This 2017 video from the USA is called Slender-horned Gazelles on Exhibit | Bronx Zoo.
From Wildlife Extra:
Slender-horned gazelles – How to count them in the Sahara?
Slender-horned gazelle – Ghost of the sands – Courtesy of Sahara Conservation Fund
April 2012. Recently the Sahara Conservation Fund, the Zoological Society of London, and the Sahelo-Saharan Interest Group have participated in surveys of the slender-horned gazelle (IUCN ‘Endangered’) in Algeria and Tunisia. Reconnaissance visits to the Algerian Erg Occidental and Erg Oriental were interspersed with camel-based surveys of the Tunisian sector of the Erg Oriental at Djebil, and most recently the Jabbes-Senghar National Park.
Mixed news – Heavily hunted, but still there
The news about this poorly known and very striking gazelle is mixed. Like ghosts of the sands, the ‘reem’ as they are known in Arabic, are always elusive and difficult to see. In spite of this, our local Tunisian partners stress that almost everywhere the gazelles suffer from uncontrolled hunting, irrespective of their protected status.
Nonetheless, it is also true that, without fail, on fieldtrips to the margins of the great sand seas, fresh gazelle tracks have proved relatively easy to find. The circumstances prompt key questions. First, are we identifying these tracks correctly and not confusing them with the more widespread dorcas gazelle, which is also present at the edge of the ergs, though apparently less so in the interiors? And second, how can we find out what these observations mean in terms of numbers of gazelle?
The great difficulty with the second question is that the tumbling dune landscape favoured by well-camouflaged and very shy slender-horned gazelles, while offering memorable desert scenery, provides an almost impossible terrain for conventional ground-based survey methods, such as those we have used for dorcas gazelles in the far less sandy habitats of the Sahel. Perhaps the best option to establish numbers will be to conduct helicopter-based surveys.