Recovery Strategy for the Eastern Ribbonsnake, Atlantic Population in Canada [Proposed] 2011: Threats

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Like other aspects of eastern ribbonsnake biology, threats are not well understood. Known and potential threats have been identified in Table 3 and ranked according to the level of concern in each threat category. The occurrence, frequency, certainty, and severity of most of these threats remain unknown and there may be additional threats to ribbonsnake populations that have not yet been identified. The assessment of threat information presented in Table 3 is based on documented research (see References Cited) or expert opinions from members of the Eastern Ribbonsnake Recovery Team.

Table 3. Classification of known and suspected threats to eastern ribbonsnake recovery in Nova Scotia
General Threat Specific Threat Potential stress Extent Occurrence Frequency Casual Certainty Severity Level of Concern
Threat Information+
A. THREAT CATEGORY: Changes in ecological dynamics or natural processes
1. Lack of information Inaction or inappropriate action(inability to recognize threats; delayed implementation of recovery actions; initiation of actions with unexpected detrimental effects) ↑mortality; Degradation of habitat WS C NA H U H
2. Small, isolated concentrations of snakes within the NS range Small population effects (inbreeding; genetic drift; increased susceptibility to stochastic events) due to isolation of populations resulting from human influences ↑mortality;
↓fecundity
U U U L U H
3. Cottage and residential development Alteration of natural disturbance regimes and functional processes Alteration of movement patterns; Alteration of genetic structure U U U L U M
B. THREAT CATEGORY: Habitat loss or degradation
1. Dam construction or removal (human or beaver) * Alteration of water level and seasonal water flow regimes; long-term cumulative habitat loss Change in habitat availability; Winter mortality; Change in prey availability; Local extinction L C U L U H
2. Cottage and residential development Habitat degradation, fragmentation, and loss; alteration of water level and seasonal water flow regimes; alteration of shorelines; long-term cumulative habitat loss ↓Habitat availability;
↑mortality;
↓movement between concentrations; local extinction
WS C R M U H
3. Road density and new road construction Habitat fragmentation; long-term cumulative habitat loss ↑mortality; isolation of concentrations; WS C U U U H
4. Climate change* Alteration of water level and seasonal water flow regimes Change in habitat availability WS A C L U M
5. Forest harvesting practices (i.e., clear cutting, harvesting in the riparian zone, rotation times) Alteration of water level and seasonal water flow; decrease in water quality; habitat degradation, fragmentation, and loss; long-term cumulative habitat loss; potential disruption of overwintering sites ↓habitat availability;
↑mortality;
↓movement between concentrations
WS C U L U M
6. Agricultural practices (i.e., tilling, crop production, cranberry growing) Alteration of water level and seasonal water flow; decrease in water quality; habitat degradation, fragmentation, and loss; long-term cumulative habitat loss ↓habitat availability;
↑mortality;
↓movement between concentrations
WS U U L U M
7. Infilling/ draining wetlands Habitat degradation, fragmentation, and loss; long-term cumulative habitat loss; loss of wetland function ↑mortality;
↓habitat availability; local extinction
L C M M H H
8. Peat mining Habitat degradation, fragmentation, and loss; long-term cumulative habitat loss ↑mortality;
↓habitat availability; local extinction
L A U M U L
C. THREAT CATEGORY: Accidental mortality
1. On and off road vehicles Vehicular mortality; increased encounters with people ↑mortality WS C C M U H
2. Cottage, residential and road development Vehicular mortality; increased encounters with people; increased predation by pets ↑mortality WS C U M U H
3. Agricultural and forestry equipment Vehicular mortality ↑mortality L C U L U L
D. THREAT CATEGORY: Disturbance and persecution
1. Negative perception of snakes Intentional killing by humans resulting from hatred or fear of snakes ↑mortality U U U L U L
2. Cottage, residential and road development Increased encounters with people, pets and machinery; disturbance to snakes and habitat features ↑mortality;
↓fecundity
WS U U L U L
E. THREAT CATEGORY: Exotic or invasive species
1. Exotic predatory fish Introduction of small mouth bass and chain pickerel; changes to ecosystem function ↑mortality;
↑competition for prey; altered prey composition
U C U L U H
F. THREAT CATEGORY: Climate change
1. Climate change* Shifts in seasonal temperatures (reduction of heat units for development of young; increased winter mortality); alteration of water level and seasonal water flow Change in fecundity; Change in prey availability; Winter mortality* WS A C L U M
G. THREAT CATEGORY: Natural Processes or activities
1. Human activities and development Increase in natural predator populations ↑mortality U U U L U L
H. THREAT CATEGORY: Pollution
1. Pesticide use (i.e., landscaping, crop and agricultural production, forestry) Direct and long-term exposure ↑mortality;
↓prey availability;
↓fecundity
U C U L U L
2. Air pollution Accelerated effect of methylated mercury impacting the food chain ↑mortality;
↓prey availability
U C U L U L

* These factors in particular could have a positive or negative effect on ribbonsnake populations.
+ Extent: WS = widespread; L = localized; U= unknown / Occurrence: C = current; A = anticipated; U = unknown / Frequency: C= continuous; R = recurrent; U = unknown; NA = not applicable / Causal Certainty: H = high; M = medium; L = low / Severity: U = unknown; H = High / Level of Concern: H= high; M= medium; L=low

The following descriptions highlight the “specific” threats as outlined in Table 3, emphasizing key points and providing additional information on the threats. As there is little published literature outlining threats to ribbonsnakes, most information presented here deals with potential threats and effects, as assessed by the Recovery Team.

While the threats below and in the table are listed separately, an important concern is the long-term cumulative effect of a variety of threats on the eastern ribbonsnake population. As human development increases, the overall impact of activities on the habitat becomes more serious at both the small and larger scales. At the landscape scale, incremental losses and multiple threats often complicate recovery efforts and confound understanding of population trends (Jensen et al. 1993).

The COSEWIC status report identified lack of information as the greatest current threat to ribbonsnake recovery (Smith 2002). Little is reported on eastern ribbonsnake ecology or threats anywhere in its range. What is reported elsewhere is not necessarily applicable to the Nova Scotia population. Up until now, there has not been an inclusion of Aboriginal Traditional Knowledge and community knowledge in recovery. At this point, it is not known what factors limit eastern ribbonsnakes in the province (geographically or demographically), how healthy the population is, or what level of population fluctuations are normal. This could prevent recovery managers from recognizing population decline or identifying significant threats. In fact, it is not known if the effect of many of the potential threats listed below will be positive or negative (especially water level and climate change). Lack of information could also result in delay of recovery actions because of uncertainty of potential detrimental effects, or risk of initiating actions that may have unanticipated negative effect(s).

The Nova Scotia eastern ribbonsnake population is geographically isolated from the species’ main range, which prevents any possibility of in-migration or a natural rescue effect. Although the full extent of the range within Nova Scotia remains unknown, it does appear to be restricted to a small number of watersheds in the southwest region of the province. This places the snakes at risk of small population effects such as inbreeding and genetic drift, and increases the population’s susceptibility to stochastic events. These risks are further exacerbated if the Nova Scotia population actually consists of numerous isolated sub-populations with little or no movement between them.

Alterations to water level and seasonal water flow are anticipated to be among the most significant threats to ribbonsnake habitat. Hydrological changes can result from many activities, including installing or removing human-made dams, removing beaver dams, forest harvesting practices, agricultural practices, infilling of wetlands, altering shorelines and climate change. Even a small change in flooding regimes could result in vegetation succession in previously wet meadows, or in preventing vegetation from establishing. While these changes to the terrestrial and aquatic habitat could affect all aspects of ribbonsnake life history, the impacts on feeding and overwintering sites are of particular concern.

Effects from either stabilizing or destabilizing water levels could be positive or negative for ribbonsnakes. We do not yet have sufficient understanding to be able to predict the type or scale of impact resulting from particular activities. Two of the sites containing the highest known densities in the province (Grafton Lake and Cobrielle Brook) have had human-made dams removed within the last decade. The destabilizing impact of natural beaver dam cycles may also be important for the local ribbonsnake population.

Habitat degradation, fragmentation, and loss can occur from many activities, including cottage and residential development, road construction, agricultural practices and forest harvesting practices, and infilling wetlands. Cottage development is of particular concern as it could result in alteration of shorelines, destruction of habitat, and fragmentation. Expansion of the road network could also result in fragmentation as well as direct mortality from vehicles and increased encounters with people and pets. In turn, fragmentation could result in isolation of individual concentrations or increased risk to individuals as they travel between concentrations or between seasonal habitats.

Changes to water quality (e.g., pollution, eutrophication, siltation) may also pose a threat to ribbonsnakes, particularly those that affect prey abundance. Based on limited data, adult ribbonsnakes in Nova Scotia appear to prey primarily on amphibians and small fish (Bell et al. 2007, NS ribbonsnake database 2010); the diet of neonate ribbonsnakes, however, is largely unknown. The extent to which prey availability limits population numbers, as well as the degree of dependence of ribbonsnakes on specific prey items, are also still unknown.

Vehicular mortality is one of the few direct sources of mortality that has been documented in Nova Scotia. This includes mortality from both automobiles and all terrain vehicles. It could also include farm or forestry equipment and lawn mowers, although these are probably a lesser threat at the present time. Vehicular mortality may be particularly significant if snakes must cross roads to travel between overwintering and summering sites, or if they are drawn to roads to bask. Since 2004, nine incidences of vehicular mortality have been recorded in Nova Scotia (8 on roads, 1 on an ATV trail). Most of these reports have been incidental and not the result of targeted road surveys, and predators are likely to pick up any road kill snakes very quickly. The true incidence of vehicular mortality is likely to be considerably higher. This is particularly disturbing given the relatively low volume of traffic in the area. As development increases, vehicular mortality is also expected to increase.

The introduction of exotic predatory fish into areas containing ribbonsnakes is of particular concern. As a result of introductions, the ranges of both smallmouth bass and chain pickerel have been expanding in Nova Scotia, including the southwestern region of the province. These species can alter trophic dynamics, which could negatively impact ribbonsnakes through either direct predation or competition. Predatory fish have been shown to dramatically reduce populations of small fish and affect amphibian abundance (Vander Zanden et al. 2004, Jackson 2002). Both of these exotic fish species are more tolerant of higher water temperatures than many of the native fish, thus increasing their potential effect on ribbonsnake prey populations (Vander Zanden et al. 2004).

Climate change may affect ribbonsnakes in Nova Scotia, and the impact may vary according to the different aspects of their life history. It is not known whether the overall effect on ribbonsnake populations, if any, will be positive, negative, or neutral. Having said this, if the effects are negative they could be very significant.

In addition to affecting water level, prey abundance, and habitat as described above, climate change may also directly impact ribbonsnake physiology. Ribbonsnakes in Nova Scotia occur near the northern limit of the species range (Bleakney 1951). Each year they spend 4-6 months in overwintering sites and have only 6-7 active months to feed and reproduce. While it might appear that an increase in annual temperatures will benefit this southern species, this may not necessarily be the case. Changes in seasonal temperature and precipitation conditions may affect growth and development of young, particularly if it results in cooler, wetter weather during the active season.

Winterkill can be a significant source of mortality for other species of Thamnophis (Shine and Mason 2004). The significance of winterkill has not been documented in ribbonsnakes, although one dead eastern ribbonsnake was found at the top of a hibernaculum in Michigan (Carpenter 1953). Snakes are at risk of freezing and dehydration over the winter and may be dependent on specific conditions inside the hibernacula. Altered winter climates may directly impact the severity of winterkill.

Snakes are at risk of predation from both natural predators and domestic pets. Predation by domestic pets has been documented in Nova Scotia (one documented cat kill and several other anecdotal reports) and is expected to increase as cottage, residential, and road development increase. Natural predators and predation rates remain unknown and until these are determined, it is difficult to identify potential anthropogenic effects on these predators and their subsequent effect on ribbonsnake predation.

Many people fear or dislike snakes and some people will kill any that they see, particularly if the snakes are found near or in their homes While intentional killing has been a significant threat in other snake species at risk (Eastern Massasauga Recovery Team 2002), and may be the cause of death of one ribbonsnake found with extensive wounds in Nova Scotia in 2007, it is believed that the overall risk is relatively low for Nova Scotia ribbonsnakes at present. People rarely venture into wetlands where ribbonsnakes are typically found, and even when they do, these snakes are cryptic and difficult to catch. Because ribbonsnakes are strongly associated with wetlands, they are not as commonly encountered on lawns or in houses as some other species in Nova Scotia. However, with increasing development near wetlands, encounters by people will become more common and the threat may increase. It is not known how effective education will be in mitigating this threat.

In 2003, the Eastern Ribbonsnake Recovery Team was formed, and several of the recovery actions outlined in the strategy have been underway since that time. Work to date has focused primarily on filling knowledge gaps and encouraging public involvement with the species through outreach and stewardship initiatives.

Extensive surveys to expand knowledge of the range of ribbonsnakes in Nova Scotia have been underway since 2004. The majority of surveys to date have been limited to the Mersey and Medway watersheds, focusing on sites with historical or reported sightings; large areas of potential habitat, particularly to the west of the known range, remain largely unexplored. These surveys have expanded the known range in the province to a third watershed (LaHave) and have confirmed a number of new sites within the known range. They have also resulted in the confirmation of relatively high densities (>20 sightings) at five sites (Table 1). Data on area searched, date, effort, and weather conditions are collected during each survey to refine survey protocols for greater efficiency. In coordination and collaboration with the Blanding’s Turtle Recovery Team, many of the wetlands previously surveyed for the presence of ribbonsnakes have been characterized; the data will ultimately be used to try to develop models that may help predict where ribbonsnakes occur.

Researchers have been conducting intensive mark-recapture surveys in a defined area on Grafton Lake since 2004 and Molega Lake since 2007 to identify seasonal habitat use and to begin collecting long-term data on abundance, survivorship, and individual site fidelity. The first overwintering site in terrestrial habitats away from the wetland was located in November 2009 and confirmed in March 2010.

While researchers have been able to document some seasonal movement patterns, efforts to date have been hampered by a lack of a reliable long-term marking technique (especially for young snakes) and a method to track snakes. Since 2004, snakes at this site have been marked by ventral scale clipping; however, using the current techniques, these marks often wear off within a single season. Beginning in 2006, some snakes were marked by PIT tagging; long-term success of this technique will be assessed in the coming years. Attempts externally attach transmitters to adults were largely unsuccessful, with transmitters only remaining on the snake up to four days (Imlay 2009). Fluorescent powder was also used to track ribbonsnakes and was found to be useful in documenting movement paths up to 16m long but not in re-locating ribbonsnakes (Imlay 2009). In 2009 a study was initiated to examine the feasibility of using trained dogs to locate ribbonsnakes by scent. Results from the pilot year of the study were promising, showing that dogs are useful in locating ribbonsnakes and helping to track escaped snakes (Gadbois et al 2009). The study will continue in 2010.

No genetic analysis had been published on eastern ribbonsnakes anywhere in their range prior to 2004, when Harwood (2005) initiated a study to develop microsatellite primers and to conduct an initial analysis of population structure in Nova Scotia. No genetic structure was found in the initial analysis; however, both sample sizes (n=44) and number of loci (n=2) evaluated were small, and Harwood (2005) recommended the continued collection of DNA samples and the development of additional primers. A follow-up study in 2007 suggested that there is detectible structure within the Nova Scotia population, with evidence of low to moderate restriction in gene flow among concentrations (McLaughlin 2008). However both sample size (n=46) and number of loci examined (n=1) were again low and insufficient for conclusive results (McLaughlin 2008).

The Recovery Team has been engaging in outreach and in soliciting sightings from the public since 2004. People have been engaged through a variety of methods, including direct landowner contact, displays at community events, presentations at local schools and community groups, field trips, interpretive programs (KNPNHS), and media presentations. In addition, a toll-free hotline has been set up at the Mersey Tobeatic Research Institute to provide a number that people can call to report all sightings of species at risk. These efforts have already produced a number of credible sightings, mostly within the known range. Volunteers have been helping with all aspects of ribbonsnake research ranging from participating in guided surveys led by Parks Canada staff to conducting independent surveys. A number of outreach tools have been developed including an information pamphlet, a Species at Risk Identification Guide, a website (www.speciesatrisk.ca/ribbonsnake), and a Landowner Stewardship Guide. The latter, first distributed in 2009, is a collaborative effort designed to inform landowners and land users of ways to minimize the impacts of their activities on ribbonsnakes, Blanding’s turtles, and Atlantic Coastal Plain Flora.

Currently, there are knowledge gaps on all aspects of the life history of eastern ribbonsnakes, including demography and current population trends, historical status, habitat requirements at specific life stages, and severity of threats. At the present time, the three most important questions are as follows:

  1. What is the current status of the Nova Scotia population of eastern ribbonsnakes?

    It is important to identify the current range of the population and the spatial distribution within that range. It is not known at what spatial scale genetic structure is evident, if ribbonsnakes from neighbouring sites interact with one another, and what factors constrain movements, if any, between concentrations of ribbonsnakes. If individual concentrations are isolated, it will be important to determine if it is historical or the result of recent anthropogenic events. Crucial information on basic life history traits such as abundance, survivorship and longevity is also lacking; all required to determine if populations are increasing, decreasing or stable. It is currently not known if high density concentrations are typically short-lived.
  2. What are the critical features of the habitat, and are they limiting?

    It is not currently known why ribbonsnakes occur in some wetlands and not in others and a suite of habitat features that would predict which habitats are suitable for ribbonsnakes have not yet been identified. It is important to understand how habitat change, connectivity and long-term habitat trends affect persistence of ribbonsnake populations.

    Much remains unknown about overwintering. It is important to know where ribbonsnakes of all life stages spend the winter, identify the characteristics of those sites, determine if sites are used communally or singly and determine if fidelity is shown to specific sites. It is not known if overwintering mortality is a significant threat to the population and have not identified how factors, such as water level fluctuations, affect winter survival.

    It is also not known if ribbonsnakes have specific habitat requirements for other activities (including feeding, basking, mating and gestation/birthing), if sites are used repeatedly over time, or if snakes aggregate at certain sites. The relationship between ribbonsnakes and their prey is not fully understood, and it is not known if there are temporal shifts in prey and feeding locations throughout the season and how significant side pools are as feeding sites.
  3. What are the threats limiting the recovery of this population?

    It is important to identify which threats are the most significant and also the appropriate scale to manage these threats. It is not known how changes in water level, habitat fragmentation, development or climate will affect populations or why the range is limited in the province. Determining if individual concentrations are currently experiencing deleterious effects from small population size (inbreeding, genetic drift, reduced fitness) is necessary to understand factors limiting the population.

    Answering these questions requires basic information on all life stages including basic demography (longevity, stage specific survivorship, population trends, predator and prey relationships), habitat use (sites used for specific life stages, large scale range, habitat characteristics, current movement patterns), and genetic structure (assessment of population structure, evaluation of inbreeding depression, estimate of genetic variation, identification of past events that may have influenced patterns seen today).

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