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Vulnerability of Cape Fold Ecoregion freshwater fishes to climate change and other human impacts
Abstract
Native freshwater fish populations throughout South Africa's Cape Fold Ecoregion (CFE) are in decline as a result of human impacts on aquatic habitats, including the introduction of non‐native freshwater fishes. Climate change may be further accelerating declines of many species, although this has not yet been studied in the CFE. This situation presents a major conservation challenge that requires assigning management priorities through assessing species in terms of their vulnerability to climate change.
One factor hindering reliable vulnerability assessments and the concurrent development of effective conservation strategies is limited knowledge of the biology and population status of many species. This paper reports on a study employing a rapid assessment method used in the USA, designed to capitalize on available expert knowledge to supplement existing empirical data, to determine the relative vulnerabilities of different species to climate change and other human impacts. Eight local freshwater fish experts conducted vulnerability assessments on 20 native and 17 non‐native freshwater fish species present in the CFE.
Results show (1) that native species were generally classified as being more vulnerable to extinction than were non‐native species, (2) that the climate change impacts are expected to increase the vulnerability of most native, and some non‐native, species, (3) that vulnerability hotspots requiring urgent conservation attention occur in the Olifants‐Doring, upper Berg and upper Breede River catchments in the south west of the region, (4) that in addition to providing guidance for prioritizing management interventions, this study highlights the need for reliable data on the biology and distribution of many CFE freshwater fishes, and (5) that identification of priority areas for protection should be based on multiple sources of data.
... South African freshwater ecosystems are no exception to the vulnerable state of systems further afield and are imperilled by a variety of threats, primarily as a result of anthropogenic interference (Darwall et al., 2009;Weyl et al., 2020). Among these threats, one of the most pressing are invasive organisms introduced to local freshwater systems, particularly predatory fish, alongside anthropogenic climate change and habitat degradation (Abell et al., 2007;Darwall et al., 2009;Tweddle et al., 2009;Filipe, Lawrence & Bonada, 2013;Ellender et al., 2017;Shelton et al., 2018a;Weyl et al., 2020). In South Africa, the Cape Fold Ecoregion (CFE) is recognised as biodiversity hotspot for freshwater fish, as despite a relative paucity of species, there is a very high degree of endemism (Tweddle et al., 2009;Ellender et al., 2017;Shelton et al., 2018a). ...
... Among these threats, one of the most pressing are invasive organisms introduced to local freshwater systems, particularly predatory fish, alongside anthropogenic climate change and habitat degradation (Abell et al., 2007;Darwall et al., 2009;Tweddle et al., 2009;Filipe, Lawrence & Bonada, 2013;Ellender et al., 2017;Shelton et al., 2018a;Weyl et al., 2020). In South Africa, the Cape Fold Ecoregion (CFE) is recognised as biodiversity hotspot for freshwater fish, as despite a relative paucity of species, there is a very high degree of endemism (Tweddle et al., 2009;Ellender et al., 2017;Shelton et al., 2018a). Current baseline scientific knowledge on the native fishes of the CFE is fairly narrow and tends to focus on either specific inquiries or notable biological traits (Ellender et al., 2017). ...
... The Olifants-Doring River System (ODRS) is characterised by a relatively high diversity of endemic and threatened fishes. In particular, the Cederberg Mountains within the ODRS catchment have been identified as "vulnerability hotspots" within an already vulnerable region (Shelton et al., 2018a). Ten of the 19 freshwater fish species endemic to the CFE are found the ODRS . ...
Anthropogenic change is a major threat to dwindling freshwater biodiversity. We present and synthesise available information regarding the fish community , ecology, threats and conservation options within The Cape Fold Ecoregion (CFE) of South Africa. The CFE is a particularly vulnerable region, with many range-restricted species and highly fragmented native fish ranges. The Rondegat River in the Olifants-Doring River System of the Western Cape province is of notable conservation value, as it hosts populations of important en-demic CFE species despite being at risk from non-native invasive species, climate change, and agriculture intensification. This river is unique, being the site of the first alien fish eradication programme of its kind in South Africa. The recovering Rondegat River imperilled cyprinid assemblage is used to frame the manner in which future environmental change may continue to disturb the ecology of the system. Conservation options and priorities are discussed in the context of a southern hemisphere Mediterranean-climate freshwater system.
... In addition to non-native fish impacts, river ecosystems in the CFE are under pressure from climate change and other human impacts (Dallas & Rivers-Moore, 2014;Shelton et al., 2018). Although the regional drought that began in 2015-2016 has abated somewhat in the wetter areas of the CFE, it still persists in drier regions, including in the Oorlogskloof catchment. ...
... Although the regional drought that began in 2015-2016 has abated somewhat in the wetter areas of the CFE, it still persists in drier regions, including in the Oorlogskloof catchment. Little is known about the implications of climate change and drought on endangered freshwater fishes in South Africa (Shelton et al., 2018), but indications from studies elsewhere raise concern that impacts could be strong and detrimental (Moyle et al., 2013). Drought alters the temperature, flow, oxygen content, turbidity, and salinity in a river, triggering a stress response and changes in physiological functioning in native fishes (Lennox et al., 2019). ...
... thermal and flow conditions to trigger spawning events, sandfish are expected to be highly influenced by projected changes in temperature and rainfall in the region (Shelton et al., 2018). ...
Freshwater fish are in decline worldwide as a result of introduced non‐native species, impoundment, water quality changes, over‐abstraction, and climate change.
The Clanwilliam sandfish Labeo seeberi is an endangered migratory cyprinid endemic to a single river system in South Africa's Cape Fold Ecoregion. It has declined across its range and persists as fragmented populations in the Doring River system.
One of the last recruiting populations occurs in the Oorlogskloof River, where three non‐native fish species are present: smallmouth bass Micropterus dolomieu , bluegill sunfish Lepomis macrochirus (both alien and invasive), and banded tilapia Tilapia sparrmanii (extralimital). Impacts of these non‐natives, together with climate change, may pose a serious threat to this important sandfish population and to other cohabiting native fish species.
A 6 year data set, collected over 9 years and spanning 25 km of the Oorlogskloof River, was analysed to characterize spatio‐temporal variation in sandfish abundance and size structure and to evaluate the relative impacts of biotic and abiotic factors on population trends.
Sandfish experienced a 92.6% decline in relative abundance from 2013 to 2018, driven by a 99.6% decline in young‐of‐the‐year individuals. A combination of extreme rainfall events and drought appear to have played a key role in the decline and subsequently prevented recovery.
Small sandfish (≤200 mm) were almost entirely absent from the centrarchid‐invaded section of the Oorlogskloof but were relatively abundant where these centrarchids were absent, suggesting a strong adverse impact of these non‐native species. Banded tilapia co‐occurred with sandfish without any apparent adverse impacts on the relative abundance or size structure of sandfish.
Improved water resource management and preventing the further spread of non‐natives must be conservation priorities. Localized eradication of non‐native species must also be considered to reclaim habitat and restore connectivity. Translocations may be required to prevent species extinctions.
... In South Africa, the Cape Fold Ecoregion (CFE) is represented by high levels of endemism, alongside rampant invasion and accelerating biodiversity loss (Tweddle et al. 2009;Ellender et al. 2017). Within this already vulnerable region, the Cederberg Mountains have been identified as "vulnerability hotspots" warranting high levels of conservation effort (Shelton et al. 2018b). In addition to historic invasions and habitat loss, the CFE is not spared by global trends in climate change, with many CFE species expected to be negatively impacted by projected thermal shifts and their associated effects (Dallas and Rivers-Moore 2014;Shelton et al. 2018b). ...
... Within this already vulnerable region, the Cederberg Mountains have been identified as "vulnerability hotspots" warranting high levels of conservation effort (Shelton et al. 2018b). In addition to historic invasions and habitat loss, the CFE is not spared by global trends in climate change, with many CFE species expected to be negatively impacted by projected thermal shifts and their associated effects (Dallas and Rivers-Moore 2014;Shelton et al. 2018b). ...
... Predicted warming under current models of climate change is likely to affect CFE river communities in variable, but generally negative, ways (Shelton et al. 2018b). The primary impacts are expected to be increased water temperatures and decreased total runoff (Dallas 2013;Dallas and Rivers-Moore 2014;Shelton et al. 2018b). ...
Shifts in temperature as a result of climate change play an important role in the long-term dynamics of resource use and resulting species interactions. Functional responses can give ecologically relevant insights of context-specific density-dependent resource use with low intensity animal use. This is especially useful when working with vulnerable species. The Rondegat River in South Africa’s Cape Fold Ecoregion (CFE) was subjected to an invasive species removal program and although the threatened cyprinid populations are in a state of recovery, they are still at risk from abiotic stressors. This community is characterised by an oligotrophic environment, shared ancestry and spatial overlap, suggesting high food resource competition between species. Functional responses of two cyprinid species were compared between two prey types (mosquito and chironomid larvae) at different field-representative temperatures (18 °C and 25 °C) in laboratory trials, with the aim to infer response and resilience to global change. Labeobarbus seeberi consistently outperformed Sedercypris calidus across prey types and temperature treatments at high prey densities. This was driven primarily by shorter handling times in L. seeberi, despite higher attack parameters in S. calidus under certain prey/temperature scenarios. Temperature increase had differential effects on prey consumption dependent on fish species and prey type. However, neither species showed significant intraspecific differences in functional response between temperature conditions for either prey species, indicating community resilience to thermal change in the CFE. Context-dependent experiments can be used in tandem with field data to identify conditions of potential ecological tipping points in imperilled systems.
... Factors heightening vulnerability to extinction of CFE endemic freshwater fish include high endemicity (20 species), limited geographical distribution and isolation in headwaters (Ellender and Weyl, 2014;Shelton et al., 2018). These factors further exacerbate the susceptibility of fish to climate change induced stressors such as changes in temperature and flow. ...
... Sixty percent of endemic freshwater fish species in South Africa's CFE are classified as either Endangered or Critically Endangered (Ellender et al., 2017). Ellender et al. (2017) and Shelton et al. (2018) identified a need for studies on the impacts of climate change of freshwater fish in the CFE and other Mediterranean regions. ...
... Galaxias zebratus is listed by the IUCN as Data Deficient (IUCN, 2018), though certain distinct lineages could be considered Critically Endangered due to their severely fragmented populations, restricted geographical range, and continuous decline as a result of habitat modification, loss of mature adults and restricted area of occupancy . There is a critical knowledge gap about the biology and ecology of CFE native fishes like G. zebratus, which limits an understanding of climate change impacts in this region (Shelton et al., 2018). ...
Compared to other climate regions of the world, Mediterranean regions are likely to experience more severe effects of climate change as rainfall decreases and temperatures increase. Global climate change models predict a reduction in rainfall and rise in the temperature of rivers in South Africa's Cape Fold Ecoregion (CFE) – a Mediterranean region in the south-west corner of the country. In the climate change context and with the prediction that stream temperatures will increase, determining thermal thresholds of freshwater fish in relation to their thermal history is a key element in understanding the potential impacts climate change and a rise in stream temperatures will have on already threatened freshwater fish.
The ability of aquatic species to withstand warming in the CFE will be determined by its upper tolerance limit (critical thermal maximum, CTmax). A fish's CTmax can be influenced by several factors, including the thermal characteristics of its environment (thermal history). In this study, we set out to examine whether the thermal tolerance of an endemic CFE fish species, the Cape Galaxias, Galaxias zebratus Castelnau, 1861, is influenced by its thermal history. We hypothesised that CTmax of G. zebratus individuals from warmer sites will have higher CTmax values than individuals from cooler sites. Hourly in situ water temperature data were collected and the CTmax values were determined for fish (n = 15 per site) from ten sites on six rivers on the Cape Peninsula of the CFE, and regression analyses revealed that G. zebratus upper thermal tolerance limits are indeed significantly influenced by its thermal history (as characterised by the seven day moving average of daily mean, Mean_7). CTmax was positively related to the thermal history of the rivers, indicating that G. zebratus, and potentially other stenothermic CFE freshwater fish species, is likely to be particularly vulnerable to climate warming. These findings broaden our understanding of thermal history patterns on fish thermal tolerances in Mediterranean rivers, and support G. zebratus conservation by determining its biological temperature thresholds and thermal requirements. Thermal data should be used to monitor and manage stream temperatures to ensure Mediterranean stenotherms can persist in their natural environment.
... In light of the ongoing and projected threats to the endemic freshwater fish fauna of the CFE (Ellender et al., 2017;Shelton et al., 2018), there is need for an assessment of the effectiveness of the current network of protected areas in mitigating these threats. Although previous studies have documented the distribution and conservation status of freshwater fishes in protected areas in the country and the region (Skelton et al., 1995;Impson et al., 2002;Russell, 2011), these studies did not evaluate long-term persistence. ...
... Historical and ongoing land transformation have resulted in major impacts on both terrestrial and aquatic habitats in lowland areas (Rouget et al., 2003a,b). Consequently, the middle and lower reaches of most rivers are impacted by unsustainable water abstraction, modification of natural flow regimes, sedimentation and pollution (Russell, 2011;de Moor and Day, 2013;Shelton et al., 2018). These impacts, coupled with widespread and established populations of non-native piscivores in mainstem habitats have resulted in highly fragmented native fish populations that persist in headwater streams that act as sanctuary areas (Chakona and Swartz, 2012). ...
... Impacts related to water over-abstraction are likely to worsen in future given climate change models that predict an increasingly dry climate, with a reduced period of river flow and temperature increases, thereby reducing water quality and quantity for aquatic species such as freshwater fish (Dallas et al., 2019). Shelton et al. (2018) reported that native fish species are vulnerable to the impacts of climate change, specifically in the CFE. Climate change was however not included in the current assessment of protection level of species due to the high level of uncertainty of specific impacts on each species and how they interact within the protected areas. ...
Freshwater systems and their associated biodiversity are among the most threatened ecosystems globally. The greatest threats to freshwater fishes are the introduction and spread of non-native species, pollution, habitat degradation and loss, and overexploitation. While many regions across the world contain extensive networks of protected areas, these are largely ineffective for protecting riverine systems and their biodiversity. This is because they were designed with the aim of prioritising conservation of terrestrial biodiversity, with limited or no consideration for aquatic systems. The Cape Fold Ecoregion, located within the Western and Eastern Cape Provinces of South Africa, is home to the highest percentage of threatened freshwater fishes in the country. The region has an extensive protected area network that protects a wide array of ecosystems, but limited information exists on the role of protected areas in conserving the endemic freshwater fish fauna of this region. This study evaluated the value of protected areas for protection of freshwater fishes in the Western Cape Province by setting species conservation targets and then intersecting species distribution data with protected area polygons. Conservation targets were set to protect the minimum viable population required for long-term persistence, with a minimum of 10 subpopulations as a target. This, along with other factors such as population viability and protected area effectiveness was used to determine whether a species was effectively protected by the current protected area network. Species were classified into one of four categories; (1) “well protected,” (2) “moderately protected,” (3) “poorly protected,” and (4) “not protected.” Our results indicate that the majority of native fishes are inadequately protected within the current protected area network in the province. This is mainly a result of the linear nature of riverine ecosystems that exposes them to impacts and threats that emanate from outside of the protected area. These limitations are not unique to the CFE, and our findings have broader implications as they highlight the need for integrating both the riverine and terrestrial ecosystems in the design, expansion and management of protected areas. This will enhance and maximise conservation and protection of riverine systems and their unique biodiversity.
... An understanding of species-habitat relationships is a fundamental requirement for management of IRES and their associated communities which are threatened by projected increases in the severity and frequency of droughts due to future global climate change (Xenopoulos et al. 2005;Magalhães et al. 2007;Jaeger et al. 2014;Leigh et al. 2016;Marshall et al. 2016). However, within Mediterranean regions, the reliable assessment of faunal vulnerability and efforts to conserve the unique and threatened aquatic fauna inhabiting IRES are hindered by the lack of knowledge regarding the ecological requirements of these animals (Shelton et al. 2018). The situation is particularly acute for the Cape Fold Ecoregion (CFE) in South Africa where much of the historic research effort in this region has focussed on the systematics and biogeography of stream fishes, whereas ecological and biological studies have been confined to selected taxa (e.g. ...
... Projections of global climate change indicate that some sections of the CFE are likely to become drier due to more frequent and severe droughts (Dallas & Rivers-Moore 2014). Intermittent streams in this region are particularly vulnerable because increased human demand for the limited water resources is likely to cause excessive water abstraction, which may result in further modification of the hydrological regimes (increase the intermittency) of these sensitive habitats, with potential deleterious impacts on the endemic and highly threatened aquatic fauna (Shelton et al. 2018). ...
... It would also be essential to undertake controlled laboratory experiments to determine the physiological tolerances of the individual fish species. This information is essential for inferring species vulnerability and adaptive capacity to projected global climate change (Comte & Olden 2017;Shelton et al. 2018). Studies that improve our understanding of the ecosystem services provided by IRES are also essential in order to justify and promote the protection and restoration of these unique ecosystems . ...
... Of particular concern was the large overlap between the distributions of threatened species and non-native species in South Africa, with the majority (58%) of threatened species co-occurring with non-native species ( Figure 6D). Non-native species can have profound and devastating impacts on both native threatened species and, more broadly, freshwater habitats as a whole, and are considered a top threat to native freshwater fish in South Africa [13,[32][33][34]75,76]. The presence of non-native species has resulted in the widescale extirpation of many native species from their historic distributions (especially in mainstem rivers), with many native species now relegated to the upper reaches of tributaries, surviving in small, fragmented populations above waterfalls or other physical barriers that have prevented invasion by non-native species [32,34,77]. ...
In South Africa, freshwater habitats are among the most threatened ecosystems, and freshwater fishes are the most threatened species group. Understanding patterns in freshwater fish diversity, threat, invasion, and protection status are vital for their management. However, few studies have undertaken such analyses at ecologically and politically appropriate spatial scales, largely because of limited access to comprehensive biodiversity data sets. Access to freshwater fish data for South Africa has recently improved through the advent of the Freshwater Biodiversity Information System (FBIS). We used occurrence records downloaded from the FBIS to evaluate spatial patterns in distribution, diversity, threat, invasion, and protection status of freshwater fishes in South Africa. Results show that record density varies spatially, at both primary catchment and provincial scales. The diversity of freshwater fishes also varied spatially: native species hotspots were identified at a provincial level in the Limpopo, Mpumalanga, and KwaZulu-Natal provinces; endemic species hotspots were identified in the Western Cape; and threatened species hotspots in the Western Cape, Mpumalanga, Eastern Cape, and KwaZulu-Natal. Non-native species distributions mirrored threatened species hotspots in the Western Cape, Mpumalanga, Eastern Cape, and KwaZulu-Natal. Some 47% of threatened species records fell outside of protected areas, and 38% of non-native species records fell within protected areas. Concerningly, 58% of the distribution ranges of threatened species were invaded by non-native species.
... ". it is imperative to ensure that these vulnerability hotspots are incorporated into areas formally demarcated for conservation, such as South Africa's Freshwater Ecosystem Priority Areas. and CapeNature's formal Protected Area Expansion Strategy" (Shelton et al., 2018). "Knowing that food availability enhances coral physiology under stress should incentivize reef managers to consider the level of natural zooplankton densities as a metric for determining [Marine Protected Area] placement sites" (Towle et al., 2017). ...
... Nonetheless, freshwater ecosystems are some of the most threatened ecosystems on Earth [38]; also threatened are the freshwater species [39] directly competing with humans for resources [28]. Due to the increasing human population demanding multiple resources from freshwater ecosystems, ranging from direct products such as water or fish to recreational ecosystem services [40], there is an increasing need for effective conservation approaches to freshwater fish, and this requires reliable data [41]. Therefore, investigating and filling the knowledge gap regarding the aquatic biodiversity data should be a priority. ...
The Wallacean shortfall refers to the knowledge gap in biodiversity distributions. There is still limited knowledge for freshwater fish species despite the importance of focusing conservation efforts towards this group due to their alarming extinction risk and the increasing human pressure on freshwater ecosystems. Here, we addressed the Wallacean shortfall for freshwater fish faunas across Europe by using the completeness indicator derived from species accumulation curves to quantify the fish sampling efforts. The multiple potential drivers of completeness that were previously related to the sampling efforts for other species (i.e., population density, nature reserves, or distance to cities) were tested using a 10 × 10 km2 grid resolution, as well as environmental (e.g., climatic) factors. Our results suggested that although there was an overall spatial pattern at the European level, the completeness was highly country-dependent. Accessibility parameters explained the sampling efforts, as for other taxa. Likewise, climate factors were related to survey completeness, possibly pointing to the river conditions required for fish sampling. The survey effort map we provide can be used to optimize future sampling, aiming at filling the data gaps in undersampled regions like the eastern European countries, as well as to account for the current bias in any ecological modeling using such data, with important implications for conservation and management.
... Africa and Madagascar (H172) are projected to see a climate-driven 10% reduction in freshwater flow that is projected to threaten the survival of ~9% of freshwater-dependent fish and birds (low confidence) (Thieme et al., 2010). Climate change is projected to increase the extinction vulnerability of most freshwater fish in the western South Africa Cape hotspot (H170) (low confidence) (Shelton et al., 2018). ...
... Future studies should focus on the effects of global climate change on freshwater systems and include both the physical and biological impacts. Currently, studies on invertebrates and fish within South African rivers are showing the potential impacts of rising water temperatures on species' thermal tolerances [41][42][43][44] ; modelling future water temperature of these rivers is vital towards the understanding of when these impacts will take effect and guide mitigation actions. ...
Freshwater systems in southern Africa are under threat of climate change, not only from altered flow regimes as rainfall patterns change, but also from biologically significant increases in water temperature. Statistical models can predict water temperatures from air temperatures, and air temperatures may rise by up to 7 °C by 2100. Statistical water temperature models require less data input than physical models, which is particularly useful in data deficient regions. We validated a statistical water temperature model in the lower Olifants River, South Africa, and verified its spatial applicability in the upper Klaserie River. Monthly and daily temporal scale calibrations and validations were conducted. The results show that simulated water temperatures in all cases closely mimicked those of the observed data for both temporal resolutions and across sites (NSE>0.75 for the Olifants River and NSE>0.8 for the Klaserie). Overall, the model performed better at a monthly than a daily scale, while generally underestimating from the observed (indicated by negative percentage bias values). The statistical models can be used to predict water temperature variance using air temperature and this use can have implications for future climate projections and the effects climate change will have on aquatic species.
Significance:
• Statistical modelling can be used to simulate water temperature variance from observed air temperature, which has implications for future projections and climate change scenarios.
• While there are many other factors affecting water temperature, air temperature accounts for up to 95% of water temperature variance.
• The model used can successfully simulate water temperature variance for different rivers.
... Africa and Madagascar are predicted to see a 10% reduction in freshwater flow which will threaten the survival of 9% of freshwater dependent fish and birds (Thieme et al., 2010). Climate change will increase the extinction vulnerability of most native and some non-native freshwater fish in the western South Africa Cape richspot (Shelton et al., 2018). ...
Because of human impacts, a greater percentage of freshwater species have gone extinct and are threatened with extinction than terrestrial and marine species. These impacts, already underway for over a century, outweigh the predicted impacts of climate change. It is imperative to reverse the effects of freshwater habitat degradation, pollution, water abstraction, over-exploitation, and the spread of human-introduced species to prevent more species extinctions, and actively restore biodiversity. These measures will also contribute to reducing any effects of anthropogenic climate change.
... This high ecosystem-level diversity sets the stage for a rich diversity of freshwater life, including 134 species of freshwater fish 1 , 161 species of frogs (Minter et al. 2004), more than 2 700 species of aquatic invertebrates, approximately 300 species of freshwater algae, and an estimated 4 000 species of riparian, wetland and aquatic plants (Glen et al. 2013;Sieben et al. 2014). Levels of endemism are high in South Africa's freshwater systems (Wishart and Hughes 2003;de Moor and Day 2013;Barber-James and Pereira-da-Conceicoa 2016;Ellender et al. 2017), but so are the levels of anthropogenic threat and environmental degradation (Shelton et al. 2018). The country's unique freshwater biodiversity is under ...
Access to long-term biodiversity datasets is vital for monitoring, managing and protecting freshwater ecosystems. Detecting critical ecosystem changes, such as losing unique biodiversity and ecosystem services, is dependent on access to data. A wealth of biodiversity data exists for river ecosystems in South Africa, but an operational information system to access these data is currently not available. This gap is the result of limited capacity for managing freshwater biodiversity data, with existing systems isolated, difficult to access and not well maintained. To address this knowledge gap, the Freshwater Biodiversity Information System (FBIS) has been developed. The FBIS is a powerful, visual, data-rich information system for hosting and serving freshwater biodiversity data. It serves as a platform for the inventory and maintenance of data, thereby facilitating the evaluation of long-term change in river biodiversity and ecosystem condition, and guiding future monitoring strategies and management decisions. System design and functionality was strongly informed by data and reporting needs of key end-user groups, including water resource managers, biodiversity and conservation managers and planners, scientific researchers, and environmental consultants. Future expansion aims to increase the diversity of data accessed, data flow, geographic coverage and strategically embed FBIS into South Africa’s main freshwater decision-making pipelines.
... However, the richness and abundance of fish biodiversity in aquatic ecosystems become more vulnerable, owing to human disturbances 7,8 . Although approximately 400 new fish species have been described annually over the past 20 years 1 , anthropogenic impacts, such as water pollution from plastic and other household waste, river dams, water withdrawal, overfishing, poaching, and habitat degradation have resulted in a catastrophic loss of fish diversity [9][10][11] . In-depth taxonomic studies of species are key to conserving biodiversity. ...
Uzbekistan is one of two doubly landlocked countries in the world, where all rivers are endorheic basins. Although fish diversity is relatively poor in Uzbekistan, the fish fauna of the region has not yet been fully studied. The aim of this study was to establish a reliable barcoding reference database for fish in Uzbekistan. A total of 666 specimens, belonging to 59 species within 39 genera, 17 families, and 9 orders, were subjected to polymerase chain reaction amplification in the barcode region and sequenced. The length of the 666 barcodes was 682 bp. The average K2P distances within species, genera, and families were 0.22%, 6.33%, and 16.46%, respectively. The average interspecific distance was approximately 28.8 times higher than the mean intraspecific distance. The Barcode Index Number (BIN) discordance report showed that 666 specimens represented 55 BINs, of which five were singletons, 45 were taxonomically concordant, and five were taxonomically discordant. The barcode gap analysis demonstrated that 89.3% of the fish species examined could be discriminated by DNA barcoding. These results provide new insights into fish diversity in the inland waters of Uzbekistan and can provide a basis for the development of further studies on fish fauna.
... Pseudobarbus skeltoni inhabits both pools and riffles (Kadye et al. 2016), and has a terminal (forward-facing) mouth orientation, indicating that it is primarily a drift-feeder on aquatic invertebrates . It is also possible that the Berg-Breede River Whitefish Pseudobarbus capensis (IUCNlisted as Endangered) a larger cyprinid species, once also occurred in the catchment (Shelton et al. 2017). ...
In response to a call from the Water Fund (TNC) the Freshwater Research Centre (FRC) initiated biodiversity, social, and governance assessments to conserve indigenous freshwater fish and associated aquatic ecosystems of the Upper Riviersonderend, Amandels and Du Toits Rivers in the Theewaterskloof Catchment (Western Cape, South Africa). These assessments are to be aligned with the necessary awareness-raising, information collation, stakeholder engagement and identification of role players required to inform the framework for the development of robust, transparent and feasible conservation intervention options.
... Whereas S. capensis sensu lato has a broad geographic range, the newly identified lineages within this species complex have more restricted distributions (Bronaugh et al., 2020), and are also likely to have smaller population sizes, making them more susceptible to extinction from multiple anthropogenic impacts such as alien fish predators, water extraction and the projected climate change (Ellender et al., 2017;Shelton et al., 2018). ...
... Remnant populations of stream fishes in the CFE are also vulnerable to the projected impacts of global climate change, particularly increases in water temperature and reductions in river flows and the concomitant increase in human demand for water(Dallas & Rivers-Moore, 2014;Shelton et al., 2018). These threats are consistent with those reported for riverine ecosystems in other Mediterranean-climate regions such as the Murray-Darling Basin in south-eastern Australia(Bond, Thomson, Reich, & Stein, 2011;Pavlova et al., 2017;Pittock & Finlayson, 2011), the Iberian Peninsula(Hermoso & Clavero, 2011;Maceda-Veiga, 2013) and California in the USA (Moyle, Kiernan, Crain, & Quiñones, 2013). ...
Understanding historical distribution patterns of freshwater fishes prior to human impacts is crucial for informing effective strategies for biodiversity conservation. However, incomplete information on species occurrence records, the existence of cryptic species and sensitivity to small sample sizes limit the application of historical records in natural history collections as well as conventional species distribution modelling algorithms to infer past distributions of species.
This study used molecular data as an alternative and objective approach to reconstruct the historical distribution ranges of four stream fishes from the Breede River system in the Cape Fold Ecoregion, a global hotspot of imperilled endemic freshwater biodiversity in southern Africa.
The study used 249 occurrence records and 208 mitochondrial cytochrome b sequences to reconstruct the potential historical ranges of four taxa: Galaxias sp. ‘zebratus nebula', Galaxias sp. ‘zebratus Riviersonderend', Pseudobarbus sp. ‘burchelli Breede' and Pseudobarbus skeltoni.
All four taxa historically had broader distribution ranges across the Breede River system before human impacts, but they have suffered severe attrition as the main‐stem populations have been extirpated.
The severe decline in the historical ranges of these four taxa is a result of multiple impacts, particularly hydrological modification, habitat degradation and the introduction of non‐native species, which are also global challenges for freshwater ecosystems.
The approach presented in this study has great potential for reconstructing historical ranges of stream‐dwelling taxa from disparate regions where fragmentation has resulted from human‐mediated impacts. This information is crucial for identifying appropriate conservation strategies such as river rehabilitation and eradication of non‐native species, as well as guiding reintroductions and informing assisted gene flow where these are deemed necessary interventions.
... regionally (Shelton et al., 2018) assessing the interaction between environmental factors and predator avoidance strategies would be beneficial. ...
We examined innate responses to conspecific and heterospecific alarm cues in a small cyprinid minnow, the Eastern Cape redfin Pseudobarbus afer. We found that redfins respond to conspecific skin extract, which contains alarm chemicals, and showed that their preferred response is to hide in refugia. Redfins also respond to skin extract from an allopatric, distantly related minnow species, the chubbyhead barb Enteromius anoplus indicating that neither sympatry nor close phylogenetic relationships are necessary for recognition of heterospecific alarm cues. Although both conspecific and heterospecific alarm cues induced similar responses, the response to heterospecific cues was less intense. This may be explained by a trade‐off between selection to maximise threat recognition and selection to avoid the costs of responding to irrelevant cues, or by differences in chemical structures of alarm cues between species. These findings have implications for the conservation of this Endangered fish species and for freshwater fishes throughout Africa.
... Nebula's predator avoidance behaviours, together with their morphological crypsis (Magellan & Swartz, 2013) and air-breathing abilities (Chakona et al., 2011;Magellan, 2015Magellan, , 2016Magellan et al., 2014), is likely to contribute to the survival of this species. This is especially important given continued threats from factors such as climate change (Shelton et al., 2018) and invasive species (Ellender & Weyl, 2014) in this priority conservation area (Ellender et al., 2017). ...
This study investigated recognition of, and behavioural responses to, predatory and non‐predatory heterospecifics by a small cryptically coloured fish species, Galaxias ‘nebula’. Nebula recognised and differentiated between predatory and non‐predatory heterospecifics and altered its behaviour facultatively. With both predatory and non‐predatory fishes, the proportion of time spent motionless increased, whereas refugia use was affected only by predators and neither heterospecific affected the time spent active. Although nebula appeared to face no conflict, in that their responses to predatory and non‐predatory heterospecifics varied in the same direction and differed only in intensity, the presence of both heterospecifics together induced responses midway between those for each heterospecific separately. Non‐predatory heterospecifics thus modified nebula's responses towards predators, potentially making time available for other essential activities such as foraging. This modified predator response may aid its survival in an increasingly threatened habitat.
... In South Africa, many headwater streams within the Cape Fold Ecoregion (CFE) and the Amatola-Winterberg Highlands, which both form part of the southern temperate climatic region, are dominated by endemic and highly threatened cyprinid minnows of the genera Pseudobarbus and Enteromius (Tweddle et al., 2009;Skelton, 2016). While recent studies have identified several threats to these minnows Shelton et al., 2017), there is limited knowledge on the ecology of these stream fishes that can be used to implement effective conservation measures. There is therefore need to provide such ecological information, particularly for headwater streams which constitute important refugia for these unique freshwater fishes of this region. ...
In temperate headwater streams, intra-annual variation in energy input is critical in influencing aquatic food webs. We used stable isotope analysis to explore how seasonal variation in energy sources likely influenced invertebrate composition together with isotopic niche patterns of a cyprinid minnow, the chubbyhead barb Enteromius anoplus within a southern temperate headwater stream. Basal food sources had lower carbon and nitrogen stable isotope values in winter and spring compared to summer and autumn. Seasonal variations in the aquatic invertebrate communities were depicted by differences in the composition of gatherer and predator groups together with occurrence of scrapers in summer. Temporal changes in the isotopic values of these invertebrate groups appeared to coincide with that of basal food resources. The chubbyhead barb exhibited seasonal variation that was characterised by larger isotopic niches in winter compared to summer. Tissue-specific comparisons revealed larger isotope niche size based on fin tissue than muscle tissue during the cold period but comparable isotope niche sizes in the warm period. Contrasting inter-tissue isotopic niche patterns, the cold period suggested the likelihood of tissue physiological differences. Comparable isotopic niche patterns in summer and autumn suggested the possibility of synchronised physiological processes for both tissues. This suggested the potential for fin tissue as non-lethal alternative when inferring food web dynamics for this species.
... Many of these non-natives (e.g. the black basses Micropterus spp.) are adapted to relatively warm, low-lying habitats and have all but eliminated once abundant native fish populations from such areas (Ellender et al. 2017). Moreover, the middle and lower reaches of most rivers are moderately to severely degraded because of other impacts like water extraction, sedimentation and pollution (Shelton et al. 2017a). This has resulted in highly fragmented native fish populations and a common situation now is to find small, isolated pockets of native fish upstream in mountainous headwater reaches of streams (Chakona and Swartz 2012;de Moor and Day 2013). ...
Introduced rainbow trout Oncorhynchus mykiss have invaded many headwater streams in South Africa’s Cape Fold Ecoregion (CFE) and pose arguably the greatest threat to several species of threatened native fishes. Trout impacts in these systems appear to be density-dependent; we hypothesized that temperature is a key factor determining trout density and corresponding impacts on native fishes. We took advantage of natural spatial and temporal thermal heterogeneity in two CFE headwater streams to investigate the influence of temperature and other environmental factors on trout density and impacts on native fish assemblages. Temperature limited trout density (negative relationship) during summer surveys (hottest months), but not during spring and autumn (cooler months). During summer, the highest trout densities were recorded at sites that remained relatively cool (7-day moving average of the daily maximum temperature (Max_7) < 27 °C), while trout were generally absent from relatively warm sites (Max_7 > 27 °C). Native fish density was best explained by trout density (inverse relationship) during summer, but by other environmental variables such as habitat complexity and current flow velocity during autumn and spring. Trout distributions expand during cooler seasons when thermal heterogeneity and maximum temperatures are relatively low, but contract into thermal refugia (habitat patches that remain relatively cool) as temperatures and thermal heterogeneity increase over summer, leaving warmer habitat patches vacant and able to function as predation refugia for native fish. We hypothesize that climate warming could reduce trout density and distribution, and associated impacts on native fish, in CFE headwater streams, but may increase the potential for invasions by other warm-adapted non-native predatory fish already established in downstream river reaches in the region.
Environmental DNA (eDNA) metabarcoding has the potential to significantly improve surveys of biodiversity in freshwater systems. However, this methodology is still infrequently used in global hotspots of endemic species, in part because of two major barriers to the success of eDNA metabarcoding: (1) insufficient regional taxonomic representation in public reference sequence databases; and (2) inconsistent species incidence and abundance estimates when compared to conventional surveys.
We sampled eDNA and conducted visual surveys in the headwaters of two rivers in the Cape Fold aquatic ecoregion, South Africa. A reference sequence database was generated for the regional diversity of fishes to improve taxonomic classification of endemic species. We also compared the consistency of incidence data and relative abundance estimates of fishes from eDNA metabarcoding sequencing results and visual surveys (snorkel and underwater cameras) at each site sampled.
Only 1% of eDNA metabarcoding reads could be classified to fish species without the supplementation of reference sequence databases for local endemic species. Once regional reference sequences were added, a total of nine species were detected and >99% reads classified. A strong positive relationship (Φ = 0.75) was observed between the patterns of detections using eDNA and visual approaches. However, eDNA metabarcoding detected more species than visual methods. In addition, the relative read frequency and abundance observed in visual surveys was significantly correlated ( R ² = 0.85–0.88, p < 0.001) in the majority of the small pools surveyed.
Incomplete public reference sequence databases hinder the use of eDNA metabarcoding in regions of high endemicity. Local reference sequence libraries can overcome these challenges. When appropriately implemented, eDNA metabarcoding shows promise, producing results consistent or better than the more frequently used and labour‐intensive visual surveys.
Efficient survey methods like eDNA metabarcoding are urgently needed to improve aquatic monitoring efforts globally. Understanding how eDNA metabarcoding sequencing results relate to conventional survey methods is a key step in its implementation in ecoregions with high endemicity.
Predicting the shift of invasive species distribution in response to climate change is essential for ecological risk assessment. In this study, the distribution of invasive largemouth bass (Micropterus salmoides) was predicted from 2016 to 2085 in the Han River basin of South Korea using HadGEM3-RA based climate change scenarios (representative concentration pathway [RCP] 4.5 and 8.5 scenarios). A random forest model was developed using largemouth bass occurrence data and environmental variables (temperature, precipitation, flow rate, water quality, elevation, and slope) for five years (2011–2015). The annual mean temperature was the second most contributing variable after elevation. The occurrence of largemouth bass in the Han River basin was expected to increase in the future with increasing annual mean temperature, especially after the 2060 s (2056–2065) in the RCP 8.5 scenario. The latitudinal, longitudinal, and altitudinal shifts of largemouth bass distribution were expected to be −1.76 km, 4.19 km, and 9.07 m per 10 years under the RCP 8.5 scenario, respectively, indicating a gradual southeastward shift to higher locations. Given that invasive fish can disturb the habitat of endemic species, three-dimensional distribution shift under climate change should be considered for the ecological risk assessment of invasive species.
Extinction risk for 101 valid species and 18 unique genetic lineages of native freshwater fishes of South Africa was assessed in 2016 following the IUCN Red List criteria. An additional five species (three new species that were described and two species that were revalidated subsequent to the 2016 assessments) were assessed in the present study. A synthesis of the outcome of the assessments of the 106 valid species and 18 genetic lineages indicates that 45 (36%) of South Africa's freshwater fish taxa are threatened (7 Critically Endangered, 25 Endangered, 13 Vulnerable). Of the remaining taxa, 17 (14%) are listed as Near Threatened, 57 (46%) are Least Concern and five (4%) are Data Deficient. More than 60% of the endemic taxa are threatened. The Cape Fold Ecoregion has the highest proportion of threatened taxa (67%) due to the existence of a unique assemblage of narrow‐range endemic species. Galaxias and Pseudobarbus have the highest number of highly threatened taxa as most of the species and lineages in these genera are classified as either CR or EN. Major threats to the native freshwater fishes of the country are invasive fish species, deterioration of water quality, impoundments and excessive water abstraction, land use changes and modification of riverine habitats. Immediate conservation efforts should focus on securing remnant populations of highly threatened taxa and preventing deterioration in threat status, because recovery is rare. Accurate delimitation of species boundaries, mapping their distribution ranges, improved knowledge of pressures and long‐term monitoring of population trends need to be prioritised to generate credible data for the 2026 IUCN threat status assessments and designation of important fish areas as part of the National Freshwater Ecosystem Priority Areas (NFEPA) initiative.
• Climate change is causing shifts in the distribution patterns of freshwater fish at various spatio-temporal scales. Tropical freshwater fish are vulnerable, especially in areas where a high impact of climate change is predicted; thus, there is an increasing need to predict these shifts to determine conservation and adaptation strategies.
• Ecological niche models offer a reliable way to predict the effects of climate change on species distribution. Potential shifts in the distribution of tropical fish were tested under two scenarios (4.5 – moderate and 8.5 – extreme) with three general circulation models for years 2050 and 2070 using maximum entropy software using as models two predatory species – the tropical gar Atractosteus tropicus and the giant cichlid Petenia splendida.
• The potential distribution of both species was associated with warm and humid–sub-humid conditions. Future projections showed a higher availability of suitable areas for both species resulting from the expansion of warmer conditions in the middle and upper basins of the Central American mountain range and centre of the Yucatan Peninsula.
• Ecological niche models of keystone or umbrella species such as A. tropicus and P. splendida could be useful to support conservation plans of protected areas. The potential distribution of both species covers areas of high suitability including six important biosphere reserves in Mexico, three protected areas in Guatemala and part of the Mesoamerican biological corridor.
• Despite the potential expansion of the present distribution range suggested by the models, it is important to consider the biological and ecological requirements of the species and the ecological implications of these potential shifts in distribution. Both scenarios could have several implications at genetic, population, and ecosystem levels.
1. The control of invasive alien fish populations using piscicides to alleviate impacts on native biota is a controversial conservation strategy because the collateral impacts on non‐target taxa are not well documented. This article documents the responses of water quality, plankton and macroinvertebrate communities to an eradication of the globally invasive common carp Cyprinus carpio Linnaeus 1758, using the piscicide rotenone in a small South African reservoir.
2. Treated and untreated reservoirs were sampled before and at intervals following rotenone treatment. Sampling endpoints included water quality parameters, plankton, macroinvertebrates and fish. These endpoints were selected to gain an understanding of the ecological impacts of the treatment at various biological levels and to document possible recovery following treatment.
3. The study showed that: (i) the common carp were successfully removed; (ii) water clarity improved following the removal of fish; (iii) invertebrate communities, including macroinvertebrates and large zooplankton, recovered within 6 months of treatment; and (iv) that small zooplankton (i.e. Rotifera) dynamics were complex but rotifer abundances had returned to pre‐treatment levels within 6 months of treatment.
4. There was a 56% similarity between the macroinvertebrate assemblages before and 6 months after treatment, showing a substantial turnover in taxa following treatment. The phytoplankton community of the treated reservoir was dominated by blue‐green and green algae prior to the treatment. The blue‐green algal communities were not present 6 months after the treatment, possibly indicating a change in the nutrient status of the reservoir resulting from lower nutrient concentrations in the water column.
5. The phytoplankton community of the reservoir changed from a community typical of eutrophic waters to a community typical of a lower nutrient state. Within each group, there were species changes, but we suggest these are likely to be part of the altered biological interaction dynamics resulting from fish removals, rather than a direct effect of rotenone.
The Cape Fold Ecoregion (CFE) is a biodiversity hotspot with high levels of endemism in its freshwater fish fauna. This study examined inter and intra‐specific variation in critical thermal maxima (TCmax) for eight native species of freshwater fish from the CFE. Cape galaxias Galaxias zebratus, Breede River redfin Pseudobarbus burchelli, Berg River redfin Pseudobarbus burgi, Clanwilliam redfin Pseudobarbus calidus and fiery redfin Pseudobarbus phlegethon were the most thermally sensitive (TCmax = 29.8–32.8°C). Clanwilliam rock‐catfish Austroglanis gilli, Eastern Cape redfin Pseudobarbus afer and Cape kurper Sandelia capensis were moderately sensitive (TCmax = 33.0–36.8°C). An increase in intra‐specific thermal sensitivity of S. capensis was observed from east to west. The results were related to in situ water temperature, which influenced TCmax for all species, suggesting that thermal history is a major driver of variation in thermal tolerance amongst populations. These thermal tolerance data for freshwater fishes in the CFE demonstrate that resilience to climate warming follows a geographical cline and that the more sensitive western species and regions are conservation priorities.
DNA‐based studies have uncovered cryptic species and lineages within almost all freshwater fishes studied thus far from the Cape Fold Ecoregion (CFE) of South Africa. These studies have changed the way the CFE is viewed, as almost all stream fishes that were previously considered to be of low conservation priority, because they were perceived to have broad geographical ranges, contain multiple historically isolated lineages, many of which are narrow‐range endemics.
As stream fishes of the CFE are of conservation concern owing to threats mainly posed by habitat degradation, invasion by alien species and hydrological modification, re‐evaluation of the distribution and conservation status of newly identified unique lineages is required to inform the development and implementation of effective conservation and management strategies.
The present study conducted an IUCN Red List conservation assessment of a newly identified lineage of the Galaxias zebratus species complex (hereafter referred to as Galaxias sp. ‘Joubertina’) to identify key threats and provide recommendations to conservation authorities on appropriate measures to reduce extinction risk.
The lineage met the qualifying threshold for the Endangered category because of its very restricted geographic range, few remaining secure populations, small known population sizes and the intensity of threats to most of the populations. Only six populations remain, one of which could be an ‘extralimital’ population potentially established through an inter‐basin water transfer scheme.
Galaxias sp. ‘Joubertina’ is threatened by invasive piscivores, habitat degradation and excessive water abstraction. These impacts have fragmented remnant populations, raising concerns about potential long‐term adverse impacts on genetic diversity and evolutionary potential of this lineage.
Immediate conservation measures should protect remnant populations from further impacts, while long‐term measures should aim to restore historical connectivity to reduce the potential deleterious effects of inbreeding in the small isolated populations.
The Eastern Cape redfin, Pseudobarbusafer, has long been considered to be a single widespread and variable species occurring in multiple isolated river systems in the Cape Fold Ecoregion (CFE) at the southern tip of Africa. Mitochondrial cytochrome b and control region sequence data of individuals from populations currently assigned to Pseudobarbusafer across the species’ distribution range revealed existence of four deeply divergent taxonomic units: (i) the Mandela lineage confined to the Sundays, Swartkops and Baakens river systems, (ii) the Krom lineage endemic to the Krom River system, (iii) the St Francis lineage occurring in the Gamtoos and adjacent river systems, and (iv) the Forest lineage occurring in several coastal river systems from the Tsitsikamma to the Klein Brak River system. The Forest lineage is closely related to Pseudobarbusphlegethon from the Olifants River system on the west coast of South Africa, suggesting that it does not belong to Pseudobarbusafer s.l. Herein we focus on the three lineages within the Pseudobarbusafer s.l. complex and provide new diagnosis for Pseudobarbusafer s.s (Mandela lineage), revalidate Pseudobarbussenticeps (Krom lineage) as a distinct species, and describe a new species Pseudobarbusswartzi (St Francis lineage). The three species exhibit subtle differences, which explains why they were previously considered to represent a single variable and widespread species. Pseudobarbussenticeps differs from both Pseudobarbusafer and Pseudobarbusswartzi by having fewer (i.e. larger) scales (25–33, mode 29 lateral line scale series; 10–12, mode 11 circumpeduncular scales) and presence of a lateral stripe which terminates in a conspicuous triangular blotch at the base of the caudal fin. Long barbels which reach or surpass the vertical through the posterior edge of the eye further separate Pseudobarbussenticeps from Pseudobarbusafer s.s. which possesses simple short barbels which do not reach the vertical through the posterior margin of the eye. Pseudobarbusafer s.s differs from Pseudobarbusswartzisp. n. by possession of fewer scale rows along the lateral line (29–35, mode 32 vs 34–37, mode 36 in Pseudobarbusswartzi), fewer scales around the caudal peduncle (12–16, mode 12 vs 13–17, mode 16 in Pseudobarbusswartzi) and a distinct mesh or net-like pigmentation pattern on latero-ventral scales.
The primary aim of this study was to assess the movement, flow and habitat requirements of two endangered fish species, i.e. the Clanwilliam yellowfish and Clanwilliam sawfin, and recommend water management strategies to ensure the persistence of remaining populations as well as to suggest a way forward for fish habitat studies in South Africa. The study was conducted on the Driehoeks River, a tributary of the Doring River system, which rises in the Cederberg mountains of the Western Cape, South Africa. A 5.9 km segment of this river was selected for the study.
Seasonal variations in the relative abundances and distribution of larval, juvenile and adult sawfin along the longitudinal profile of the study segment were investigated prior to, during and after the spring spawning period (November to January) and these variations were interrogated in terms of the spatial arrangement of physical habitat units within the segment. Dive surveys served to identify the location and extent of critical reproductive and nursery habitats, as well as to characterise the dispersal and/or movement of larval and juvenile fish to nursery habitats following the spawning season.
Habitat Suitability Criteria (HSC) were used to describe the hydraulic (velocity and depth) as well as substratum habitat use by Clanwilliam yellowfish and sawfin. The study included habitats deemed most limiting to fish production, i.e. those used for foraging, early life stages and reproduction. The suitability of a two-dimensional hydraulic modelling programme (River2D) for simulating habitat of the Clanwilliam yellowfish and sawfin was investigated. HSC derived for Clanwilliam yellowfish and sawfin were combined with the simulated depths and velocities generated by River2D and measured substratum particle sizes to produce Combined Suitability Indices (CSIs). To evaluate the consequences of alternative flows on habitat availability, Weighted Usable Area (WUA) – an aggregate of the product of the CSI at each node in the model and the area associated with that node (CSI × surface area) – was then calculated for each species and life stage and for each site over a range of discharges. To test the ability of River2D to accurately predict microposition choice by yellowfish and sawfin, the correspondence between observed fish positions and the spatial distribution of the simulated habitat suitabilities was investigated.
Increment deposition rate was validated using known-age larvae reared under laboratory conditions and the early development stages of sawfin eggs and larvae were recorded. Age-length relationships for larval and early juvenile sawfin were then established from wild-caught fish. Younger fish could be aged more accurately than older fish (>20 days) since increment spacing was more compressed in older fish. The results of the aging study were used to investigate the influence of environmental conditions, particularly flow and water temperature on the spawning and recruitment patterns of sawfin in the Driehoeks River. This was achieved by back-calculating spawning dates using the age-length models developed in the aging study of random samples of fish collected from the Driehoeks River towards the end of the low-flow season in two consecutive years. Since Clanwilliam yellowfish did not spawn over the study period, it was not possible to include them in the study.
The principle findings were that sawfin require access to a broad range of critical habitat units in a river to complete the different stages of their life cycle. Although sawfin used deeper habitats (> 1.2 m) throughout the year, faster-flowing, shallower habitats (< 1.2 m) were only occupied by fish over the spawning period (November to January). It was established that sawfin are non-guarding, open substratum, lithophilic spawners, selecting riffles and runs with loosely embedded cobble substrata, shallower water (0.13-0.36 m). Current speeds measured in spawning habitats were the highest recorded for this species (0.3-0.8 m s-1). Differences in microhabitat use between life-stages were large enough for them to be considered separate ‘ecological species’.
Sawfin larvae and juveniles lay down increments on their otoliths at a rate of one per day, and the first visible increment is laid down approximately two days post-fertilisation, or upon hatching. Once they hatch larvae attach themselves to the substratum by means of an adhesive pad. Swim-up occurs after a period of 10-13 days when they are washed into downstream slackwaters. Sawfin spawned over a period of roughly 100 days between November and January. Peak recruitment events were associated with temperature of ~19 °C and continuously rising temperatures over seven days or more.
The HSC derived in this study were compared with Flow Classes currently used to describe fish habitat in South Africa. Several points emerged from this comparison: (1) both sawfin and yellowfish use a much smaller subset of the habitat defined by each Flow Class; (2) there are considerable differences between life-stages as well as differences between behaviours (e.g. feeding vs spawning) and (3) connectivity between habitat patches is an important consideration. Flow Classes provide a useful alternative to HSC where these are not available. The risk of applying Flow Classes arbitrarily, however, is that habitat may not be perceived by a fish species in exactly the same way leading to reduced availability or elimination of certain critical categories of habitat. There was a discrepancy between the discharges required for optimal spawning habitat as predicted by River2D and the conditions under which the sawfin actually spawned as suggested by spawning-date distributions. These differences serve to highlight the limitations of hydraulic habitat modelling and the value of hydrological information for identifying flows of ecological importance. An over-reliance on instantaneous measures of habitat is therefore not advised.
Ecological niche theory predicts that coexistence is facilitated by resource partitioning mechanisms that are influenced by abiotic and biotic interactions. Alternative hypotheses suggest that under certain conditions, species may become phenotypically similar and functionally equivalent, which invokes the possibility of other mechanisms, such as habitat filtering processes. To test these hypotheses, we examined the coexistence of the giant redfin Pseudobarbus skeltoni, a newly described freshwater fish, together with its congener Pseudobabus burchelli and an anabantid Sandelia capensis by assessing their scenopoetic and bionomic patterns. We found high habitat and isotope niche overlaps between the two redfins, rendering niche partitioning a less plausible sole mechanism that drives their coexistence. By comparison, environment–trait relationships revealed differences in species–environment relationships, making habitat filtering and functional equivalence less likely alternatives. Based on P. skeltoni's high habitat niche overlap with other species, and its large isotope niche width, we inferred the likelihood of differential resource utilization at trophic level as an alternative mechanism that distinguished it from its congener. In comparison, its congener P. burchelli appeared to have a relatively small trophic niche, suggesting that its trophic niche was more conserved despite being the most abundant species. By contrast, S. capensis was distinguished by occupying a higher trophic position and by having a trophic niche that had a low probability of overlapping onto those of redfins. Therefore, trophic niche partitioning appeared to influence the coexistence between S. capensis and redfins. This study suggests that coexistence of these fishes appears to be promoted by their differences in niche adaptation mechanisms that are probably shaped by historic evolutionary and ecological processes.
Changes made to the scientific names of southern African freshwater fishes since 2001 are explained and discussed. Adjustments to the phylogeny and classification of the fauna are outlined. Recent systematic studies on cyprinines are discussed and changes to the genera Labeobarbus (expanded concept), Pseudobarbus (expanded concept), and Enteromius are supported. The introduction of the family names Alestidae and Nothobranchiidae is discussed. Adjustments made to the genera Nannocharax, Micropanchax, Tilapia, Coptodon and Mastacembelus are explained. Species name changes for Hepsetus and Zaireichthys are detailed. New species described from the region, or resurrected from synonymy, since 2001 are listed.
The salmonids rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta are amongst the world’s worst invaders with devastating impacts where introduced. Information on their invasive potential is key to predicting range expansion in recipient environments. Salmonids were introduced into the Keiskamma River system, South Africa in the late 1890s, established and spread throughout its headwaters. This provided an opportunity to document their distribution in relation to stream thermal regimes. Salmonids conformed to documented thermal tolerances predominantly occupying cool-water sites (13.7 ± 3.5 °C). Salmonid probability of occurrence was assessed using seven-day moving average of daily mean water temperatures (MWAT) and exceedances of 100 and 59 days reduce the probability of occurrence for S. trutta and O. mykiss to 0.5 respectively, with probability of occurrence falling to zero at 150 days for both species. Greater tolerance of MWAT exceedance was observed in impoundment (233 days) rather than riverine (146 days) habitats. Epilimnetic releases from impoundments increased temporal heat loads and average temperatures were 3 °C higher below than immediately above impoundments. Salmonids did not occupy all sites within their thermal preferendum, indicating invasion debt and further potential to spread. These models highlight subtle ecological niche differences between both salmonids with O. mykiss more likely to survive warmer water temperatures than S. trutta, but at the expense of a lower altitudinal range and with a greater susceptibility to extinction with an increase in water temperatures. Aquaculture and fisheries enhancements using salmonids are increasing, and these results may contribute to risk assessments for salmonid invasions globally.
African sharptooth catfish Clarias gariepinus is native to most of Africa and small parts of Asia, but has been introduced to 37 countries mainly for aquaculture. This review of introductions, establishment, spread and impact of C. gariepinus in Brazil and outside of its native range in South Africa provides evidence that the species has been able to overcome all barriers to invasion in both countries. Following initial introductions across geographical barriers, containment seems to have been impossible and escape from aquaculture facilities and spread by illegal introductions is an invasion pathway in both countries. There is evidence of individuals dispersing rapidly following escape, and surviving and reproducing at multiple sites in a wide spectrum of habitats in both countries. There is a severe paucity of research on impacts, many of which are inferred from field and laboratory observations, but have not been demonstrated at population or community level. Such impact studies are urgently required to better understand the consequences of these invasions and to develop appropriate strategies to mitigate impacts and spread.
A genetically distinct population of the Maloti minnow Pseudobarbus quathlambae (Lesotho's only endemic fish) is known only from the Mohale catchment, and was formerly abundant in the Senqunyane, Bokong and Jorodane rivers which flow into Mohale Reservoir.
Situated ~4 km downstream of Mohale Reservoir, the Semongkoaneng waterfall has historically prevented larger fish species from moving upstream into areas inhabited by P. quathlambae . After the filling of the Mohale Reservoir in 2003, an inter‐basin transfer (IBT) linking it to Katse Reservoir was opened and in 2006 the smallmouth yellowfish Labeobarbus aeneus , a larger more aggressive species, was recorded in the reservoir, presumably introduced via the IBT.
The objectives of the present study were to: (1) establish whether any additional non‐native fish species were present in the Mohale catchment; (2) ascertain whether L. aeneus has dispersed into the rivers flowing into Mohale Reservoir; and (3) gauge whether the Mohale population of P. quathlambae is in decline. Twenty‐eight sites situated on major rivers flowing into the reservoir, and four sites in the reservoir itself, were surveyed to evaluate changes in fish populations and habitat quality.
Results indicate that P. quathlambae has all but disappeared from its natural range: only five individuals were recorded in the Jorodane and Bokong rivers, and none were recorded in the Senqunyane River – a former stronghold for the species. On the other hand, L. aeneus was recorded in all three rivers and is probably responsible for the decline of the P. quathlambae population, given that there does not appear to have been major deterioration in habitat conditions. Another non‐native fish, the Orange River mudfish Labeo capensis , was recorded in the Mohale catchment for the first time. Urgent conservation action is required to prevent the Mohale lineage of P. quathlambae from becoming extinct.
Copyright © 2016 John Wiley & Sons, Ltd.
3.1 Overview of the regional fauna
Thieme et al. (2005) listed the ecoregions of Africa, the reasons for their consideration as distinct entities, and described each ecoregion. The southern African regioncovered in this report contains 22 of the defined ecoregions (see Chapter 1: Figure 1.1 and Table 1.2). In terms of the fish fauna, however, there is considerable overlap between the ecoregions, and Skelton (2001) provided a more general classification in which herecognised the following six major aquatic ecoregions: tropical east coast region, tropical interior region, highveld (temperate) region, montane-escarpment region, Cape Fold Mountains region and Kalahari-Karoo-Namib region (Figure 3.1). Skelton (2001) further divided the fauna broadly into two groups, the tropical “Zambezian” fauna and a temperate southern fauna, which is further subdivided into the Karoo group and the Cape group.
The distribution of fishes is a result of the geomorphological history of the region and a brief description of this history helps to explain the current distributions and our adoption of a simplified selection of ecoregions based on actual river systems.
There is increasing pressure on conservation agencies to allow access to natural resources within protected areas for human benefit. Alien fishes are often seen as a convenient resource because their harvest does not conflict with conservation goals. However, allowing such access may have unintended consequences for managers. This opinion essay is intended to provide some insights into how promoting access to alien fish resources can add to the complexity of conservation interventions, may facilitate additional fish introductions and create dependencies on alien fish that could compromise potential eradication efforts.
Conservation implications: Management plans for the utilisation of alien fishes by external stakeholders must include clear exit strategies so that the ability to eradicate when necessary or feasible is not compromised.
Non-native rainbow trout Oncorhynchus mykiss have been widely introduced in the Cape Floristic Region (CFR) at the south-western tip of Africa and may pose a serious threat to endemic freshwater fishes in the region. Quantitative information about trout impacts in the CFR is scarce but is urgently needed to guide legislation and management efforts. We used a combination of comparative and experimental approaches to evaluate impacts of introduced trout on native fish populations in headwater streams draining the upper Breede River catchment in the CFR. Fish populations were surveyed, and 19 environmental variables measured, in 24 minimally-disturbed streams, half of which had been invaded by trout. The mean densities of native Breede River redfin Pseudobarbus burchelli, Cape kurper Sandelia capensis and Cape galaxias Galaxias zebratus, were 89–97 % lower in invaded streams than in streams without trout. Furthermore, while native fish were present at all 12 sites without trout, they were not recorded at seven of the 12 invaded sites. None of the measured environmental variables differed significantly between sites with and without trout, and distance-based linear models identified trout density as the best predictor of redfin and kurper density, while galaxias density was best predicted by other environmental variables (riparian vegetation, canopy cover, substrate length, site slope). Native fish ≤40 mm in length were largely absent from invaded streams, but generally abundant in streams without trout, and a field experiment confirmed that trout selectively consume small redfin. Taken together, these findings constitute evidence that trout have depleted the abundance of CFR-endemic fishes through size-selective predation. It is recommended that managers aim to prevent new trout introductions and consider eradicating trout populations where they pose a threat to highly threatened native species.
The National Freshwater Ecosystem Priority Areas (NFEPA) project was a multi-partner project between the Council for Scientific and Industrial Research (CSIR), South African National Biodiversity Institute (SANBI), Water Research Commission (WRC), Department of Water Affairs (DWA), Department of Environmental Affairs (DEA), Worldwide Fund for Nature (WWF), South African Institute for Aquatic Biodiversity (SAIAB) and South African National Parks (SANParks). The NFEPA project aimed to: 1. Identify Freshwater Ecosystem Priority Areas (hereafter referred to as ‘FEPAs’) to meet national biodiversity goals for freshwater ecosystems; and 2. Develop a basis for enabling effective implementation of measures to protect FEPAs, including freeflowing rivers. The NFEPA study responded to the high levels of threat prevalent in river, wetland and estuary ecosystems of South Africa. It provides strategic spatial priorities for conserving the country’s freshwater ecosystems and supporting sustainable use of water resources. These strategic spatial priorities are known as Freshwater Ecosystem Priority Areas, or ‘FEPAs’. Intended key users of NFEPA products include: the national departments of Water Affairs and Environmental Affairs, catchment management agencies and their associated stakeholders, the national and provincial departments of agriculture, the Department of Mineral Resources, South African National Biodiversity Institute, South African National Parks, bioregional programmes, provincial conservation agencies, provincial environmental affairs departments, municipalities, non-governmental organisations, conservancies and environmental consultants. The purpose of this report was to document the scientific methods and results used in generating the NFEPA map products, and describe the approach and concepts used to guide the project in developing an institutional basis for effective uptake of these maps.The project atlas and implementation manual are more appropriate tools for communicating the project results and outputs in a less technical manner.The project atlas and implementation manual are more appropriate tools for communicating the project results and outputs in a less technical manner. The Atlas of Freshwater Ecosystem Priority Areas packages the map products and provides a DVD of all NFEPA products and shapefiles. The Implementation Manual for Freshwater Ecosystem Priority Areas explains how to use NFEPA map products within the existing policy and legislation, and provides freshwater ecosystem management guidelines. Both the atlas and implementation manual are available from the Water Research Commission, or can be downloaded in electronic format from http://bgis.sanbi.org.
Freshwater resources in South Africa are under severe pressure from existing anthropogenic impacts and global climate change is likely to exacerbate this stress. This review outlines the abiotic drivers of climate change, focusing on predicted changes in temperature and precipitation. The consequences of global climate change for freshwater ecosystems are reviewed, with effects grouped into those related to water quantity, water quality, habitat and aquatic biological assemblages. Several guiding principles aimed at minimising the potential impact of climate change on freshwater ecosystems are discussed. These guidelines include those focused on water quantity and the maintenance of appropriate environmental flows, integration of global climate change into water quality management, conservation planning for freshwater biodiversity, the promotion of ecosystem resilience, and extending climate change science into policy and public discourse. Proactive assessment and monitoring are seen as key as these will allow for the identification of ecological triggers and thresholds, including thresholds of vulnerability, which may be used to monitor and inform decisions, as well as to improve the ability to forecast based on this knowledge.
Freshwater fishes are highly vulnerable to human-caused climate change. Because quantitative data on status and trends are unavailable for most fish species, a systematic assessment approach that incorporates expert knowledge was developed to determine status and future vulnerability to climate change of freshwater fishes in California, USA. The method uses expert knowledge, supported by literature reviews of status and biology of the fishes, to score ten metrics for both (1) current status of each species (baseline vulnerability to extinction) and (2) likely future impacts of climate change (vulnerability to extinction). Baseline and climate change vulnerability scores were derived for 121 native and 43 alien fish species. The two scores were highly correlated and were concordant among different scorers. Native species had both greater baseline and greater climate change vulnerability than did alien species. Fifty percent of California's native fish fauna was assessed as having critical or high baseline vulnerability to extinction whereas all alien species were classified as being less or least vulnerable. For vulnerability to climate change, 82% of native species were classified as highly vulnerable, compared with only 19% for aliens. Predicted climate change effects on freshwater environments will dramatically change the fish fauna of California. Most native fishes will suffer population declines and become more restricted in their distributions; some will likely be driven to extinction. Fishes requiring cold water (
Understanding the ability of species to shift their distribution ranges in response to climate change is crucial for conservation biologists and resources managers. Although freshwater ecosystems include some of the most imperilled fauna worldwide, such range shifts have been poorly documented in streams and rivers and have never been compared to the current velocity of climate change. Based on national monitoring data, we examined the distributional changes of 32 stream fish species in France and quantified potential time lags in species responses, providing a unique opportunity to analyze range shifts over recent decades of warming in freshwater environments. A multi-facetted approach, based on several range measures along spatial gradients, allowed us to quantify range shifts of numerous species across the whole hydrographic network between an initial period (1980–1992) and a contemporary one (2003–2009), and to contrast them to the rates of isotherm shift in elevation and stream distance. Our results highlight systematic species shifts towards higher elevation and upstream, with mean shifts in range centre of 13.7 m decade−1 and 0.6 km decade−1, respectively. Fish species displayed dispersal-driven expansions along the altitudinal gradient at their upper range limit (61.5 m decade−1), while substantial range contractions at the lower limit (6.3 km decade−1) were documented for most species along the upstream–downstream gradient. Despite being consistent with the geographic variation in climate change velocities, these patterns reveal that the majority of stream fish have not shifted at a pace sufficient to track changing climate, in particular at their range centre where range shifts lag far behind expectation. Our study provides evidence that stream fish are currently responding to recent climate warming at a greater rate than many terrestrial organisms, although not as much as needed to cope with future climate modifications.
Freshwater ecosystems provide goods and services of critical importance to human societies, yet they
are among the most heavily altered ecosystems with an overproportional loss of biodiversity. Major
threats to freshwater biodiversity include overexploitation, water pollution, fragmentation, destruction
or degradation of habitat, and invasions by non-native species. Alterations of natural flow regimes by
man-made dams, land-use changes, river impoundments, and water abstraction often have profound
impacts on lotic communities. An understanding of the functional interactions and processes in freshwater
ecosystems presents a major challenge for scientists, but is crucial for effective and sustainable
restoration. Most conservation approaches to date have considered single species or single level strategies.
In contrast, the concept of ‘Integrative Freshwater Ecology and Biodiversity Conservation’ (IFEBC)
proposed herein addresses the interactions between abiotic and biotic factors on different levels of organization
qualitatively and quantitatively. It consequently results in a more holistic understanding of
biodiversity functioning and management. Core questions include modeling of the processes in aquatic
key habitats and their functionality based on the identification and quantification of factors which control
the spatial and temporal distribution of biodiversity and productivity in aquatic ecosystems. The
context and importance of research into IFEBC is illustrated using case studies from three major areas
of research: (i) aquatic habitat quality and restoration ecology, (ii) the genetic and evolutionary potential
of aquatic species, and (iii) the detection of stress and toxic effects in aquatic ecosystems using
biomarkers. In conclusion, our understanding of the functioning of aquatic ecosystems and conservation
management can greatly benefit from the methodological combination of molecular and ecological
tools.
Rivers in mediterranean regions are subject to hydrological extremes. They range from highly stable, perennial ground- or snow-fed systems to highly ephemeral, unpredictable ones in semi-arid environments. Spatial and temporal complexity inherent in these systems presents challenges for ecological status assessment and defining reference conditions, particularly as many areas have been extensively transformed through anthropogenic activities. Temporal variability driven by sequential and predictable, seasonal events of flooding and drying accentuates the need to take season and/or hydrological period into account. Intermittent streams, which are common in mediterranean regions (med-regions) and which have aquatic communities distinct from perennial streams, are often not incorporated in bioassessment and present distinct challenges. Med-regions are also known for their high biodiversity and rates of endemism, as well as large numbers of introduced species. Med-regions are expected to be among the most affected by global climate change and, in these systems, climate change is an additional driver influencing ecosystems that are already stressed. From this review it is evident that an understanding of responses of indices, metrics, and models to climate change in comparison to existing stresses, and the development of thermally specific bioassessment tools are needed for this region.
In the southern Appalachian Mountains, the distributions of native brook trout Salvelinus fontinalis and introduced rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta are presently limited by temperature and are expected to be limited further by a warmer climate. To estimate trout habitat in a future, warmer climate, we produced a regional map of wild trout habitat based on information from stream samples, expert knowledge, and suitable land cover. We then developed a quantile regression model of the elevation–latitude boundary for the present distribution of trout; this constitutes a more direct, spatially explicit approach to modeling trout distribution than the use of thermal limits. In combination with a lapse rate model, the boundary model was used to project future wild trout distributions over a range of higher temperatures. If the predictions of the Hadley Centre global circulation model (GCM) are assumed, about 53% of trout habitat would be lost; if the more extreme Canadian Centre GCM is used, 97% would be lost. With increasing temperature, fragmentation would increase, leaving populations in small, isolated patches vulnerable to extirpation because of the decreased likelihood of recolonization. The regional trout habitat map and the models produced here were useful for making these predictions, and the map could be used for assessing the impacts of other regional stressors.
We present a new map depicting the first global biogeographic regionalization of Earth's freshwater systems. This map of freshwater
ecoregions is based on the distributions and compositions of freshwater fish species and incorporates major ecological and
evolutionary patterns. Covering virtually all freshwater habitats on Earth, this ecoregion map, together with associated species
data, is a useful tool for underpinning global and regional conservation planning efforts (particularly to identify outstanding
and imperiled freshwater systems); for serving as a logical framework for large-scale conservation strategies; and for providing
a global-scale knowledge base for increasing freshwater biogeographic literacy. Preliminary data for fish species compiled
by ecoregion reveal some previously unrecognized areas of high biodiversity, highlighting the benefit of looking at the world's
freshwaters through a new framework.
Freshwater species worldwide are experi-encing dramatic declines partly attributable to ongoing climate change. It is expected that the future effects of climate change could be particularly severe in med-iterranean climate (med-) regions, which host many endemic species already under great stress from the high level of human development. In this article, we review the climate and climate-induced changes in streams of med-regions and the responses of stream biota, focusing on both observed and anticipated ecological responses. We also discuss current knowl-edge gaps and conservation challenges. Expected climate alterations have already been observed in the last decades, and include: increased annual average air temperatures; decreased annual average precipitation; hydrologic alterations; and an increase in frequency, intensity and duration of extreme events, such as floods, droughts and fires. Recent observations, which are concordant with forecasts built, show stream biota of med-regions when facing climate changes tend to be displaced towards higher elevations and upper latitudes, communities tend to change their composi-tion and homogenize, while some life-history traits seem to provide biota with resilience and resistance to adapt to the new conditions (as being short-lived, small, and resistant to low streamflow and desicca-tion). Nevertheless, such responses may be insufficient to cope with current and future environmental changes. Accurate forecasts of biotic changes and possible adaptations are difficult to obtain in med-regions mainly because of the difficulty of distin-guishing disturbances due to natural variability from the effects of climate change, particularly regarding hydrology. Long-term studies are needed to disentan-gle such variability and improve knowledge regarding the ecological responses and the detection of early warning signals to climate change. Investments should focus on taxa beyond fish and macroinvertebrates, and in covering the less studied regions of Chile and South Africa. Scientists, policy makers and water managers must be involved in the climate change dialogue because the freshwater conservation concerns are huge.
Invasions by non‐native species can compromise the conservation value of otherwise pristine headwater streams. While both developed and developing countries recognize this threat, few of the latter have suitable budgets to implement control programmes.
This study assessed the effectiveness of a mechanical project to remove non‐native rainbow trout Oncorhynchus mykiss from a 6 km section of the upper Krom River, a small headwater stream in the Cederberg Mountains in South Africa's Cape Floristic Region (CFR).
From October 2013 to February 2014, 354 O. mykiss were removed by angling (58%), fyke netting (28%) and gill netting (14%). This resulted in a marked reduction, but not eradication, of the O. mykiss population (fish relative abundance decreased from 0.53 ± 0.09 fish per net per night in October 2013 to 0.21 ± 0.09 fish per net per night in February 2014). Following the cessation of manual removals, the relative abundance of O. mykiss had increased to 0.56 ± 0.18 fish per net per night by March 2016, suggesting that without sustained removal effort, the population will rapidly return to its pre‐removal abundance level.
Further work is needed to refine the methodology and test the effectiveness of mechanical removal of non‐native freshwater fish in a variety of ecological settings in the CFR. This approach holds potential for meeting the dual goals of reducing the ecological impacts of non‐native fishes and generating employment opportunities in line with the policy objectives of developing nations.
Mediterranean climate regions are globally recognized as hotspots of endemism in fishes; however, these unique assemblages are increasingly threatened by human mediated impacts including water abstraction, damming and non‐native species introductions.
The Cape Fold aquatic ecoregion (CFR) of South Africa supports an assemblage of range‐restricted endemic freshwater fishes, the majority of which are conservation priorities because they are under severe threat of extinction. Effective conservation and management are constrained by the lack of readily available information on this imperilled group of fishes because research efforts over the last century have been temporally disjointed and relatively uncoordinated.
This review provides an exhaustive appraisal of published literature on the taxonomy, biogeography, life history, ecology and physiology of freshwater fishes in the CFR, and the human impacts that affect them. Its aim is to direct future research needs for effective management and conservation of this imperilled group.
Only 103 peer‐reviewed articles on CFR fishes were recorded and the majority of available research is on taxonomy and biogeography (40.8%), followed by ecological investigations (22.3%), conservation (19.4%) and human impacts (17.5%).
Despite a plethora of studies on taxonomy and biogeography, recent genetic evidence suggests that fish diversity in the CFR has been severely underestimated and requires urgent attention. Human impacts severely threaten the existence of many native CFR fishes and require further study. Information on the biology and ecology of CFR fishes is limited to studies on selected species; of particular note is the lack of physiological information which is particularly pertinent given projected climate change scenarios.
The introduction and spread of non-native species is one of the least reversible human-induced global changes. In South Africa, non-native fish introductions have occurred over the last two and a half centuries. Resultant invasions have been cited as a primary threat to imperilled South African fishes and other aquatic fauna. Addressing a problem of this magnitude requires an organised approach. The aim of this paper is to summarise the current knowledge, risk and ecological impacts associated with non-native freshwater fish introductions in South Africa. A total of 55 fishes have been introduced into novel environments in South Africa. Of these, 27 were alien and 28 were extralimital introductions. Only 11 introduced species failed to establish and of the 44 species that have established, 37% are considered fully invasive. Introductions for angling were responsible for the highest proportion (55%) of fully invasive species with the remainder linked to inter-basin water transfers (15%), bio-control (15%), ornamental fish trade (10%) and aquaculture (5%). There was a general paucity of published literature on the introduction, establishment and spread of non-native fishes, and recent research has largely focused on impacts on native biota. While documented impacts spanned multiple levels of biological organisation, most papers focused on individual and population level impacts. Large taxonomic biases were also observed, and invasive impacts were estimated for less than 50% of fully invasive fishes. There is also an extensive knowledge gap on the impacts of associated parasites and diseases introduced with non-native fishes. These knowledge gaps constrain effective management of non-native fishes in South Africa and research at all invasion stages (introduction, establishment, spread and impact) is necessary to guide conservation practitioners and managers with information to manage current invasions and curb future introductions.
Nonnative fishes threaten native fish communities in many rivers of the world. In South Africa's Cape Floristic Region, predation by nonnative fishes has severely impacted native fish populations and more than half of the 17 endemic fish species are endangered. To preserve the unique endemic fish fauna, removal of nonnative fish from conservation areas is a priority in this region. In February 2012, South Africa's first nonnative fish eradication using rotenone took place in the Rondegat River, a small headwater stream that had been invaded by Smallmouth Bass (Micropterus dolomieu). The successful treatment culminated from a decade-long process that was facilitated through collaboration among a South African nature conservation authority (CapeNature), the South African Institute for Aquatic Biodiversity, and the American Fisheries Society Fish Management Chemicals Subcommittee. The successful removal of alien fish and almost instantaneous increase in biodiversity is anticipated to encourage more endemic fish restorations in South Africa.
The Cape mediterranean region, part of South Africa’s Cape Floristic Realm (CFR), is recognised for its rich diversity and high degree of endemism of terrestrial vegetation. We review the biodiversity of the aquatic flora and fauna using literature sources and museum data. Geological, palaeohistorical and climate data are examined in relation to the formation of the winter-rainfall regime. Prehistoric humans had minimal impact on the aquatic biotas. Patterns and processes relating to the present-day climate, ecosystem status, distribution and diversity of plants, invertebrates and vertebrates in the CFR are reviewed. The proportion of endemic CFR species relative to the total number of species known from southern Africa is estimated. Observed distribution patterns are evaluated against temperate Gondwana vicariance, old African migrations, the role of the ancient Cape fold mountains and Pangaea. The lack of Pleistocene glaciations in Africa, the oligotrophic nature of the river systems and the palaeohistorical origin and distribution of taxa are considered when assessing reasons for disjunct distribution patterns. Impacts of anthropogenic interference with aquatic ecosystems are evaluated. Fragmented jurisdiction of nature conservation authorities is seen as a problem for attaining adequate conservation of CFR aquatic ecosystems. Systematic conservation planning is under way for the region.
A new cyprinid species, Pseudobarbus skeltoni sp. nov, is described from material recently collected in the upper Riviersonderend River (a major tributary of the Breede River system) and the Krom River (a tributary of the Molenaars River in the upper Breede River) in the Cape Floristic Region of South Africa. The new species is readily distinguished from congeners, except P. burgi and P. burchelli, by having two pairs of prominent oral barbels. Pseudobarbus skeltoni can be distinguished from P. burgi and P. burchelli by the following combination of characters: distinctive terminal (vs. subterminal) mouth in adults; mouth inferior in sub-adults and young adults of P. skeltoni but lower lips are unretracted (vs. retracted) and lack a distinct cartilaginous plate; snout prominent; more slender head (head depth 64.2% of HL, vs. 70.1% of HL in P. burchelli and 74.1% of HL in P. burgi); and a longer head relative to standard length (30.5 % vs. 26.8% in P. burchelli and 25.8% in P. burgi). The new species attains the largest size of any Pseudobarbus. The restricted distribution and the small remaining population sizes of P. skeltoni indicate that this species is highly threatened and requires immediate conservation attention.
The Berg River system in the southwestern Cape South Africa was historically populated by at least four species of highly endemic fish species. A litany of anthropogenic changes, including large-scale land transformation, invasion by alien plant species, modification of the natural flow regime of the river, changes to water chemistry, siltation, and introduction of alien fish species, has transformed the system to the extent that some of these species were believed to have been completely eradicated from the system while others had become severely restricted in terms of the ranges they now occupy. This paper pulls together all available data and information (mostly anecdotal) on historical abundance and distribution patterns of indigenous fish species in the system and on the introduction and spread of alien fish species through the system. It also presents results of a series of surveys undertaken in recent years which provide a snapshot of present day abundances and distributions patterns of both the indigenous and alien fish species in the system. These recent surveys are focussed mostly on the main stem of the system but cover the full length of the river from the upper reaches to the estuary. Methods employed in the recent surveys included beach seine netting, gill netting, electrofishing and snorkelling. These surveys have revealed the presence of only three indigenous fish species in the system—the Berg River redfin, Pseudobarbus burgi, the Cape kurper, Sandelia capensis, and the Cape galaxias, Galaxias zebratus. In spite of once being abundant and widespread in the system these species are now confined to the extreme upper reaches of the mainstem and in the upper tributaries where alien species have not yet managed to penetrate and water quality remains pristine. A fourth indigenous species, once reported as being widespread through the system, the witvis, Barbus andrewi, appears to have been extirpated from the system in its entirety. At least ten species of alien species are present in the system and include rainbow trout, Onchorhynchus mykiss, smallmouth bass, Micropterus dolomieu, spotted bass, M. punctulatus, large mouth bass, M. salmoides, Mozambique tilapia, Oreochromis mossambicus, banded tilapia, Tilapia sparrmanii, sharptooth catfish, C. gariepinus, bluegill sunfish, Lepomis macrochirus, carp, Cyprinus carpio, and mosquito fish, Gambusia affinis. These species are most abundant in the mainstem of the river and lower portions of the tributaries, being prevented from penetrating further upstream by a combination of physical barriers, low winter temperature, and turbulent flow patterns which characterise the upper reaches of the Berg River system. Historical surveys of freshwater fish populations in the Berg River system relied mostly on surface observations and angling as survey methods, and thus most of the results of these studies are of an anecdotal nature. However, using these as a base, it has been possible to pinpoint with a reasonable degree of accuracy the time at which most of the alien species were originally introduced into the Berg River system as well as their spread through the system, and the simultaneous decline of indigenous species in the river. We conclude from this analysis that the strong correlation between the spread of alien species through the Berg River system and the concomitant decline of indigenous species is strongly suggestive of a causative relationship. The paper concludes with some speculation on the prognosis for both indigenous and alien fish species in the Berg River system, focusing on the impacts that the newly constructed Berg River Dam may have on these fauna, as well as potential opportunities this may present for their conservation.
Some native fish in New Zealand do not coexist with introduced salmonids. Previous studies of disjunct distributions of exotic brown trout Salmo trutta and native galaxiids demonstrated native extirpation except where major waterfalls prevented upstream migration of trout. In the Manuherikia River system, we predicted that water abstraction might be a further factor controlling the spatial distribution of both the invader and a native fish.
We applied multiple discriminant function analyses to test for differences in environmental conditions (catchment and instream scales) at sites with roundhead galaxias Galaxias anomalus and brown trout in sympatry and allopatry. We then used a supervised artificial neural network (ANN) to predict the presence–absence of G. anomalus and brown trout (135 sites). The quantification of contributions of environmental variables to ANN models allowed us to identify factors controlling their spatial distribution.
Brown trout can reach most locations in the Manuherikia catchment, and often occur upstream of G. anomalus . Their largely disjunct distributions in this river are mediated by water abstraction for irrigation, together with pool habitat availability and valley slope. Trout are more susceptible than the native fish to stresses associated with low flows, and seem to be prevented from eliminating galaxiid populations from sites in low gradient streams where there is a high level of water abstraction.
Synthesis and applications . In contrast to many reports in the literature, our results show that hydrological disturbance associated with human activities benefits a native fish at the expense of an exotic in the Manuherikia River, New Zealand. Water abstraction is also known to have negative impacts on native galaxiids, therefore we recommend restoring natural low flows to maintain sustainable habitats for native galaxiids, implementing artificial barriers in selected tributaries to limit trout predation on native fish, and removing trout upstream.
Abstract – Warm stream temperatures may effectively limit the distribution and abundance of Pacific salmon Oncorhynchus spp. in streams. The role of cold thermal refugia created by upwelling groundwater in mediating this effect has been hypothesized but not quantitatively described. Between June 21 and September 15, 1994, rainbow trout O. mykiss abundance within 12 northeast Oregon (USA) stream reaches was inversely correlated with mean ambient maximum stream temperatures (r=−0.7, P<0.05). Some rainbow trout used thermal refugia (1–10 m2 surface area) that were on average 3–8°C colder than ambient stream temperatures. Within the warmest reaches, high ambient stream temperatures (>22°C) persisted from mid-June through August, and on average 10–40% of rainbow trout were observed within thermal refugia during periods of midday maximum stream temperatures. Frequency of cold-water patches within reaches was not significantly associated with rainbow trout density after accounting for the influence of ambient stream temperature (P=0.06; extra sum of squares F-test). Given prolonged high ambient stream temperatures in some reaches, the thermal refugia available in the streams we examined may be too small and too infrequent to sustain high densities of rainbow trout. However, these refugia could allow some rainbow trout to persist, although at low densities, in warm stream reaches.
General circulation models predict increases in air temperatures from 1°C to 5°C as atmospheric CO2 continues to rise during the next 100years. Thermal regimes in freshwater ecosystems will change as air temperatures increase
regionally. As air temperatures increase, the distribution and intensity of precipitation will change which will in turn alter
freshwater hydrology. Low elevation floodplains and wetlands will flood as continental ice sheets melt, increasing sea-levels.
Although anadromous salmonids exist over a wide range of climatic conditions along the Pacific coast, individual stocks have
adapted life history strategies—time of emergence, run timing, and residence time in freshwater—that are often unique to regions
and watersheds. The response of anadromous salmonids will differ among species depending on their life cycle in freshwater.
For pink and chum salmon that migrate to the ocean shortly after they emerge from the gravel, higher temperatures during spawning
and incubation may result in earlier entry into the ocean when food resources are low. Shifts in thermal regimes in lakes
will change trophic conditions that will affect juvenile sockeye salmon growth and survival. Decreased summer stream flows
and higher water temperatures will affect growth and survival of juvenile coho salmon. Rising sea-levels will inundate low
elevation spawning areas for pink salmon and floodplain rearing habitats for juvenile coho salmon. Rapid changes in climatic
conditions may not extirpate anadromous salmonids in the region, but they will impose greater stress on many stocks that are
adapted to present climatic conditions. Survival of sustainable populations will depend on the existing genetic diversity
within and among stocks, conservative harvest management, and habitat conservation.
Climate change and water resources in southern Africa: Studies on scenarios, impacts, vulnerabilities and adaptation
- B. Hewitson
- M. Tadross
- C. Jack
Capacity development. Have our provincial aquatic conservation scientists become critically endangered?Water Wheel
- N D Impson
Impson, N. D. (2016). Capacity development. Have our provincial aquatic
conservation scientists become critically endangered? Water Wheel,
September/October, 20-23.
Unintended consequences of using non‐native fish
- Weyl O. L. F.
Weyl, O. L. F., Ellender, B. R., Wasserman, R. J., & Woodford, D. J. (2015).
Unintended consequences of using non-native fish. Koedoe, 57. Art.
#1264, https://doi.org/10.4102/koedoe.v57i1.1264
The status and distribution of freshwater biodiversity in southern Africa
- D. Tweddle
- R. Bills
- E. R. Swartz
- W. Coetzer
- L. Da Costa
- J. Engelbrecht
- K. G. Smith
Effect of an intensive mechanical removal effort on a population of non-native rainbow trout Oncorhynchus mykiss in a South African headwater stream
- Shelton
National Environmental Management: Biodiversity Act (10/2004): Draft Biodiversity Management Plan for Labeo seeberi
Department of Environmental Affairs. (2014). National Environmental
Management: Biodiversity Act (10/2004): Draft Biodiversity Management
Plan for Labeo seeberi. Government Gazette, Vol. 593 No. 38187.
Pretoria, 7 November 2014.
ArcGIS Desktop: Release 10. Environmental systems Research
- Esri
ESRI. (2011). ArcGIS Desktop: Release 10. Environmental systems
Research Institute, Redlands, CA.
Atlas of freshwater ecosystem priority areas in South Africa: Maps to support sustainable development of water resources
- J L Nel
- A Driver
- W F Strydom
- A Maherry
- C Peterson
- L Hill
- L B Smith-Adao
Nel, J. L., Driver, A., Strydom, W. F., Maherry, A., Peterson, C., Hill, L., …
Smith-Adao, L. B. (2011). Atlas of freshwater ecosystem priority areas
in South Africa: Maps to support sustainable development of water
resources. Water Research Commission Report No. TT 500/11. Pretoria, South Africa: Water Research Commission.
Capacity development Water Wheel
- N D Impson