Browsing by Author "Shelton, Jeremy"

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    Population crash of an endemic South African cyprinid: the role of non-native fish, drought and other environmental factors
    (2020) Cerrilla, Cecilia; Shelton, Jeremy; Paxton, Bruce; Schumann, Mandy; Reed, Cecile
    Native freshwater fish are in decline worldwide due to human impacts including impoundment, changes to water quality, over-abstraction, climate change and the introduction of non-native species. South Africa's Cape Fold Ecoregion (CFE) harbours exceptionally high freshwater fish endemism, yet the majority of these species are threatened with extinction. The Clanwilliam sandfish (Labeo seeberi), an endangered cyprinid, has declined across its range in the CFE and currently exists in only a handful of tributaries of the Doring River in severely fragmented populations. The last remaining recruiting sandfish population occurs in the Oorlogskloof River, making this tributary one of critical conservation value. In this study, I analysed a six-year dataset comprising fish survey data from 38 sites along 25 km of the Oorlogskloof River to characterise spatio-temporal variation in sandfish abundance and size structure and evaluate the relative influence of different environmental factors on sandfish population trends. The environmental factors considered included other fish in the system, especially three non-native fishes (banded tilapia Tilapia sparrmanii, smallmouth bass Micropterus dolomieu and bluegill sunfish Lepomis macrochirus), temperature, precipitation, habitat characteristics and a range of physicochemical factors. The results show that sandfish have experienced a 93% decline in the sampled stretch of the Oorlogskloof River since 2013 and that the ongoing drought may be preventing recovery. They also suggest that banded tilapia do not adversely affect the Oorlogskloof River sandfish population, while predation of juveniles by smallmouth bass and/or bluegill sunfish apparently reduces the abundance of sandfish, especially of juveniles, where these non-native fish are present. Future studies should attempt to isolate the relative impacts of the different invasive fish species and examine habitat requirements of different sandfish life stages. Management of the river's sandfish population should focus on precautionary actions such as continued monitoring and landowner engagement, as well as clearing dams of non-native species high in the catchment, to prevent the further upstream invasion of smallmouth bass and bluegill sunfish. Proactive measures, such as eradicating smallmouth bass and bluegill sunfish from the Oorlogskloof River, are also necessary to restore connectivity of suitable sandfish habitat in the Doring River system.
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    The Role of Images in Freshwater Conservation in South Africa: An Analysis of Images and Perceptions of Freshwater Fish
    (2021) Burnette, Jessica; Shelton, Jeremy; Amar, Arjun; Weyl, Olaf
    Freshwater biodiversity is highly threatened, but under-represented in media, and less well known than marine and terrestrial counterparts. The current lack of public awareness of freshwater species and ecosystems may limit freshwater conservation as a popular cause. The manner in which species are portrayed in the popular media can influence awareness and support for conservation. In this digital age, images in particular may play a major role in public support for conservation. In this study, I examined images sourced from the web of ten native South African freshwater fish species and images of a general search for ‘freshwater fish South Africa' to investigate the kinds of images people are exposed to. Results show that only 28% of speciesspecific images showed the fish in a water habitat, with the remaining images showing the fish out of water, often with the presence of humans. I then conducted an online survey of people's perceptions of freshwater fish images. Respondents were shown images of native South African fish in water and out of water. From this survey, 73% of respondents stated they would choose images of fish in water in their natural habitat to communicate the importance of conserving freshwater ecosystems and freshwater fish. Over 95% of respondents, agreed that images play an important role in rallying support for nature conservation in general. When shown images of fish in water, 57% of respondents stated the in-water images evoked a desire to know more about freshwater environments and 49% stated a desire to know more about freshwater fish. The survey also investigated respondent willingness to donate money and time to freshwater conservation and explored whether showing either ‘in-water' or ‘out of water' images beforehand influenced this response. The results suggested that the type of images presented beforehand had little to no effect on willingness to donate, but other factors such as gender, natural sciences background, and history of visiting freshwater environments influenced respondent willingness to donate time and money. Overall this study suggests that future considerations should be given to how freshwater fish species are portrayed in science communication and environmental education through imagery.
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    Tolerating climate change: a study on the influence of thermal history on thermal tolerance of Galaxias zebratus in rivers of the Cape Peninsula, South Africa
    (2018) Olsen, Toni; Dallas, Helen; Shelton, Jeremy; Reed, Cecile
    Global climate change models predict a reduction in rainfall and rise in air temperature for the Cape Peninsula of South Africa’s Cape Floristic Region (CFR). The CFR is a biodiversity hotspot renowned for its high level of floral endemism, but the high level of endemism also applies to the region’s freshwater fish assemblage. Whereas the current threats to endemic freshwater fish include habitat modification, water abstraction, pollution and impacts of non-native species, climate change is predicted to further exacerbate negative impacts on fish communities. The endemic CFR fish species, Cape Galaxias, Galaxias zebratus Castelnau, 1861, is widespread throughout the region, and occurs in both non-perennial and perennial rivers, and wetlands. The species is thought to be a relict group of ancient species originating from the break up of Gondwanaland 180 – 135 million years ago. Endemic CFR freshwater fish, like G. zebratus, may be sensitive to the thermal regime of their environment and may thus be influenced by climate warming. The most commonly used experimental approach for determining the effect of elevated temperature on freshwater biota is the Critical Thermal Method (CTM). The CTM determines the upper thermal tolerance limit or critical thermal maximum (CTmax) of a species. Thermal history is the range of temperatures experienced by an organism in its natural habitat over time and this may be an important factor determining the thermal tolerance of species. The aim of this study was to evaluate the influence of thermal history, reflecting a stream’s thermal profile, on upper thermal tolerance limits of G. zebratus. We hypothesised that G. zebratus from warmer sites would have a higher CTmax than individuals at cooler sites. To examine the influence thermal history has on the thermal tolerance of G. zebratus, hourly water temperature data were collected and the CTmax values were determined for fish (n=30 per site) from 10 different sites in rivers of the Cape Peninsula. The CTmax values from all sites for the November-December experimental period ranged from 30.00°C to 32.45°C. CTmax values for all sites from the JanuaryFebruary experimental period ranged from 31.29°C to 33.42°C. Upper thermal tolerance limits of G. zebratus increased from the November-December experiments to the January-February experiments. Regression analyses show that G. zebratus upper thermal tolerance limits are significantly influenced by its thermal history as characterised by the seven day moving average of daily mean (Mean_7) two weeks preceding the experiments, implying that changes to the thermal regime will influence the thermal tolerance of G. zebratus. The resultant regression equation allows G. zebratus CTmax to be predicted by thermal history based on Mean_7, providing valuable information to set thermal limits of G. zebratus and guide future research. This is the first study on the thermal ecology of G. zebratus in the CFR and in Africa. The data not only enhance understanding of the thermal ecology of the species, but also further our understanding of their potential vulnerability to climate change.