Amphibian population and pathogen surveys in the Dehcho and Sahtu, Northwest Territories, 2007 and 2008
Dates
Year
2009
Citation
Schock, Danna Michelle, 2009, Amphibian population and pathogen surveys in the Dehcho and Sahtu, Northwest Territories, 2007 and 2008: Dept. of Environment and Natural Resources, Govt. of the Northwest Territories, 1 online resource (xvi, 106 p.).
Summary
Five species of amphibians, all anurans, are known to occur in the Northwest Territories (NT): wood frogs (Rana sylvatica = Lithobates sylvaticus; Family Ranidae), northern leopard frogs (Rana pipiens = Lithobates pipiens; Family Ranidae), western toads (Bufo boreas = Anaxyrus boreas; Family Bufonidae), Canadian toads (Bufo hemiophrys = Anaxyrus hemiophrys; Famiily Bufonidae) and boreal chorus frogs (Pseudacris maculata; Family Hylidae). Of these five, wood frogs, western toads, and boreal chorus frogs, are known from the Dehcho whereas wood frogs and boreal chorus frogs are known from the Sahtu. Baseline information on species distribution and abundance is key to identifying and then addressing declines on regional and local [...]
Summary
Five species of amphibians, all anurans, are known to occur in the Northwest Territories (NT): wood frogs (Rana sylvatica = Lithobates sylvaticus; Family Ranidae), northern leopard frogs (Rana pipiens = Lithobates pipiens; Family Ranidae), western toads (Bufo boreas = Anaxyrus boreas; Family Bufonidae), Canadian toads (Bufo hemiophrys = Anaxyrus hemiophrys; Famiily Bufonidae) and boreal chorus frogs (Pseudacris maculata; Family Hylidae). Of these five, wood frogs, western toads, and boreal chorus frogs, are known from the Dehcho whereas wood frogs and boreal chorus frogs are known from the Sahtu. Baseline information on species distribution and abundance is key to identifying and then addressing declines on regional and local scaales. The amphibians that occur in the NT, and those that potentially occur in the NT, tend to be widespread species at the northern edges of their ranges. While some information exists on these species elsewhere in their respective ranges, information for NT populations is incomplete. This is of immediate concern for two species in the NT, northern leopard frogs and western toads because they require multi-jurisdictional management plans under the federal Species at Risk Act. There were four objectives for the project:iv • Improve our understanding of the distribution and abundance of all amphibian species found in the Dehcho and Sahtu Regions. • Collect recent data on western toads and northern leopard frogs to aid in developing NT information for implementation of the federal Species at Risk Act. • Collect information on amphibians for the Protected Areas Strategy by confirming species presence in proposed protected areas in the Dehcho. • Provide information on the presence of infectious diseases in NT populations of amphibians, particularly chytrid fungus and ranaviruses, which are implicated in amphibian population declines worldwide. A total of 47 sites were visited in 2007 (28 in the Dehcho, 19 in the Sahtu). No amphibians were encountered at 11 sites (4 in the Dehcho, 7 in the Sahtu). Or, stated otherwise, 77% (36/47) of sites were inhabited by amphibians overall, with 86% (24/28) of sites inhabited in the Dehcho and 58% (11/19) inhabited in Sahtu. In 2008, a total of 40 sites in Dehcho were visited. Of these 40 sites, no amphibians were encountered at 7 sites; or, 83% (33/40) sites were inhabited by amphibians. No calculations were made for the Sahtu in 2008 due to the nature of the site visits. Wood frogs were found at several sites in the Dehcho and Sahtu, including Nahanni National Park Reserve (NPR), and were detected at all sites where amphibians were detected. Western toads were detected at two sites near Ft. Liard, including one site where tadpoles were found both years. The breeding site is within a gravel pit areas that is frequented by all-terrain-vehicle users. Western toads were not found in Nahanni NPR despite focused efforts to verify reports of the species in the Yohin Lake area. Boreal chorus frogs were found at several sites in the Dehcho although not in Norman Wells, as suggested they would be by widely available distribution maps. During surveys in 2007 and 2008, a total of 396 wood frogs (223 tadpoles, 173 frogs), 61 boreal chorus frogs (51 tadpoles, 10 frogs), and 99 western toads (95 tadpoles, 4 frogs) were screened for chytrid fungus and ranaviruses. Both chytrid fungus and ranaviruses were detected in amphibian populations in the NT, greatly extending the known range of both pathogens. Although ranaviruses were found widely, including in Norman Wells, they were detected only in wood frogs. In contrast, chytrid fungus was found in only the Ft. Liard area but was detected in all three species of amphibians. Detection of chytrid fungus in the Dehcho is not congruent with current predicted distribution ranges based on niche models, and further research is needed to determine what is permitting the pathogen to persist in the area. The identity of the ranavirus detected in our study was confirmed to be Frog Virus 3 by sequence analysis of the major capsid protein gene and shares 99%+ similarity in that area of the genome to ranaviruses isolated from wood frogs elsewhere in North America. As well as chytrid fungus and ranaviruses, a single wood frog was found with a malformed hind foot, and several wood frog tadpoles were found in Norman Wells that appeared to have a white fungal growth associated with the cloaca. The identity of the infectious agent is not resolved but does not appear to be Saprolegnia. Several recommendations arise from the findings of this project. Among the recommendations are an investigation into the feasibility of a coordinated, vi long-term monitoring program at even a modest number of locations – Ft. Liard, Ft. Simpson and Norman Wells, for example. A program would be valuable in terms of understanding the biology of northern amphibian populations. In addition to monitoring populations over the longer term, thereby providing important baseline information, these programs could also resolve whether or not boreal chorus frogs occur in the Norman Wells area. Second, concrete or rock obstacles should be installed in and around western toad breeding habitats to prevent destruction due to ATV’s and other motorized vehicles. Third, until visual proof of northern leopard frogs is obtained from the Dehcho, its occurrence there should be classified as unconfirmed. If northern leopard frogs are eventually located in the Dehcho, genetic work is recommended to test whether they are endemic to the area or if they may have been translocated from elsewhere, possibly as a result of use as fish bait. Fourth, any future pathogen screening that involves the widely used protocol swabs should store swabs in the freezer as soon as possible or put the swabs directly into a lysis buffer that is thermally stable at the temperatures likely to be encountered in the field. Finally, field hygiene protocols should be adopted that prevent the incidental translocation of pathogens among sites. These protocols should not be limited to workers directly involved with amphibians because pathogens can be spread by anyone.
