Poblana alchichica: A threatened silverside species?

The status of local endemic species such as Poblana alchichica is difficult to assess, and therefore conservation measures are not efficiently implemented. However, in recent years several methods have helped compare status of different species based on objective criteria. The method to evaluate the extinction risk of Mexican native species (MER), partially based on Gardenfors et al. (2001), considers 4 criteria regarding the taxon: (1) distribution extent in Mexico, (2) habitat condition, (3) intrinsic biological vulnerability, and (4) human impact on the species. Numerical values are assigned to each criterion in ascending risk order. According to Tambutti et al. (2002), each criterion is independent from the others, and the addition comes to be an accumulative evaluation of risk (SEMARNAT 2002). Even if independently evaluating criteria 2 and 4 is difficult, the grade of each criterion is required to obtain the final assessment. The lack of studies on P. alchichica (Pisces: Atherinidae) – and quite probably for many other species – prevents the accurate quantification of 3 of these 4 criteria (except distribution extent) required for the extinction risk assignation. Previous studies on P. alchichica (Fig. 1) are solely taxonomic. De Buen (1945) described the new silverside species collected from Lake Alchichica. Later, Alvarez (1950) and Guerra Magana (1986) considered Alchichica’s silverside to be a subspecies (P. alchichica alchichica). However, Miller (1986), in his study on the origin and geography of the fishes of Central Mexico, and Espinosa et al. (1993), in their list of Mexican freshwater fishes, re-evaluated the specific status of P. alchichica. Our study aimed to provide scientific data to support (a) the actual risk status of P. alchichica by identifying the factors imposing risk to the species through habitat alteration and population status, and (b) to design adequate protection programs for this species.