141 results on '"Weyl, OLF"'
Search Results
2. Standardisation of alien invasive Australian redclaw crayfish 'Cherax quadricarinatus' sampling gear in Africa
- Author
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Madzivanzira, TC, South, J, Nhiwatiwa, T, and Weyl, OLF
- Published
- 2021
3. Gill net catch composition and catch per unit effort in flag boshielo Dam, limpopo Province, south Africa
- Author
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Sara, JR, Weyl, OLF, Marr, SM, Smit, WJ, Fouche, PSO, and Luus-Powell, WJ
- Published
- 2017
4. An assessment of recreational bank angling in the free state Province, south Africa, using licence sale and tournament data
- Author
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Barkhuizen, LM, Weyl, OLF, and van As, JG
- Published
- 2017
5. A qualitative and quantitative analysis of historic commercial fisheries in the Free State Province in South Africa
- Author
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Barkhuizen, LM, Weyl, OLF, and van As, JG
- Published
- 2016
6. Fish community of a small, temperate, urban river in South Africa
- Author
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Muller, C, Strydom, NA, and Weyl, OLF
- Published
- 2015
7. Reproductive biologies of Psammogobius knysnaensis and Caffrogobius gilchristi in a warm-temperate South African estuary.
- Author
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Ndaleni, PM, James, NC, South, J, and Weyl, OLF
- Subjects
SIZE of fishes ,ESTUARIES ,PREY availability ,SPRING ,GOBIIDAE ,BIOLOGY - Abstract
Reproductive biologies (spawning period, length at maturity and fecundity) of the Knysna sand goby Psammogobius knysnaensis and the Prison goby Caffrogobius gilchristi were investigated between September 2018 and August 2019 in the warm-temperate Sundays Estuary, South Africa. The two species reproduced during the same period (spring and summer) with peak reproduction occurring in January. P. knysnaensis egg production was higher than C. gilchristi and was not affected by fish size. Although C. gilchristi egg production increased with fish size, this was not significant. P. knysnaensis reached L
M50 at smaller sizes than C. gilchristi. Reproductive periods were likely coupled with prey availability, as phytoplankton and zooplankton abundances are highest in warm-temperate estuaries during this period. The ability of these gobies to reproduce at small sizes (< 40 mm TL), which is an adaptive trait of many r-selected species, underpins their high abundance in South African estuaries as they are well adapted to stochastic environments. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
8. Macro- and micronutrient composition of estuarine roundherring (Gilchristella aestuaria) (Pisces: Clupeidae) in the Eastern Cape, South Africa: a potential dietary source of essential nutrients
- Author
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Zvavahera, M, Hugo, S, Vine, NG, and Weyl, OLF
- Subjects
animal-sourced food ,deficiency ,food security ,recommended dietary allowance ,small fish species - Abstract
South Africa lacks research on the nutritional value of inland small fish species available to poor rural communities, despite the potential of such species to mitigate micronutrient deficiencies. Here we provide the first nutrient composition analysis for estuarine roundherring Gilchristella aestuaria, a widespread small fish species that is abundant in many estuarine and freshwater habitats. Protein, fat, calcium, iron, zinc and vitamin A content of G. aestuaria from five estuarine and two freshwater habitats were analysed. We found no difference in nutrient content between estuarine and freshwater habitats, and no significant correlation (Spearman’s test) between levels of each nutrient and variation in temperature, turbidity, pH, chlorophyll a, phosphates, nitrates and ammonia. Compared with other small fish species consumed in other countries, G. aestuaria has comparable iron, zinc, calcium, fat and protein, but very low levels of vitamin A. When considering the recommended dietary allowance of infants aged two or more, adult men and women, and pregnant and lactating women, we found that G. aestuaria is an excellent source of all these nutrients, except vitamin A.
- Published
- 2022
9. Biological and life-history parameters for Labeo rosae Steindachner, 1894 and Oreochromis mossambicus (Peters, 1852) from Flag Boshielo Dam, Olifants River, South Africa.
- Author
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Hlungwani, HA, Marr, SM, Weyl, OLF, and Sara, JR
- Subjects
MOZAMBIQUE tilapia ,SUSTAINABLE fisheries ,DAMS ,FISH surveys ,GILLNETTING - Abstract
Inland fisheries contribute towards food security for rural communities living close to large aquatic systems. However, sustainable inland fisheries rely on accurate biological information for the target species at the proposed fishery location. In this study, the biological information for Labeo rosae Steindachner, 1894 and Oreochromis mossambicus (Peters, 1852) were determined at Flag Boshielo Dam, Olifants River system, Limpopo province, as part of a larger study to evaluate a small-scale gill net fishery at this impoundment. Nine fish surveys were conducted from February 2016 to April 2017 using mixed sampling gears. Labeo rosae exhibited positive allometric growth (b > 3) while O. mossambicus displayed negative growth (b < 3). For L. rosae, the asymptotic length was 391 mm L
∞ , and the length-at-50% sexual maturity 165.8 mm. For O. mossambicus, the asymptotic length was 420 mm L∞ , and the length-at-50% sexual maturity 166.5 mm. Both species population stocks showed signs of exploitation. Total mortality for L. rosae was 0.57 yr−1 with a fishing exploitation of 0.21 yr−1 , while total mortality of 0.78 yr−1 and fishing exploitation of 0.50 yr–1 were estimated for O. mossambicus. The biological data collected, apart from the length–weight parameters for O. mossambicus, are suitable for conducting a fisheries assessment for these species at Flag Boshielo Dam. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
10. Validation of growth zone formation in Oreochromis mossambicus otoliths collected from an irrigation pond in the Sundays River Valley, Eastern Cape, South Africa.
- Author
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Mofu, L, Dalu, T, Wasserman, RJ, Woodford, DJ, and Weyl, OLF
- Subjects
OTOLITHS ,MOZAMBIQUE tilapia ,FISH population estimates ,LIFE history theory ,MARK & recapture (Population biology) ,PONDS ,FISHERIES ,FISH tagging - Abstract
In fisheries science, life-history trait information is widely used to estimate fish population recruitment, growth, and mortality. The aging and growth of Oreochromis mossambicus from the Sundays River Valley irrigation pond in the Eastern Cape province of South Africa were determined using otoliths. Mark recapture of chemically-tagged wild fish was used to confirm the periodicity of growth zone creation. A total of 150 specimens of O. mossambicus were obtained using a combination of seine and fyke nets. Female total lengths (L
t ) ranged from 20 to 340 mm, while male Lt ranged from 82 to 374 mm. Growth zone deposition rates of wild O. mossambicus otoliths fluorochrome-marked with oxytetracycline hydrochloride (OTC) and recaptured after one year was consistent with the deposition of one growth increment annually. According to the three-parameter von Bertalanffy model, growth was described using different coefficients for females and males, respectively. The maximum age estimate for both females and males was 12 years. Oreochromis mossambicus in this warm temperate pond had relatively long life spans compared to subtropical populations, which suggest likely long-term population persistence within cooler, novel environments. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
11. Seasonal variation and drivers of zooplankton, macroinvertebrate and littoral fish communities from irrigation ponds in a semi-arid region in the Eastern Cape (South Africa)
- Author
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Mofu, L, Dalu, T, Wasserman, RJ, Woodford, DJ, Khosa, D, and Weyl, OLF
- Abstract
Irrigation ponds are increasingly abundant globally, particularly in water-stressed countries with limited natural surface waters, yet knowledge of their ecology is limited. Here, we assessed zooplankton, macroinvertebrate, and littoral fish communities from irrigation ponds located in the Sundays River Valley in South Africa. This study assessed the seasonal community patterns in response to physico-chemical and biotic components. Water temperature, water depth, Secchi depth, and ammonium concentrations differed significantly across seasons. Similarly, Chlorophyll-a concentrations differed seasonally, with water transparency identified as the main driver. Zooplankton was dominated by Rotifera, Copepoda and Cladocera. Seasonal changes in temperature and subsequent fluctuations in water levels resulted in changes in zooplankton community. Macroinvertebrates were dominated by insects, notably the families Corixidae and Naucoridae. The littoral fish community comprised of Glossogobius callidus, Oreochromis mossambicus and Gambusia affinis. Zooplankton, macroinvertebrates and littoral fish abundances, species richness, diversity and assemblage composition differed significantly across seasons with temperature identified as the main driver of these differences. This study demonstrates that bottom-up processes are the dominant drivers of the irrigation pond communities in the Sundays River Valley and highlights the relevance of seasonal abiotic drivers in structuring these communities, particularly G. callidus and G. affinis.
- Published
- 2021
12. Evidence for overfishing of tigerfish Hydrocynus vittatus (Castelnau 1861) in the Kavango River, Namibia.
- Author
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Jacobs, FJ, Naesje, TF, Ulvan, EM, Hay, CJ, Khaebeb, FH, and Weyl, OLF
- Subjects
FISHERIES ,FISHING ,MARINE resources ,OVERFISHING ,GILLNETTING - Abstract
The fishery for the African tigerfish Hydrocynus vittatus in northern Namibia makes a substantial contribution to surrounding food security and stimulates the local economy through subsistence and recreational fishing. However, local fishers suggest that catch rates of H. vittatus have declined and the fish are now smaller. The Namibian Ministry of Fisheries and Marine Resources conducted annual gill net surveys in the Kavango River from 1994 to 2018. These standardised surveys were used to compare catch per unit effort data and length frequencies of H. vittatus between intensively fished areas and a freshwater protected area (FPA). The catch per unit effort (by numbers and mass) and proportion (56% vs 10–20%) of mature fish (males >180 mm fork length and females >280 mm fork length) were higher inside the FPA, compared with those outside. The H. vittatus populations, both outside and inside the FPA, are subject to overfishing and management actions should be taken to secure this important fishery resource for subsistence and recreational fishers. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
13. In a Pinch: Mechanisms Behind Potential Biotic Resistance Toward Two Invasive Crayfish by Native African Freshwater Crabs
- Author
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South, J, Madzivanzira, TC, Tshali, N, Measey, J, and Weyl, OLF
- Abstract
It is essential to incorporate mechanisms of biotic resistance into predictions of ecological impact conferred by invasive species. Trophically and functionally analogous native species have high potential to confer biotic resistance or to be susceptible to competitive exclusion by the invading species. In species with dominance hierarchies and high aggression the role of weapons, such as chelae, is emphasised and selected for. Differences in traits such as crushing capacity can indicate prey handling capabilities, while correlations between closing force and morphology can be used to understand the role of signaling in agonistic contests. Closing force strength can be used to infer the outcomes of both direct (predation) and indirect (competition) trophic interactions. Southern Africa has been invaded by two freshwater crayfish species (Cherax quadricarinatus and Procambarus clarkii). Biotic resistance of freshwater crabs toward crayfish invasions varies between geographic location and co-evolutionary history, thus comparing invasion histories without incorporating geographic context can produce unequivocal conclusions. We compared the closing force and chelae morphology of both crayfish species with a native trophically analogous freshwater crab, Potamonautes perlatus. Closing force increased significantly with mass for all species. There was significant interaction between sex and species on closing force. Potamonautes perlatus females showed significantly stronger maximum chela closing force than male P. perlatus, both sexes of P. clarkii and female C. quadricarinatus. Contrastingly, male C. quadricarinatus had significantly higher closing forces than both sexes of P. clarkii and female C. quadricarinatus, however, there was no difference between female P. perlatus. Native P. perlatus has the capacity to hold a competitive mechanical advantage over both invaders, but this varies with sex. Chelae length was not a significant predictor for closing strength in any of the species, which may be related to dishonest signaling in decapod species. This makes it imperative to assess whether factors such as closing force actually translate to resource holding potential in a contest scenario. We thus provide evidence that African freshwater crabs may exhibit biotic resistance toward invasion and the first measurements for C. quadricarinatus closing force strength.
- Published
- 2020
14. Evaluating the suitability of fyke nets for small-scale fisheries in the Free State Province of South Africa
- Author
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Barkhuizen, LM and Weyl, OLF
- Subjects
fyke net ,Cyprinus carpio ,small-scale fisheries ,Clarias gariepinus ,catch composition ,catch rate - Abstract
South Africa is under increasing pressure to develop small-scale fisheries in inland waters. To inform appropriate development of this sector in the Free State Province, the catch rate of double-ended fyke nets was evaluated using survey data from 20 impoundments sampled during the 2013/2014 summer season. Fyke nets were set over night and the total sample effort was 114 fyke net nights. Overall catch per unit effort (CPUE) was 16.8 ± 28.3 kg·net−¹·night−¹ and catch composition was dependent on impoundment, but generally comprised of a mixture of common carp Cyprinus carpio, African sharptooth catfish Clarias gariepinus, smallmouth yellowfish Labeobarbus aeneus, Orange River mudfish Labeo capensis and moggel Labeo umbratus. The influence of temperature and the potential benefits of baiting the nets were subsequently evaluated through monthly sampling in the hyper-eutrophic Krugersdrift Dam and at the oligotrophic Gariep Dam. Baiting did not significantly influence CPUE, which was significantly higher at Krugersdrift Dam (19.97 ± 23.22 kg·net−¹·night−¹) than at Gariep Dam (5.02 ± 6.05 kg·net−¹·night−¹). Increasing temperature had a positive effect on CPUE at Krugersdrift Dam but not at Gariep Dam. Species composition also differed between impoundments and, as a result, we conclude that seasonal catch rates and species compositions will need to be evaluated prior to implementation of fyke net fisheries in specific localities.
- Published
- 2020
15. Per-recruit analysis and proposed sustainable harvest strategy for rednose labeo <italic>Labeo rosae</italic> and Mosambique tilapia <italic>Oreochromis mossambicus</italic> in Flag Boshielo Dam, Olifants River, South Africa.
- Author
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Marr, SM, Hlungwani, HA, Weyl, OLF, and Sara, JR
- Subjects
- *
FISHING catch effort , *MOZAMBIQUE tilapia , *GILLNETTING , *FISHING nets , *FISHERIES - Abstract
Inland fisheries development in South Africa has been proposed to improve rural livelihoods and food security. However, inland fisheries are susceptible to collapse through overfishing. Therefore, establishing biological reference points for these fisheries is essential for long-term sustainability. Here, spawner-biomass-per-recruit (SBR) analysis was used to set biological reference points for a gillnet fishery targeting the rednose labeo
Labeo rosae and Mozambique tilapiaOreochromis mossambicus at Flag Boshielo Dam on the Oliphants River in Limpopo Province, South Africa. Both species are currently exploited at the impoundment by subsistence fishers that keep their entire catch. The current yields are estimated at 59 and 172 g yr−1 forL. rosae andO. mossambicus , respectively. The per-recruit analysis showed that age-at-first-capture for both species should be 4 years, at minimum lengths of 280 mm TL and 250 mm TL forL. rosae andO. mossambicus , respectively, with fishers using a minimum mesh size of 100 mm to reduce the risk of stock collapse. To maintain a SBR value greater than 25% of a pristine population, theL. rosae yield could be increased to 98 g yr−1, while theO. mossambicus yield could be increased to 176 g yr−1, following implementation of the recommended mesh size and size limits. A per-recruit analysis forO. mossambicus that includes recruitment variability and error to accurately calculate the biological reference points is recommended. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
16. Identifying multiple geographically restricted phylogeographic lineages of Moggel (Cyprinidae: Labeo umbratus) in South Africa.
- Author
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Ramoejane, M, Weyl, OLF, Swartz, ER, and Gouws, G
- Subjects
- *
CYPRINIDAE , *NUCLEAR DNA , *WATERSHEDS , *FRESHWATER fishes , *GEOGRAPHICAL distribution of fishes , *RIBOSOMAL DNA , *MITOCHONDRIAL DNA - Abstract
Labeo umbratus (Smith, 1841) is a widespread species with populations distributed across isolated southern African river systems. Given that cryptic lineages have been detected in freshwater fishes with a similar distribution, a phylogeographic study of L. umbratus was conducted, considering populations sampled from nine currently isolated river systems between 2008 and 2013. Analyses of mitochondrial DNA (cyt b) and nuclear DNA (S7) sequence data demonstrated that two unique lineages occur in the west-flowing Orange River and south-flowing drainages, respectively. The southern lineage was further divided into three sublineages: one restricted to the Gouritz River, the second largely confined to the Gamtoos River and the last distributed across catchments to the east (the Sundays, Bushmans, Great Fish, Keiskamma, Buffalo and Nahoon rivers). The Great Escarpment and deep incisions along the south coast were identified as potentially influencing the geographic genetic structure of this species. For conservation purposes and pending future taxonomic assessment, the two major lineages were identified as Evolutionarily Significant Units, and Management Units were identified within the southern lineage. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
17. Can bait improve the efficiency of underwater video monitoring of fish in headwater streams? A case study from the Rondegat River, South Africa.
- Author
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Bajaba, SZ, Hugo, S, van Wyk, AJ, Marr, SM, Vine, NG, and Weyl, OLF
- Subjects
VIDEO monitors ,UNDERWATER cameras ,FISH populations ,FISHING baits ,WILDLIFE monitoring ,CAMCORDERS ,STREAMING video & television - Abstract
The use of action cameras for underwater video sampling provides a non-harmful alternative for monitoring endangered and threatened fish populations in clear headwater streams. Here, we examine the use of baited remote underwater video systems (BRUVS) for the monitoring of vulnerable species in the clear headwater streams of the Cederberg Wilderness Area, South Africa. We tested whether baits (bread and Marmite™) increased the number of individuals recorded in comparison to un-baited BRUVS. Overall, baiting cameras increased the number of individuals recorded, with bread outperforming Marmite™. Numbers recorded varied notably among species and sites. We conclude that BRUVS are a useful monitoring tool, but caution that monitoring programmes should first determine the effectiveness of a range of baits to attract each species expected at the study sites. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
18. Preliminary evaluation of non-native rainbow trout (Oncorhynchus mykiss) impact on the Cederberg ghost frog (Heleophryne depressa) in South Africa’s Cape Fold Ecoregion
- Author
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Avidon, S, Shelton, JM, Marr, SM, Bellingan, TA, Esler, KJ, and Weyl, OLF
- Subjects
Amphibian, endemic species, freshwater fish, kick-sampling, Olifants-Doring River Catchment, underwater video analysis, waterfall barrier - Abstract
We evaluated the impact of non-native rainbow trout Oncorhynchus mykiss on a population of endemic Cedarberg ghost frog Heleophryne depressa in the upper Krom River (Olifants-Doring River Catchment, Cape Fold Ecoregion). We compared H. depressa abundance (using kick-sampling and underwater video analysis) and environmental conditions between sites above and below a waterfall that marks the upper distribution limit of O. mykiss. Heleophryne depressa abundance was significantly greater above the waterfall than that below it, and, because there was no significant difference in measured environmental variables, O. mykiss presence is identified as the most likely explanation for the observed decrease in H. depressa abundance.Keywords: Amphibian, endemic species, freshwater fish, kick-sampling, Olifants-Doring River Catchment, underwater video analysis, waterfall barrier
- Published
- 2018
19. Ten research questions to support South Africa's Inland Fisheries Policy.
- Author
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Weyl, OLF, Barkhuizen, L, Christison, K, Dalu, T, Hlungwani, HA, Impson, D, Sankar, K, Mandrak, NE, Marr, SM, Sara, JR, Smit, NJ, Tweddle, D, Vine, NG, Wepener, V, Zvavahera, M, and Cowx, IG
- Subjects
- *
FISHERY policy , *FISH populations , *FRESHWATER fishes , *FISH diseases , *SMALL-scale fisheries , *VALUE chains , *WATER levels , *FISH stocking - Abstract
South Africa is in the process of developing a National Freshwater (Inland) Wild Capture Fisheries Policy. A properly focused research strategy is essential to guide the policy development process, and thus a dedicated 'Inland Fisheries' workshop was convened by the South African Society for Aquatic Scientists in June 2018 to update and further develop a list of priority knowledge requirements for inland fisheries in the country. The main themes that emerged during the workshop were developed and contextualised as ten research questions. These were: (1) What is the exploitation potential of inland fisheries? (2) What are the health risks from consuming freshwater fishes? (3) Who currently uses inland fisheries and what are their harvests? (4) What can we learn from historical constraints to inland fisheries development? (5) How will governance of fisheries have to change in an evolving sectoral environment? (6) What are the options for fisheries enhancement? (7) What are the most appropriate fisheries technologies? (8) What value chains and employment opportunities are associated with inland fisheries? (9) What is the impact of water level fluctuations on fish production? (10) What are the impacts of pathogenic diseases on fish populations? [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
20. The abundance of an invasive freshwater snail Tarebia granifera (Lamarck, 1822) in the Nseleni River, South Africa
- Author
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Jones, RW, Hill, JM, Coetzee, JA, Avery, TS, Weyl, OLF, and Hill, MP
- Subjects
distribution, invasion, Mollusca, physicochemical drivers, Quilted Melania - Abstract
The invasive freshwater snail Tarebia granifera (Lamarck, 1822) was first reported in South Africa in 1999 and it has become widespread across the country, with some evidence to suggest that it reduces benthic macroinvertebrate biodiversity. The current study aimed to identify the primary abiotic drivers behind abundance patterns of T. granifera, by comparing the current abundance of the snail in three different regions, and at three depths, of the highly modified Nseleni River in KwaZulu-Natal, South Africa. Tarebia granifera was well established throughout the Nseleni River system, with an overall preference for shallow waters and seasonal temporal patterns of abundance.Although it is uncertain what the ecological impacts of the snail in this system are, its high abundances suggest that it should be controlled where possible and prevented from invading other systems in the region.Keywords: distribution, invasion, Mollusca, physicochemical drivers, Quilted Melania
- Published
- 2017
21. Invader Relative Impact Potential: a new metric to understand and predict the ecological impacts of existing, emerging and future invasive alien species
- Author
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Dick, JTA, Laverty, C, Lennon, JJ, Barrios-O'Neill, D, Mensink, PJ, Robert Britton, J, Médoc, V, Boets, P, Alexander, ME, Taylor, NG, Dunn, AM, Hatcher, MJ, Rosewarne, PJ, Crookes, S, MacIsaac, HJ, Xu, M, Ricciardi, A, Wasserman, RJ, Ellender, BR, Weyl, OLF, Lucy, FE, Banks, PB, Dodd, JA, MacNeil, C, Penk, MR, Aldridge, DC, Caffrey, JM, Aldridge, David [0000-0001-9067-8592], and Apollo - University of Cambridge Repository
- Subjects
invasive alien species ,functional response ,relative impact potential metric ,taxonomic and trophic groups ,ecological impacts ,numerical response ,risk assessment ,Life Sciences ,maximum feeding rate ,prediction ,species abundance ,Biology - Abstract
Predictions of the identities and ecological impacts of invasive alien species are critical for risk assessment, but presently we lack universal and standardized metrics that reliably predict the likelihood and degree of impact of such invaders (i.e. measurable changes in populations of affected species). This need is especially pressing for emerging and potential future invaders that have no invasion history. Such a metric would also ideally apply across diverse taxonomic and trophic groups. We derive a new metric of invader ecological impact that blends: (i) the classic Functional Response (FR; consumer per capita effect) and Numerical Response (NR; consumer population response) approaches to determining consumer impact, that is, the Total Response (TR = FR × NR), with; (ii) the ‘Parker–Lonsdale equation’ for invader impact, where Impact = Range × Abundance × Effect (per capita effect), into; (iii) a new metric, Relative Impact Potential (RIP), where RIP = FR × Abundance. The RIP metric is an invader/native ratio, where values > 1 predict that invader ecological impact will occur, and increasing values above 1 indicate increasing impact. In addition, the invader/invader RIP ratio allows comparisons of the ecological impacts of different invaders. Across a diverse range of trophic and taxonomic groups, including predators, herbivores, animals and plants (22 invader/native systems with 47 individual comparisons), high-impact invaders were significantly associated with higher FRs compared to native trophic analogues. However, the RIP metric substantially improves this association, with 100% predictive power of high-impact invaders. Further, RIP scores were significantly and positively correlated with two independent ecological impact scores for invaders, allowing prediction of the degree of impact of invasive alien species with the RIP metric. Finally, invader/invader RIP scores were also successful in identifying and associating with higher impacting invasive alien species. Synthesis and applications. The Relative Impact Potential metric combines the per capita effects of invaders with their abundances, relative to trophically analogous natives, and is successful in predicting the likelihood and degree of ecological impact caused by invasive alien species. As the metric constitutes readily measurable features of individuals, populations and species across abiotic and biotic context-dependencies, even emerging and potential future invasive alien species can be assessed. The Relative Impact Potential metric can be rapidly utilized by scientists and practitioners and could inform policy and management of invasive alien species across diverse taxonomic and trophic groups. © 2016 The Authors. Journal of Applied Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.
- Published
- 2017
22. Habitat utilisation of Pseudobarbus afer and Sandelia capensis in headwaters of the Swartkops River, Eastern Cape, South Africa.
- Author
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Hannweg, B, Marr, SM, Bloy, LE, and Weyl, OLF
- Subjects
ARTIFICIAL habitats ,HABITATS ,POLYVINYL chloride pipe ,ENDEMIC fishes ,FRESHWATER fishes - Abstract
Habitat degradation is one of the greatest threats to endemic freshwater fish in the Cape Fold Ecoregion. One habitat restoration strategy is the replication of critical habitat using artificial materials. In this paper, we evaluate the habitat occupancy of two small, endemic headwater fish of the Cape Fold Ecoregion, namely the Eastern Cape redfin Pseudobarbus afer (Peters, 1864) and the Cape Kurper Sandelia capensis (Cuvier, 1829). Habitat occupancy was observed in five pool microhabitats (inflow, woody debris, deep open, fern-root wads, and outflow) using action cameras. Changes in habitat occupancy were assessed following the introduction of an artificial habitat in the form of PVC pipes. Pseudobarbus afer preferred deeper open habitats, whereas Sandelia capensis preferred more structured woody debris habitat. Habitat occupancies differed significantly across all microhabitats for both species; excluding those between the inflow and outflow, and the open deep and fern-root wads for Sandelia capensis. Pseudobarbus afer and S. capensis occupancies in the natural microhabitats reduced significantly following the introduction of the artificial habitat. For species restricted to degraded habitats that require habitat restoration, the use of artificial habitat may be beneficial in accelerating the recovery of such species. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
23. Using action cameras to estimate the abundance and habitat use of threatened fish in clear headwater streams.
- Author
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Hannweg, B, Marr, SM, Bloy, LE, and Weyl, OLF
- Subjects
RARE fishes ,FISH populations ,FISH surveys ,FRESHWATER fishes ,RIVERS - Abstract
Snorkel and electrofishing surveys are the traditional baseline methods for fish surveys in clear headwater streams. However, action cameras provide a non-harmful alternative to monitor freshwater fish populations to develop informed conservation management initiatives. In this paper, estimates from photographs and videos from action cameras are compared with snorkel survey estimates of the density of a threatened endemic minnow species in a headwater stream, Eastern Cape, South Africa. Photograph-based relative abundances of fish summed over five microhabitats in each pool returned equivalent results to snorkel surveys, whereas the equivalent video-based abundance estimates were approximately 50% greater than the snorkel estimates. Therefore, photograph-derived estimates could be used as an alternative to snorkel surveys for fish population monitoring and habitat use studies in clear headwater streams. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
24. Diet of Glossogobius callidus (Teleostei: Gobiidae) in freshwater impoundments in the Sundays River Valley of the Eastern Cape, South Africa.
- Author
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Mofu, L, Woodford, DJ, Wasserman, RJ, Dalu, T, and Weyl, OLF
- Subjects
GOBIIDAE ,VALLEYS ,ECOLOGY ,MOLLUSKS ,ANIMAL nutrition ,OSTEICHTHYES ,AQUATIC invertebrates - Abstract
Despite the high abundance of the gobiid fish Glossogobius callidus in many freshwater ecosystems in South Africa, very few studies have assessed the biology and ecology of the species. Here, we investigated the diet of G. callidus populations sourced from Sundays River irrigation ponds. A total of 571 fish grouped into two size classes (TL, range ± SD: juveniles of 20–60 ± 45 mm; adults of 61–140 ± 85 mm) were sampled by seine netting; prey items were removed from the guts and identified and sorted to obtain dietary information for each prey group. Of the examined guts, 97% contained prey comprising 17 taxa within 10 taxonomic groups. Teleosts were identified to species level, whereas most dietary components were identified to a broad taxonomic group. Aquatic invertebrates were the most important component of the diet of G. callidus, but the index of relative importance (%IRI) of dominant invertebrate taxa varied according to ontogenetic stage of G. callidus and season. Prey taxa included: Diptera, Hemiptera, Trichoptera, Odonata, Cladocera, Copepoda, Hydracarina, Amphipoda, Mollusca and Teleostei. Dipteran prey taxa were consistently encountered in both size classes and across all seasons. G. callidus can therefore be regarded as a generalist invertivore. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
25. Species-specific impact of introduced largemouth bass Micropterus salmoides in the Groot Marico Freshwater Ecosystem Priority Area, South Africa
- Author
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Kimberg, PK, Woodford, DJ, Roux, H, and Weyl, OLF
- Abstract
Largemouth bass Micropterus salmoides are among the world’s 100 worst invaders and negatively affect aquatic biodiversity in many regions worldwide. In South Africa there is a paucity of empirical studies describing their impacts. The impact of M. salmoides on the fish community in the Groot Marico River catchment, an otherwise near-pristine river ecosystem and a freshwater ecosystem priority area, was assessed from surveys conducted in 2012. Fish presence and abundance were enumerated using multiple survey techniques, and their association with key habitat variables and the presence or absence of M. salmoides were assessed. A total of 14 native fish species were recorded, besides introduced M. salmoides, which occupied the majority of the mainstem and several tributaries downstream of barriers to upstream movement. Canonical correspondence analysis showed that only one native species, the Marico barb Barbus motebensis, had a negative spatial association with M. salmoides. Assessment of relative distributions showed this species to be excluded from M. salmoides-invaded river reaches, whereas the other native species were not visibly affected by the invader. This species-specificity of the impact of M. salmoides indicates that their impacts in South African streams may be dependent on predator-naiveté of prey.Keywords: Barbus motebensis, barriers, conservation, environmental guild, invasion, predationAfrican Journal of Aquatic Science 2014, 39(4): 451–458
- Published
- 2015
26. Analysis of active rotenone concentration during treatment of the Rondegat River, Cape Floristic Region, South Africa
- Author
-
Slabbert, E, Jordaan, MS, and Weyl, OLF
- Abstract
Most endemic freshwater fish species of the Cape Floristic Region are listed as threatened, due mainly to the impacts of invasive alien fish species. The piscicide rotenone has been identified as a potential tool to aid the conservation of indigenous species through the removal of invasive fish. Rotenone was used in the Rondegat River, Cederberg, where smallmouth bass Micropterus dolomieu had extirpated the indigenous fish. An initial rotenone treatment in March 2012 was followed by another in March 2013. Due to concerns following the first treatment about possible build-up of rotenone between treatment stations, the second treatment included monitoring of rotenone concentrations during the treatment. Measured concentrations were consistently below the selected treatment concentration of 37.5 μg l−1 and dropped to below the tested effective piscicidal concentration of 12.5 μg l−1 at some sampling points. There was no build-up of rotenone within the treatment zones, but rotenone took longer than expected to clear out of the treatment area. The rotenone was effectively neutralised when the neutralisation station was operational, but was still detectable after neutralisation was terminated.Keywords: freshwater fish, invasive fish, high-performance liquid chromatography, Micropterus dolomieu, piscicideAfrican Journal of Aquatic Science 2014, 39(4): 467–472
- Published
- 2015
27. First record of Labeo capensis (Smith, 1841) in the Crocodile River (West) system: another successful non-native freshwater fish introduction in South Africa.
- Author
-
Erasmus, JH, Malherbe, W, Gerber, R, Weyl, OLF, Sures, B, Wepener, V, and Smit, NJ
- Subjects
FRESHWATER fishes ,FISH as food ,NATIVE fishes ,WATERSHEDS ,CROCODILES ,INTRODUCED fishes ,COMPETITION (Biology) - Abstract
South Africa is one of six global fish invasion hotspots and as a result, non-native fishes are common components of the fish assemblages in all of the major river systems. The rate of establishment for introduced fish into South African rivers is high (79%) and the vector responsible for the highest establishment rate is interbasin transfer schemes with 80%. Introductions of non-native fish into river systems can negatively affect native fish species through hybridisation, competition for food sources and predation, and the introduction of associated parasites and diseases. The aims of the current study were to provide evidence of the introduction of Labeo capensis into the Crocodile River (West) system, using morphological and molecular techniques, and to record the fish health and gonadosomatic index to determine the invasive status of L. capensis. From the fish health assessment index and gonadosomatic index of L. capensis collected from Olifantsnek Dam, it can be concluded that L. capensis is a healthy reproducing population. Because this fish species can survive and reproduce in newly colonised river systems, it has the potential to compete with the native fish species for food and habitat, but can also hybridise with native Labeo species. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
28. The diet and trophic ecology of non-native Micropterus salmoides in two South African impoundments.
- Author
-
Taylor, GC, Hill, JM, and Weyl, OLF
- Subjects
PREY availability ,LARGEMOUTH bass ,PELAGIC fishes ,FORAGE fishes ,SOUTH Africans ,TOP predators ,STABLE isotope analysis - Abstract
Largemouth bass Micropterus salmoides is a highly successful predator that preys on fish and invertebrates. Highly popular with anglers, it is one of the most introduced and invasive fish globally, with strong potential to alter ecosystem structure and functioning. A better understanding of the trophic dynamics of M. salmoides populations is critical for effective management of its ecological impacts in their invasive range. This study investigated the diets and dietary ontogenetic shifts of M. salmoides in two South African dams along with its trophic positioning relative to other fish community members, through stomach content and stable isotope analyses. Micropterus salmoides was a top predator in both dams. In the Mankazana Dam, it depended predominately on insect prey, demonstrating a generalised feeding strategy, with shifts to include increasing proportions of fish prey with increasing size. Contrastingly, in the Wriggleswade Dam, M. salmoides displayed no ontogenetic shifts and preferred Gilchristella aestuaria, likely indicating a shift to a predominantly fish-based diet at smaller sizes, in the presence of small pelagic fish prey. Overall, M. salmoides diet was opportunistic, likely associated with prey morphology and behaviour (associated with refuge availability) and therefore directly linked to prey abundance and availability, which consequently dictated feeding strategy. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
29. Modelling expected trout ranges under current and future water temperature regimes in the Eastern Cape, South Africa.
- Author
-
Rivers-Moore, NA, Ellender, BR, and Weyl, OLF
- Subjects
TROUT ,SEA trout ,BROWN trout ,WATER currents ,RAINBOW trout ,FISH stocking - Abstract
Different values have resulted in conflicts between anglers and conservation lobbies in the management of trout in South Africa. Key to the conflict is the demarcation of boundaries to areas in which brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss currently occur, or are likely to establish following stocking for angling. To provide a longer-term perspective on these areas, we developed models to link salmonid biological thermal thresholds to elevation. These, when applied spatially using a digital elevation model with a probability of occurrence model, provided the basis for estimating potentially available thermal habitat for these two cold water species. Here, we acknowledge that other variables (stocking history; river connectivity) also play a role in understanding trout distributions. Using a simple scenario of an increase in mean daily water temperatures of 2 °C, we demonstrated that both brown and rainbow trout are likely to exhibit considerable range reductions in the future. Because it is possible that these range restrictions will result in an increasing desire to introduce trout into areas above their current distribution limits for the maintenance of angling opportunities, conservation managers should prioritise these areas, with management interventions seeking to understand what will help to limit introductions. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
30. Determining the minimum effective dose of rotenone for eradication of alien smallmouth bass Micropterus dolomieu from a South African river
- Author
-
Jordaan, MS and Weyl, OLF
- Abstract
In February 2012 the Rondegat River, in the Cape Floristic Region, was the first river in South Africa where the piscicide rotenone was used to remove an alien invasive fish, smallmouth bass Micropterus dolomieu. In preparation for this treatment, the sensitivity of smallmouth bass to various concentrations of the rotenone formulation CFT Legumine (5% active rotenone) was evaluated a week prior to treatment using standard toxicity tests to determine the minimum effective dose (MED) that would result in 100% mortality after exposure for 4 h. The MED was 0.0125 mg l-1 rotenone. Adverse effects, including erratic swimming, loss of equilibrium and death, occurred in a dose-dependent manner with smaller fish responding faster than larger ones. Standard operating procedures for the use of rotenone recommend treatment at a minimum of twice the calculated MED. Given the uncertainty associated with rotenone losses through hydrolysis and photolysis under field conditions, and the possible occurrence of smallmouth bass more tolerant than those tested, a concentration of twice the recommended treatment dose (0.050 mg l-1 rotenone) was finally used to treat the Rondegat River for a duration of 6 h.Keywords: behaviour effects, biodiversity conservation, effective concentration, mortality, rotenone toxicityAfrican Journal of Aquatic Science 2013, 38(Suppl.): 91–95
- Published
- 2013
31. Evaluation of acoustic transmitter implantation and determination of post-translocation behaviour of largemouth bass Micropterus salmoides in a South African impoundment
- Author
-
Huchzermeyer, CF, Weyl, OLF, and Cowley, PD
- Abstract
Largemouth bass Micropterus salmoides are an important angling species that are often displaced during catchand-release fishing tournaments. The impact of acoustic transmitter implantation on this species and the effect of displacement distance on their behaviour were tested. In April 2010, 10 fish with surgically implanted dummy acoustic transmitters and 10 control individuals were kept for 20 weeks under laboratory conditions. Wound healing, hepatosomatic index, gonadosomatic index and viscerosomatic index did not differ between treatment and control groups. However, fish with implanted dummy transmitters lost weight more rapidly than control fish. In 2010, an array of passive data-logging receivers was used at Wriggleswade Dam, Eastern Cape, to record movements of 10 acoustically tagged bass that had been displaced for distances ranging from 0.1 to 4.3 km. Fish displaced by up to 3.5 km remained within 3–4 km of their release site, but fish displaced 4.3 km immediately returned to their capture locations. Seven weeks after the initiation of the experiment, with the onset of winter, fish that had been holding in the vicinity of their release site near the Kubusi River inlet moved into the deeper basin of the impoundment. The results suggest that largemouth bass displaced for up to 4.3 km during fishing tournaments return to their capture localities.Keywords: acoustic telemetry, angling, displacement, health, movement behaviour, specific growth rateAfrican Journal of Aquatic Science 2013, 38(2): 229–236
- Published
- 2013
32. Population dynamics of the invasive fish, Gambusia affinis, in irrigation impoundments in the Sundays River Valley, Eastern Cape, South Africa
- Author
-
Howell, DH, Woodford, DJ, Weyl, OLF, and Froneman, W
- Subjects
invasive success ,Mosquitofish, population growth rate, invasive success, establishment ,Mosquitofish ,establishment ,population growth rate - Abstract
The alien invasive Gambusia affinis is one of the most widely introduced fish species on the planet, and has established in freshwater ecosystems across South Africa. The invasion ecology and, in particular, the population dynamics of the species in this country are, however, poorly understood. In this study the relative abundance and population dynamics of G. affinis were quantified in 5 interconnected irrigation impoundments within the Sundays River Valley, Eastern Cape.Four fish surveys were conducted from early summer (February 2012) to early winter (June 2012). Repeated-measures ANOVA analyses on the catch per unit effort (CPUE) of G. affinis between sampling events and dams revealed significant differences in population dynamics among dams, although an overall trend of rapid increase followed by plateau in summer, with a rapid decline in winter was seen in most dams. A general linear model assessing the role of biotic and abiotic factors on G. affinis CPUE found that water temperature and the presence of the native fish Glossogobius callidus had significant effects on the CPUE of G. affinis. While winter drops in temperature are likely to have caused mortality in G. affinis populations, and may act as the primary regulator of G. affinis establishment success in South African impoundments, the negative effect of G. callidus densities on G. affinis suggests competitive or predator-prey interactions with the native species.Keywords: Mosquitofish, population growth rate, invasive success, establishment
- Published
- 2013
33. Record of Blue tilapia Oreochromis aureus (Steindachner, 1864) in the Eerste River catchment, Western Cape province, South Africa.
- Author
-
Marr, SM, Gouws, G, Avlijas, S, Khosa, D, Impson, ND, van der Westhuizen, M, and Weyl, OLF
- Subjects
GENETIC barcoding ,OREOCHROMIS aureus ,MITOCHONDRIAL DNA ,MAXIMUM entropy method ,BIOLOGICAL specimens - Abstract
Oreochromis aureus was imported from Israel into South Africa in 1959 but data on its current status in South Africa are lacking. Genomic DNA was extracted and the COI gene amplified at the South African Institute for Aquatic Biodiversity. The identity of the sequences and specimens was determined using the Barcode of Life Data Systems and GenBank. Morphological and genetic assessment demonstrated that 11 specimens collected from two farm dams in the Eerste River System, Western Cape province, were Oreochromis aureus. A MaxEnt model compiled using global distribution, rainfall and temperature data predicted that large areas of southern Africa were climatically suitable for this species, indicating considerable invasion debt in southern Africa. As a result, surveys to assess for the extent of the invasion in South Africa and eradication of existing populations, if feasible, are recommended management actions. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
34. Diet of bluegill <italic>Lepomis macrochirus</italic> in a South African reservoir during winter and summer.
- Author
-
Ndaleni, PM, Wasserman, RJ, Ellender, BR, and Weyl, OLF
- Subjects
BLUEGILL ,FISH feeds ,MARINE biodiversity ,FISH ecology ,ZOOPLANKTON - Abstract
Alien fishes are considered a major threat to aquatic biodiversity in South Africa, yet relatively little regional information on their biology and ecology is available for many of these species. Seasonal changes in the diet of the bluegill
Lepomis macrochirus in Howieson’s Poort Dam, Grahamstown, were assessed during summer and winter in 2014-2015, using stomach content analysis. In winter, juvenile and adult fish diets were dominated by crustacean zooplankton and insects, respectively. In summer, juvenile fish fed on crustaceans and insects, whereas adults consumed mostly fish eggs, indicating a potential impact by these invasive fish on native fish through oophagy. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
35. Invasion status of Florida bass Micropterus floridanus (Lesueur, 1822) in South Africa.
- Author
-
Weyl, OLF, Schirrmann, MK, Hargrove, JS, Bodill, T, and Swartz, ER
- Subjects
- *
FLORIDA largemouth bass , *MARINE biological invasions , *INTRODUCED aquatic species , *FISHES , *MITOCHONDRIAL DNA , *SPECIES distribution , *BLACK bass - Abstract
Largemouth bassMicropterus salmoidesare a popular North American angling species that was introduced into South Africa in 1928. To enhance the largemouth bass fisheries, Florida bassMicropterus floridanuswere introduced into KwaZulu Natal, South Africa, in 1980. Knowledge on the status ofM. floridanusin South Africa is required, because it lives longer and reaches larger sizes thanM. salmoides, which may result in heightened impacts on native biota. BecauseM. floridanusare morphologically similar, but genetically distinct fromM. salmoides, the distribution of this species was assessed by genetically screening 185Micropterussp. individuals sampled from 20 localities across South Africa using the mitochondrial ND2 gene. Individuals with mitochondrial DNA matchingM. salmoideswere recovered from 16 localities, whereasM. floridanusmitochondrial DNA was recovered from 13 localities. At nine localities (45%), the mitochondrial DNA of both species was detected. These results demonstrateM. floridanusdispersal to multiple sites across South Africa. [ABSTRACT FROM PUBLISHER]
- Published
- 2017
- Full Text
- View/download PDF
36. Freshwater crayfish invasions in South Africa: past, present and potential future.
- Author
-
Nunes, AL, Zengeya, TA, Measey, GJ, and Weyl, OLF
- Subjects
CRAYFISH ,MARINE biological invasions ,INTRODUCED freshwater organisms ,CRAYFISH culture ,SPECIES distribution ,CHERAX cainii ,CHERAX destructor ,CHERAX quadricarinatus - Abstract
Freshwater crayfish invasions have been studied around the world, but less so in Africa, a continent devoid of native freshwater crayfish. The present study reviews historical and current information on alien freshwater crayfish species introduced into South Africa and aims to indicate which areas are at risk from invasion. As is the case elsewhere, South Africans have shown a keen interest in both farming and keeping freshwater crayfish as pets, which has resulted inCherax cainii,Cherax destructor,Cherax quadricarinatusandProcambarus clarkiibeing introduced to the country. There is evidence of successful establishment in the wild forC. quadricarinatusandP. clarkiiin different parts of the country. Species distribution models suggest that the eastern part of the country and parts of the Eastern and Western Cape are at higher risk of invasion. At present, illegal translocations represent the most likely pathway of crayfish spread in South Africa. A continued risk of invasion by freshwater crayfish species in South Africa is highlighted, which reinforces the need for more research, as well as for strong mitigation measures, such as stronger policing of existing regulations, management or eradication where feasible and public education. [ABSTRACT FROM PUBLISHER]
- Published
- 2017
- Full Text
- View/download PDF
37. Short NoteDiet of Anguilla mossambica (Teleostei, Anguillidae) elvers in the Sundays River, Eastern Cape, South Africa
- Author
-
Wasserman, RJ, Pereira-da-Conceicoa, LL, Strydom, NA, and Weyl, OLF
- Abstract
No Abstract.African Journal of Aquatic Science 2012, 37(3): 347–349
- Published
- 2012
38. Short CommunicationValidation of growth zone deposition rate in otoliths and scales of flathead mullet Mugil cephalus and freshwater mullet Myxus capensis from fish of known age
- Author
-
Ellender, BR, Taylor, GC, and Weyl, OLF
- Abstract
Flathead mullet Mugil cephalus and freshwater mullet Myxus capensis are important components in South African estuarine fish communities and fisheries, but there is little information on their age and growth or age validation. This study validated the periodicity of growth zone formation in sectioned sagittal otoliths and scales of fish of known age that had been at liberty for 10 years. For both M. cephalus and M. capensis, the number of growth zones counted on otolith sections did not differ significantly from the known age of the fish. There were significantly fewer growth zones on scales than the known age of both M. cephalus and M. capensis. Growth zone deposition rate could therefore be validated as annual for otoliths but not for scales of the two species. It is recommended that future ageing studies focus on otoliths rather than scales.Keywords: age validation, growth zones, sagittal otoliths, South AfricaAfrican Journal of Marine Science 2012, 34(3): 455–458
- Published
- 2012
39. New distribution record for the Asian tapeworm Bothriocephalus acheilognathi Yamaguti, 1934 in the Eastern Cape province, South Africa
- Author
-
Stadtlander, T, Weyl, OLF, and Booth, AJ
- Abstract
No abstract.African Journal of Aquatic Science 2011, 36(3): 339–343
- Published
- 2012
40. The effect of largemouth bass Micropterus salmoides on aquatic macroinvertebrate communities in the Wit River, Eastern Cape, South Africa
- Author
-
Weyl, PSR, de Moor, FC, Hill, MP, and Weyl, OLF
- Abstract
Fish predation is one of the driving forces of freshwater invertebrate community structures, with alien predators having a pronounced effect. A quantitative assessment of aquatic invertebrates in the Wit River, Sundays River catchment, Eastern Cape, South Africa, was undertaken to assess the impact of the alien fish Micropterus salmoides on their relative abundance and community structure. Communities in the stones-in-current and marginal vegetation biotopes were sampled in the presence and absence of M. salmoides in late summer (February–April) 2008. Results suggest that the presence of M. salmoides does have an impact on indigenous macroinvertebrate fauna and communities. Community structure in the stones-in-current biotopes did not differ significantly between sections of the river with or without fish. However, there was a significant difference in community structure in marginal vegetation between sections of river. In sections with M. salmoides several large or conspicuous taxa (Odonata, Hemiptera and Coleoptera) were significantly reduced (p < 0.05) or even absent, while cryptic/inconspicuous taxa (Trichoptera, Leptoceridae and Mollusca, Physidae) were significantly more abundant (p < 0.05).Keywords: community structure, conspicuous taxa, invasive predators, predationAfrican Journal of Aquatic Science 2010, 35(3): 273–281
- Published
- 2010
41. Short CommunicationOtoliths and vertebrae as potential hard structures for ageing South African yellowfin tuna Thunnus albacares
- Author
-
Filmalter, JD, Weyl, OLF, and Sauer, W
- Abstract
Sagittal otoliths and vertebrae from 46 yellowfin tuna Thunnus albacares (118–175 cm fork length) collected off the west coast of South Africa were assessed for potential usefulness in age estimation. Growth increments were found on both structures. Comparisons of growth increment counts showed that agreement in the counts of the number of growth increments was low (33–44%) but that most (90–94%) agreed to within one growth increment. Growth increment counts from whole otoliths, sectioned otoliths and vertebrae were not significantly different (t-test, p < 0.05). Among-reader precision was high for both whole otoliths (average percent error [APE] = 9.8%) and vertebrae (APE = 12.1%), but low for sectioned otoliths (APE = 34.9%). Age-bias plots indicated non-linear bias when sectioned otoliths were assessed in relation to other structures. Whole otoliths and whole vertebrae were considered equally precise, but the practicality of collecting vertebrae from the commercial fishery was better. Vertebrae are recommended as the most suitable structure for ageing yellowfin tuna. Keywords: age estimation; annuli; otoliths; precision; South Africa; vertebraeAfrican Journal of Marine Science 2009, 31(2): 271–276
- Published
- 2009
42. DNA barcoding of South Africa’s ornamental freshwater fish – are the names reliable?
- Author
-
van der Walt, KA, Mäkinen, T, Swartz, ER, and Weyl, OLF
- Subjects
GENETIC barcoding ,FRESHWATER fishes ,INTRODUCED species ,GENETIC databases ,DNA fingerprinting - Abstract
Trade in freshwater ornamental fish in South Africa is currently regulated by a ‘blacklist’ to prevent potentially invasive taxa from establishing in the country. Because its effective implementation requires accurate identification, the aim of the present study was to test whether DNA barcoding is a useful tool to identify freshwater fishes in the South African pet trade. A total of 351 aquarium fish specimens, representing 185 traded taxa, were sequenced for the mitochondrial COI barcoding marker in 2011 and 2012. Lake Malawi cichlids were treated as a single group due to a lack of resolution in their COI marker, resulting in a data set of 137 successfully sequenced taxa. The Barcode Of Life Database (BOLD) and GenBank were used for taxonomic assignment comparisons. The genetic identification matched the scientific name inferred from the trade name for 60 taxa (43.8%) using BOLD, and for 67 taxa (48.9%) using GenBank. A genetic ID could not be assigned in 47 (34.3%) cases using BOLD and in 37 cases (27%) using GenBank. Whereas DNA barcoding can be a useful tool to help identify imported freshwater fishes, it requires further development of publicly available databases to become a reliable means of identification. [ABSTRACT FROM PUBLISHER]
- Published
- 2017
- Full Text
- View/download PDF
43. Parasites of fishes in the recently inundated ephemeral Lake Liambezi, Namibia.
- Author
-
Mchugh, Kj, Weyl, Olf, and Smit, Nj
- Subjects
- *
PARASITOLOGY , *NEMATODE larvae , *LAKES , *TRYPANOSOMA ,FISH parasite life cycles - Abstract
Lake Liambezi forms the periodic connection between the upper Zambezi, Kwando and Okavango rivers. A full parasitological assessment was conducted on 86 fish, representing 14 species in six families sampled in August 2011. Parasite diversity was low and dominated by species with complex life cycles involving intermediate hosts. Most prevalent were larval nematodes (Contracaecumsp.) infecting 12 andTrypanasomasp. infecting nine of the 14 host species. The intra-erythrocytic parasiteBabesiosoma mariaewas found in the blood ofCoptodon rendalliandOreochromis andersoniiwith prevalence of 50% and 60%, respectively. The host-specific monogeneanAnnulotrema hepsetiwas recorded only fromH. cuvieriwith a prevalence of 100%. Notable absences were the copepod and branchiuran parasites that have direct lifecycles and usually occur in high prevalence and abundance in the region. Because parasites with direct life cycles can only be transported into the lake on the host fish, their absence suggests limited immigration of infected fishes into the lake. This suggests that internal recruitment dominates over immigration in the fish population dynamics in Lake Liambezi. [ABSTRACT FROM PUBLISHER]
- Published
- 2016
- Full Text
- View/download PDF
44. Influence of the annual flood-pulse on catch per unit effort, condition and reproduction of Clarias gariepinus from the upper Okavango Delta, Botswana.
- Author
-
Bokhutlo, T, Weyl, OLF, Mosepele, K, and Wilson, GG
- Subjects
- *
CLARIAS , *CLARIAS gariepinus , *BIOLOGY , *FISH reproduction , *BEHAVIOR - Abstract
Catch per unit effort (CPUE), length, weight and maturity data forClarias gariepinuswere collected during monthly gillnet surveys in the upper Okavango Delta between 2001 and 2009 to investigate their relationship with the annual flood-pulse. CPUE, condition factor (K) and the proportion of ripe-running fish (PRR) in the population followed a unimodal annual cycle that could be modelled using water temperature and flood-pulse hydrology. Increased CPUE during declining water levels was most likely a result of feeding migrations and aggregation behaviour. The observed increase inKduring low floods in October and November preceded the increase inPRR, which increased mainly with increasing temperature but appeared less dependent on flow. This study provided quantitative evidence that the biology of fish in the Okavango Delta is mainly dependent on the annual flood regime and, therefore, that conservation efforts should be focused on maintaining natural flow patterns in the face of climate change and potential water extraction schemes upstream. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
45. An assessment of the reproductive biology of the Marico barb Barbus motebensis from the upper Groot Marico catchment, South Africa.
- Author
-
Kindler, D, Wagenaar, GM, and Weyl, OLF
- Subjects
BARBUS ,FISH fertility ,WATERSHEDS ,SPAWNING ,HISTOLOGY ,FISH conservation - Abstract
Barbus motebensisis endemic to the Groot Marico River catchment in the North West province, South Africa, and is considered of particular conservation importance due to being Red-Listed as Vulnerable. Due to its vulnerable conservation status, the aim of this study was to provide information on its condition factor, breeding season, gonadosomatic index, fecundity range and length at maturity from specimens collected by means of electrofishing and seine-netting between November 2012 and May 2014 from the Draaifonteinspruit and Kaaloog se Loop. Length at maturity was estimated as 37.5 mm TL for males and 44.5 mm TL for females. Microscopic gonad staging and gonadosomatic index demonstrated thatB. motebensishas an extended breeding season from spring to summer. Relative (578 eggs g−1) and absolute (3 728 eggs) fecundity were relatively high for small barbs. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
46. Ecology, fish and fishery of Lake Liambezi, a recently refilled floodplain lake in the Zambezi Region, Namibia.
- Author
-
Peel, RA, Tweddle, D, Simasiku, EK, Martin, GD, Lubanda, J, Hay, CJ, and Weyl, OLF
- Subjects
MACROPHYTES ,CICHLIDS ,PHRAGMITES australis ,SCHILBEID catfishes ,FLOODPLAIN ecology - Abstract
Lake Liambezi (300 km2) refilled in 2009 after a prolonged 22-year dry period. Its aquatic macrophyte populations, fish fauna and fishery shortly after refilling are described. The emergent aquatic macrophytePhragmites australisformed dense stands covering large parts of the lake, while extensive beds of submergedLagarosiphon ilicifoliusandNajas horridaoccurred in shallower areas. Twenty-nine fish species were recorded in experimental gillnets. Catches were dominated byBrycinus lateralisandSchilbe intermedius, contributing 39.5% and 38.5% by weight, respectively. Large-meshed (3–4.5 inch) monofilament and multifilament gillnets emulating those used in the commercial fishery caught mostlyOreochromis andersonii(42.7% by weight) andSerranochromis macrocephalus(28.3% by weight), respectively. Commercial gillnet catch per unit effort (CPUE) averaged 7.0 kg 100-m net−1night−1, and the annual yield for 2011/2012 was estimated at 2 700 tonnes. Aquatic macrophytes and fishes quickly recolonised the lake and, just two years after refilling, the lake supported a thriving fishery that yielded 4.5 times more than the 600 tonnes recorded in 1974. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
47. Why suggesting Australian redclaw crayfish Cherax quadricarinatus as biological control agents for snails is a bad idea.
- Author
-
Weyl, OLF, Nunes, AL, Ellender, BR, Weyl, PSR, Chilala, AC, Jacobs, FJ, Murray-Hudson, M, and Douthwaite, RJ
- Subjects
- *
CHERAX quadricarinatus , *CRAYFISH , *PHYSIOLOGICAL control systems , *SNAILS -- Control , *SCHISTOSOMA , *FRESHWATER fishes , *INTRODUCED aquatic species - Published
- 2017
- Full Text
- View/download PDF
48. Effect of rotenone on gill-respiring and plastron-respiring insects.
- Author
-
Booth, AJ, Moss, S, and Weyl, OLF
- Subjects
ROTENONE ,AQUATIC insects ,RESPIRATION ,MOZAMBIQUE tilapia ,PISCICIDES ,CELL respiration ,CORIXIDAE ,INSECTS - Abstract
Rotenone, a commonly-used piscicide, interferes with the cellular respiration of aquatic vertebrates and invertebrates by preventing the uptake of oxygen. While dose-response relationships have been developed for fish, there are limited comparative data available on aquatic insects that respire either with tracheal gills or with a plastron – a thin layer of air trapped by hairs on the exterior of the body. This study assesses the temperature-dependent toxicity of rotenone to gill-respiring aquatic insects, family Coenagrionidae, and plastron-respiring aquatic insects, family Corixidae, at concentrations that are lethal to Mozambique tilapiaOreochromis mossambicus. Both groups of insects were found to be differentially susceptible to rotenone, with survival decreasing as functions of both increased concentration and temperature. The dose-response relationship of Mozambique tilapia was found to be similar to that of other fishes, with 100% mortality achieved at 0.025 mg l-1at both 20 °C and 28 °C. At this concentration, mortality in gill-respiring insects after 48 h was 10% at 20 °C and 28% at 28 °C, which was higher than that of plastron-respiring insects, being 2% and 7% at the same temperatures. At higher concentrations (0.05–0.10 mg l-1), however, mortality of both gill- (>50%) and plastron-respiring (>10%) insects became substantial. [ABSTRACT FROM PUBLISHER]
- Published
- 2015
- Full Text
- View/download PDF
49. Rapid bioassessment of the effects of repeated rotenone treatments on invertebrate assemblages in the Rondegat River, South Africa.
- Author
-
Villet, MH, Bellingan, TA, Woodford, DJ, Weyl, OLF, and Gouws, J
- Subjects
ROTENONE ,INVERTEBRATE communities ,RIVERS ,PISCICIDES ,SMALLMOUTH bass ,REHABILITATION - Abstract
The potential collateral effects of eradicating invasive fishes in streams necessitate the monitoring of invertebrate communities during treatment. In an environmental rehabilitation programme, non-native smallmouth bass were removed from the lower reaches of the Rondegat River, Western Cape, South Africa, in 2012 and again in 2013 using the piscicide rotenone. A monitoring programme tracked the ecological response of organisms to these activities using quantitative sampling of macroinvertebrates on stones and the ISO-certified SASS5 rapid bioassessment method for assessing macroinvertebrate community integrity. We recorded a significant decrease in macroinvertebrate densities from the stones-in-current biotope following both rotenone treatments. The average score per taxon (ASPT) declined after the first treatment, indicating a loss of taxa sensitive to diminished water quality, then recovered prior to the second treatment, and subsequently no decline was detected after the lower dose used in the 2013 treatment. The SASS values were too variable to reveal trends. The ASPTs indicated that the community may have been resistant to low dose and resilient to high dose, due to inter-treatment recovery following the 2012 treatment, suggesting that the invertebrate assemblage is resilient to the conservative use of rotenone for localised river rehabilitation when upstream sources of recruitment exist. [ABSTRACT FROM PUBLISHER]
- Published
- 2015
- Full Text
- View/download PDF
50. Analysis of active rotenone concentration during treatment of the Rondegat River, Cape Floristic Region, South Africa.
- Author
-
Slabbert, E, Jordaan, MS, and Weyl, OLF
- Subjects
ROTENONE ,FISH farming ,WILDLIFE conservation ,NEUTRALIZATION (Chemistry) ,FRESHWATER fishes - Abstract
Most endemic freshwater fish species of the Cape Floristic Region are listed as threatened, due mainly to the impacts of invasive alien fish species. The piscicide rotenone has been identified as a potential tool to aid the conservation of indigenous species through the removal of invasive fish. Rotenone was used in the Rondegat River, Cederberg, where smallmouth bassMicropterus dolomieuhad extirpated the indigenous fish. An initial rotenone treatment in March 2012 was followed by another in March 2013. Due to concerns following the first treatment about possible build-up of rotenone between treatment stations, the second treatment included monitoring of rotenone concentrations during the treatment. Measured concentrations were consistently below the selected treatment concentration of 37.5 µg l−1and dropped to below the tested effective piscicidal concentration of 12.5 µg l−1at some sampling points. There was no build-up of rotenone within the treatment zones, but rotenone took longer than expected to clear out of the treatment area. The rotenone was effectively neutralised when the neutralisation station was operational, but was still detectable after neutralisation was terminated. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
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