Movement behaviour of largemouth bass Micropterus salmoides in a South African impoundment
- Howell, Dylan H, Cowley, Paul D, Childs, Amber-Robyn, Weyl, Olaf L F
- Authors: Howell, Dylan H , Cowley, Paul D , Childs, Amber-Robyn , Weyl, Olaf L F
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443893 , vital:74169 , https://doi.org/10.1080/15627020.2015.1040837
- Description: The objectives of this study were to describe movements and area use patterns of largemouth bass Micropterus salmoides in relation to abiotic factors (water temperature, river inflow and water level). The study was conducted in the Kubusi arm of Wriggleswade Dam, Eastern Cape, South Africa where nine largemouth bass (310–385 mm FL) were surgically implanted with individually coded acoustic transmitters and monitored for nine months (May 2010 to January 2011) using an array of five moored acoustic data-logging receivers. The daily position occupied by largemouth bass was significantly affected by water temperature (P0.001) and river inflow (P0.001), whereas water level had no effect. Largemouth bass spent little or no time in the shallow river inlet areas when water temperature was 12.5 °C, but as water temperature increased, their utilisation of shallow areas increased significantly. The results from this study demonstrate the importance of environmental factors, particularly water temperature, on the movement of largemouth bass.
- Full Text:
- Date Issued: 2015
- Authors: Howell, Dylan H , Cowley, Paul D , Childs, Amber-Robyn , Weyl, Olaf L F
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443893 , vital:74169 , https://doi.org/10.1080/15627020.2015.1040837
- Description: The objectives of this study were to describe movements and area use patterns of largemouth bass Micropterus salmoides in relation to abiotic factors (water temperature, river inflow and water level). The study was conducted in the Kubusi arm of Wriggleswade Dam, Eastern Cape, South Africa where nine largemouth bass (310–385 mm FL) were surgically implanted with individually coded acoustic transmitters and monitored for nine months (May 2010 to January 2011) using an array of five moored acoustic data-logging receivers. The daily position occupied by largemouth bass was significantly affected by water temperature (P0.001) and river inflow (P0.001), whereas water level had no effect. Largemouth bass spent little or no time in the shallow river inlet areas when water temperature was 12.5 °C, but as water temperature increased, their utilisation of shallow areas increased significantly. The results from this study demonstrate the importance of environmental factors, particularly water temperature, on the movement of largemouth bass.
- Full Text:
- Date Issued: 2015
Population dynamics and biology of an invasive population of mosquitofish Gambusia affinis in a temperate estuarine lake system
- Sloterdijk, Hans, James, Nicola C, Smith, M Kyle S, Ekau, Werner, Weyl, Olaf L F
- Authors: Sloterdijk, Hans , James, Nicola C , Smith, M Kyle S , Ekau, Werner , Weyl, Olaf L F
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443919 , vital:74171 , https://doi.org/10.1080/15627020.2015.1021169
- Description: This study investigates the distribution, relative abundance, population growth and biology of the alien invasive fish Gambusia affinis in the Wilderness Lakes System, a coastal lake system in the warm-temperate region of South Africa. Fish were collected throughout the system during four seasonal sampling trips in spring (October 2010), summer (February 2011), autumn (May 2011) and winter (July 2011). Gambusia affinis were widespread and abundant in all habitats from the freshwater reaches of the inflowing Touw River to the more saline lakes and estuary. Sex ratio was generally female dominated and mean length at maturity was 14.7 mm standard length (SL) for males and 20.3 mm SL for females. Reproduction was strongly seasonal with reproductively active fish sampled in spring and summer but not in autumn and winter. Relative abundance also varied seasonally, with populations following typical ‘boom and bust’ population dynamics. By winter, the population in all habitats was lower with mortality rates as high as 85%. The stronghold of the population appears to be in the channels between the lakes, where relative abundance was more consistent and winter mortality rates were lower. The survivors, which are primarily females, then reconstitute the population in the spring and summer months.
- Full Text:
- Date Issued: 2015
- Authors: Sloterdijk, Hans , James, Nicola C , Smith, M Kyle S , Ekau, Werner , Weyl, Olaf L F
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443919 , vital:74171 , https://doi.org/10.1080/15627020.2015.1021169
- Description: This study investigates the distribution, relative abundance, population growth and biology of the alien invasive fish Gambusia affinis in the Wilderness Lakes System, a coastal lake system in the warm-temperate region of South Africa. Fish were collected throughout the system during four seasonal sampling trips in spring (October 2010), summer (February 2011), autumn (May 2011) and winter (July 2011). Gambusia affinis were widespread and abundant in all habitats from the freshwater reaches of the inflowing Touw River to the more saline lakes and estuary. Sex ratio was generally female dominated and mean length at maturity was 14.7 mm standard length (SL) for males and 20.3 mm SL for females. Reproduction was strongly seasonal with reproductively active fish sampled in spring and summer but not in autumn and winter. Relative abundance also varied seasonally, with populations following typical ‘boom and bust’ population dynamics. By winter, the population in all habitats was lower with mortality rates as high as 85%. The stronghold of the population appears to be in the channels between the lakes, where relative abundance was more consistent and winter mortality rates were lower. The survivors, which are primarily females, then reconstitute the population in the spring and summer months.
- Full Text:
- Date Issued: 2015
Rapid bioassessment of the effects of repeated rotenone treatments on invertebrate assemblages in the Rondegat River, South Africa
- Bellingan, Terence A, Woodford, Darragh J, Gouws, J, Villet, Martin H, Weyl, Olaf L F
- Authors: Bellingan, Terence A , Woodford, Darragh J , Gouws, J , Villet, Martin H , Weyl, Olaf L F
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/442279 , vital:73972 , https://doi.org/10.2989/16085914.2014.984651
- Description: 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.
- Full Text:
- Date Issued: 2015
- Authors: Bellingan, Terence A , Woodford, Darragh J , Gouws, J , Villet, Martin H , Weyl, Olaf L F
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/442279 , vital:73972 , https://doi.org/10.2989/16085914.2014.984651
- Description: 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.
- Full Text:
- Date Issued: 2015
Histological confirmation of epizootic ulcerative syndrome in two cyprinid species from Lake Liambezi, Zambezi Region, Namibia
- McHugh, Kyle J, Smit, Nico J, Christison, Kevin W, Weyl, Olaf L F
- Authors: McHugh, Kyle J , Smit, Nico J , Christison, Kevin W , Weyl, Olaf L F
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443354 , vital:74110 , https://hdl.handle.net/10520/EJC160489
- Description: Epizootic ulcerative syndrome (EUS) is a fish disease caused by an infection of the oomycete, Aphanomyces invadans. During a fish biodiversity assessment of Lake Liambezi, Zambezi Region, Namibia, in August 2011, two Barbus haasianus and three Barbus unitaeniatus with circular ulcerative skin lesions were collected. Lake Liambezi receives inflow from the Zambezi, Chobe and Linyanti rivers. The presence of EUS in the two species was confirmed histologically by: a loss of epidermis at the site of the lesion; hyphae visible deep into the muscle layer with an associated granulomatous inflammatory reaction; and muscle fibre degeneration visible with associated penetrating hyphae. This paper provides further histological confirmation of EUS from Lake Liambezi and the first record of the disease in B. haasianus.
- Full Text:
- Date Issued: 2014
- Authors: McHugh, Kyle J , Smit, Nico J , Christison, Kevin W , Weyl, Olaf L F
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443354 , vital:74110 , https://hdl.handle.net/10520/EJC160489
- Description: Epizootic ulcerative syndrome (EUS) is a fish disease caused by an infection of the oomycete, Aphanomyces invadans. During a fish biodiversity assessment of Lake Liambezi, Zambezi Region, Namibia, in August 2011, two Barbus haasianus and three Barbus unitaeniatus with circular ulcerative skin lesions were collected. Lake Liambezi receives inflow from the Zambezi, Chobe and Linyanti rivers. The presence of EUS in the two species was confirmed histologically by: a loss of epidermis at the site of the lesion; hyphae visible deep into the muscle layer with an associated granulomatous inflammatory reaction; and muscle fibre degeneration visible with associated penetrating hyphae. This paper provides further histological confirmation of EUS from Lake Liambezi and the first record of the disease in B. haasianus.
- Full Text:
- Date Issued: 2014
Life-history characteristics of an age-validated established invasive African sharptooth catfish, Clarias gariepinus, population in a warm-temperate African impoundment
- Wartenberg, Reece, Weyl, Olaf L F, Booth, Anthony J, Winker, A Henning
- Authors: Wartenberg, Reece , Weyl, Olaf L F , Booth, Anthony J , Winker, A Henning
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443542 , vital:74130 , https://hdl.handle.net/10520/EJC145790
- Description: It has been suggested that the invasive, omnivorous Clarias garipienus is capable of rapid invasions and long-term persistence in recently inhabited freshwater systems. To test this hypothesis, the life history of the established, extralimital Darlington Dam (33°10'31"S, 25°09'13"E) population was investigated. By counting post-fluorescent mark increments on otoliths from 21 chemically tagged wild fish recaptured 244-537 days later, the deposition of growth zones, comprising alternating opaque and translucent bands, was validated as annual. Examination of sectioned otoliths from 175 fish revealed that the oldest fish, two males of 840 and 1074 mm total length (TL), were 25 years old - 10 years older than previously described for any C. gariepinus population. The oldest female was 885 mm TL and 21 years old. Length-at-age was subsequently described using the von Bertalanffy growth model. Combined-sex growth was best described as Lt = 931.7 ( 1 - exp(-0.15(t +2.43))) mm TL. Total mortality (Z) was calculated using catch curve analysis and the Chapman and Robson estimator to be 0.35/yr. The presence of specimens 15 years and older indicates that these fish established quickly and supports the finding that mortality rates are low, which, in turn, suggests likely long-term population persistence.
- Full Text:
- Date Issued: 2014
- Authors: Wartenberg, Reece , Weyl, Olaf L F , Booth, Anthony J , Winker, A Henning
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443542 , vital:74130 , https://hdl.handle.net/10520/EJC145790
- Description: It has been suggested that the invasive, omnivorous Clarias garipienus is capable of rapid invasions and long-term persistence in recently inhabited freshwater systems. To test this hypothesis, the life history of the established, extralimital Darlington Dam (33°10'31"S, 25°09'13"E) population was investigated. By counting post-fluorescent mark increments on otoliths from 21 chemically tagged wild fish recaptured 244-537 days later, the deposition of growth zones, comprising alternating opaque and translucent bands, was validated as annual. Examination of sectioned otoliths from 175 fish revealed that the oldest fish, two males of 840 and 1074 mm total length (TL), were 25 years old - 10 years older than previously described for any C. gariepinus population. The oldest female was 885 mm TL and 21 years old. Length-at-age was subsequently described using the von Bertalanffy growth model. Combined-sex growth was best described as Lt = 931.7 ( 1 - exp(-0.15(t +2.43))) mm TL. Total mortality (Z) was calculated using catch curve analysis and the Chapman and Robson estimator to be 0.35/yr. The presence of specimens 15 years and older indicates that these fish established quickly and supports the finding that mortality rates are low, which, in turn, suggests likely long-term population persistence.
- Full Text:
- Date Issued: 2014
First Record of an Introduction of the Giant Pangasius, Pangasius sanitwongsei Smith 1931, Into an African River
- Mäkinen, Tuuli, Weyl, Olaf L F, van der Walt, Kerry-Ann, Swartz, Ernst R
- Authors: Mäkinen, Tuuli , Weyl, Olaf L F , van der Walt, Kerry-Ann , Swartz, Ernst R
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443340 , vital:74109 , https://hdl.handle.net/10520/EJC145782
- Description: A catfish captured in the Breede River (33°56'41.6"S 20°4'45.6"E) in South Africa was identified using morphological and genetic techniques as the giant pangasius, Pangasius sanitwongsei Smith 1931, a new record for South Africa. The wild-caught specimen was a genetic match to juveniles purchased from the pet trade, and most likely originated from a release by an aquarist. Pangasius sanitwongsei is not on the list of fishes currently permitted for import into South Africa, and its presence in the pet trade illustrates the difficulty associated with preventing illegal introductions.
- Full Text:
- Date Issued: 2013
- Authors: Mäkinen, Tuuli , Weyl, Olaf L F , van der Walt, Kerry-Ann , Swartz, Ernst R
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443340 , vital:74109 , https://hdl.handle.net/10520/EJC145782
- Description: A catfish captured in the Breede River (33°56'41.6"S 20°4'45.6"E) in South Africa was identified using morphological and genetic techniques as the giant pangasius, Pangasius sanitwongsei Smith 1931, a new record for South Africa. The wild-caught specimen was a genetic match to juveniles purchased from the pet trade, and most likely originated from a release by an aquarist. Pangasius sanitwongsei is not on the list of fishes currently permitted for import into South Africa, and its presence in the pet trade illustrates the difficulty associated with preventing illegal introductions.
- Full Text:
- Date Issued: 2013
Using a unified invasion framework to characterize Africa’s first loricariid catfish invasion
- Jones, Roy W, Weyl, Olaf L F, Hill, Martin P, Swartz, Ernst R
- Authors: Jones, Roy W , Weyl, Olaf L F , Hill, Martin P , Swartz, Ernst R
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/418081 , vital:71507 , xlink:href="https://doi.org/10.1007/s10530-013-0438-7"
- Description: This paper presents evidence of establishment of a loricariid population in the Nseleni River in South Africa and uses a unified framework to determine its invasion stage. Specimens were identified morphologically as Pterygioplichthys disjunctivus (Weber 1991), but genetic barcoding results indicated close association with specimens that may have a hybrid history. The species was introduced into South Africa via the pet trade and the first record of introduction into the wild was in 2004. Samples collected in 2011 and 2012 demonstrated that there were multiple length cohorts in the population including juveniles (12–130 mm total length TL) and large (>300 mm TL) adult fish. Gonadal assessment of adults demonstrated the presence of reproduction capable specimens. The concurrent occurrence of mature adults and juvenile fish demonstrated establishment. Locality records indicate that P. disjunctivus has already spread between two rivers through an inter basin water transfer. Using a unified framework for invasions this invasion was categorized as a self-sustaining population in the wild with individuals surviving and reproducing a significant distance from their original point of introduction. Containment is suggested as potential management strategy.
- Full Text:
- Date Issued: 2013
- Authors: Jones, Roy W , Weyl, Olaf L F , Hill, Martin P , Swartz, Ernst R
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/418081 , vital:71507 , xlink:href="https://doi.org/10.1007/s10530-013-0438-7"
- Description: This paper presents evidence of establishment of a loricariid population in the Nseleni River in South Africa and uses a unified framework to determine its invasion stage. Specimens were identified morphologically as Pterygioplichthys disjunctivus (Weber 1991), but genetic barcoding results indicated close association with specimens that may have a hybrid history. The species was introduced into South Africa via the pet trade and the first record of introduction into the wild was in 2004. Samples collected in 2011 and 2012 demonstrated that there were multiple length cohorts in the population including juveniles (12–130 mm total length TL) and large (>300 mm TL) adult fish. Gonadal assessment of adults demonstrated the presence of reproduction capable specimens. The concurrent occurrence of mature adults and juvenile fish demonstrated establishment. Locality records indicate that P. disjunctivus has already spread between two rivers through an inter basin water transfer. Using a unified framework for invasions this invasion was categorized as a self-sustaining population in the wild with individuals surviving and reproducing a significant distance from their original point of introduction. Containment is suggested as potential management strategy.
- Full Text:
- Date Issued: 2013
Life history strategy and population characteristics of an unexploited riverine cyprinid, Labeo capensis, in the largest impoundment in the Orange River Basin
- Winker, A Henning, Weyl, Olaf L F, Booth, Anthony J, Ellender, Bruce R
- Authors: Winker, A Henning , Weyl, Olaf L F , Booth, Anthony J , Ellender, Bruce R
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124910 , vital:35709 , https://doi.10.3377/004.047.0124
- Description: Common carp (Cyprinus carpio) is one of the world’s most widely introduced and established freshwater fishes (Casal 2006). The species is considered to be one of the eight most invasive freshwater fishes (Lowe et al. 2000) and worldwide, it accounts for most of the records of successful establishments and adverse ecological effects (Casal 2006; Kulhanek et al. 2011). This invasive success suggests that feral C. carpio is equipped with a set of adaptable life history attributes that allow it to successfully colonise a wide range of habitats (Koehn 2004; Zambrano et al. 2006; Britton et al. 2007). Where feral C. carpio occurs in high densities, it is often perceived as an invasive pest species (Sivakumaran et al. 2003; Brown and Walker 2004; Koehn 2004) because it can have severe impacts on habitat heterogeneity and biodiversity by increasing water turbidity through its bottom feeding behaviour, increasing nutrient availability, decreasing benthic and macrophyte density and diversity, altering zooplankton assemblages and decreasing endemic fish abundance (Zambrano et al. 2001; Khan 2003; Kulhanek et al. 2011). Within south-east Australia, for example, C. carpio comprises the largest proportion of the ichthyobiomass in the continent’s largest river system – the Murray–Darling Basin (Gehrke et al. 1995). As a consequence, serious concerns about its threat to endemic freshwater species (Koehn 2004) have prompted several of the most recent investigations into its life history (e.g. Sivakumaran et al. 2003; Smith and Walker 2004; Brown et al. 2005). Other potential threats posed also include competition with indigenous species and the spread of diseases and parasites (Dudgeon et al. 2006). In South Africa, for example, Asian tapeworm Bothriocephalus acheilognathi is now widely distributed in seven river systems and has infected eight novel cyprinid hosts due to the translocation of infected by C. carpio from a centralized aquaculture facility (Stadtlander et al. 2011).
- Full Text:
- Date Issued: 2012
- Authors: Winker, A Henning , Weyl, Olaf L F , Booth, Anthony J , Ellender, Bruce R
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124910 , vital:35709 , https://doi.10.3377/004.047.0124
- Description: Common carp (Cyprinus carpio) is one of the world’s most widely introduced and established freshwater fishes (Casal 2006). The species is considered to be one of the eight most invasive freshwater fishes (Lowe et al. 2000) and worldwide, it accounts for most of the records of successful establishments and adverse ecological effects (Casal 2006; Kulhanek et al. 2011). This invasive success suggests that feral C. carpio is equipped with a set of adaptable life history attributes that allow it to successfully colonise a wide range of habitats (Koehn 2004; Zambrano et al. 2006; Britton et al. 2007). Where feral C. carpio occurs in high densities, it is often perceived as an invasive pest species (Sivakumaran et al. 2003; Brown and Walker 2004; Koehn 2004) because it can have severe impacts on habitat heterogeneity and biodiversity by increasing water turbidity through its bottom feeding behaviour, increasing nutrient availability, decreasing benthic and macrophyte density and diversity, altering zooplankton assemblages and decreasing endemic fish abundance (Zambrano et al. 2001; Khan 2003; Kulhanek et al. 2011). Within south-east Australia, for example, C. carpio comprises the largest proportion of the ichthyobiomass in the continent’s largest river system – the Murray–Darling Basin (Gehrke et al. 1995). As a consequence, serious concerns about its threat to endemic freshwater species (Koehn 2004) have prompted several of the most recent investigations into its life history (e.g. Sivakumaran et al. 2003; Smith and Walker 2004; Brown et al. 2005). Other potential threats posed also include competition with indigenous species and the spread of diseases and parasites (Dudgeon et al. 2006). In South Africa, for example, Asian tapeworm Bothriocephalus acheilognathi is now widely distributed in seven river systems and has infected eight novel cyprinid hosts due to the translocation of infected by C. carpio from a centralized aquaculture facility (Stadtlander et al. 2011).
- Full Text:
- Date Issued: 2012
Life-history characteristics of an age-validated established invasive African sharptooth catfish, Clarias gariepinus, population in a warm–temperate African impoundment
- Wartenberg, Reece, Weyl, Olaf L F, Booth, Anthony J, Winker, A Henning
- Authors: Wartenberg, Reece , Weyl, Olaf L F , Booth, Anthony J , Winker, A Henning
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124921 , vital:35710 , https://doi.10.3377/004.048.0225
- Description: African sharptooth catfish Clarias gariepinus (Burchell, 1822) is a widely distributed fish that has now invaded water bodies in South America, Eastern Europe, Asia and South Africa (Cambray 2003). In South Africa it is native as far south as the Orange-Vaal river system, but inter-basin water transfer schemes (IBWTs), illegal stocking by anglers and from aquaculture has resulted in the establishment of extralimital populations in almost all river systems (van Rensburg et al. 2011). Within the Eastern Cape Province, C. gariepinus has invaded the Great Fish and Sundays rivers through IBWTs, that connect the Orange River to the Great Fish River and then to the Sundays River system which flows directly into Darlington Dam (Kadye & Booth 2013a) (Fig. 1). Soon after the completion of the IBWTs sharptooth catfish were recorded in Grassridge Dam in 1976 (Laurenson & Hocutt 1985), and later from Darlington Dam in 1981 (Scott et al. 2006). Although Cambray & Jubb (1977) are of the opinion that the species was translocated prior to the IBWT connection, there is now a permanent corridor between the Orange River and its receiving river systems that can facilitate the continued introduction of non-native Orange River fishes and other aquatic biota.
- Full Text:
- Date Issued: 2012
- Authors: Wartenberg, Reece , Weyl, Olaf L F , Booth, Anthony J , Winker, A Henning
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124921 , vital:35710 , https://doi.10.3377/004.048.0225
- Description: African sharptooth catfish Clarias gariepinus (Burchell, 1822) is a widely distributed fish that has now invaded water bodies in South America, Eastern Europe, Asia and South Africa (Cambray 2003). In South Africa it is native as far south as the Orange-Vaal river system, but inter-basin water transfer schemes (IBWTs), illegal stocking by anglers and from aquaculture has resulted in the establishment of extralimital populations in almost all river systems (van Rensburg et al. 2011). Within the Eastern Cape Province, C. gariepinus has invaded the Great Fish and Sundays rivers through IBWTs, that connect the Orange River to the Great Fish River and then to the Sundays River system which flows directly into Darlington Dam (Kadye & Booth 2013a) (Fig. 1). Soon after the completion of the IBWTs sharptooth catfish were recorded in Grassridge Dam in 1976 (Laurenson & Hocutt 1985), and later from Darlington Dam in 1981 (Scott et al. 2006). Although Cambray & Jubb (1977) are of the opinion that the species was translocated prior to the IBWT connection, there is now a permanent corridor between the Orange River and its receiving river systems that can facilitate the continued introduction of non-native Orange River fishes and other aquatic biota.
- Full Text:
- Date Issued: 2012
Otoliths versus scales: evaluating the most suitable structure for ageing largemouth bass, Micropterus salmoides, in South Africa
- Taylor, Geraldine C, Weyl, Olaf L F
- Authors: Taylor, Geraldine C , Weyl, Olaf L F
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443907 , vital:74170 , https://doi.org/10.1080/15627020.2012.11407562
- Description: The suitability of scales for ageing Micropterus salmoides was determined by comparing the precision of growth zone counts on scales with those obtained from sectioned sagittal otoliths from a sample of 496 fish collected from Wriggleswade and Mankazana Impoundments in the Eastern Cape, South Africa. Otoliths (1.4% rejected) were more readable than scales (41.7% and 7.5% rejected) for Wriggleswade and Mankazana Impoundments respectively. Otolith readings were more precise (average percentage error (APE) = 13.6%; coefficient of variation (CV) = 15.8%) than scales (APE = 18.0%; CV = 21.9%) for the total sample. Growth zone counts between structures were not symmetrically distributed around the agreed ages (otolith age = scale age) of the fish from Wriggleswade Impoundment (Bowker’s test H2: χ2 = 136, d.f. = 27, P 0.05) and graphical comparison showed that scales tended to underestimate age, particularly for fish older than five years. Scales are therefore not suitable structures for ageing South African M. salmoides which may attain ages of up to 13 years.
- Full Text:
- Date Issued: 2012
- Authors: Taylor, Geraldine C , Weyl, Olaf L F
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443907 , vital:74170 , https://doi.org/10.1080/15627020.2012.11407562
- Description: The suitability of scales for ageing Micropterus salmoides was determined by comparing the precision of growth zone counts on scales with those obtained from sectioned sagittal otoliths from a sample of 496 fish collected from Wriggleswade and Mankazana Impoundments in the Eastern Cape, South Africa. Otoliths (1.4% rejected) were more readable than scales (41.7% and 7.5% rejected) for Wriggleswade and Mankazana Impoundments respectively. Otolith readings were more precise (average percentage error (APE) = 13.6%; coefficient of variation (CV) = 15.8%) than scales (APE = 18.0%; CV = 21.9%) for the total sample. Growth zone counts between structures were not symmetrically distributed around the agreed ages (otolith age = scale age) of the fish from Wriggleswade Impoundment (Bowker’s test H2: χ2 = 136, d.f. = 27, P 0.05) and graphical comparison showed that scales tended to underestimate age, particularly for fish older than five years. Scales are therefore not suitable structures for ageing South African M. salmoides which may attain ages of up to 13 years.
- Full Text:
- Date Issued: 2012
A comparison of three techniques for fluorochrome marking of juvenile Clarias gariepinus otoliths
- Wartenberg, Reece, Booth, Anthony J, Weyl, Olaf L F
- Authors: Wartenberg, Reece , Booth, Anthony J , Weyl, Olaf L F
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123520 , vital:35450 , https://doi.10.3377/004.046.0119
- Description: African sharptooth catfish, Clarias gariepinus (Burchell 1822), is widely distributed with a natural range that extends from southern Turkey to the Orange River, South Africa (Skelton 2001). In addition to translocations within its southerly range (Cambray 2003), Cambray (2005) noted that as a result of poor aquaculture practices and introductions from a number of unknown sources, C. gariepinus has now invaded South America, Europe, Asia, and Australia. Its life history characteristics include a fast growth rate to a maximum length of 1300mmtotal length (TL) (Bruton 1976), a high fecundity, an omnivorous diet and the ability to breathe air (de Moor & Bruton 1988; Cambray 2003). Understanding the biology and population dynamics of this invader would assist in its management and possibly eradication.
- Full Text:
- Date Issued: 2011
- Authors: Wartenberg, Reece , Booth, Anthony J , Weyl, Olaf L F
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123520 , vital:35450 , https://doi.10.3377/004.046.0119
- Description: African sharptooth catfish, Clarias gariepinus (Burchell 1822), is widely distributed with a natural range that extends from southern Turkey to the Orange River, South Africa (Skelton 2001). In addition to translocations within its southerly range (Cambray 2003), Cambray (2005) noted that as a result of poor aquaculture practices and introductions from a number of unknown sources, C. gariepinus has now invaded South America, Europe, Asia, and Australia. Its life history characteristics include a fast growth rate to a maximum length of 1300mmtotal length (TL) (Bruton 1976), a high fecundity, an omnivorous diet and the ability to breathe air (de Moor & Bruton 1988; Cambray 2003). Understanding the biology and population dynamics of this invader would assist in its management and possibly eradication.
- Full Text:
- Date Issued: 2011
A comparison of three techniques for fluorochrome marking of juvenile Clarias gariepinus otoliths
- Wartenberg, Reece, Booth, Anthony J, Weyl, Olaf L F
- Authors: Wartenberg, Reece , Booth, Anthony J , Weyl, Olaf L F
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446742 , vital:74557 , https://doi.org/10.1080/15627020.2011.11407480
- Description: Intramuscular injection of the antibiotic oxytetracycline (OTC) has been the only method previously employed for chemically marking C. gariepinus otoliths for ageing studies. This study compared intramuscular injection, immersion, and dietary incorporation methods of administering OTC to determine the most effective technique. No differences in either growth or mortality were found between experimental groups while intramuscular injection of OTC was found to be superior to either mass immersion or dietary inclusion of OTC when marking Clarias gariepinus otoliths.
- Full Text:
- Date Issued: 2011
- Authors: Wartenberg, Reece , Booth, Anthony J , Weyl, Olaf L F
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446742 , vital:74557 , https://doi.org/10.1080/15627020.2011.11407480
- Description: Intramuscular injection of the antibiotic oxytetracycline (OTC) has been the only method previously employed for chemically marking C. gariepinus otoliths for ageing studies. This study compared intramuscular injection, immersion, and dietary incorporation methods of administering OTC to determine the most effective technique. No differences in either growth or mortality were found between experimental groups while intramuscular injection of OTC was found to be superior to either mass immersion or dietary inclusion of OTC when marking Clarias gariepinus otoliths.
- Full Text:
- Date Issued: 2011
Diet of largemouth bass, Micropterus salmoides (Centrarchidae), an invasive alien in the lower reaches of an Eastern Cape river, South Africa.
- Wasserman, Ryan J, Strydom, Nadine A, Weyl, Olaf L F
- Authors: Wasserman, Ryan J , Strydom, Nadine A , Weyl, Olaf L F
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443325 , vital:74108 , https://hdl.handle.net/10520/EJC18195
- Description: Largemouth bass (Micropterus salmoides) have been introduced to many South African river systems where they become invasive and pose a threat to native biota. The diets of small (32-138 mm TL) and large (192-448 mm TL) sized bass were analysed and compared in a marine fish nursery area in the lower Kowie River on the warm temperate coast of South Africa over a one-year period from March 2009 to February 2010. Dietary differences were detected between the two size groups. Amphipod sp. (% index of relative importance (IRI) = 69.2) and dipterans (Insecta) (%IRI = 21.9) dominated gut contents of small bass while larger bass preyed mostly on odonates (Insecta) (%IRI = 16.3) and the brachyuran Potamonautes sidneyi (%IRI = 80.0). Fish prey was of low importance during this study but comparisons with previous work on the lower Kowie River showed that when the river is flowing, young marine fish recruiting into the freshwater from the estuary become important prey items. These data suggest that in the lower Kowie River bass utilize invertebrate prey at low fish prey abundance and opportunistically feed on migrant fish when these are available.
- Full Text:
- Date Issued: 2011
- Authors: Wasserman, Ryan J , Strydom, Nadine A , Weyl, Olaf L F
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443325 , vital:74108 , https://hdl.handle.net/10520/EJC18195
- Description: Largemouth bass (Micropterus salmoides) have been introduced to many South African river systems where they become invasive and pose a threat to native biota. The diets of small (32-138 mm TL) and large (192-448 mm TL) sized bass were analysed and compared in a marine fish nursery area in the lower Kowie River on the warm temperate coast of South Africa over a one-year period from March 2009 to February 2010. Dietary differences were detected between the two size groups. Amphipod sp. (% index of relative importance (IRI) = 69.2) and dipterans (Insecta) (%IRI = 21.9) dominated gut contents of small bass while larger bass preyed mostly on odonates (Insecta) (%IRI = 16.3) and the brachyuran Potamonautes sidneyi (%IRI = 80.0). Fish prey was of low importance during this study but comparisons with previous work on the lower Kowie River showed that when the river is flowing, young marine fish recruiting into the freshwater from the estuary become important prey items. These data suggest that in the lower Kowie River bass utilize invertebrate prey at low fish prey abundance and opportunistically feed on migrant fish when these are available.
- Full Text:
- Date Issued: 2011
Invasion of a headwater stream by non-native fishes in the Swartkops River system, South Africa
- Ellender, Bruce R, Weyl, Olaf L F, Swartz, Ernst R
- Authors: Ellender, Bruce R , Weyl, Olaf L F , Swartz, Ernst R
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446866 , vital:74566 , https://doi.org/10.1080/15627020.2011.11407477
- Description: In South Africa, fishes in headwater streams are increasingly being threatened by non-native fish invasions. These invasions originate primarily from source populations in mainstream rivers and impoundments. In the Blindekloof stream, a Swartkops River headwater tributary, the non-native Micropterus salmoides was eradicated from the stream by conservation authorities in 1989. As a result of this eradication subsequent occurrences of non-native fishes are most likely a result of upstream invasions from the mainstream Swartkops River. The Blindekloof stream therefore provided a unique opportunity to investigate whether M. salmoides would reinvade after its removal in 1989 and if the more recently introduced Clarias gariepinus and Tilapia sparrmanii would invade the Blindekloof stream. During snorkel and electrofishing surveys four non-native species were recorded (M. salmoides, M. dolomieu, T. sparrmanii, C. gariepinus ).
- Full Text:
- Date Issued: 2011
- Authors: Ellender, Bruce R , Weyl, Olaf L F , Swartz, Ernst R
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446866 , vital:74566 , https://doi.org/10.1080/15627020.2011.11407477
- Description: In South Africa, fishes in headwater streams are increasingly being threatened by non-native fish invasions. These invasions originate primarily from source populations in mainstream rivers and impoundments. In the Blindekloof stream, a Swartkops River headwater tributary, the non-native Micropterus salmoides was eradicated from the stream by conservation authorities in 1989. As a result of this eradication subsequent occurrences of non-native fishes are most likely a result of upstream invasions from the mainstream Swartkops River. The Blindekloof stream therefore provided a unique opportunity to investigate whether M. salmoides would reinvade after its removal in 1989 and if the more recently introduced Clarias gariepinus and Tilapia sparrmanii would invade the Blindekloof stream. During snorkel and electrofishing surveys four non-native species were recorded (M. salmoides, M. dolomieu, T. sparrmanii, C. gariepinus ).
- Full Text:
- Date Issued: 2011
Invasion of a South African Anguilla mossambica (Anguillidae) population by the alien gill worm Pseudodactylogyrus anguillae (Monogenea)
- Parker, Denham, Weyl, Olaf L F, Taraschewski, Horst
- Authors: Parker, Denham , Weyl, Olaf L F , Taraschewski, Horst
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443367 , vital:74111 , https://hdl.handle.net/10520/EJC18196
- Description: The parasitic gill monogenean Pseudodactylogyrus anguillae is alien to Africa. In an investigation of 227 longfin eel, Anguilla mossambica, and 26 mottled eel, Anguilla marmorata, sampled from four river systems in the Eastern Cape, South Africa, this parasite was only present on the gills of A. mossambica sampled from the Great Fish River system. In the Great Fish River, it infected 73.2% of the sampled population at a mean intensity of 63.8 ± 34.3 parasites per fish. High prevalence and intensity are indicative of a well-established alien invasive parasitic species. Results showing the absence of P. anguillae from the co-occurring but less abundant A. marmorata indicate that this species may be less susceptible to P. anguillae infection.
- Full Text:
- Date Issued: 2011
- Authors: Parker, Denham , Weyl, Olaf L F , Taraschewski, Horst
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443367 , vital:74111 , https://hdl.handle.net/10520/EJC18196
- Description: The parasitic gill monogenean Pseudodactylogyrus anguillae is alien to Africa. In an investigation of 227 longfin eel, Anguilla mossambica, and 26 mottled eel, Anguilla marmorata, sampled from four river systems in the Eastern Cape, South Africa, this parasite was only present on the gills of A. mossambica sampled from the Great Fish River system. In the Great Fish River, it infected 73.2% of the sampled population at a mean intensity of 63.8 ± 34.3 parasites per fish. High prevalence and intensity are indicative of a well-established alien invasive parasitic species. Results showing the absence of P. anguillae from the co-occurring but less abundant A. marmorata indicate that this species may be less susceptible to P. anguillae infection.
- Full Text:
- Date Issued: 2011
Invasive alien freshwater fishes in the Wilderness Lakes System, a wetland of international importance in the Western Cape Province, South Africa
- Olds, Alexis A, Smith, M K S, Weyl, Olaf L F, Russell, I A
- Authors: Olds, Alexis A , Smith, M K S , Weyl, Olaf L F , Russell, I A
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446879 , vital:74567 , https://doi.org/10.1080/15627020.2011.11407491
- Description: The Wilderness Lakes System incorporates a RAMSAR listed wetland. Previous ichthyological surveys reported three invasive freshwater fishes; Oreochromis mossambicus (Mozambique tilapia), Gambusia affinis (mosquitofish) and Micropterus salmoides (largemouth bass) from this system. To assess the status of these alien fishes, the fish assemblages in the lakes system were sampled with seine nets and fyke nets in 2009 and 2010. A total of 87 893 fish comprising 16 species were caught. In addition to confirming the persistence of O. mossambicus and G. affinis in the system, the current study also reports the presence of a new invader, Cyprinus carpio (common carp). M. salmoides were absent from 2009 and 2010 samples.
- Full Text:
- Date Issued: 2011
- Authors: Olds, Alexis A , Smith, M K S , Weyl, Olaf L F , Russell, I A
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446879 , vital:74567 , https://doi.org/10.1080/15627020.2011.11407491
- Description: The Wilderness Lakes System incorporates a RAMSAR listed wetland. Previous ichthyological surveys reported three invasive freshwater fishes; Oreochromis mossambicus (Mozambique tilapia), Gambusia affinis (mosquitofish) and Micropterus salmoides (largemouth bass) from this system. To assess the status of these alien fishes, the fish assemblages in the lakes system were sampled with seine nets and fyke nets in 2009 and 2010. A total of 87 893 fish comprising 16 species were caught. In addition to confirming the persistence of O. mossambicus and G. affinis in the system, the current study also reports the presence of a new invader, Cyprinus carpio (common carp). M. salmoides were absent from 2009 and 2010 samples.
- Full Text:
- Date Issued: 2011
Life history and population dynamics of invasive common carp, Cyprinus carpio, within a large turbid African impoundment
- Winker, A Henning, Weyl, Olaf L F, Booth, Anthony J, Ellender, Bruce R
- Authors: Winker, A Henning , Weyl, Olaf L F , Booth, Anthony J , Ellender, Bruce R
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124898 , vital:35708 , https://doi.10.1071/MF11054
- Description: Common carp (Cyprinus carpio) is one of the world’s most widely introduced and established freshwater fishes (Casal 2006). The species is considered to be one of the eight most invasive freshwater fishes (Lowe et al. 2000) and worldwide, it accounts for most of the records of successful establishments and adverse ecological effects (Casal 2006; Kulhanek et al. 2011). This invasive success suggests that feral C. carpio is equipped with a set of adaptable life history attributes that allow it to successfully colonise a wide range of habitats (Koehn 2004; Zambrano et al. 2006; Britton et al. 2007). Where feral C. carpio occurs in high densities, it is often perceived as an invasive pest species (Sivakumaran et al. 2003; Brown and Walker 2004; Koehn 2004) because it can have severe impacts on habitat heterogeneity and biodiversity by increasing water turbidity through its bottom feeding behaviour, increasing nutrient availability, decreasing benthic and macrophyte density and diversity, altering zooplankton assemblages and decreasing endemic fish abundance (Zambrano et al. 2001; Khan 2003; Kulhanek et al. 2011). Within south-east Australia, for example, C. carpio comprises the largest proportion of the ichthyobiomass in the continent’s largest river system – the Murray–Darling Basin (Gehrke et al. 1995). As a consequence, serious concerns about its threat to endemic freshwater species (Koehn 2004) have prompted several of the most recent investigations into its life history (e.g. Sivakumaran et al. 2003; Smith and Walker 2004; Brown et al. 2005). Other potential threats posed also include competition with indigenous species and the spread of diseases and parasites (Dudgeon et al. 2006). In South Africa, for example, Asian tapeworm Bothriocephalus acheilognathi is now widely distributed in seven river systems and has infected eight novel cyprinid hosts due to the translocation of infected by C. carpio from a centralized aquaculture facility (Stadtlander et al. 2011).
- Full Text:
- Date Issued: 2011
- Authors: Winker, A Henning , Weyl, Olaf L F , Booth, Anthony J , Ellender, Bruce R
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124898 , vital:35708 , https://doi.10.1071/MF11054
- Description: Common carp (Cyprinus carpio) is one of the world’s most widely introduced and established freshwater fishes (Casal 2006). The species is considered to be one of the eight most invasive freshwater fishes (Lowe et al. 2000) and worldwide, it accounts for most of the records of successful establishments and adverse ecological effects (Casal 2006; Kulhanek et al. 2011). This invasive success suggests that feral C. carpio is equipped with a set of adaptable life history attributes that allow it to successfully colonise a wide range of habitats (Koehn 2004; Zambrano et al. 2006; Britton et al. 2007). Where feral C. carpio occurs in high densities, it is often perceived as an invasive pest species (Sivakumaran et al. 2003; Brown and Walker 2004; Koehn 2004) because it can have severe impacts on habitat heterogeneity and biodiversity by increasing water turbidity through its bottom feeding behaviour, increasing nutrient availability, decreasing benthic and macrophyte density and diversity, altering zooplankton assemblages and decreasing endemic fish abundance (Zambrano et al. 2001; Khan 2003; Kulhanek et al. 2011). Within south-east Australia, for example, C. carpio comprises the largest proportion of the ichthyobiomass in the continent’s largest river system – the Murray–Darling Basin (Gehrke et al. 1995). As a consequence, serious concerns about its threat to endemic freshwater species (Koehn 2004) have prompted several of the most recent investigations into its life history (e.g. Sivakumaran et al. 2003; Smith and Walker 2004; Brown et al. 2005). Other potential threats posed also include competition with indigenous species and the spread of diseases and parasites (Dudgeon et al. 2006). In South Africa, for example, Asian tapeworm Bothriocephalus acheilognathi is now widely distributed in seven river systems and has infected eight novel cyprinid hosts due to the translocation of infected by C. carpio from a centralized aquaculture facility (Stadtlander et al. 2011).
- Full Text:
- Date Issued: 2011
Adult African sharptooth catfish, Clarias gariepinus, population dynamics in a small invaded warm-temperate impoundment
- Booth, Anthony J, Traas, Graham R L, Weyl, Olaf L F
- Authors: Booth, Anthony J , Traas, Graham R L , Weyl, Olaf L F
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123596 , vital:35461 , https://doi.10.3377/004.045.0208
- Description: African sharptooth catfish, Clarias gariepinus (Burchell 1822), is a potamodromous species that is naturally distributed from Turkey to the Orange River, South Africa (Skelton 1993). It is omnivorous, feeding on plankton, vegetation, invertebrates, carrion and fish (de Moor & Bruton 1988) and may exhibit pack-hunting behaviour when foraging for small fish (Bruton 1979; Merron 1993). Clarias gariepinus is a large (>150 cm TL, >30 kg; Bruton 1976), long-lived (validated to at least 15 years, Weyl & Booth 2008) and fast-growing (Bruton & Allanson 1980; Quick & Bruton 1984; Richardson et al. 2009) fish that attains sexual maturity within two years of age (de Moor & Bruton 1988). It is eurythermic (80–35°C), mesohalic (0–10 ppt) and has the ability to airbreathe. These attributes predispose it to surviving in all but the most adverse of conditions and have directly contributed to its wide use as an aquaculture species. These attributes have also contributed to its ability to invade waterbodies beyond its natural range (de Moor & Bruton 1988) and after inadvertent introductions such as by escape from aquaculture facilities or through water transfer schemes, C. gariepinus has established populations in many non-native environments. Such invasions include the Philippines (Mercene 1997), Bangladesh (Arthur & Ahmed 2002), Thailand (Vidthayanon 2005), India (Bhakta & Bandyopadhyay 2007) and Brazil (Cambray 2005; Vitule et al. 2006; Rocha & Schiavetti 2007). In South Africa, C. gariepinus invaded the temperate Great Fish River catchment after the species was translocated from the Orange River through a Interbasin Water Transfer (IBWT) scheme (Laurenson et al. 1989). Potential threats include predation of and competition with indigenous species, habitat degradation, and the spread of diseases and parasites (Dudgeon et al. 2006).
- Full Text:
- Date Issued: 2010
- Authors: Booth, Anthony J , Traas, Graham R L , Weyl, Olaf L F
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123596 , vital:35461 , https://doi.10.3377/004.045.0208
- Description: African sharptooth catfish, Clarias gariepinus (Burchell 1822), is a potamodromous species that is naturally distributed from Turkey to the Orange River, South Africa (Skelton 1993). It is omnivorous, feeding on plankton, vegetation, invertebrates, carrion and fish (de Moor & Bruton 1988) and may exhibit pack-hunting behaviour when foraging for small fish (Bruton 1979; Merron 1993). Clarias gariepinus is a large (>150 cm TL, >30 kg; Bruton 1976), long-lived (validated to at least 15 years, Weyl & Booth 2008) and fast-growing (Bruton & Allanson 1980; Quick & Bruton 1984; Richardson et al. 2009) fish that attains sexual maturity within two years of age (de Moor & Bruton 1988). It is eurythermic (80–35°C), mesohalic (0–10 ppt) and has the ability to airbreathe. These attributes predispose it to surviving in all but the most adverse of conditions and have directly contributed to its wide use as an aquaculture species. These attributes have also contributed to its ability to invade waterbodies beyond its natural range (de Moor & Bruton 1988) and after inadvertent introductions such as by escape from aquaculture facilities or through water transfer schemes, C. gariepinus has established populations in many non-native environments. Such invasions include the Philippines (Mercene 1997), Bangladesh (Arthur & Ahmed 2002), Thailand (Vidthayanon 2005), India (Bhakta & Bandyopadhyay 2007) and Brazil (Cambray 2005; Vitule et al. 2006; Rocha & Schiavetti 2007). In South Africa, C. gariepinus invaded the temperate Great Fish River catchment after the species was translocated from the Orange River through a Interbasin Water Transfer (IBWT) scheme (Laurenson et al. 1989). Potential threats include predation of and competition with indigenous species, habitat degradation, and the spread of diseases and parasites (Dudgeon et al. 2006).
- Full Text:
- Date Issued: 2010
Adult African sharptooth catfish, Clarias gariepinus, population dynamics in a small invaded warm-temperate impoundment
- Booth, Anthony J, Traasg, Graham L, Weyl, Olaf L F
- Authors: Booth, Anthony J , Traasg, Graham L , Weyl, Olaf L F
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446759 , vital:74558 , https://www.tandfonline.com/doi/abs/10.1080/15627020.2010.11657279
- Description: African sharptooth catfish, Clarias gariepinus, is a successful aquatic invader as it has a eurytopic physiology, is highly fecund, grows quickly and has an omnivorous diet. Despite possible threats that include predation of and competition with indigenous species, habitat degradation, and the spread of diseases and parasites, there is a lack of knowledge regarding its ecology and population dynamics within invaded systems. This study presents a mark–recapture experiment to investigate its population structure, natural mortality rate, population size and density within a population inhabiting a small, 76 ha invaded water supply reservoir in the temperate Eastern Cape region, South Africa.
- Full Text:
- Date Issued: 2010
- Authors: Booth, Anthony J , Traasg, Graham L , Weyl, Olaf L F
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446759 , vital:74558 , https://www.tandfonline.com/doi/abs/10.1080/15627020.2010.11657279
- Description: African sharptooth catfish, Clarias gariepinus, is a successful aquatic invader as it has a eurytopic physiology, is highly fecund, grows quickly and has an omnivorous diet. Despite possible threats that include predation of and competition with indigenous species, habitat degradation, and the spread of diseases and parasites, there is a lack of knowledge regarding its ecology and population dynamics within invaded systems. This study presents a mark–recapture experiment to investigate its population structure, natural mortality rate, population size and density within a population inhabiting a small, 76 ha invaded water supply reservoir in the temperate Eastern Cape region, South Africa.
- Full Text:
- Date Issued: 2010
An assessment of a light-attraction fishery in southern Lake Malawi
- Weyl, Olaf L F, Kazembe, Jacqueline, Booth, Anthony J, Mandere, D S
- Authors: Weyl, Olaf L F , Kazembe, Jacqueline , Booth, Anthony J , Mandere, D S
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123683 , vital:35472 , https://doi.org/10.2989/16085910409503787
- Description: This study provides the first quantitative assessment of the light-attraction component of a small-scale purse seine, locally known as a chilimira net, fishery in two areas of southern Lake Malawi. For monitoring purposes the shoreline of Lake Malawi is divided into a number of statistical strata. Two strata (‘2.1’ in the southeast arm and ‘3.1’ in the southwest arm of the lake) were selected for this study. Catch per unit effort in stratum 2.1 was generally lower than that recorded in stratum 3.1 but nets in stratum 2.1 fished more frequently, leading to similar annual catches in the two strata. Annual catch was estimated as 19.4 (CI = 15.9–23.5) tons net–1 year–1 in stratum 2.1 and 23.5 (CI = 19.5–28.1) tons net–1 year–1 in stratum 3.1 respectively. A total of 62 species from 28 cichlid genera, and 13 species from nine non-cichlid genera, were identified from the samples. Of the 37 genera identified, only five; Copadichromis, Dimidiochromis, Engraulicypris, Oreochromis and Rhamphochromis, contributed more than 5% to the total annual catch in either stratum. Their combined contribution to the annual catch was in excess of 85% in both strata. Comparisons showed that catch-composition was dependent on area. Length-frequency distributions of major target species in the catch showed that the fishery targeted juveniles in stratum 2.1, while in stratum 3.1 most individuals were harvested after reaching their lengthat-maturity. The dependence of catch-composition and size-selection on area indicates that management interventions for this fishery need to be area-specific. Since the fishery targets a diverse species assemblage, effort limitation or area closure may be the only viable management options, until such time as additional biological and fisheries data are available for the application of stock assessment models.
- Full Text:
- Date Issued: 2010
- Authors: Weyl, Olaf L F , Kazembe, Jacqueline , Booth, Anthony J , Mandere, D S
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123683 , vital:35472 , https://doi.org/10.2989/16085910409503787
- Description: This study provides the first quantitative assessment of the light-attraction component of a small-scale purse seine, locally known as a chilimira net, fishery in two areas of southern Lake Malawi. For monitoring purposes the shoreline of Lake Malawi is divided into a number of statistical strata. Two strata (‘2.1’ in the southeast arm and ‘3.1’ in the southwest arm of the lake) were selected for this study. Catch per unit effort in stratum 2.1 was generally lower than that recorded in stratum 3.1 but nets in stratum 2.1 fished more frequently, leading to similar annual catches in the two strata. Annual catch was estimated as 19.4 (CI = 15.9–23.5) tons net–1 year–1 in stratum 2.1 and 23.5 (CI = 19.5–28.1) tons net–1 year–1 in stratum 3.1 respectively. A total of 62 species from 28 cichlid genera, and 13 species from nine non-cichlid genera, were identified from the samples. Of the 37 genera identified, only five; Copadichromis, Dimidiochromis, Engraulicypris, Oreochromis and Rhamphochromis, contributed more than 5% to the total annual catch in either stratum. Their combined contribution to the annual catch was in excess of 85% in both strata. Comparisons showed that catch-composition was dependent on area. Length-frequency distributions of major target species in the catch showed that the fishery targeted juveniles in stratum 2.1, while in stratum 3.1 most individuals were harvested after reaching their lengthat-maturity. The dependence of catch-composition and size-selection on area indicates that management interventions for this fishery need to be area-specific. Since the fishery targets a diverse species assemblage, effort limitation or area closure may be the only viable management options, until such time as additional biological and fisheries data are available for the application of stock assessment models.
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- Date Issued: 2010