Rocky Roads: Key Findings on Using Rip-Rap and Paved Shoulders to Deter Turtle Nesting on Roads

Across eastern Georgian Bay, turtles face a perilous challenge—busy roads that cut through their habitats. In response, people are coming together to protect vulnerable turtle populations by testing innovative approaches to reducing road threats. 

In 2020, routine road maintenance in the Township of The Archipelago (TOA) created an opportunity to explore new ways to reduce road threats for turtles. As part of the Maamwi Anjiakizwin initiative, the Georgian Bay Mnidoo Gamii Biosphere (GBB) and Shawanaga First Nation (SFN) partnered with the TOA, engineers, and road construction companies to test a strategy for reducing the threats posed by road construction and daily traffic. 

Using standard construction materials—rip-rap and paved road shoulders—the strategy aimed to deter turtles from nesting on the road shoulder, with the hopes of reducing the risk of road mortality for both nesting females and their offspring. To study the effectiveness of this strategy, project partners collaborated with Dr. Jackie Litzgus and Jenna Kentel from Laurentian University as part of a master’s research project. This month’s blog post shares key insights gained from the research.

The Problem: Risky Roadside Nesting

Female turtles often use road shoulders as nesting sites because these areas provide ideal conditions – sunny, open habitat with exposed gravel. Unfortunately, this puts them at high risk of being struck and killed by vehicles, which can significantly harm turtle populations. Similarly, turtles nesting along roadsides offer a buffet of eggs for local meso-predators (raccoons, skunks, foxes, and ravens), further reducing potential recruitment back into the local turtle population. 

Turtles have long lifespans and rely on the survival of mature females for population stability. Accordingly, protecting them from road threats is crucial for their long-term survival. One common mitigation strategy involves exclusion fencing paired with underpasses to prevent turtles from accessing roads, while directing them to a location which allows them to cross safely. However, this method is costly, requires ongoing maintenance to prevent gaps, and isn’t always practical due to the surrounding landscape or budget constraints.

Despite the need for effective solutions, few new strategies have been explored to tackle the long-term threat that roads pose to turtles.

The Strategy: Rip-Rap and Paving to Deter Nesting

The strategy being tested aimed to reduce turtle nesting on road shoulders along an 11.7 km stretch of road intersecting key wetland habitats. Five wetland crossings were selected for treatment with rip-rap (large, angular rocks) and tar-and-chip paving, while other sections remained untreated.

Rip-rap (300 mm in diameter) was placed on 100-metre sections of road embankments, covering the exposed gravel. Tar-and-chip paving covered 300-metre sections of road shoulders, meeting the rip-rap to further deter turtles from nesting on the road (Figures 1 and 2).

Study Design: A Before-During-After Study

To evaluate the effectiveness of the mitigation strategy, a Before-During-After study was conducted. Turtle nesting activity was monitored over three summer seasons from 2020-2022, comparing the number of nests in treated (mitigated) and untreated sections of the road. Success was measured by the strategy’s ability to reduce nesting on road shoulders, thereby limiting turtles’ exposure to vehicles.

1. Before (No Mitigation): In 2020, no mitigation measures were in place, giving turtles full access to the road shoulders for nesting. After the nesting season, construction occurred at the five wetland crossings including the following activities:

  • Culverts were upgraded at the five wetland crossings to allow turtles to move safely under the road.
  • 100-metre sections of rip-rap were added around the culverts to deter nesting on the road embankments.

2. During (Partial Mitigation): In 2021, road resurfacing occurred during the turtle nesting season (late May – early July). During this time, the old pavement was removed, leaving exposed gravel that increased the likelihood of turtle nesting. GBB and SFN biologists worked closely with the construction crew to ensure that any eggs laid on the road were safely collected for incubation (Figure 3). 

Following removal of the old pavement, the road was raised by 2.5 cm, and tar-and-chip resurfacing was completed after the nesting season, covering 300-metre sections of road shoulders.

3. After (Full Mitigation): In 2022, all mitigation measures were in place, no further construction was needed. However, two concerns remained:

  1. The tar-and-chip road shoulders were only semi-compact, leaving loose tar-and-chip gravel that would still allow turtles to nest.
  2. A gap between the rip-rap and the paved shoulder left a small area where turtles could still potentially nest.

Key Findings: Mixed Success

The total number of turtles nesting on the road remained similar between the before and after periods, with 133 turtles nesting in the before period and 138 in the after period. While the overall numbers did not change, the study revealed a shift in where the turtles chose to nest.

Success in Rip-Rap Sections

The rip-rap was effective at preventing turtles from nesting directly in the treated 100-metre sections. No nests were found in the rip-rap areas, indicating that this part of the mitigation strategy worked as planned.

Ongoing Nesting on Paved Shoulders

Despite the success of the rip-rap, many turtles continued to nest on the road in the during period and in the tar-and-chip paved shoulders that were only semi-compact in the after period of the study.

In the during period, when the road was being resurfaced, female turtles were found nesting in the exposed gravel in the traffic lanes, which increased their risk of road mortality (Figures 4 and 5). 

After the mitigation (rip-rap and paved shoulders) was fully in place, about 42% of the nests were still found on the paved road shoulders. The semi-compact tar-and-chip surface did not fully deter turtles from nesting, including 11 nests that were laid in the exposed gap between the rip-rap and road shoulder (Figures 6 and 7).

Persistent Hotspots

Spatial analysis showed that nesting hotspots persisted in some mitigated areas and shifted to untreated sections with exposed gravel, particularly near wetland crossings. While rip-rap altered behaviour, it did not fully deter turtles from nesting on road shoulders. 

Challenges with Rip-Rap

Though adult turtles navigated the rip-rap easily, a juvenile painted turtle was found trapped between the rocks, raising concerns about potential entrapment risks for smaller turtles, including hatchlings, if roadside nesting continues.

Bigger Picture: What These Results Mean

This study highlights the complexity of turtle nesting behaviour and the challenges of developing effective, low-cost mitigation strategies. While the rip-rap successfully reduced nesting in the targeted 100-metre sections, turtles continued to find exposed gravel to nest in further down the road. Ultimately, the mitigation strategy was determined to be ineffective overall and should not be applied without further research.

The study also emphasized the importance of scheduling road construction outside of key nesting periods. When that is not possible, partnerships like those with GBB or SFN are crucial. Having biologists on-site can reduce risks to turtles and support egg incubation and release efforts.

Next Steps

With all turtle species in the Biosphere being at-risk, it is essential to continue exploring new mitigation strategies. Evaluating these strategies over several years, both before and after mitigation efforts, is key to adequately assessing their effectiveness. If road mortality continues to threaten nesting females, additional mitigation may be necessary. Possible measures could include:

  • Backfilling rip-rap with smaller aggregate to fill gaps.
  • Installing seasonal signage and implementing reduced speed limits.
  • Establishing community-based nest protector programs through citizen science initiatives.
  • Enhancing natural nesting habitat to provide safer alternatives.
  • Applying exclusion fencing where feasible to direct turtles away from roads.

Further research and monitoring of nesting activities is recommended. Additional research needs include: 

  • Tracking where females continue to nest to help understand the effectiveness of this mitigation design.
  • Studying the long-term effects of construction materials like rip-rap on herpetofauna. For example, investigating how different rock sizes affect turtles of various ages to prevent unintended risks.
  • Exploring nesting habitat restoration options, including natural nest enhancement in the surrounding landscape to provide alternatives to nesting on the road shoulder.

Long-term monitoring and collaboration between conservation groups, First Nation communities, local governments, and road planners are critical to developing and applying successful road mitigation strategies. Continued partnerships will help ensure that the survival of vulnerable turtle populations is supported as conservation strategies adapt to changing landscapes.

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