Recovery Strategy for the Blanding's Turtle, Nova Scotia Population, in Canada [proposed] 2011: Threats

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Existing and suspected threats have been identified in Table 2.

Threat Level of Concern4 Extent Occurence Frequency Severity5 Causal Certainty 6
Habitat loss or degradation
Cottage and residential development High Widespread Current / historic One-time / recurrent Moderate High
Forestry practices (e.g. clearcutting, harvesting in riparian zone) Medium Widespread Current / historic Recurrent High Low
Road development High Widespread Current / historic Recurrent High High
Agricultural practices (e.g. Cranberry growing, tilling, crop production) Low Localized Unknown Rare Moderate Medium
Recreational use of nesting areas (e.g. beaches, OHV trails) Medium Localized Current / historic Seasonal Moderate Medium
Peat Mining Low Localized Unknown Rare Moderate Medium
Accidental Mortality
Mortality from on and off road vehicles and machinery High Widespread Current / historic Seasonal - rare High High
Motorboat use Medium Localized Unknown Seasonal - rare High Medium
Collection for museum specimens7 Low Localized (KP) Historic One-time High High
Collection for food7 Low Widespread Unknown Rare High High
Compaction or destruction of nests Low Localized Unknown Seasonal - rare Low Low
Changes in Ecological Dynamics or Natural Processes
Hydroelectric dam operation Medium Localized Current / historic Continuous Moderate Medium
Human alteration of beaver dams Medium Localized Current / historic One-time / recurrent Moderate Medium
Introduction/ establishment of exotic predatory fish (small mouth bass and chain pickerel) Medium Widespread Anticipated Continuous Unknown Low
Changes in predator populations resulting from human activities Medium Localized Current / historic Recurrent Moderate Low
Climate and natural disasters
Climate change Medium Widespread Anticipated Continuous Unknown Low
Stochastic events that increase adult mortality8 Medium Localized Unknown Unknown High High
Disturbance or persecution
Collection for pets and / or relocation Medium Localized Current / historic Unknown High Medium
Pesticide and herbicide use Low Localized Unknown One-time / recurrent Unknown Low
Contaminants from mine tailings Low Localized Historic Recurrent Unknown Low

4 Level of Concern: signifies that managing the threat is of (high, medium or low) concern for the recovery of the species, consistent with the population and distribution objectives. (This criterion considers the assessment of all the information in the table).

5 Severity: reflects the population-level effect (High: very large population-level effect, Moderate, Low, Unknown).

6 Causal certainty: reflects the degree of evidence that is known for the threat (High: available evidence strongly links the threat to stresses on population viability; Medium: there is a correlation between the threat and population viability e.g. expert opinion; Low: the threat is assumed or plausible).

7 Threats known to have occurred previously and/or do occur in other parts of the species range. These currently have a low level of concern, but there is a high causal certainty that they would significantly impact the population.

8 High causal certainty that this will significantly impact the population, however, currently a medium level of concern as it is not regularly occurring.

The following highlights major threats outlined in Table 2, emphasizing key points and providing additional information on the threats. Evidence suggests significant population-level impacts exists for threats with a "high" for both 'level of concern' and 'causal certainty'; other threats are identified as being potentially significant if they were to occur. While threats are listed separately, an important concern is the long-term cumulative effect of a variety of threats on the Blanding`s turtle population. As human development increases, the overall impact of activities on the habitat becomes more serious at both the small and large scale. At the landscape scale, incremental losses and multiple threats often complicate recovery efforts and confound understanding of population trends (Jensen et al. 1993).

Mortality, habitat loss and changes to ecological processes associated with human activities

Increased adult mortality is a potential yet very serious threat to the Blanding's turtle, as it is known to cause major declines in turtle populations (Congdon et al. 1983). Blanding's turtles' longevity and late maturation make their populations particularly vulnerable to even small increases in adult mortality (Congdon et al. 1983, Congdon et al. 1993). By reducing lifetime reproductive output, even these small changes can drive populations to local extinction (Heppel 1998, Congdon et al. 1993). Although younger life stages have higher natural mortality rates, sustained increases in mortality in these stages will also cause a population to decline (Bourque et al 2006); the decline may be difficult to detect in the short term due to the species long generation time and the more cryptic nature of juveniles.

Human activities can affect survivorship of all life stages both directly and indirectly. In the Nova Scotia population, collection for museum specimens (historic) and vehicle collisions (on and off road) have contributed directly to mortality (Penny 2004). When first described in the early 1950's, it is known that more than a dozen turtles, most believed to be female, were removed as samples; additionally, there have been 4 known instances where vehicle mortality has occurred in adults, again all females, and several instances of vehicle mortality in hatchlings and juveniles. Indirectly, habitat destruction and fragmentation from cottage development and forestry and agricultural practices disrupt population structure by reducing the amount of habitat and impeding movements within and between populations (Hartwig 2004). This can force turtles to travel through higher risk areas; additionally, in some cases, human activities actually create habitat which attracts turtles, particularly for nesting (Congdon et al. 2008). Both of these put turtles at increased risk for encounters with people, machinery and pets. Additionally, nesting areas near human development may have unusually high populations of opportunistic predators such as raccoons, which could substantially increase predation on eggs and hatchlings; if sustained, this would decrease lifetime reproductive output (Hartwig 2004). In Ontario, an increase in the predation of nests by sarcophagid fly larvae has been identified as a potentially significant threat, although the cause of increase is unknown (COSWEIC 2005). In Nova Scotia only a small number of eggs have been found to contain maggots that may be from the sarcophagid fly (NS Blanding's turtle database 2010), although this may pose a future threat (Bolton et al, 2008).

Blanding's turtles require seasonally predictable water levels at all seasonal habitats. Hydropower generation in this region tends to accentuate variability and unpredictability in water level (Herman et al. 2003). Lake draw-downs in mid and late summer reduce or eliminate drought refuges and create large uninhabitable expanses; in the winter, they can potentially increase mortality by exposing overwintering turtles. Retention of water during wet summers can flood shoreline nests (NS Blanding's turtle database 2010). In contrast, impoundments controlled by beavers reduce variability and increase predictability in water level. Removal or control of beaver activity by cottage owners, farmers, foresters and highway maintenance crews potentially threatens all life stages of the turtle.

Human activities can also affect availability of food such as aquatic invertebrates and amphibians. Invasive predatory fish species, such as smallmouth bass and chain pickerel, reduce populations of amphibians and small fish (Jackson 2002, Vander Zanden et al. 2004), and may also pose a direct predatory threat to hatchlings. While not yet documented at Blanding's turtle sites, the ranges of both of these species has been expanding in southwestern Nova Scotia though human introductions. Likewise, pollution and pesticides may directly affect the turtles themselves, as well as system productivity and the availability of food. This reduced productivity could affect growth of the turtles at a local scale, which may explain differences in sizes seen among populations in Nova Scotia.

Climate change and natural disasters

In the longer term, Blanding's turtles in Nova Scotia face an uncertain climatic future and it is not known if the overall effects of climate change will be positive or negative. Because of their limited physiological tolerance and long generation time (approximately 40 years), they are limited in ability to respond genetically to climatic change (Herman and Scott 1992). Substantial changes in climate may occur within the lifetime of an individual turtle; adaptive responses to such changes would have to be behavioral rather than genetic (Herman and Scott 1992). Changes to overall temperatures and seasonal water flow could affect habitat at any life stage.

Additionally, climate change could alter nest temperatures which could result in skewed sex ratios or decreased fitness in the population over time. The sex of hatchlings is determined by the temperature at which they were incubated in the nest, with lower incubation temperatures producing males and higher temperatures producing females (Gutze and Packard 1987). Sub-optimal temperatures or moisture levels during incubation can result in nest failure, increased incidents of deformities, or decreased overall fitness in hatchlings (Packard 1999, Standing et al 2000).

Natural disasters that increase adult mortality can be a serious threat to this small isolated population, for reasons described above.

The long term objectives are to achieve a self-sustaining population of Blanding's turtles in Nova Scotia, over the current range, (as measured by 95% probability of persistence in each recognized population when projected over 10 generations (400 years)), and to maintain sufficient gene flow to prevent any single population from becoming genetically isolated.

The long term objectives include the three currently recognized populations. The status of the two small concentrations is currently unknown, with less than 5 turtles identified at each. Further study is needed to determine if they are currently, or were historically, viable populations.

In the interim, the following short term objectives will be measured in terms of their contribution to the long term objective:

Current range (area of occupancy) was chosen as the benchmark as there is no information available on historic range of the species in Nova Scotia. Because our current knowledge of distribution is incomplete, loss of range is difficult to assess and requires surveys to locate additional populations. Protecting Blanding's turtle habitat does not necessarily mean that no human activities can occur, but that necessary ecosystem processes be maintained so that survivorship, fecundity and gene flow are not negatively affected.

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