Invasive freshwater fishes in a South African RAMSAR wetland

 The Wilderness Lakes system, situated in the Western Cape of South Africa, forms a major component of the SANParks managed Garden Route National Park. The lakes and interconnecting channels are part of a RAMSAR site. As a result of introductions into the catchment area, four alien fishes occur in the lakes system. Three of these, the common carp Cyprinus carpio, Mozambique tilapia Oreochromis mossambicus and largemouth bass Micropterus salmoides are popular angling species and the fourth, the mosquitofish Gambusia affinis was most likely introduced for mosquito control. These alien fishes are recognised as being among the worst invasive fish species worldwide. Elsewhere, they have been linked to a variety of impacts including competition with native biota, alterations of invertebrate and vertebrate communities through predation, habitat alteration and introduction of fish diseases. Understanding the status and establishment of these fishes in the Wilderness Lakes is therefore important for the development of strategies with which to manage these invasions.

In an ongoing assessment of the fish fauna initiated in 2009 through a SANParks/South African Institute for Aquatic Biodiversity collaboration. The main aim is to better understand the functioning of the wilderness lakes system and the long term impacts that alien fishes may have on the system. The research has has also had considerable training impacts with more than 30 BSc Honours students from Rhodes University learning through participating in the research over the last four years. This year, the field trip was held from the 6th to 11th May and 8 honours students participated in a variety of sampling techniques including setting and retrieval of gill nets and fyke nets as well as seine netting. Students also undertook biological analyses on some of the fish sampled which involved dissection, sex and maturity determinations, otolith removal and isotope sample collection.

Group photo of the Honours class

Dr Olaf Weyl out in the field with his students