Occurrence of amphibians in British Columbia north of 57[degrees]N.
Key words: Ambystoma macrodactylum, Anaxyrus boreas, Boreal Chorus Frog, Columbia Spotted Frog, distribution, Lithobates sylvaticus, Long-toed Salamander, northern British Columbia, Pseudacris maculata, Rana luteiventris, Western Toad, Wood Frog
Five amphibian species are known to occur in British Columbia (BC) north of 57[degrees]N: Western Toad, Anaxyrus boreas; Boreal Chorus Frog, Pseudacris maculata; Columbia Spotted Frog, Rana luteiventris; Wood Frog, Lithobates sylvaticus; and Long-toed Salamander, Ambystoma macrodactylum. To date, the limited data on the occurrence of amphibians in BC north of 57[degrees]N (Matsuda and others 2006) have been applied subjectively and inconsistently in the compilation of range maps (Stebbins 2003; Jones and others 2005; Corkran and Thorns 2006) based on historical knowledge (for example, Hodge 1976), naturalist accounts and reports, and observation records from a database maintained by the Conservation Data Centre of the BC Ministry of Environment. Point occurrences are predicted to underrepresent ranges in remote regions that have not been systematically or thoroughly surveyed. Resulting interpretive range polygons may thus be inaccurate due to erroneous assumptions having been made about range limits and gaps.
I have previously contributed unpublished amphibian occurrence records to the BC Ministry of Environment's database for BC north of 57[degrees]N (Matsuda and others 2006; occurrences to 2004) and I suggested range extrapolation polygons to Stebbins (2003). Here I provide a comprehensive documentation of recent amphibian records from northern BC, current to 2012. Areas that were searched, and in which a targeted species was not found, are noted. My data not only provide a source for future range mapping, but can also be an important resource for conservation status assessment. Amphibians face many threats globally and are declining more rapidly than are either birds or mammals (Stuart and others 2004). Areas of occupancy and extent of occurrences are essential data for determining the conservation status of species (IUCN Standards and Petitions Subcommittee 2013).
The study area is BC north of 57[degrees]N latitude. This is part of the most remote, inaccessible, and sparsely populated region of the province. Its remoteness and small human population, and the insufficient resources that have been allocated to this region by the Provincial Government, have contributed to the under-sampling of the amphibian fauna, about which little is known. My amphibian surveys took place near the following road corridors: the Alaska Highway (BC Highway 97, Yukon Highway 1); the Stewart-Cassiar Highway (BC Highway 37); and the South Klondike Highway (BC Highway 2); by boat access along lake corridors (Tagish, Atlin and Teslin lakes); and through hiking access (Chilkoot Trail National Historic Site). These efforts were supplemented by reports of the occurrence of species, or by specimens submitted to me by various individuals.
I compiled a database from published and unpublished sources exclusive of historical data presented by Matsuda and others (2006). However, some records have been replicated in unpublished reports and publications, but original field notes were used to confirm the coordinates of all my personal observations. I ranked the reliability of each record employing the following criteria: (1) museum specimen, photo, or detailed sighting by an experienced observer; or (2) sighting by an observer with indeterminate or limited qualifications.
Unpublished sources consulted for data on the species occurring in the focal area were: Gartner Lee Limited (2008), Houwers (2000), Mennell (1997), Mennell and Slough (1998), Slough (2004, 2005a, 2005b), Slough and others (2002), and Thompson (2003). Columbia Spotted Frog data collected by Slough and others (2002) were published in part by Slough (2002). Western Toad data from various sources, including new occurrences, were published by Slough (2009). Recent Wood Frog collections were made by Lee-Yaw and others (2007), and Long-toed Salamander collection sites were reported by Thompson (2003). Additional data on observations and specimens not reported or published were assembled from my surveys and from reports or specimens submitted to me by observers. Dedicated amphibian surveys typically employed visual encounter surveys and dipnetting of terrestrial, semi-terrestrial (wetland), and aquatic habitats (Crump and Scott 1994; Thorns and others 1997).
An assessment of each of the 5 amphibian species known to occur in BC north of 57[degrees]N latitude is discussed below.
RESULTS AND DISCUSSION
The Wood Frog was found in all of the areas searched (Fig. 1), supporting the statements of Matsuda and others (2006), who described the distribution of this species as encompassing northern BC. Gaps in the mapped occurrences (Fig. 1) are confidently attributable to lack of survey effort rather than to the absence of this species from those areas.
Boreal Chorus Frog
No new records are reported for the Boreal Chorus Frog in northern BC; however, there is strong evidence for its wider occurrence there. Its range was described by Matsuda and others (2006) as encompassing the Peace River region, although 3 of the locations near Fort Nelson are situated in the Liard and Hay River basins (Fig. 2). In Alberta, there are records further east on the Hay River (Russell and Bauer 2000). In the Yukon, the species is found near the La Biche River, a tributary of the Liard River less than 5 km north of the BC border (shown on Fig. 2; Slough and Mennell 2006; 60.04[degrees]N, -123.97[degrees]W), and in the Northwest Territories this species is considered common and widespread at least as far north as the South Nahanni River (on the Liard River at approximately 61[degrees]N; NWTENR 1998). This species has also been found near Fort Liard, Northwest Territories, 46 km northeast of the Yukon location and 34 km from the BC border (60.30 [degrees]N, -123.32[degrees] W; Schock and others 2009). It is highly probable that the Boreal Chorus Frog occurs in other locations east of the Rocky Mountains in the Liard and Hay River drainages.
There are several verified observations and specimens of the Long-toed Salamander from locations in, and east of, the Coast Mountains in northwestern BC (Fig. 3). These observations extend as far north as the Nakina River (59[degrees]N) in the upper Taku River basin. An unverified report of Long-toed Salamander eggs (Houwers 2000) was made further north near Atlin Lake (59.2[degrees]N). Matsuda and others (2006) show 5 locations for the Long-toed Salamander as far north as 57.44[degrees]N (Fort Ware) in the Rocky Mountain Trench and 58.7[degrees]N in the Coast Mountains. The known distribution in Alberta reaches its northern limit on the Peace River just east of the BC border (Russell and Bauer 2000), compatible with the BC distribution. There are also unconfirmed sightings in the Fort Liard area of the Northwest Territories (60.24[degrees]N, -123.48[degrees]W), approximately 25 km north of the BC border (NWTENR 2006).
Columbia Spotted Frog
In agreement with Matsuda and others (2006), the Columbia Spotted Frog occurs across northern BC west of the Rocky Mountains (Fig. 4). A recent observation in the Hyland River area on a lake that straddles the BC-Yukon border (see Fig. 4; Slough and Mennell 2006) extends the north-central range of this species in BC. The species was not found during a survey of the Teslin Lake area or during numerous surveys of the Tagish Lake area, suggesting that significant gaps in the distribution of this species occur at the northern edge of its range.
The Western Toad was found to be very common and widespread in northern BC (Fig. 5), being encountered in all areas surveyed except for the Teslin Lake watershed, in which there is an apparent gap in distribution. The unverified acoustic observation east of Teslin Lake should be considered questionable, because the site has been surveyed 4 times subsequently with no further encounter. Furthermore, Western Toads in this region do not possess a vocal sac necessary for producing loud advertisement calls (as they do in much of Alberta; Pauly 2008; Long 2010); rather they emit a quiet series of chirps like the peeping of a chick. These calls are sometimes referred to as release calls (Russell and Bauer 2000), although they may be used for other purposes such as advertisement. Release calls have been heard by the author at the Atlin Warm Springs, in the present study area, where they attenuate rapidly beyond about 50 m. Additional locations were found in the Liard River basin, and it has also been reported from the Liard River basin in the Northwest Territories (NWTENR 2006). Western Toads are likely absent from the extreme northeast, based on similar findings for adjacent regions of Alberta (Russell and Bauer 2000) and the Northwest Territories (NWTENR 2006; Schock and others 2009).
The ranges of amphibians of northern BC were heretofore incompletely understood, largely as a result of the lack of survey effort. This lack of effort has sometimes been misinterpreted as being indicative of gaps in the distribution of particular species. The occurrences presented in this paper have increased our knowledge of amphibian species ranges in northern BC. The Western Toad, Columbia Spotted Frog, and Long-toed Salamander are more widespread than was previously recorded. Evidence suggests that the Boreal Chorus Frog is also more widespread. The accepted ubiquitous presence of the Wood Frog is supported.
Examples of amphibian range polygons that are inaccurate are those for the Western Toad in Wind and Dupuis (2002) and Jones and others (2005). COSEWIC (2012) used data from this project to update the range map. Stebbins (2003) gives the most accurate depiction of the northern range of the Western Toad, although the species is now known to occur in the Liard River basin of the Northwest Territories (NWTENR 2006). The range of the Boreal Chorus Frog is likely not discontinuous in northern BC as given by Jones and others (2005). These data will also be useful for producing more accurate point occurrence maps for BC amphibian field guides (for example, Matsuda and others 2006; Ovaska and Govindarajulu 2010).
Data upon which this project is based have been contributed to and are available from the BC Ministry of Environment and the author.
I thank all those who submitted observations including M Connor, Taku River Tlingit First Nation; K Heinemeyer, Round River; D Cresswell, Carcross/ Tagish First Nation; D van de Wetering, Canadian Wildlife Service; R Rivard, Parks Canada; S Badhwar; E Miskey; G Dick; D Lacroix; and K Rees. I was accompanied in the field by L Ash, L Mennell, M Dunn, M Milligan, K Slough, K Schmok, and C Hedgecock (Parks Canada). D Demarchi, Ecosystem Information Section, BC Ministry of Environment, supplied BC occurrence data. Maps were produced by M Leung. K Lohman, B Matsuda, and A Russell reviewed the draft manuscript.
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Submitted 12 December 2012, accepted 30 June 2013. Corresponding Editor: Kirk Lohman.
BRIAN G SLOUGH
35 Cronkhite Road, Whitehorse, YT Y1A 5S9 Canada
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|Author:||Slough, Brian G.|
|Publication:||Northwestern Naturalist: A Journal of Vertebrate Biology|
|Date:||Dec 22, 2013|
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