A management plan for a declining population of the Souss valley tortoise in an arid steppe-land of west-central Morocco

Abstract

The endangered Moorish tortoise Testudo graeca is the unique terrestrial chelonian species in North-west Africa. In west-central Morocco, the endemic subspecies, the Souss valley tortoise T. g. soussensis, occupies semi-arid to arid low-quality habitats, and is subject to serious threats. A long-term mark-recapture programme from 2001 to 2012 allowed estimating population size and structure, sex ratio, and survivorship in one of the well-known populations in a degraded and overgrazed arid steppe-land of west-central Morocco. Spring population size considerably decreased to more than half in less than 10 years, with a mean density lower than 3 ind.ha-1 in 2012 compared to its last known density estimat-ed in 2003. In spring 2012, the population structure exhibited an unbalanced male-biased sex ratio (61:39) and a scarcity of juveniles (<5%). We identified five major conservation problems in the study area: (i) habitat destruction and overgrazing; (ii) over-collecting of tortoises for pet trade , iii) direct dis-turbance; iv) tortoise handling mostly for field research, and v) increased extinction risk due to the small population size. We carried out a population viability analysis using the VORTEX software based on published and obtained data on population and life history parameters. With no management action, the population will go extinct during the forthcoming 40 years after the last estimate. The most efficient management option for a long-term persistence of the population would be reducing the nest and neo-nate mortality by 90%. To attenuate the impact of the threatening factors, we developed a management plan that includes population reinforcement and habitat restoration options.

Testudo graeca Linnaeus 1758 (Western Subspecies Clade: Testudo g. graeca, T. g. cyrenaica, T. g. marokkensis, T. g. nabeulensis, T. g. whitei) – Mediterranean Spur-thighed Tortoise, Moorish Tortoise, Libyan Tortoise, Moroccan Tortoise, Tunisian Tortoise, Souss Valley Tortoise

“…Testudo g. whitei has been known in Doñana since 1765-1774 (Granados 1987;Andreu et al 2000), and its distribution was more widespread historically, reaching the villages of Almonte and El Rocío (Machado 1859), and perhaps further west (López-Jurado et al 1979). In the middle of the 20th century, several hundred specimens corresponding to the subspecies T. g. marokkensis were introduced from Morocco (Valverde 1967).…”