Conservation of the native freshwater fishes of the Cape Floristic Region (South Africa): management of non-native species

Freshwater fishes are among the most threatened taxa in the world. Increasing demand for freshwater, habitat degradation and the introduction of non-native species, will continue to place pressure on the remaining native freshwater fishes. A meta-analysis estimated that more than 90% of river habitat in three major catchments has been invaded by non-native fish and that catchments covering less than 1% of Cape Floristic Region have no recorded non-native fish introductions, the major rivers containing 10 or more non-native species. The majority of the native fishes continue to be threatened by the presence of non-native fish.
Profound taxonomic and functional changes to freshwater fish assemblages in Mediterranean-climate regions resulting from non-native fish introductions were identified. Phylogenetic preference was exhibited for species selected with more than 90% of introductions originating from five taxonomic orders. The pathways for introductions were consistent across all Mediterranean-climate regions. The results show strong evidence of on-going taxonomic and functional homogenization of freshwater fish faunas. Characteristics suitable for risk assessment databases in Mediterranean-climate regions were identified.
The difficulties associated with attempting to identify the reasons for the decline of a critically endangered fish, even for a relatively simple system, were demonstrated. Water quality, pesticide exposure, instream and riparian zone habitat, and dietary overlap between native and non-native species were explored. The results of the study were inconclusive. The results do indicate that native and non-native species can co-occur in the complex habitat of one tributary, but not in the simple habitat of the other.
A social survey of freshwater anglers showed that angling for non-native species is important to the anglers and that they are not likely to switch to angling for native species, with the possible exception of Clanwilliam yellowfish. The anglers considered the conservation of native fishes extremely important but less than half believed that the conservation authority were doing a good job in conserving native fishes. The results indicate that support for the conservation authority's proposed piscicide project is low but that it could increase support for conservation projects by using large cyprinids as flagship species. Many options are available to the conservation authority to improve their efforts to manage non-native fishes in the region. The most important of these are the delineation of roles and responsibilities and the compilation of a comprehensive conservation plan.