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BC Conservation Data Centre: Conservation Status Report

Contia tenuis
Common Sharp-tailed Snake



 
Scientific Name: Contia tenuis
English Name: Common Sharp-tailed Snake
English Name Synonyms: Sharp-tailed Snake
   
Provincial Status Summary
Status: S1S2
Date Status Assigned: January 16, 2012
Date Last Reviewed: March 30, 2018
Reasons: Found in a few locations within dry woodlands in the Gulf Islands and southeastern Vancouver Island - regions which are rapidly being developed. Since 2011, there have been confirmed sighting of Sharp-tailed Snake in the Pemberton area, which has significantly increased the known range of this species. The threats remain high and should be re-assessed if more snakes are discovered.
 
Range
Range Extent: D = 1,000-5,000 square km
Range Extent Comments: 2017: Sharp-tailed Snake occurs in southwestern B.C., from southern Vancouver Island and the Gulf Islands (North and South Pender, Saltspring, Galiano), and near Pemberton on the mainland. There is also an unverified historical record near Chase (B.C. Ministry of Environment 2015k). 
2011: based on mapped occurrences, the CDC calculated the range to be 3,660 km squared 
2009: 995 km2 (COSEWIC 2009e).
2007: known from southern Vancouver Island and the southern Gulf Islands, the current range is roughly 300 km square. There is a specimen recorded from McGillivray Lake (Spalding 1995) and near Chase in the southern interior (Gregory and Campbell 1984; Spalding 1995) that is not included in the range estimate.
Area of Occupancy (km2): BE = 2-125
Area of Occupancy Comments: 2017:
2015: 132km2 (33 2x2 grid cells) (B.C. Ministry of Environment 2015k). 
2011 - 112 km2 (28 2x2 grid cells), based on calculations done by B.C. CDC
2009: 96km2 (24 2x2 grid cells) (COSEWIC 2009e)
2007: the area of occupancy of populations verified since 1996 on the southern Gulf Islands and Vancouver Island is around 40km square based on 10 occurrences if calculated using a 2km square grid.
 
Occurrences & Population
Number of Occurrences: C = 21 - 80
Comments: Since 1996 the Sharp-tailed Snake has been confirmed at several sites on the Southern Gulf Islands and southern Vancouver Island. As of 2017, the B.C. CDC has 27 occurrences mapped.The 1857-61 specimen is labeled Vancouver Island, but it is not clear why the collection site is thought to be Cowichan District (Spalding 1995). On North Pender Island, attempts to verify the existence of a population at the location of the 1949 sighting were made between 1996 and 1999 (Engelstoft and Ovaska 1998) but were not successful. However, the Magic Lake population on North Pender Island has been monitored since 1996. On South Pender a population on Spalding Road was verified and a new discovery was made next to Brooks Point, 2.2 km away. On Saltspring Island the snake is found in several places in Vesuvius and surrounding areas. It has not been possible to confirm the site where it was first found (Spalding 1995) because the exact location is unknown. A snake was found on the north tip of Saltspring Island in 2003. It has not been possible to verify the population that was allegedly found on Galiano Island (Spalding 1995). Two specimens were said to be collected at McGillivray Lake in the southern Interior (Spalding 1995), but this population's existence needs to be confirmed. In 2011, a confirmed sighting of a Sharp-tailed Snake was found in the Pemberton area (L. Anthony pers. comm. 2011) and there have been additional records in the area since that time (B.C. Ministry of Environment 2015k).
Number of Occurrences with Good Viability / Ecological Integrity: Rank Factor not assessed
Number of Occurrences Appropriately Protected & Managed: CD = 4 - 40
Comments: Under Canada?s Species at Risk Act, the Sharp?tailed Snake is listed as Endangered on Schedule 1, the official list of wildlife species at risk. At present, the provisions of the Act apply to federal lands where the species occurs: two Department of National Defence properties and a National Research Council property on Vancouver Island; and a National Park on South Pender Island (COSEWIC 2009e). Other other occurrences are within Provincial Parks, Capital Regional District parks, Municipal Parks and lands holding conservation covenants (B.C. Ministry of Environment 2015k).
Population Size: CD = 250 - 2,500 individuals
Comments: With its diminutive size and secretive behaviour (fossorial and nocturnal tendencies), this species is easily overlooked unless specifically sought. Based on the assumption that the population at each of 17 known localities have 30 adults, the total miminum number is 510 with an upper value of probably much less than 2500 (COSEWIC 2009e). The number of Sharp-tailed Snakes appears low when compared with the number of garter snakes. 2011: with the discovery of a snake in the Pemberton area, the population is likely higher. More inventory is needed to determine the population size.
 
Threats (to population, occurrences, or area affected)
Degree of Threat: B = High
Comments: 2017: The overall, province-wide Threat Impact for this species was scored ?High.? Major threats include expansion of housing and urban areas, which results in habitat loss and degradation, and roads, which fragment habitat, constrain movements, and can result in roadkill (B.C. Ministry of Environment 2015k)

2012:The most serious threat to the Sharp-tailed Snakes is habitat loss and degradation (Ovaska 2004). It appears that the species can coexist with humans in rural settings where essential habitat features remain. However, current developments in and around known sites do not protect habitat and could decrease probability of persistence of these populations. For example, a talus slope thought to be important for this species was destroyed in Metchosin, Southern Vancouver Island. With increases in human population, accidental mortality from development, roadkill, predation by domestic cats, and other sources such as molluscicides, pesticides and direct persecution also increase (Ovaska 2004). Habitat fragmentation could also pose a threat to this species. If juveniles disperse from natal sites, then fragmentation resulting from human encroachment will severely restrict recruitment into populations. The small number of juveniles found at monitored sites supports the suggestion that fragmentation is decreasing juvenile recruitment rates (P. Govindarajulu, pers. comm. 2007). Because of the discovery of an individual snake in 2011 well outside of it's previously known range, the threats should be re-assessed if more are found.
 
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: FG = Decline of <30% to relatively stable
Comments: 2017: From B.C. Ministry of Environment (2015): Trends are poorly known and difficult to study due to the secretive habits of these snakes and their localized distribution patterns. From 1997 to 2002, capture re-capture studies occurred at four sites - one site each on Saltspring and North Pender and two sites on Vancouver Island. Over this 6-year period,  this population was estimated to be stable or slightly declining (Govindarajulu et al. 2011).

2012: The range of this species is in the Gulf Islands and southern Vancouver Island which are undergoing rapid development. Residential and other forms of human encroachment lead to sharp declines in suitable habitat for this species. Population declines are difficult to detect in the absence of long-term monitoring. The only population that has been monitored from 1997 to 2005 is at Magic Lake on North Pender Island. The population here appears to be slightly declining although 95% confidence intervals just overlap (0.89 (95% CI: 0.79 to 1.1). In this study, small juveniles were almost never recaptured which suggests either high juvenile mortality or dispersal of the juveniles from natal sites. High survival rates of adults may mask ongoing long-term demographic decline due to low juvenile recruitment rates (P. Govindarajulu, pers. comm. 2007).
Long-Term Trend: U = Unknown
Comments: Unknown. There is not enough historical data to determine a trend.
 
Other Factors
Intrinsic Vulnerability: B=Moderately vulnerable
Comments: We have a poor understanding of the snakes' reproductive biology, and very few females have been found with eggs. Estimated time to maturity of female Sharp-tailed snakes in BC is five years. Although no nests or clutches have been found, palpitation of gravid females to count the number of eggs through the abdominal wall suggests approximate mean clutch size of 3.6 ± 1.1 eggs (mean ± SD). There is also an indication that females do not breed every year in BC. These life-history traits may limit rapid recovery of declining populations (P. Govindarajulu, pers. comm. 2007).
Environmental Specificity: B=Narrow. Specialist or community with key requirements common.
Comments: It appears that the Sharp-tailed Snake can live in several different types of habitat, but egg laying sites might be of special importance.
Other Rank Considerations:
 
Information Gaps
Research Needs: "Research is needed to clarify threats from road mortality and to fill in data gaps on habitat use, genetic structure of populations, demographic patterns, and life history. The most urgent need is to collect information necessary to identify critical- habitats, including seasonal pattern of habitat use, movements, and important micro- and macro-habitat features" (Sharp-tailed Snake Recovery Team 2008).
Inventory Needs: Efforts to extend its known range on Vancouver Island should be initiated. There should also be inventory techniques developed to identify nest sites and over-wintering areas. Efforts should be made in the McGillivray Lake area to verify the existence of this population (Ovaska 2004); this should be a high priority.
 
Stewardship
Protection: Considering that most of the known populations are found on private land, mechanisms to protect these populations should be promoted (Ovaska 2004).
Management: Areas where there are dens, important foraging areas or concentrations should be protected. Life history requirements such as nesting and over wintering needs, dispersal routes and potential prey species preferences need to be determined to help establish conservation and stewardship priorities.
 
Version
Author: Engelstoft, C., P. Govindarajulu and L. Gelling
Date: March 30, 2018
 
References
Brodie, E., R. Nussbaum, and R. Storm. 1969. An egg-laying aggregation of five species of Oregon reptiles. Herpetologica 25(3):223-227.
COSEWIC. 2009e. COSEWIC assessment and status report on the Sharp-tailed Snake Contia tenuis in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 38 pp. www.sararegistry.gc.ca/status/status_e.cfm).
Engelstoft, C. and K. Ovaska. 1999. Sharp-tailed snake study on the Gulf Islands and southeastern Vancouver Island, March-November 1998. Final Report. Prepared for the Ministry of Environ., Lands and Parks, Vancouver Island Regional Office.
Govindarajulu, P., L.-A. Isaac, C. Engelstoft, and K. Ovaska. 2011. Relevance of life history parameter estimation to conservation listing: case of the Sharp-tailed Snake (Contia tenuis). J. Herpetol. 45:300?307
Gregory, L.A., and P.T. Gregory. 1999. The Reptiles of British Columbia, A taxonomic catalogue. B.C. Minist. Environ., Lands and Parks, Victoria. Wildl. Bull. B-88. 28pp.
Gregory, P.T., and R.W. Campbell. 1984. The Reptiles of British Columbia. Royal B.C. Mus. Handb. 102pp.
Ovaska, K.E., and C. Engelstoft. 1998. Status Report on the Sharp-tailed Snake, Contia tenuis Baird and Girard, in Canada. Draft rep. submitted to Comm. on the Status of Endangered Wildl. in Can. 29pp. plus figures.
Sharp-tailed Snake Recovery Team. 2008. Recovery Strategy for the Sharp-tailed Snake (Contia tenuis) in British Columbia. Prepared for the B.C. Ministry of Environment, Victoria, BC. 27 pp.
Spalding, D.J. 1993. Status of the Sharp-tailed Snake in British Columbia. B.C. Minist. Environ., Lands and Parks, Wildl. Branch. Working Rep. WR-57. 15pp.
Storm, R.M., and W.P. Leonard, eds. 1995. Reptiles of Washington and Oregon. Seattle Audubon Soc., The Trailside Ser., Seattle, WA. 176pp.
 

Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.

Suggested Citation:

B.C. Conservation Data Centre. 2018. Conservation Status Report: Contia tenuis. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Mar 29, 2024).