Recovery Strategy for the Ermine, haidarum subspecies, in Canada [Proposed] : Background

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Common name: Ermine, subspecies Scientific name: : Threatened Reason for Designation: A distinct subspecies that appears to have greatly declined in density and whose habitat has been severely affected by introduced mammals. A comparison of results of a recent, intensive sampling program with historic trapping records suggests a decline in numbers. Last Examination and Change: May 2001 Canadian Occurrence: British Columbia Status History: Designated Special Concern in April 1984. Status re-examined and designated Threatened in May 2001. Last assessment based on an update status report.

The Ermine, haidarum subspecies (Mustela erminea haidarum) has been described as “the most morphologically distinct” of all ermine (Reimchen and Byun 2005; Eger 1990; Cowan 1989; Foster 1965). Originally classified as a distinct species (Preble 1868 in Edie 2001), it is now recognized as a subspecies of the Ermine (also known as holarctic short-tailed weasel; Hall 1951 in Edie 2001).

Genetic work has shown Ermine haidarum belong to a unique lineage of short-tailed weasel that has been isolated from continental and Beringial lineages since prior to the latest glaciation (Fleming and Cook 2002; Byun 1998). The haidarum subspecies is closely related to two sub-species found on Alaskan islands across Dixon Entrance from Haida Gwaii (also known as the Queen Charlotte Islands): M. e. celenda, found on Prince of Wales Island and M. e. seclusa on Suemez and Heceta Islands (Fleming and Cook 2002). Genetic evidence suggests that these three subspecies are likely glacial relics which persisted through the Wisconsin glaciation, possibly in a coastal refugium (Fleming and Cook 2002; Byun 1998; Heusser 1989).

Ermine or Short-tailed Weasels are members of the family Mustelidae, which also includes American Mink (Neovison vison), American Marten (Martes americana), Northern River Otter (Lontra canadensis), Sea Otter (Enhydra lutris), and Wolverine (Gulo gulo). Ermine are a small mustelid with males measuring 251 to 315 mm, weighing 67 to 106 g and females measuring 2/3 that weight and length. Ermine, haidarum show much less sexual dimorphism than other ermine (Eger 1990; Foster 1965). Ermine have long, slender bodies, a small face, furred tail, short oval ears, and scent glands which produce a strong musky odour. In summer, pelage is reddish-brown above and creamy white below. The tail-tip remains black throughout the year. Ermine on Haida Gwaii moult to a white coat during winter, which may not be advantageous since snow cover at low elevations is infrequent.

Ermine haidarum is globally ranked as G5T2, meaning that while the species is globally secure, the haidarum subspecies is globally imperilled (NatureServe 2008). Nationally, Ermine haidarum is N2 (nationally imperilled) and has been reassessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as Threatened. COSEWIC up-listed Ermine haidarum status from its earlier status of Special Concern based on small population size and continued decline (COSEWIC 2001). In British Columbia (B.C.) Ermine haidarum is ranked S2 and is on the provincial Red list, indicating it is considered a candidate for provincial listing as endangered or threatened (Conservation Data Centre 2003). The B.C. Ministry of Environment has assigned Ermine haidarum as priority 2 under Goal 1 of the B.C. Conservation Framework (see http://www.env.gov.bc.ca/conservationframework/ for details).

Ermine haidarum is endemic to Haida Gwaii. The Haida Gwaii archipelago is approximately 300 km long and lies some 80 km west of the B.C. mainland (Figure 1). The range extent ofErmine haidarum is approximately 9,276 km2, the total area of the islands from which haidarum is known.

Haida Gwaii / Queen Charlotte Islands

Figure 1. Location of Haida Gwaii.

Ermine haidarum are thought to have occurred at naturally low numbers since at least the most recent glaciation (Foster 1965; Cowan 1989). Current abundance of Ermine haidarum is unknown, but based on sightings, trapping records, and live-trapping efforts for inventory purposes, it continues to be very rare (Reid et al. 2000).

Detailed historic and present population data to definitively describe population trends are not available and indirect evidence of any population trend is difficult to discern. However, there is evidence that Ermine haidarum numbers are lower today than in historic times based on a substantial but unsuccessful effort to inventory the population during the 1990s. Although ermine are not shy or secretive animals, only two individuals were captured in over 6,700 trap nights from 1992 through 1997. Almost 23 km of snow tracking and 2,692 track-plate station-nights in 1997 and 1998 failed to return any signs of ermine (Reid et al. 2000). More recent surveys have met with a similar lack of success; extensive use of live traps, hair snares, den boxes, and automatic camera stations have only yielded two possible ermine scats (see Table 1).

Table 1. Methods used and efforts expended to detect Ermine haidarum presence*
Activity Years Survey effort Results
Live traps 1992-97 6700+ days/nights 2 Ermine haidarum
Track plates 1997-98 2692 days/nights no Ermine haidarum tracks
Snow tracking 1997-98 23 km surveyed no Ermine haidarum tracks
Trap type test 2004-05 100+ days/nights 2 American Marten, 1 rat, numerous mice
Hair snares 2004-05 871 days/nights 11 samples: 8 American Marten, 3 unknown
Den boxes 2004-06 3460 days/nights 3 scats (thought to be 2 Ermine haidarum and 1 American Marten, currently being analyzed)
Marten carcasses 2003-06 Carcasses collected
from trappers for
stomach analysis
57 American Marten carcasses examined.
No ermine found in their diet.
Cameras (film) 2004-07 99 photos American Marten, American Robin (Turdus migratorius), mouse, Northern Goshawk (Accipiter gentilis laingi) , and Black Bear (Ursus americanus)
Cameras (digital) 2005-07 598 photos American Marten, Black Bear, deer, Northern Goshawk, mouse, Ravens (Corvus corax), Raccoons (Procyon lotor), Bald Eagle (Haliaeetus leucocephalus), Red Squirrel (Tamiasciurus hudsonicus), rats (Rattus spp., dogs (Canis familiaris), and cat(Felis catus)
*Data sources: Burles et al. 2008, Wijdeven, unpublished data, Reid et al. 2000.

Ermine haidarum were trapped by settlers throughout the 1900s, but never in great quantities (Buck 1998) and most occurred as by-catch in leg-hold traps set for American Marten. Of the 19 active trappers interviewed in 1997/98 only four reported ever catching an ermine (Buck 1998). Local ermine never fetched high prices on fur markets, as Haida Gwaii winters are too short and mild for high quality furs to develop. With the introduction of body-gripping traps and the move to tree-sets, ermine by-catch has been greatly reduced. All contemporary trappers, however, have observed ermine tracks in the snow. Many reported sightings and some reported bait removed by ermine (Buck 1998).

Interviews with trappers and others further indicate that Ermine haidarum numbers appear to have decreased (Buck 1998; Reid et al. 2000; Edie 2001). Edie (2001) concluded that early collection data suggested ermine were more common in the early 1900s.

On a more positive note, Ermine haidarum sightings continue to be reported: three in 2003, seven in 2004, two in 2005, six in 2006, eight in 2007, and three in 2008 (B. Wijdeven unpub. data). While the accuracy of all of these sighting could not be confirmed, observers include conservation officers, wildlife technicians, and others with established observation skills. Due to the lack of a formal reporting structure, the number of yearly sightings is likely greater than what has been communicated.

Ermine haidarum have been recorded on only four of the major Haida Gwaii islands: Graham, Moresby, Louise, and Burnaby (Figure 2). The majority of records originate from eastern parts of Graham Island and the north-east corner of Moresby Island, though this may be a reflection of human use rather than distribution of Ermine haidarum within the archipelago (Burles et al. 2004). Most of the sightings (93%; Reid et al. 2000) have occurred within the wet, hypermaritime coastal western hemlock subzone (CWHwh1) (Meidinger and Pojar 1991).

Distribution of historic Haida Ermine records on Haida Gwaii

Figure 2. Distribution of historic Ermine haidarum records (observed, trapped or tracks) on Haida Gwaii (Source: Burles et al. 2004).

The proximate factors which affect the spatial distribution of Ermine haidarum across the multitude of islands which make up Haida Gwaii are undetermined. There is no known estimate of how wide a body of water ermine are able to swim. However, islands on which Ermine haidarum have not been detected are separated by a minimum of 100 meters of water from the nearest inhabited island (Burles et al. 2004).

Ermine haidarum distribution on smaller islands is not well documented. A longhouse on SGaang Gwaii island was named for a hole in the ground frequented by an ermine (Guujaaw, pers. comm. 2003), indicating that ermine were present at least historically.

The Haida, who have lived on these islands for some 10,000 years, have been well aware of the presence of ermine. This is reflected in the number of clans which chose the ermine as a crest component. The Ninstints people of the Raven Clan, Stawaas xaad iagaii (Witch People), Naay yu aans xaada gaay (People of the Big House), Na saga xaada gaay (People of the Rotten House) and Qaay llnagaay (People of the Sea-lion town) of the Eagle Clan all incorporated ermine as a crest figure. Ermine, or “Tllga” in Haida, also occasionally found their way into Haida lore as in the SGaang Gwaii story mentioned above (Burles et al. 2004).

In spite of this rich history, there is sparse contemporary knowledge regarding the Haida relationship to Ermine haidarum (Collison 2004). It is therefore not known whether the Haida trapped ermine. During the sea otter fur-trading period, ermine pelts were a popular commodity brought to the islands as a trade item (Howay 1932). Though the head regalia of Haida Chiefs include decorations with ornamental ermine, it is impossible to determine without physical analysis whether these pelts were sourced locally or obtained as trade goods (Figure 3).

Ermine Head Regalia

Figure 3. Ermine Head Regalia. American Museum of Natural History Collection, New York.

Current habitat associations and features for Ermine haidarum are not well documented. Inferences can be made from empirical data gathered elsewhere in North America and from occurrence data collected on Haida Gwaii.

Ermine are usually classified as habitat generalists (King 1989; Fagerstone 1987; King 1983). In Washington’s Olympic Peninsula (habitat similar to that on Haida Gwaii), ermine were captured most often in thinned second-growth Douglas-fir (Pseudotsuga menziesii) stands with dense understory (Wilson and Carey 1996). Ermine in southwest Yukon were found mostly in open areas, consistent with the habitat of their main vole (Microtus spp.) prey (O’Donoghue et al. 2001). In Ontario boreal forests, ermine showed no preferences for stand age or cut vs. uncut areas (Thompson et al. 1989).

At a coarse level, some inferences can be made from the occurrence database gathered by Reid et al. (2000). Virtually all sightings of Ermine haidarum (93%, n=121) were from the Coastal Western Hemlock, Submontane Wet Hypermaritime biogeoclimatic subzone (CWHwh1), which comprises most of the eastern side of the Haida Gwaii archipelago below approximately 350 m (Figure 4). Eighty seven percent of sightings occurred within forested landscapes with 69 % from coniferous forests. Eighty eight percent of sightings were below 50 m in elevation, and 77% of sightings were within 100 m of water, usually the ocean, a creek or river (Reid et al. 2000). These results should be interpreted with caution. Most human activity occurs in areas within the CWHwh1 variant. Consequently, occurrence data may reflect human habitat use more than that of Ermine haidarum. The paucity of ermine sightings on the west coast of the archipelago may reflect low human use rather than lack of ermine. However, Mowat et al. (2000), working in northwestern Vancouver Island habitats very similar to those on Haida Gwaii, also detected few ermine (M. e. anguinae) overall and only in open, shrubby habitats in the relatively drier, eastern sections of their study area. They found no sign of ermine in the wetter and higher western sections.

Biogeoclimatic zones on Haida Gwaii

Figure 4. Biogeoclimatic subzone variants on Haida Gwaii.

Despite the biased distribution of observers in Haida Gwaii, Reid et al. (2000) conclude that the clumping of Ermine haidarum sightings is likely a fairly accurate reflection of ermine distribution. Even along major roads, sightings tended to be clumped at water courses and river mouths. Despite an extensive network of logging roads, there were virtually no records of ermine from upland sites, with only 12% of sightings located above 50 m in elevation.

Ermine habitat associations from elsewhere support these coarse level findings. Higher use in riparian areas than upland sites has been documented in the Olympic Peninsula (Wilson and Carey 1996), northern Vancouver Island (Mowat et al. 2000), and B.C.’s Okanagan Valley (Gyug 1994). Using sooted track plates and cameras in coastal western hemlock forests of northwestern Vancouver Island, Mowat et al. (2000) detected ermine in edge habitats associated with forest openings and riparian habitats. They suggest that ermine in CWH forests of northwestern Vancouver Island are “likely to be found in areas where the forest has been removed or opened naturally, in river estuaries for example” (Mowat et al. 2000). Others also note that ermine are more common in early successional stands (Simms 1979a; Simms 1979b) with low densities of regenerating trees (Sullivan et al. 2001).

Coarse woody debris has been identified as beneficial to ermine although this may be more important in areas where their main prey are voles which heavily utilize debris piles (Lisgo et al. 2002; Gyug 1994). On Haida Gwaii, potential Ermine haidarum prey appear to be more associated with herbaceous ground cover (Doyle 1990), though specifics remain unknown. Coarse woody debris imparts a degree of protection to ermine and their prey from predation by larger animals (Reid et al. 2000; Samson and Raymond 1998; Doyle 1990). Retaining and recruiting large woody debris in second-growth stands is an important aspect to forest management for ermine and other ground-dwelling wildlife species (Lofroth 1998; Stevens 1997).

The distribution of Ermine haidarum is likely best explained by a combination of prey availability and protection from predators (Burles et al. 2004) as well as specific habitat features. Based on local distribution data and ermine studies elsewhere, the following qualitative habitat features may be key to the survival and recovery of Ermine haidarum on Haida Gwaii:

The two species assumed to comprise the majority of Ermine haidarum prey, Dusky Shrew (Sorex monticolus) and Northwestern Deermouse (also known as Keen’s Mouse) (Peromyscus keeni) are associated with a diversity of habitats. Shrews may be more prevalent in moist or riparian habitats with dense undergrowth, while avoiding open fields, wet meadows, and grassland (Burles et al. 2004). The Northwestern Deermouse is found in virtually all terrestrial sites, from sea shore to alpine. Their abundance is more related to food supply than physical features of habitat (Hanley and Barnard 1999).

Food

Ermine are predominantly arvicolid rodent (vole) specialists (Fagerstone 1987). There are no voles, however, on Haida Gwaii. Native mammalian prey species are limited to Northwestern Deermouse and Dusky Shrew. Mice and shrews are less preferred by ermine where arvicolid prey are available (Fagerstone 1987; Nams 1981). Stomach, intestine and scat analyses of Ermine haidarum, though limited (n=9), have found remnants of Northwestern Deermouse (Peromyscus keeni), a small fish (gunnel or prickle back), Winter Wren (Troglodytes troglodytes), Dusky Shrew (Sorex monticolus), and a large unidentified bird (probably gull) (D. Nagorsen unpubl. data).

Though primarily vole specialists, ermine readily prey on a wide variety of food. The list of dietary items includes insects, rats, birds, fruit and berries, earthworms, and eggs (King 1983). It appears Ermine haidarum will utilise ground- and shrub-nesting bird species and their eggs as prey. However, these birds have been affected by wide-spread removal of ground cover and understory by introduced Sitka Black-tailed Deer (Odocoileus hemionus; deCalesta 1994; Vila et al. 2001). This has increased their vulnerability to nest predation not only by ermine but also by other introduced species such as red squirrels, rats, and raccoons with a subsequent reduction in the availability of birds as prey.

Ermine are not aquatic. However, they may feed on marine invertebrates in intertidal zones and scavenge post-spawning salmon, especially those moved inland by Black Bears (Reimchen 2000).

There is some indication Ermine haidarum occasionally hunt introduced Roof Rats (Rattus rattus) and Red Squirrels (Tamiasciurus hudsonicus) as alternative food sources (Reid et al. 2000). However, ermine studies elsewhere suggest that the Ermine haidarum's relatively small size may limit its effectiveness as a predator of squirrels and rats (Lisgo 1999).

The abundance of Northwestern Deermouse, and to a lesser extent, Dusky Shrew, fluctuate widely from year to year on Haida Gwaii (Burles et al. 2004). Further, high marten numbers and other introduced mammals are believed to increase competition for an already limited food source (Reid et al. 2000).

Reproduction

Ermine can reproduce in their first year and in most populations females are pregnant annually (Fagerstone 1987). Litter sizes of ermine in North America range from four to thirteen, averaging about six (Hamilton 1933 in Fagerstone 1987). Given the lack of voles and low diversity of alternate prey, mean litter sizes for Ermine haidarum may be in the lower part of the range (Edie 2001). The only data on litter size in Ermine haidarum comes from a necropsy performed on a cat-killed pregnant female. Three foetuses were present in the uterus, but it was not possible to determine foetus sex or records of previous implantation (H. Schwantje unpubl. data).

Ermine are polygamous – males breed with several females and the home range of males can contain several exclusive female home ranges (Erlinge 1977). Like most mustelids, ermine exhibit delayed implantation (King 1983). Mating may occur in the spring shortly after the young are born but implantation is delayed for nine to ten months (Fagerstone 1987). Suspected low population densities may provide limited mating opportunities, leading to demographic effects that can negatively affect population viability (Shaffer 1981). Whether reproduction is a factor limiting Ermine haidarum recovery remains uncertain. Ermine rely on high reproductive output to maintain population size since turnover of populations is generally high (King 1983). Annual survival rate elsewhere is estimated at 40% and average life expectancy is about 1 to 1.5 years (Fagerstone 1987).

Reproduction in weasels is closely tied to prey availability. Least weasels (Mustela nivalis) require minimum spring prey densities before breeding will take place (Erlinge 1974) and ermine reproduction is depressed with increased competition for food resources (Erlinge 1983). When food is limited, implantation may not proceed even if breeding occurs.

Ermine are a mid-level predator. Their abundance is closely tied to both their prey species and potential predators (Fagerstone 1987). Endemic terrestrial mammalian predators on Haida Gwaii are limited to Ermine, haidarum, American Marten, and Black Bear (Cowan 1989). Elsewhere, ermine populations play an important role in controlling prey populations (Korpimäki et al. 1991; Fagerstone 1987). On Haida Gwaii, Ermine haidarum may historically have contributed to regulation of Northwestern Deermouse populations.

The apparent association of ermine with low elevation and riparian areas in Haida Gwaii (Reid et al. 2000) suggests that there may be an association between Ermine haidarum and aquatic habitats. Ermine may partially fill the ecological niche of a water-land interface predator left vacant by the absence of American Mink in Haida Gwaii (Eagle and Whiteman 1987).

Table 2. Classification of threats and limiting factors to Ermine haidarum.
Threat Threat Level
Habitat changes brought about by introduced species High
Small range and low abundance High
Predation by native predators Medium
Competition for food Medium
Trapping Medium
Forest harvesting Low
Habitat changes brought about by introduced species

Extended isolation from other subspecies and lineages has allowed Ermine haidarum to become a unique subspecies. This isolation may also have contributed to it having become at risk. Island taxa typically have higher risk of extinction (Purvis et al. 2000; MacArthur and Wilson 1967) and introduced species can increase this risk (Diamond 1989).

Exotic species are often cited as threats to species at risk (Lawler et al. 2002). Non-native mammal species introduced to Haida Gwaii over the past 120 years (see Table 3) represent a significant ecological threat to the endemic island taxa (Engelstoft and Bland 2002; Golumbia 2000). For Ermine haidarum, introduced species likely exacerbate other threats, particularly competition for food and increased predation.

Table 3. Mammal species introduced to Haida Gwaii and possible effects on Ermine haidarum.
Species Introduced Possible effects on Haida ermine
Sitka Black-tailed Deer (Odocoileus hemionus) 1880 – 19251
  • Habitat alteration – removal of understory and ground cover leading to increased predation risk and lower habitat quality for prey.
  • As carrion, possible food source to ermine, but more available to marten.
Wapiti
(Cervus elaphus)
19292
  • Impacts may be similar to deer, but much less pronounced because of a limited distribution.
Common Muskrat
(Ondatra zibethicus)
unknown
  • Very limited food source as carrion
  • Likely insignificant impact
Red Squirrel (Tamiasciurus hudsonicus) 19473
  • Possible prey
  • Likely major food source for marten leading to increased competition and predation risk from increased marten populations.
American Beaver (Castor canadensis) 19473
  • Limited food source as carrion
  • Habitat alteration
House Mouse
(Mus musculus)
unknown
  • Prey source
Roof (Black) Rat (Rattus rattus) late 1700s ?1
  • Prey source
Brown (Norway) Rat
(Rattus norvegicus)
more recent than late 1700s1
  • Prey source
Raccoon
(Procyon lotor)
1940s1
  • Competitor for food
  • Likely preys opportunistically on ermine
Domestic Cat
(Felis catus)
unknown
  • Competitor for food
  • Preys opportunistically on ermine
Domestic Dog (Canis familiaris) unknown
  • Could prey opportunistically on ermine

1 after Golumbia (2000); 2 after Engelstoft and Bland (2002); 3 after Cowan (1989).

Sitka Black-tailed Deer, introduced between 1880 and 1925, have had some of the greatest impacts on forest ecosystems in Haida Gwaii and have affected most native species directly or indirectly. The removal of understory cover by Sitka Black-tailed Deer in Haida Gwaii (Daufresne and Martin 1997) may have particular consequences for Ermine haidarum and its prey. In coastal cedar hemlock forests ermine are typically more common in sites with substantial understory (Mowat et al. 2000; Wilson and Carey 1996). Deer carrion may provide an additional food source to ermine, but can also benefit competing species such as American Marten (Nagorsen 2006; Burles et al. 2004).

Introduced species such as Red Squirrel, Roof Rat, Brown Rat, and Common Muskrat provide additional food sources for Ermine haidarum; Reid et al. (2000) recorded observations of ermine chasing rats and scavenging a dead muskrat. These species, however, tend to be on the upper end of the scale of accessible food sizes (Burles et al. 2004; Lisgo 1999) as Ermine haidarum are significantly smaller than other ermine subspecies (Byun 1998; Eger 1990; Foster 1965). Introduced species have more notably facilitated an increase in American Marten populations, with probable resulting negative effects on ermine populations through increased competition (Nagorsen 2006; Reid et al. 2000).

Ermine haidarum may be naturally limited by prey availability and several researchers have argued that this factor, rather than predation, is what drives ermine population levels (summarised in Nagorsen 2006). The presence of introduced species competing with ermine for food thus may be an important threat.

Introduced predators also pose a threat to Ermine haidarum. Domestic Cats are known to depredate the subspecies (H. Schwantje unpubl. data; Reid et al. 2000) and anecdotal evidence suggests that Ermine haidarum were less frequently sighted at Masset Inlet (Graham Island) after Raccoons were introduced to the archipelago (J. Gifford-Brown pers. comm. 2006), though this may be caused by increased competition for limited prey rather than by predation.

Small range and low abundance

Small populations are inherently more at risk of extinction than large ones due to their vulnerability to stochastic events and other factors such as inbreeding. Ermine haidarum are therefore at increased risk of extinction as a result of their geographically limited range and low abundance (Purvis et al. 2000; Simberloff 1998).

Predation by native predators

Predation by native predators may also affect erminenumbers. Craighead and Craighead (1956 in Powell 1973) found that raptors predated approximately 70% of the post-reproduction spring ermine population in southern Michigan. This number is probably not as high in Haida Gwaii where forest birds of prey such as northern goshawk (Accipiter gentilis laingi), sharp-shinned hawk (Accipiter striatus), and northern saw-whet owl (Aegolius acadicus brooksi) are not as numerous (F. Doyle pers. comm. 2006).

Reduced cover as a result of increased deer browse likely increases risk of predation by native and non-native predators. Ermine generally prefer habitats with dense understory and ground cover (Mowat et al. 2000; Wilson and Carey 1996; Fagerstone 1987; Simms 1979a). Understory provides both habitat structure for prey species as well as visual protection and escape cover for ermine from predators, especially avian ones.

American Marten have been implicated as a factor in the presumed decline of ermine on Haida Gwaii. While fur returns specific to Haida Gwaii are not available prior to 1985 (G. Schultze pers. comm. 2003), registered trappers generally agree that marten populations have increased five- to ten-fold since the 1940s (Edie 2001; Reid et al. 2000). Due to low fur market values, few trappers are currently actively trapping marten, so local populations remain high.

Marten will prey on ermine (Jędrzejewski et al. 1995; Thompson and Colgan 1990; Weckworth and Hawley 1962), however this predation is likely opportunistic, with ermine representing a very minor prey item. Nagorsen (2006) reviewed 26 diet studies on American Marten and found that ermine remains were reported in only four studies, with a frequency of occurrence from 0.5% to 1.6% (Nagorsen 2006). Nagorsen et al. (1991) reported no ermine remains in 97 Haida Gwaii marten examined for diet analysis, and Nagorsen (2006) compared the contents of 55 marten stomachs with a re-examination of those from the 1991 study and found no evidence of ermine. Weckwerth and Hawley (1962) found no more than 0.1% of 1,758 marten scats in Montana to contain ermine remains. Edie (2001) argues that because ermine numbers are very low, even a very low level of marten predation could have a significant impact on ermine populations. However, given the current state of knowledge (Nagorsen 2006), marten predation of ermine should be considered at most a moderate threat.

Predation on Ermine haidarum during winter months on Haida Gwaii may be higher than in other populations. Snow at lower elevations across the archipelago is rare and ephemeral but Ermine haidarum still turn white, likely making them more visible to predators. Decreased vegetation cover may exacerbate this threat.

Competition for food

American Marten are likely competitors for food. Higher marten numbers on Haida Gwaii and significant diet overlap between marten and ermine likely result in less food being available to Ermine haidarum. Whether this is due to a reduction in prey numbers or to competitive exclusion is currently unknown.

Trapping

Trapping has been closed to ermine on Haida Gwaii since 1985 but Ermine haidarum are still occasionally captured in traps set for marten. Since it is likely not all incidents are reported, rates of annual bycatch rate are unknown. Based on conversations with trappers, rates were thought to be minimal (G. Husband and J. LaRose pers. comm. 2004). However, the introduction in 2007 of certified marten traps which comply with the Agreement on International Humane Trapping Standards coincided with the by-catch kills of five Ermine haidarum. While it is too early to determine whether the new traps are responsible for this sudden increase in reported Ermine haidarum by-catch, trapping continues to present a threat.

Forest harvesting

Approximately 25% of CWHwh1 forests on Haida Gwaii have been logged or are included in existing logging plans (A. Cober pers. comm. 2003). However, given the broad habitat associations of ermine and the possibility of increased abundance of mice, shrews, and songbirds in early successional forest stands, logging is not thought to be a major threat to Ermine haidarum.

Forest harvesting may indirectly negatively affect Ermine haidarum. Deer browse limits regeneration of forest stands and reduces ground cover. If deer browse increases in recent cutblocks, this may leave ermine at greater predation risk due to loss of protective cover.

The following recovery and management actions for Ermine haidarum have occurred or have been initiated to date:

Effective recovery of the Ermine haidarum will be hampered by a substantial lack of information regarding the species. Population dynamics, habitat requirements, prey selection, and threats are inferred rather than observed. Substantially more information is required to enable effective recovery efforts.

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