Application of extinction risk and conservation criteria for assessing fish species in the lower La Plata River basin, South America

The Lower La Plata River basin contains between 160 and 260 native species depending on the river segment, with a few stretches containing locally endemic species. Extinction risk analysis for 185 freshwater fish in the lower La Plata River basin is presented for the first time on the basis of regionally standardized International Union for Conservation of Nature (IUCN) Red List criteria and is compared with alternative methods within the region. There were 11 threatened species (6%), of which three were considered as Endangered and eight as Vulnerable. A further three were rated as Near Threatened; while 121 (66%) were assessed as being of Least Concern, and 49 (26%) remained Data Deficient. The application of regional guidelines after using the global criteria did not change the categories established. The application of the IUCN criteria A and B presented considerable challenges because of insufficient information, with criterion C being inapplicable; whereas criterion D proved valid in five instances where endemic species were found highly restricted in geographical range and only inhabiting small streams. The use of other approaches, such as the Sum of Index (SUMIN) method and the Assessment Method of Threat Degree (MEGA), resulted in only an 11% agreement with the IUCN results for the main commercial and recreational target species. The discrepancies between the IUCN and the other methods may be explained in that the former measures the extinction risk by population decline as the main criterion, whereas the latter two put more emphasis on the assessment of intrinsic vulnerability and the threat status, with these additional criteria being incorporated in order to define conservation priorities. Further research is strongly recommended for the application and improvement of the IUCN regional criteria based on better ecological information, particularly data on non‐target species inhabiting small tributaries, wetlands, and headwaters across the basin.