Our first post and thoughts about watercraft-turtle collisions

Authored by Clay Shearer and Katie Black

Welcome! Thank you very much for supporting our project. At least once every two weeks, come here to find posts of field stories and observations that we find to be particularly noteworthy. If you have anything to contribute, we'd love to hear from you.

Our field work started in early May and will continue until October 2023. We are recording observations of wildlife, especially turtles, on County roads and adjacent habitat in Leeds and Grenville. A subsample of 12 locations on County roads were chosen for field surveys based on their predicted mortality risk: low, medium, or high. The high risk sites had known turtle occurrences and suitable habitat, the medium risk sites had suitable habitat but no record of turtle occurrences, and the low risk sites had neither. We have four road transects associated with each risk level; half are in Leeds and half are in Grenville to capture landscape variation between the two regions. Each transect is 200 m in length, which we survey twice each week on foot. We also include incidental and volunteer observations from County roads in Leeds and Grenville. These important contributions have been made by people local to the transect areas and members of this iNaturalist project. We would like to thank all of you! Observations submitted to iNaturalist will be used to refine our predictions of road mortality risk across the County, which will help us develop location- and risk-specific mitigation measures.

One of our transect sites is located at a bridge crossing on County Road 42 in Newboro, where the road spans a lock associated with the Rideau Canal system. We originally thought this site had a medium risk of road mortality because it was not affiliated with turtle occurrence records but appeared to be associated with suitable turtle habitat. Despite an absence of turtle records, we typically observe Northern Map Turtles in the canal. This species is listed as Special Concern under the Endangered Species Act. We have observed up to seven Northern Map Turtles basking on the same granitic boulder at once. It did not take us long to notice that many of these turtles had shell abnormalities. After seeing multiple motorboats pass through the canal and right by the turtles, we wondered if these could be attributed to propeller injuries. Please follow this link to see images of these turtles: https://www.inaturalist.org/observations/161471335

We set out to study wildlife-vehicle collisions on roads, but this observation got us thinking about watercraft-turtle collisions. Both pose significant threats to freshwater turtles, while the latter is sorely understudied. Northern Map Turtles are particularly susceptible to collisions with watercraft, and females may be at greater risk because they are typically twice the size of males and tend to venture farther from shore (Bulte et al., 2010). In a study conducted on the Trent–Severn Waterway, it was found that 28.6% of female Northern Map Turtles exhibited propeller injuries, with males showing 12.8% (Bennett et al., 2014). When motorboat collisions occur, chance of turtle survival is very low. Bulte et al. (2010) found that Northern Map Turtles hit by boats in nearby Lake Opinicon and the St. Lawrence River near Thousand Islands National Park have almost a zero percent chance of survival, with the odds being lower for females.

Vehicles and boats alike can negatively impact turtles, and while our study is focused on mitigating collisions with vehicles, we think that some mitigation measures typically used for roads could also be applied to waterways. For instance, perhaps a buoy with a turtle crossing sign and limiting boat speed would reduce risk of watercraft collisions with turtles. Public outreach to promote awareness would be beneficial, especially considering that the public is more familiar with turtle mitigation on roads than on waterways.

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References

Bulté, G., M. A. Carriere, and G. Blouin-Demers. 2010. Impact of recreational power boating on two populations of northern map turtles (Graptemys geographica). Aquatic Conservation: Marine and Freshwater Ecosystems, 20(1): 31-38. https://doi.org/10.1002/aqc.1063

Bennett, A. M., and J. D. Litzgus. 2014. Injury rates of freshwater turtles on a recreational waterway in Ontario, Canada. Journal of Herpetology, 48(2): 262-266. http://dx.doi.org/10.1670/12-161

Posted on July 10, 2023 05:47 PM by knoir