Contrasting impact of invasive alien sport fish in the Cape Floristic Region : a focus on Micropterus dolomieu

Thesis (MScConsEcol)--Stellenbosch University, 2014.ENGLISH ABSTRACT: The number of introductions of alien species is on the rise globally. The resulting impacts on the invaded environments are diverse and often contrasting. Many deliberately introduced species have positive social and economic impacts as people use them to achieve a goal. These goals can be recreational, such as mountain biking in a plantation of alien trees or commercial such as harvesting alien trees for timber. Conflict often arises when the goals of the individuals using the alien species clash with the goals of those trying to mitigate negative impacts of the introductions. As many scientists are more inclined to favour native over alien species, the negative impacts of alien species are better documented in scientific literature. It is valuable to document contrasting impacts of alien species so that they may be managed in a way which does not cause unnecessary conflict. This thesis documents contrasting impacts of Micropterus dolomieu (smallmouth bass) within the Cape Floristic Region (CFR). It does this using the Rondegat River in the Olifants-Doring River system and the Clanwilliam Dam, in the same system, as case studies. Smallmouth bass, were removed from the Rondegat River using a piscicide called rotenone by the Western Cape nature conservation authorities; CapeNature. This thesis documents the results of snorkel observations and underwater filming of the river over this process. Native fish densities increased from 0.29 to 11.81 fish/100m2 following smallmouth bass removal, providing further insight into the negative ecological impacts of the species. The results of the monitoring show that smallmouth bass had extirpated three native species from the invaded reaches and was preying heavily upon juveniles that were dispersing downstream. The removal of the smallmouth bass from the Rondegat River was a project which cost CapeNature both money and time. Through personal communication with implementers of the project and through access to CapeNature financial records, this thesis documents the costs of the Rondegat River smallmouth bass eradication project. It cost CapeNature R 358 068 per kilometre of river to eradicate smallmouth bass from the Rondegat. An estimated 5079 man hours were spent on the final planning and implementing of the two rotenone treatments. These costs represent a negative economic impact of smallmouth bass and are useful in estimating the costs of future eradication projects. These two negative impacts are contrasted with the positive socio-economic impacts of the species. The Clanwilliam Dam, further downstream, hosts a large smallmouth bass population and is considered to be one of South Africa’s premier smallmouth bass fishing destinations. Anglers who travel to the dam in order to catch smallmouth bass often spend money at local businesses, thus contributing to the local economy. This expenditure is a positive economic impact of smallmouth bass. Anglers were interviewed at the dam and it was estimated that they spend R2 000 721.61 in the town of Clanwilliam every year. This is taken as the economic impact of smallmouth bass angling upon the town. This expenditure has a positive impact on local businesses and their employees. Smallmouth bass therefore, have contrasting impacts within the CFR and it is important that they are all considered in the management of the species. The Rondegat River smallmouth bass eradication project is an example of how the negative impacts of smallmouth bass can be mitigated without affecting its positive impacts and is a case study that could potentially inform how management of the genus proceeds in South Africa.AFRIKAANSE OPSOMMING: Die aantal toevoegings van nie-inheemse spesies is besig om wêreldwyd te vermeerder. Die gevolglike impakte op nuwe omgewings is divers en ook gereeld kontrasterend. Baie spesies wat doelbewus toegevoeg word het positiewe sosiale en ekonomiese impakte omdat mense hierdie spesies gebruik met ’n spesifieke doelwit in gedagte. Sodanige doelwitte kan met ontspanning te doen hê, byvoorbeeld om in ’n plantasie nie-inheemse bome met ’n bergfiets te kan ry, of kan kommersieel van aard wees, byvoorbeeld die inoesting van nie-inheemse bome vir werkhout. Daar ontstaan egter gereeld konflik as die doelwitte van die individue wat die nie-inheemse spesies gebruik bots met die doelwitte van diegene wat hierdie spesies se negatiewe inpakte probeer teëwerk. Aangesien baie wetenskaplikes geneig is meer gunstig teenoor inheemse as teenoor nie-inheemse spesies te wees, word die negatiewe impakte van nie-inheemse spesies beter gedokumenteer in die wetenskaplike literatuur. Dit is waardevol om die kontrasterende impakte van nie-inheemse spesies te dokumenteer sodat hierdie spesies op so ’n manier bestuur word dat onnodige konflik vermy kan word. Hierdie tesis dokumenteer kontrasterende impakte van Micropterus dolomieu (kleinbekbaars) in die Kaapse Floraryk deur van die Rondegat-rivier in die Olifants-Doring-rivierstelsel en die Clanwilliam-dam (in dieselfde stelsel) as gevallestudies gebruik te maak. Kleinbekbaars is deur die Wes-Kaapse natuurbewaringsowerhede, CapeNature, met ’n gifstof genaamd rotenone uit die Rondegat-rivier verwyder. Hierdie tesis dokumenteer die resultate van visuele en fisiese monitering van die rivier. Ná die verwydering van kleinbekbaars het inheemse digthede van 0.29 tot 11.81 vis/100m2 verhoog. Dit verskap verdere insig in die negatiewe ekologiese impakte van swartbaars. Die resultate van die monitering toon dat kleinbekbaars drie inheemse spesies uitgeroei het in die rivierrakke waar hierdie spesie ingedring het, en ook dat kleinbakbaars besig was om hewig jag te maak op jongvisse wat stroomaf uitswerm. Die verwydering van die kleinbekbaars uit die Rondegat-rivier was ’n projek wat CapeNature geld, sowel as tyd, gekos het. Deur gebruik te maak van persoonlike kommunikasie met implementeerders van die projek en deur toegang tot CapeNature- finansiële rekords, dokumenteer hierdie tesis die koste van die projek om kleinbekbaars uit die Rondegat-rivier te verwyder. Dit het CapeNature R358 068 per kilometer van die rivier gekos om kleinbekbaars in die Rondegat uit te wis. Dit het verder ’n beraamde 5079 man-ure gekos om die twee rotenone-behandelings toe te dien. Hierdie koste verteenwoordig ’n negatiewe ekonomiese impak van swartbaars en is waardevol om die koste van toekomstige uitwissingsprojekte te beraam. Hierdie twee negatiewe impakte word in kontras gestel met die positiewe sosio-ekonomiese impakte van die spesie. Die Clanwilliam-dam, verder stroom af, het ’n groot swartbaarspopulasie en word gesien as een van Suid-Afrika se topbestemmings vir swartbaarshengel. Onderhoude is met hengelaars gevoer en dit is bepaal dat hulle R2 000 721.61 elke jaar in die dorp Clanwilliam spandeer. Dit is geneem as die ekonomiese impak van swartbaarshengel op die dorp. Dit het ’n positiewe impak op plaaslike besighede en hulle werknemers. Kleinbekbaars het dus kontrasterende impakte in die Kaapse Floraryk en dit is belangrik dat al die impakte in oorweging geneem word met die bestuur van die spesies. Die kleinbekbaars-uitwissingsprojek in die Rondegat-rivier is ’n voorbeeld van hoe negatiewe impakte van swartbaars teëgewerk kan word sonder om die positiewe aspekte van die spesies te beïnvloed, en die projek dien as ’n model vir hoe om die bestuur van die genus in Suid-Afrika voort te sit