Climate change can have profound impacts on aquatic ecosystems and associated species, particularly reptiles with temperature-dependent sex determination (TSD). This study aimed to evaluate assisted migration and adjustments to protected area boundaries as strategies to support the survival of the marsh crocodile (Crocodylus palustris Lesson, 1831) under climate change. To this end, changes in habitat suitability were projected under four climate scenarios up to 2070 to identify potential climatic refugia. Modeling results indicated that a portion of the Gando Protected Area would remain suitable under the RCP2.6 scenario, whereas the entire area would become unsuitable under other scenarios. Consequently, reliance on current protected area management alone is insufficient for species conservation, emphasizing the necessity of assisted migration. Accordingly, a revised boundary for the Gando Protected Area was proposed based on the results, incorporating climatic refugia, population critical zones, potential human crocodile conflict areas, and natural watershed boundaries. Permanent monitoring plots were also established, and priority sites for feasibility studies on species translocation to new habitats were mapped.
Introduction
Climate change is an inevitable ecological change that can significantly impact aquatic ecosystems and their dependent species, particularly reptiles with temperature-dependent sex determination (TSD). Therefore, this study aimed to evaluate assisted migration and adjustments to protected area boundaries as strategies to support the survival of the marsh crocodile (Crocodylus palustris Lesson, 1831) under the influence of climate change.
Material and Methods
Southeast Iran was selected as the study area, which includes the northwesternmost extent of the global distribution of the marsh crocodile. For this purpose, changes in the suitable habitat range of the marsh crocodile under four climate scenarios (RCP2.6, RCP4.5, RCP6.0 and RCP8.5) through the year 2070 were projected using maximum entropy modeling (MaxEnt) and bioclimatic variables from the KGClim_V1 data bank. The MTSS threshold was used to classify the habitat suitability layer based on historical data and future scenarios. The common suitable areas in historical and future data indicated climatic refuges for this species.
By overlaying Boolean layers representing potential changes in habitat suitability due to climate change with the Gando Protected Area layer- as the species’ main habitat- the feasibility of future species conservation was assessed through the designation of restoration zones or boundary adjustments of protected areas. The network of protected areas was also examined in supporting the survival of the species in the future.
In addition to analyzing the population trend using previous studies and expert opinions from field observations, critical population areas were also mapped based on changes in habitat suitability. For this purpose, based on the Boolean layers of historical and future habitat suitability, zones were classified from low-risk (suitable under both historical and all four future scenarios) to high-risk (suitable only under the historical and one future scenario).
To identify potential future human/crocodile conflicts, settlements (cities and villages) and road networks were overlaid with historically and future-predicted suitable habitat areas (areas common across all four climate scenarios).
Based on the results and the natural boundaries of watersheds, a revised boundary for the Gando Protected Area was proposed.
Also, permanent population monitoring plots for the species were identified in this area based on the results of the modeling and the species' presence. Finally, priority areas for conducting local studies on assisted migration were identified within the main watershed of the species' distribution and its neighboring watershed.
Results and Discussion
The modeling results showed that in all climate scenarios, an increase in the area of the suitable habitat area is expected by 2070, with the largest increase in the RCP2.6 scenario and the smallest in RCP6.0. It was also predicted that part of the Gando Protected Area would fall outside the suitable habitat under RCP2.6, and the entire area would become unsuitable under the other scenarios. Similarly, other protected areas will not fall within the projected suitable habitat areas.
Consequently, depending only on the management of protected areas or establishing restoration zones within them will not be enough to conserve this species. This phenomenon is attributed to temperature-dependent sex determination (TSD) in the species, where fluctuations in temperature can influence the sex ratio of hatchlings, potentially resulting in long-term changes in the population's structure and composition. Therefore, revising protected area boundary and implementing management strategies that support the assisted migration of this species are necessary conservation actions. In this regard, a revised boundary for the Gando Protected Area was proposed based on the results of modeling including: climatic refuges, population critical areas, historical species distribution, crocodile/human conflict, and consideration of watershed boundaries.
The permanent plots were also located for monitoring the population of the marsh crocodile. Additionally, spatial prioritization for feasibility studies on the species’ assisted migration to new habitats was conducted in the southern Balochestan watershed—the primary distribution area of the species—and in the adjacent watershed (Bandar Abbas–Sedij). Projected areas of human/crocodile conflict by 2070 were also identified.
Conclusion
The present study was conducted to investigate the possibility of protecting the marsh crocodile in the Gando Protected Area, and showed that in addition to the Gando Protected Area, which is the main habitat of the species, the existing network of protected areas will not be effective in supporting the survival of the species in the future. Maintaining the current habitat configuration or defining a restoration zone within climatically unsuitable portions of the protected area will not be feasible, as these areas are projected to become unsuitable under future climate scenarios. Given the high probability of habitat suitability shifts, assisted migration will be inevitable for the survival of the species.
The ability of the marsh crocodile to move according to climate change will increase the human/crocodile conflicts, and therefore, the migration path of the species should be consciously paved through assisted migration.
Accordingly, based on the modeling conducted, critical population areas and climatic refuges for the species were located to show the human/crocodile conflicts, propose a revised boundary for the Gando Protected Area, population monitoring plots for this species, and prioritize target sites for local and field-based feasibility studies supporting the implementation of assisted migration actions.
Acknowledgements
This article is an excerpt from the project with contract number 1402/600/55755, dated February 27, 2024 (1402/12/8 SH), funded by Department of Environment. The authors wish their full appreciation and sincere gratitude to all the respected officials and esteemed experts from the headquarters in and provinces who participated in the advancement of this project. The authors report administrative and non-financial support was provided by the University of Zabol, Office of Research, by grant number IR-UOZ-GR-4956.