Remote Sensing Data Reveal a Significant Reduction in the Area of the Nesting Habitat of Rafetus euphraticus in the Tigris River, Southeastern Turkey

Abstract

The Euphrates Softshell Turtle (Rafetus euphraticus) is an endangered freshwater turtle native to the Tigris-Euphrates river system. Habitat destruction caused by dams and sand mining poses a major threat to the species. This study quantitatively assesses the occurrence of sandy areas in the upper Tigris in Turkey as a key component of their nesting habitat, utilizing remote sensing data. An ensemble approach was employed, applying and combining Generalized Additive Models (GAM), Generalized Boosting Models (GBM), Generalized Linear Models (GLM), and Random Forests (RF) for classification. The models indicate that, compared to 2018, the occurrence of sandbanks-assumed to be crucial nesting habitat for this species-was reduced by 41% in 2022 following the construction of a large dam. Additionally, sand mining and flooding of adjacent lands have fragmented and degraded the remaining sandbanks. The survival of the Turkish population of the Euphrates Softshell Turtle requires immediate and effective action.

Keywords: Euphrates Softshell Turtle; conservation; dam; habitat suitability; sand mining.

FIGURE 1

Euphrates Softshell Turtles ( Rafetus euphraticus ) basking on the banks of the Tigris River.

FIGURE 2

Map of the upper parts of the Tigris and Euphrates Rivers in Turkey (inset), along with the study area (solid lines) which is restricted to the main channel and major tributaries of the Tigris River delineated by two overlapping adjacent Sentinel‐2 image tiles (dashed lines, see text). The localities of dams mentioned in the text were also shown.

FIGURE 3

Sand quarries in the large areas in the upper part of the Tigris causing severe habitat destruction.

FIGURE 4

Percentual distribution of grouped cell values by years in the ensemble model raster maps indicating quality loss in the nesting habitats of Rafetus euphraticus in the upper part of the Tigris. The probability of sand habitats is represented by blue and red dots, with blue indicating lower probability and red indicating higher probability. The sand habitats are mainly separated by the threshold, which is shown by the vertical dashed line.

FIGURE 5

An example location indicating dramatic disappearances of sand banks (red patches) on the potential nesting zone (dark blue coastal areas) before (top panel) and after (bottom panel) the water retention by the Ilısu Dam in the upper Tigris area (insets).