Status update of the endemic and critically endangered cave catfish Clarias cavernicola Trewavas 1936, from the Aigamas Cave system, Namibia

Abstract

Knowledge of population sizes of threatened fish species is essential for formulation and implementation of effective conservation and management policies. Visual counts (VC) from two SCUBA diving expeditions during February and May 2019 were used to estimate the population size of the subterranean blind clariid cave-catfish Clarias cavernicola Trewavas 1936 in the Aigamas Cave system in Namibia. Two additional cave pools accessed through an entrance along the same fault, were explored during the May expedition. Two divers recorded 111 and 119 individuals in February and 35 and 41 individuals in May for the Aigamas Cave pool. Although the surveys were done to a depth of 40 m, individuals were only recorded to a maximum depth of 17 m. The difference between the February and May VC was 77 fish. This suggests that the catfish may potentially move to other pools through subterranean connections. The two new pools were found approximately 87 m below ground surface. A VC from above the surface by two observers showed that the first pool had at least 62 individuals of C. cavernicola and the second had at least 14 individuals. This survey has thus marginally, but importantly extended the range of this species to include two additional pools in the Aigamas Cave system. A reassessment of the conservation status of this species following the IUCN criteria, indicates that this species qualifies to be classified as Critically Endangered under criterion D, because of its limited geographic range and multiple threats, such as from excessive underground water abstraction, pollution and illegal collection by aquarists.