Assessing population status of Parachondrostoma arrigonis (Steindachner, 1866), threats and conservation perspectives

Abstract

Biodiversity is currently declining in the Mediterranean, particularly in freshwater ecosystems. The Iberian Peninsula is not an exception with many fish species threatened or endangered. This is the case of Parachondrostoma arrigonis, which has experienced a marked reduction of more than 80 % in both number and area of occupancy in the last 20 years. Species historical records showed a widespread distribution in the Jucar Basin, but according to recent records, P. arrigonis was completely absent in the main river course, being restricted to only some tributaries. Current fish distribution was grouped into only seven fish population nuclei geographically isolated among them. Only two population nuclei showed with well-developed fish populations. Factors affecting P. arrigonis distribution are associated to human activities, such as river channelization, flow regulation, pollution and habitat degradation, being concentrated in the middle and lower river reaches where the Jucar nase is in marked regression. Another key factor was the presence of introduced species, reporting a strong spatial segregation with the translocated Pseudochondrostoma polylepis, an ecologically similar species, and with the exotic piscivorous Micropterus salmoides and Esox lucius, which are currently occupying most of the P. arrigonis historical range. Because its dramatic situation, conservation measures must be urgently taken, for instance, by establishing conservation areas, an exotic fish removal programme, and by developing a flow regulation program to minimize dam effects. However it is necessary to increase our knowledge regarding the habitat requirements of the Jucar nase and its interactions with invasive species. If measures are not implemented its extinction seems inevitable.