Name: Campos JC

Biodeserts supervisor: Brito JC

Co-supervisor: Sillero N

Title: Water detection in desert environments: Evaluating the performance of Normalized Difference Water Indexes to identify potential dispersal corridors for Nile crocodiles in Mauritania

Institution: University of Porto

Status: Completed

 

Abstract

Global biodiversity is experiencing a tragic period due to climate change and habitat fragmentation. Migration corridors could mitigate these effects, since they allow the input of new genes from adjacent populations. The habitat connectivity is crucial for populations living in desert environments, where resources are scarce and temporally variable. In the Sahara Desert, mountain systems could act as possible refugia for many relict species. The Nile crocodile (C. niloticus) is one of the species whose relict populations still persist in the mountains of Mauritania. Dispersing crocodiles are known to occur along temporary water-corridors, but the determination of aquatic habitats and associated hydrological connections is difficult. This work evaluates the state of populations of C. niloticus along the Senegal River, as well as the hydrological characteristics of Mauritanian mountains and the performance of remote-sensed tools for water delineation. A 9-day field mission was developed in 2010 along the Senegal River for assessing crocodile populations. Using a multi-temporal satellite series, water maps with seasonal and permanent features were derived through the application of three water indexes (MNDWI, NDWI1 and NDWI2). The indexes performances were compared based on control points extracted in previous fieldworks in Mauritania and tested using different thresholds for image reclassification. The fieldwork provided additional distribution data for nine localities with distinct population status. Water maps revealed seasonal and permanent features that might serve as dispersal corridors for crocodile populations living in Mauritanian mountains. The thresholds indicated different performances of each index in distinguishing water/non-water and seasonal/permanent points. Overall, the NDWI1 and MNDWI were the most consistent indexes in this study. Mauritanian mountains are crucial for the subsistence of crocodile populations and they may be acting as source of individuals to the sink-populations along the Senegal River. The importance of water systems in the connectivity of desert environments highlights the need for improvements of water detection methods.