Modeling the impacts of natural and human factors on the hatching success of the loggerhead sea turtle Caretta caretta along the coasts of Italy

Abstract

Coastal biodiversity is globally threatened by climate change and human pressures, including habitat destruction, overfishing, eutrophication, and pollution, which alter natural coastal ecosystem processes. Caretta caretta, hereafter referred to as loggerhead sea turtle, is listed as "Vulnerable" at global level and "Least Concern" in the Mediterranean Sea by the International Union for Conservation of Nature (IUCN). This species is the only sea turtle nesting along Italian coasts, making it crucial to understand the factors affecting its reproductive success for effective conservation strategies. However, key aspects of the ecology and life cycle in Italian waters, such as spatial distribution, reproductive site selection, and factors influencing reproductive outcomes and migratory movements, remain unknown. This study aimed to identify factors influencing the reproductive success of the loggerhead sea turtle. Data from 237 nests between 2019 and 2023 across 14 Italian regions were recovered, quality-checked, and analyzed. A statistical model predicting reproductive success, represented by hatching success, was developed, incorporating various environmental variables from marine and terrestrial spheres, along with local pressures from urbanization and anthropization. These predictors were related to hatching success using a generalized linear model (GLM) accounting for zero-inflated data. The best models identified both environmental variables, such as temperature and extreme wave events, and human-controlled factors, including the presence of dunes and coastal urbanization, as key predictors of hatching success. Coastal anthropization and beachfront disturbances were particularly important. While human activities can pose notable challenges to the loggerhead sea turtle, their identification also offers opportunities for enhancing its reproductive success through targeted management actions focused on mitigating pressures. Our findings highlight the urgent need for targeted conservation efforts to address both local and global challenges to protect and enhance the reproductive success of the loggerhead sea turtle and possibly other coastal species. Effective management can and should focus on mitigating human-induced pressures. Policymakers and conservationists need to work together to implement strategies that consider both the immediate human impacts and the long-term effects of climate change, ensuring the sustainable management of coastal ecosystems and the protection of endangered species like the loggerhead sea turtle.

Fig 1. Regional distribution and geographical division of the analyzed nests across coastal regions of Italy over 2019-2023.

(AB = Abruzzo; BA = Basilicata; CL = Calabria; CM = Campania; ER = Emilia-Romagna; LA = Lazio; LI = Liguria; MA = Marche; MO = Molise; PU = Puglia; SA = Sardegna; SI = Sicilia; TO = Toscana; VE = Veneto; N = North; C = Center; S =  South; n = 237) (All utilized geographical data are under the Creative Commons Attribution License (CC BY 4.0). Software: QGIS 3.3. Note: Own elaboration).

Fig 2. Distribution of nests along the Italian coasts divided by year (A:2019; B:2020; C:2021; D:2022; E:2023; F: Trend of registered nests along the Italian coast between 2019 and 2023; n

= 237). (All utilized geographical data are under the Creative Commons Attribution License (CC BY 4.0). Software: QGIS 3.3. Note: Own elaboration).

Fig 3. A: Trend of average latitude of the analyzed nest (n = 237) (blue line = max latitude, yellow line

= mean latitude, red line = min latitude; grey area = standard deviation). B: Trend of average longitude of the analyzed nest (n = 237) (blue line = max longitude, yellow line = mean longitude, red line = min longitude; grey area = standard deviation).

Fig 4. A: Nesting activity distribution (n = 237); B: Hatching activity distribution (n = 237).

Fig 5. A: Incubation period grouped by 10 days (n = 237); B: Total eggs grouped by 10 (n

= 237).

Fig 6. Hatching success along the Italian coast (nest success is grouped by 10%) (n

= 237).

Fig 7. Bivariate relationships between A: Deposition Month and Hatching Success, B: Hatching Month and Hatching Success, C: Deposition Month and Incubation period (days), D: Incubation Period (in days) and Hatching Success (n = 237; * : p-value < 0.05; **: p-value < 0.01).