Ecology and conservation of Garra ghorensis, an endangered freshwater fish in Jordan
Authors: Hamidan, N.A.
The focal species of the research was the freshwater cyprinid fish Garra ghorensis. Endemic to the southern Dead Sea basin of the Middle East, it is ‘Red listed’ by the IUCN as ‘endangered’. It inhabits the small rivers of the basin (‘wadis’), existing within fish communities of very low species diversity. The aim of the research was to inform conservation strategies for the species through investigations into their phylogeny, current distribution, life history traits and feeding relationships.
Analysis of the mitochondrial DNA of G. ghorensis with other fishes of the Garra genus tested two contrasting hypotheses on their biogeographic origin: whether they were descended from Garra tibancia in the Arabian Peninsula or from a common ancestor shared with Garra rufa, which would have indicated dispersal from the Mediterranean basin and Mesopotamia. The phylogenetic tree clearly indicated that G. ghorensis shared a common ancestor with G. rufa and thus was of Mediterranean origin. These phylogenetic analyses were then important for interpreting G. ghorensis biogeography in relation to their natural range and current distribution. Surveys completed in 2010 provided data on their spatial distribution; this distribution was at least partially explained by historical geological and water salinity changes of the proto-lakes of Lake Samra and Lisan. These surveys also revealed that during the 2000s, there had been little change in G. ghorensis distribution, with populations still present in wadis that were recorded in 2002. However, at the surveyed sites, some alterations to the physical habitats and hydrology of the wadis were apparent, such as construction of impoundments.
To assess the life history traits and feeding relationships of G. ghorensis, three locally abundant populations were studied. These were an allopatric population, a population sympatric with the native cyprinid Capoeta damascina and a population sympatric with the invasive cichlid Oreochromis aureus. The allopatric and sympatric native populations were present in wadis with minimal habitat disturbance, whereas the sympatric invasive population was present in a wadi with substantial alteration, including some impoundments that deepened the main channel and reduced the flow. Analyses of ages, growth rates and reproductive traits revealed that life spans, growth rates and reproductive investment were greatest at this disturbed site, despite being relatively altered from the apparently preferred habitat of the species. These results suggested that providing the hydrological disturbance at sites where G. ghorensis is present still enables the completion of their life cycle then their populations can withstand some aspects of habitat disturbances from anthropogenic activities.
The feeding relationships of G. ghorensis were then assessed in relation to the presence of C. damascina and O. aureus in two of the sites, and used a combination of stomach contents analyses and stable isotope analysis. Results from both methods revealed whilst there were some overlaps in the trophic niches of the fishes, diets were based mainly on detritus and algae. These items are rarely limiting in freshwaters and thus whilst resources were shared, it was unlikely to result in high levels of inter-specific competition.
Thus, an important ecological feature of G. ghorensis populations is their plasticity in life history traits and their resource use that enables some adaptation to disturbed environments. This suggests that their conservation management does not necessarily have to return their habitats to pristine conditions, as their adaptive capacity should enable some adaptation to the new conditions and thus continued population sustainability. Consequently, providing that development schemes prevent the destruction of the key habitats required for the completion of the G. ghorensis lifecycle, then their populations could remain sustainable in the face of continued development in the region.