The global impact of alien trout species — a review; with reference to their impact in South Africa

Abstract

Rainbow and brown trout have been introduced into at least 82 countries, where they have significantly impacted indigenous fish, aquatic invertebrates and amphibians. In many studies the second, and sometimes the first, most serious identified threat to indigenous aquatic fauna is introduced fish species. Brown trout, Salmo trutta, and rainbow trout, Oncorhynchus mykiss, were first introduced into South African waters as angling species in the later part of the nineteenth century, when environmental impact studies were neither considered nor undertaken. Trout have since been introduced mainly into the cooler upper catchments of rivers, many of which are now known to contain rare endemic aquatic species which urgently require conserving. Countries such as South Africa need to review the environmental costs of the presence of trout, and to take these costs into consideration when new policies and legislation are promulgated. Whilst there should be a complete ban on the introduction of trout into currently troutless sections of river, some rivers, particularly those harbouring threatened species, urgently need to be rehabilitated by having their trout eradicated. Part of the cost of this exercise should be borne by anglers from fees collected at approved trout angling areas. A number of recommendations are presented to help solve the present problems.


Keywords: alien fish species; Oncorhynchus mykiss; Salmo trutta; aquatic biodiversity; conservation legislation; fish conservation; hatcheries; impact; river rehabilitation; South Africa


(Afr J Aqua Sci: 2003 28(1): 61-67)