting by observer with undetermined or limited qualifications; (5) Tracks; and (6) Record containing insufficient or questionable description or locality data. Reliability rating follows Aubry and Houston (1992). (b) Reliable harvest records or sightings of Fisher were not routinely documented until 1980; thus, lack of ratings does not indicate that no Fishers were harvested or sighted during this time period.
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|Author:||Jung, Thomas S.; Slough, Brian G.|
|Publication:||Northwestern Naturalist: A Journal of Vertebrate Biology|
|Date:||Mar 22, 2011|
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