Recovery strategy for the Eastern ribbonsnake (Thamnophis sauritus), Atlantic population in Canada
6. Critical habitat
- 6.1 Rationale for partial critical habitat identification
- 6.2 Identification of critical habitat
- 6.3 Schedule of studies to identify critical habitat
- 6.4 Examples of activities likely to result in destruction of critical habitat
Critical habitat is defined in the Species at Risk Act (S.C. 2002, c.29) as “…the habitat that is necessary for the survival or recovery of a listed wildlife species and that is identified as the species’ critical habitat in the recovery strategy or in an action plan for the species” (s. 2(1)). Critical habitat for the eastern ribbonsnake is identified below, to the extent possible, using the best available information. However, at this time, sufficient information is available for only the partial identification of critical habitat and it is recognized that that this may be insufficient to achieve the population and distribution objectives for the species. Included below is a summary of the rationale for partial identification, followed by the identification of critical habitat which includes a summary of the approach and guidelines employed. The schedule of studies (section 6.3) outlines the activities required to identify additional critical habitat necessary for the recovery of the species.
6.1 Rationale for partial critical habitat identification
This is a partial identification of critical habitat. The current distribution of ribbonsnakes is still being ascertained. In particular, the assessment of wetlands used by ribbonsnakes is incomplete, and the terrestrial use by ribbonsnakes for overwintering and movement among concentrations is poorly understood. As such, the precautionary approach is employed to identify critical habitat in wetlands and immediately adjacent terrestrial areas based on the best available current knowledge.
Describing critical habitat for the eastern ribbonsnake is challenging since little is known about the distribution, population trends, densities or habitat requirements in Nova Scotia. Additionally, the detectability of ribbonsnakes is low and may be influenced by season, weather, and habitat conditions. This may confound the interpretation of visual survey results; ribbonsnakes present in significant numbers in an area could be missed by occasional surveys. Despite fairly high search effort over the last several years (>5000 person hours over 50+ waterbodies), only five sites with a high density of ribbonsnake sightings (>50 sightings) have been identified. For most of the remaining areas there are less than ten sightings per waterbody (Table 7). There are many possible interpretations for this observed distribution pattern, including: 1) snake densities may fluctuate greatly over time at all sites; 2) snakes may exist in high densities in these areas but were not seen due to little or no search effort, effort in the wrong place, effort under sub-optimal conditions (weather, season), or lower detectability due to the habitat; 3) snakes may naturally exist in low densities in these habitats; 4) snakes may be declining at these sites due to unidentified threats.
Overwintering habitat for ribbonsnakes is poorly understood. Laboratory experiments have shown that they can endure immersion in water for extended periods of time so it is possible that at a portion of the population overwinters in the wetlands within habitats that are at least temporarily flooded (Todd et al. 2009, Todd 2007). Still, there is evidence that ribbonsnakes overwinter in terrestrial habitats well away from wetlands (Nova Scotia ribbonsnake database, 2010). The extent of terrestrial habitat use is unknown. It is certainly possible that terrestrial areas are a very important component of critical habitat for ribbonsnakes. Until this is more thoroughly understood critical habitat can only be partially identified.
Critical habitat for the species will be identified based on an occupancy approach and the precautionary principle. Although little is known about ribbonsnakes in Nova Scotia, their occurrence has been confirmed at a number of locations on three watersheds in the province (Table 7). Location data include: historic sightings (1950-1997), current unconfirmed sighting reports (1998-2009), current general observations (1998-April 2010), sightings from snake-specific search efforts (2004-April 2010), and sightings incidental to Blanding’s turtle research (1999-2009). The majority of the sightings, particularly those resulting from snake-specific search effort and Blanding’s turtle research, can be pinpointed to specific sites (within 20 m or less).
Critical habitat identification will be based on known currently occupied locations (confirmed sightings within the last 10 years). Because ribbonsnakes are difficult to locate, a single recent, confirmed sighting is considered to be enough to suggest that a concentration of ribbonsnakes likely exists at that location.
6.2 Identification of critical habitat
Critical habitat will encompass all wetlands falling within an identified location as well as the terrestrial and aquatic zone that extend 100 m around each wetland. This is not a buffer zone; it is fundamentally part of the critical habitat used by ribbonsnakes and their prey. The location is the geographical place where ribbonsnakes occur (e.g., the entire lake, fen or bog, or selected portions of a river or stream). Although locations in their entirety are not identified as critical habitat, they are both functional ecological units and recognized political units; identifying these locations will facilitate management and recovery. All wetlands within the location will be included in critical habitat identification based on the precautionary principle and the reasonable inference that ribbonsnakes, if found in one wetland, are also likely to be found in other wetlands within that location. This reflects a balance between a minimal identification of critical habitat at wetlands where they have been observed and the identification of all wetlands within the range providing suitable habitat. Given the low detectability of ribbonsnakes it is reasonable to suspect that ribbonsnakes occur in adjacent wetlands at the same location (waterbody).
In this strategy, wetlands are defined according to the accepted legal definition in the Nova Scotia Environment Act (S.N.S. 1994-95, c. 1) which states that “‘wetland’ means land commonly referred to as a marsh, swamp, fen or bog that either periodically or permanently has a water table at, near or above the land’s surface or that is saturated with water, and sustains aquatic processes as indicated by the presence of poorly drained soils, hydrophytic vegetation and biological activities adapted to wet conditions” (s. 3(bg)). Eastern ribbonsnakes have been found in a variety of wetland types and very little is currently known about their ecology. Some of the more typical wetland habitats in which ribbonsnakes have been found are described in Section 1.8, and include, but are not limited to, slow flowing water, abundant aquatic and terrestrial vegetation, and the presence of shallow pools and side channels.
The zone extending 100 m out from the edges of the wetlands is part of critical habitat for ribbonsnakes. It recognizes occasional use of terrestrial habitats by ribbonsnakes, including travel to and from, and use of, hibernacula in forested areas adjacent to wetlands. Moreover, the one confirmed hibernacula at the time of writing is 155m from the closest adjacent wetland. Eleven ribbonsnakes were identified in this area between mid-November 2009 and late March 2010. Several other sightings in late spring and early fall, of up to 140 m away from the wetlands, have indicated that this isn't the only inland hibernacula. More study is required to better define this usage. This component of critical habitat also includes the incorporation of difficult to define wetland edges, seasonal flooding zones, vernal pools, beaver channels, and other areas that may not fit into the traditional definition of wetlands but do, on occasion, provide seasonal habitat for ribbonsnakes. Finally, this is consistent with literature of other semi-aquatic reptiles and amphibians with respect to habitat use adjacent to the aquatic component of wetland areas (Semlitsch and Bodie 2003, Semlitsch and Jensen 2001).They recommend including areas ranging from 164-304m from the edge of the wetland. The use of 100m for ribbonsnake critical habitat in Nova Scotia is conservative. This number may have to be revised once terrestrial habitat use by ribbonsnakes adjacent to wetlands is better understood.
6.2.1 Guidelines for delineating critical habitat
Critical habitat was mapped at each location, using the guidelines for mapping critical habitat, outlined in Table 6. Maps show the approximate boundaries of the location and the critical habitat areas (as of April 15, 2010). A summary of locations is presented in Table 7.
Critical habitat was mapped based on existing wetland spatial geographic information system (GIS) data provided by the Nova Scotia Department of Natural Resources (Figures figure6 and figure7). This dataset does not necessarily contain all wetlands that fall within the above wetland definition (e.g. vernal pools, treed bogs and other small wetlands may not by identified as such on the existing spatial data) and that the extent of wetlands varies seasonally. Current ribbonsnake sightings at the water's edge that did not fall within a wetland polygon in the spatial dataset, are indicated with a 200m buffer. This was done to help us deal with resolution challenges for identifying small wetlands in the spatial dataset.
Currently known critical habitat locations are identified in Table 7 and the location and extent of critical habitat is shown in Figure 8. A fine-scale version of Fig. 8 is available and more detailed information will be provided to affected parties upon request.
Table 6. Guidelines for mapping ribbonsnake locations.
Only include locations with current confirmed sightings occurring near waterbodies:
- Sightings were considered confirmed if reported by a knowledgeable observer (e.g., researcher, park interpreter, experienced volunteer) or if supporting evidence was provided (e.g., photograph, specimen).
- Current sightings are those that occurred from 1998- April 2010).
- Sightings >100m from a waterbody were not incorporated at this time due to lack of knowledge of terrestrial habitat requirements.
- Locations with only unconfirmed reports and/or historical sightings were added to the list of priority sites for future surveys. Additional critical habitat will be identified in the future as sightings are confirmed (Section 5.3).
Use official Nova Scotia place names to identify locations:
- Locations will be identified using official Nova Scotia Place Names, as documented in the Nova Scotia Atlas, and the description will include the ‘NS Atlas Square Reference’ (Province of Nova Scotia, 2001).
- In instances where a location does not have an official place name, the name used is noted in Table 1 along with UTM (NAD 83) coordinates (Table 7).
- In places where two or more named waterbodies form a single functional ecological unit, it will be considered as one location, but both official names will be included in the location description (e.g., McGowan-Deans Lake).
Lake locations include the entire lake:
- For sightings that occur on a lake, the entire lake will be included as the location. This will also include all wetlands on the lake, including those along stream inlets and outlets that are within 100 m of the lake.
River or stream locations include only the occupied portion of the river/stream:
- For sightings occurring on a stream or river, the location will be named separately from the associated lake.
- The location will include the extent of the sightings along the brook/stream or river as well as an additional 200 m linear area downstream and upstream of the outermost sightings.
- Where portions of adjacent wetlands occur within the extent of the sightings and the 200 m zones downstream or upstream, the entire wetland will be included in the location. This definition uses the precautionary principle, and is justified by field observations of individual snakes moving up to a maximum of 391 m along waterways (Imlay 2009). For unusually long contiguous wetlands (> 500m beyond the 200m buffer), a natural breakpoint was chosen through reasonable inference.
Figure 6: Example of critical habitat identification on a lake (These maps are included for illustration purposes only)
Description of Figure 6
Both maps are of the same lake. The map on the left shows the outline of the lake and includes the entire waterbody and surrounding wetlands. This map also shows eastern ribbonsnake sightings in this area. The map on the right shows the identified critical habitat, including the lakeshore and nearby wetlands. The map shows that all of the sightings found in this area fall within the critical habitat.
Figure 7: Example of critical habitat identification along a stream (These maps are included for illustration purposes only)
Description of Figure 7
Both maps are of the same brook. The map on the left shows all the sightings in the area and the outline of the brook and its associated wetlands, up and down-stream 200m from the sightings. The map on the right shows the identified critical habitat, which includes all of the wetlands that fall within the outlined location (the brook) in this example. The map shows that all of the sightings found in this area fall within the critical habitat.
|Current (1998-April 2010)||Historic Sightings (<1998)||Total sightings||Land ownership|
|Sightings from survey effort||Other sightings|
|Barren Meadow Brook / Keddy Brook||Medway River|
|P9||141.5||49||39||0||88||Provincial / Private|
|Barren Meadow Brook||Medway River|
|Bull Moose Brook||Medway River Queens Co||N10||15.0||0||1||0||1||Provincial / Private|
|Charlotte Lake||Medway River|
|L11||0.0||0||1||0||1||Provincial / Private|
|Cobrielle Lake / Cobrielle Brook / Peskowesk Lake complex||Mersey River|
Annapolis / Queens / Digby Co.
|Cow Moose Brook||Mersey River|
|Deep Brook||Medway River|
|East Lake||Medway River|
|Eel Lake||Medway River|
|Eighteen Mile Brook||Medway River|
|Faulkenham Brook||Medway River|
|Fox Lake||Medway River|
|Grafton Lake / Grafton Brook / Little Kempton Lake / Sweeney Brook complex||Mersey River|
|Harmony Lake||Medway River|
|Herring Cove Lake||Medway River|
|Hog Lake Lake*|
(UTM 347356 4918566)
|Hog Lake offshoot* (UTM 348117 4917065)||Medway River|
|Horseshoe Lake||Mersey River|
Annapolis / Digby
|Joe Tom Brook||Medway River|
|Kejimkujik Lake / George Lake / Snake Lake||Mersey River|
|Lake Rossignol||Mersey River|
|I16||36.7||3||1||5||9||Provincial / Private / First Nations|
|Little Rocky Lake / Moccasin Lake Brook||Mersey River|
|L14||0.0||0||2||0||2||Provincial / Private|
|Long Lake||Medway River|
|Mary Lake||Medway River|
|McBride Brook||Medway River|
|McGowan Lake / Deans Lake / Schroders Swamp||Medway River|
Annapolis / Queens
|McGuire Lake and Bradley Lake Brook||Medway River|
(UTM 354700 4923630)
|Medway River (upstream of Ponhook Lake)||Medway River|
|Mersey River (upstream of Lake Rossignol)||Medway River|
|Mersey River (at Big Guzzle Island)||Medway|
|Molega Lake / Hog Lake / Beavertail Lake||Medway River|
|011||830.6||360||46||13||419||Private / Provincial / First Nations|
|North Brookfield Pond (UTM 346195 4919955)||Medway River|
|North Cranberry Lake||Mersey River|
|Ponhook Lake – Cameron Lake complex||Medway River|
|Second Christopher Lake||Medway River|
|Seven Mile Lake||LaHave River|
|Shinglemill Brook||Medway River|
|Ten Mile Lake / Little Ten Mile Lake / Lower Great Brook complex||Mersey River|
|Tupper Lake – Hen Lake||Medway River|
(UTM 339469 4921991)
All sightings are listed with official Nova Scotia place names (Province of Nova Scotia 2001), unless otherwise indicated with an asterisk. For more details see the full resolution version of Figure 8 posted on the SARA registry.
Figure 8: Critical habitats identified for eastern ribbonsnake in Nova Scotia (as of April 2010). Full resolution version of this map (27 MB)
Description of Figure 8
This map identifies critical habitat for the Eastern ribbonsnake in southwestern Nova Scotia. The map is intended as a companion resource for "The recovery strategy for the Eastern ribbonsnake (Atlantic Population) developed under the Federal Species at Risk Act (SARA). This map allows landowners, disposition holders and other interested members of the public to view critical habitat at various levels of details and magnification. When interpreting this map, users should keep in mind the critical habitat attributes and the activities likely to destroy these habitats as outlined in the recovery strategy.
Critical habitat was identified for all locations with current, confirmed ribbonsnake sightings (1998-April 2010). The location is the geographical place where ribbonsnakes occur (e.g., the entire lake, fen or bog, or selected portions of a river or stream). Critical habitat will encompass all wetlands failling within an identified location as well as the terrestrial and aquatic zone that extend 100 m around each wetland.
6.3 Schedule of studies to identify critical habitat
At this time, only a partial identification of critical habitat is possible; more information about the basic biology, distribution, movement patterns, and habitat requirements of ribbonsnakes at all life stages is necessary for a full identification. In particular, this recovery strategy does not incorporate habitat over 100 m away from wetlands that may be used by ribbonsnakes and could be important in maintaining connections between sites. A number of priority sites have been identified for future surveys to confirm the presence of ribbonsnakes. Critical habitat identification will be reviewed on a regular basis as more information becomes available. A schedule of studies for identifying further critical habitats is listed in Table 8.
|Study to be undertaken||Outcome/Rationale||Timeline|
|Determine location and habitat characteristics of overwintering sites||Will permit the identification of terrestrial habitat to ensure that critical overwintering habitat characteristics are not adversely changed.||2012|
|Determine extent of overland movements and other connections between concentration sites||Will permit the identification of terrestrial habitat to ensure that critical overland habitat corridors are not adversely changed.||2014|
|Determine the population abundance and genetic structure to refine population and critical habitat targets to achieve viable populations||Will achieve population and habitat targets for a viable population(s).||2015|
6.4 Examples of activities likely to result in destruction of critical habitat
The Species at Risk Act (S.C. 2002, c. 29) contains prohibitions against the destruction of critical habitat on federal lands (s. 58(1)). Current federal policy (Government of Canada 2009) defines how destruction of habitat will be assessed. “Destruction is determined on a case by case basis. Destruction would result if part of the critical habitat were degraded, either permanently or temporarily, such that it would not serve its function when needed by the species. Destruction may result from a single or multiple activities at one point in time or from the cumulative effects of one or more activities over time. When critical habitat is identified in a recovery strategy or an action plan, examples of activities that are likely to result in its destruction will be provided.” Any activity that may result in the destruction of critical habitat as described above must therefore be managed, mitigated, or prohibited to ensure the continued protection of critical habitat.
Activities may have impacts on critical habitat sites or the entire location the critical habitat is in, or both. It is important to identify the scale(s) at which various activities may have an impact to ensure the protection of critical habitat. Activities likely to result in the destruction of critical habitat include, but are not limited to, the examples listed in Table 9.
|Entire location||Critical habitat|
|Road and trail development that fragments habitat, alters the natural hydrologic regime and/or damages vegetation||yes||yes|
|Causeway development that fragments habitat, alters hydrologic regime and/or damages vegetation||yes||yes|
|Off-highway vehicle use that damages vegetation||yes|
|Cottage and residential development that fragments habitat, alters hydrologic regime and/or damages vegetation||yes|
|Shoreline alterations that degrade habitat, including such activities as mowing and raking or construction of breakwaters||yes||yes|
|Draining and infilling of wetlands or other direct removal of vegetation||yes||yes|
|Hydroelectric dam operations that impact shoreline and wetland vegetation due to water level alterations||yes||yes|
|Crop and animal production resulting in degradation of water quality or the alteration of the natural hydrologic regime||yes||yes|
|Forest harvesting practices resulting in alteration of water quality or the hydrologic regime||yes||yes|
|Industrial development resulting in alteration of water quality or the hydrologic regime||yes||yes|
|Extensive trapping of beavers or removal of beaver dams that result in significant changes in the hydrological regime.||yes||yes|
|Peat mining that eliminates or degrades habitat||yes|
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