Monitoring of invertebrate and fish recovery following river rehabilitation using rotenone in the Rondegat River
- Weyl, Olaf L F, Barrow, S, Bellingan, Terence A, Dalu, Tatenda, Ellender, Bruce R, Esler, K, Impson, D, Gouws, Jeanne, Jordaan, M, Villet, Martin H, Wasserman, Ryan J, Woodford, Darragh J
- Authors: Weyl, Olaf L F , Barrow, S , Bellingan, Terence A , Dalu, Tatenda , Ellender, Bruce R , Esler, K , Impson, D , Gouws, Jeanne , Jordaan, M , Villet, Martin H , Wasserman, Ryan J , Woodford, Darragh J
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/442411 , vital:73982 , https://www.wrc.org.za/wp-content/uploads/mdocs/2261.pdf
- Description: Fish invasions have been cited as a primary threat to imperilled South African fishes and other aquatic fauna. As a result, the management and control of alien invasive species is a legislated priority in South Africa. From a river rehabilitation perspective, eradicating alien fish allows for the rehabilitation of several kilometres of river, with very significant benefits for the endangered fish species present and for the associated aquatic biota. In South Africa, the piscicide rotenone is one of the preferred methods for achieving eradication.
- Full Text:
- Authors: Weyl, Olaf L F , Barrow, S , Bellingan, Terence A , Dalu, Tatenda , Ellender, Bruce R , Esler, K , Impson, D , Gouws, Jeanne , Jordaan, M , Villet, Martin H , Wasserman, Ryan J , Woodford, Darragh J
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/442411 , vital:73982 , https://www.wrc.org.za/wp-content/uploads/mdocs/2261.pdf
- Description: Fish invasions have been cited as a primary threat to imperilled South African fishes and other aquatic fauna. As a result, the management and control of alien invasive species is a legislated priority in South Africa. From a river rehabilitation perspective, eradicating alien fish allows for the rehabilitation of several kilometres of river, with very significant benefits for the endangered fish species present and for the associated aquatic biota. In South Africa, the piscicide rotenone is one of the preferred methods for achieving eradication.
- Full Text:
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:
- 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:
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:
- 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 ).
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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:
- 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).
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Quantifying the annual fish harvest from South Africa’s largest freshwater reservoir
- Ellender, Bruce R, Weyl, Olaf L F, Winker, A Henning, Booth, Anthony J
- Authors: Ellender, Bruce R , Weyl, Olaf L F , Winker, A Henning , Booth, Anthony J
- Date: 2010
- Language: English
- Type: Article
- Identifier: vital:7149 , http://hdl.handle.net/10962/d1011852
- Description: South African inland fisheries are poorly developed and their contribution to near-shore communities is poorly understood. This study is the first comprehensive assessment of recreational and subsistence angling undertaken in an inland fishery in South Africa. The study was conducted on the 360 km2 Lake Gariep, South Africa’s largest freshwater reservoir. A total of 508 anglers were interviewed between February 2007 and January 2008. Of those interviewed, 67% were subsistence anglers and 33% recreational anglers. Catch per unit effort (CPUE) did not differ significantly between sectors. CPUE fluctuated seasonally, ranging between 0.37 (95% CI= 0.26 to 0.51) kg·angler-1·h-1 in winter and 0.88 (0.67 to 1.17) kg·angler- 1·h-1 in summer. The duration of a fishing day ranged from 5.99 (5.24 to 6.74) h in mid-winter to 7.26 (6.88 to 7.63) h in early summer. Expected end-of-day catch (CPUE × fishing-trip duration) ranged from 2.2 to 6.4 kg·angler-1·d-1 depending on the season. The number of anglers ranged from 22 (8 to 53) anglers·d-1 in June/July to 74 (25 to 176) anglers·d-1 in April. Total annual catch from the roving creel survey was estimated at 71.4 (57.4 to 91.4) t·yr-1. Another 7.5 t∙yr-1 were landed during recreational angling competitions. The resultant total catch divided by the lakeshore population equated to a per capita fish supply of 11.1 kg·yr-1. More than 70% of the catch was the alien invasive carp Cyprinus carpio and there was no evidence of overfishing. The fish resource of Lake Gariep is of significant recreational and subsistence value. As a result of the low fish price (ZAR5.72 ± 2.60·kg-1) subsistence fishing was considered a low-revenue activity that mainly augmented food security in lakeshore communities. The relatively high CPUE indicated that the fishery may be an important safety-net during periods when alternate sources of livelihoods are limited. Consequently, we recommend that the importance of angling to local communities needs to be taken into account when planning fisheries development and developing an inland fisheries policy
- Full Text:
- Authors: Ellender, Bruce R , Weyl, Olaf L F , Winker, A Henning , Booth, Anthony J
- Date: 2010
- Language: English
- Type: Article
- Identifier: vital:7149 , http://hdl.handle.net/10962/d1011852
- Description: South African inland fisheries are poorly developed and their contribution to near-shore communities is poorly understood. This study is the first comprehensive assessment of recreational and subsistence angling undertaken in an inland fishery in South Africa. The study was conducted on the 360 km2 Lake Gariep, South Africa’s largest freshwater reservoir. A total of 508 anglers were interviewed between February 2007 and January 2008. Of those interviewed, 67% were subsistence anglers and 33% recreational anglers. Catch per unit effort (CPUE) did not differ significantly between sectors. CPUE fluctuated seasonally, ranging between 0.37 (95% CI= 0.26 to 0.51) kg·angler-1·h-1 in winter and 0.88 (0.67 to 1.17) kg·angler- 1·h-1 in summer. The duration of a fishing day ranged from 5.99 (5.24 to 6.74) h in mid-winter to 7.26 (6.88 to 7.63) h in early summer. Expected end-of-day catch (CPUE × fishing-trip duration) ranged from 2.2 to 6.4 kg·angler-1·d-1 depending on the season. The number of anglers ranged from 22 (8 to 53) anglers·d-1 in June/July to 74 (25 to 176) anglers·d-1 in April. Total annual catch from the roving creel survey was estimated at 71.4 (57.4 to 91.4) t·yr-1. Another 7.5 t∙yr-1 were landed during recreational angling competitions. The resultant total catch divided by the lakeshore population equated to a per capita fish supply of 11.1 kg·yr-1. More than 70% of the catch was the alien invasive carp Cyprinus carpio and there was no evidence of overfishing. The fish resource of Lake Gariep is of significant recreational and subsistence value. As a result of the low fish price (ZAR5.72 ± 2.60·kg-1) subsistence fishing was considered a low-revenue activity that mainly augmented food security in lakeshore communities. The relatively high CPUE indicated that the fishery may be an important safety-net during periods when alternate sources of livelihoods are limited. Consequently, we recommend that the importance of angling to local communities needs to be taken into account when planning fisheries development and developing an inland fisheries policy
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Validation of growth zone deposition in otoliths of two large endemic cyprinids in Lake Gariep, South Africa
- Winker, A Henning, Ellender, Bruce R, Weyl, Olaf L F, Booth, Anthony J
- Authors: Winker, A Henning , Ellender, Bruce R , Weyl, Olaf L F , Booth, Anthony J
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446812 , vital:74562 , https://doi.org/10.1080/15627020.2010.11657263
- Description: We tested the hypothesis that growth zones in the astericus otoliths of smallmouth yellowfish (Labeobarbus aeneus) and Orange River mudfish (Labeo capensis) were deposited annually. Two methods, fluorochrome marking and edge analysis of otoliths were used. For fluorochrome marking, specimens of both species were injected with 60 mg/kg fish mass oxytetracycline hydrochloride (OTC) and released into large earthen ponds under ambient conditions adjacent to Lake Gariep. Twenty-three L. aeneus and one L. capensis were recaptured 10–14 months later. Edge analysis was based on the optical interpretation of L. aeneus (n = 342) and L. capensis (n = 512) otolith margins collected between November 2006 and May 2008 from Lake Gariep. The frequency distribution of opaque margins over time was fitted using a binomial periodic regression. The estimated cycle length was not significantly different from a hypothesized 12 months for both species. The number of growth zones distal to the OTC mark was consistent with findings from the edge analysis, providing evidence that growth zones in astericus otoliths of both species can be interpreted as annuli.
- Full Text:
- Authors: Winker, A Henning , Ellender, Bruce R , Weyl, Olaf L F , Booth, Anthony J
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446812 , vital:74562 , https://doi.org/10.1080/15627020.2010.11657263
- Description: We tested the hypothesis that growth zones in the astericus otoliths of smallmouth yellowfish (Labeobarbus aeneus) and Orange River mudfish (Labeo capensis) were deposited annually. Two methods, fluorochrome marking and edge analysis of otoliths were used. For fluorochrome marking, specimens of both species were injected with 60 mg/kg fish mass oxytetracycline hydrochloride (OTC) and released into large earthen ponds under ambient conditions adjacent to Lake Gariep. Twenty-three L. aeneus and one L. capensis were recaptured 10–14 months later. Edge analysis was based on the optical interpretation of L. aeneus (n = 342) and L. capensis (n = 512) otolith margins collected between November 2006 and May 2008 from Lake Gariep. The frequency distribution of opaque margins over time was fitted using a binomial periodic regression. The estimated cycle length was not significantly different from a hypothesized 12 months for both species. The number of growth zones distal to the OTC mark was consistent with findings from the edge analysis, providing evidence that growth zones in astericus otoliths of both species can be interpreted as annuli.
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Who uses the fishery resources in South Africa’s largest impoundment? Characterising subsistence and recreational fishing sectors on Lake Gariep
- Ellender, Bruce R, Weyl, Olaf L F, Winker, A Henning
- Authors: Ellender, Bruce R , Weyl, Olaf L F , Winker, A Henning
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6778 , http://hdl.handle.net/10962/d1008088
- Description: The African Union’s prioritisation of inland fisheries as an investment area for poverty alleviation and regional economic development will require the development of management plans. These should be based on sound knowledge of the social dynamics of the resource users. In South Africa the social dynamics of resource users of inland fisheries have never been assessed. The purpose of this study was to assess the human dimensions of the anglers utilising the fishery in Lake Gariep, South Africa’s largest impoundment. The study was based on 357 first-time interviews conducted on the lakeshore between October 2006 and December 2007. Anglers were categorised as recreational (39%) or subsistence (61%) based on their residency, occupation, primary motivation for angling, mode of transport and gear use. Subsistence anglers were local (99%), residing within 10 km of the place where they were interviewed, while recreational anglers included both local resident and non-resident members. The racial composition of anglers was dependent on user group and differed significantly (p ≤ 0.05) from the demographic composition of the regional population. Recreational anglers were predominantly White (≥ 60% of interviews) and Coloured (≥ 25%), while 84% of subsistence anglers were Coloured and 16% Black African. Most recreational anglers had permanent employment or were pensioners while <30% of subsistence anglers were permanently employed. Most recreational users (82%) accessed the lake with their own vehicle while subsistence anglers mainly walked (63%) or used a bicycle (28%). Recreational interviewees either consumed (59%), sold (11%), gave away (10%) or released (20%) some of their catch. Subsistence anglers either ate their catch (53%) and/or sold (41%) their catch. Within the subsistence sector no anglers released fish after capture or gave some of the catch away. We conclude that this inland fishery contributes to the livelihood of the rural poor who use the lake on a subsistence basis and that recreational-angler based tourism may contribute to increased income and employment opportunities through related service industries.
- Full Text:
- Authors: Ellender, Bruce R , Weyl, Olaf L F , Winker, A Henning
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6778 , http://hdl.handle.net/10962/d1008088
- Description: The African Union’s prioritisation of inland fisheries as an investment area for poverty alleviation and regional economic development will require the development of management plans. These should be based on sound knowledge of the social dynamics of the resource users. In South Africa the social dynamics of resource users of inland fisheries have never been assessed. The purpose of this study was to assess the human dimensions of the anglers utilising the fishery in Lake Gariep, South Africa’s largest impoundment. The study was based on 357 first-time interviews conducted on the lakeshore between October 2006 and December 2007. Anglers were categorised as recreational (39%) or subsistence (61%) based on their residency, occupation, primary motivation for angling, mode of transport and gear use. Subsistence anglers were local (99%), residing within 10 km of the place where they were interviewed, while recreational anglers included both local resident and non-resident members. The racial composition of anglers was dependent on user group and differed significantly (p ≤ 0.05) from the demographic composition of the regional population. Recreational anglers were predominantly White (≥ 60% of interviews) and Coloured (≥ 25%), while 84% of subsistence anglers were Coloured and 16% Black African. Most recreational anglers had permanent employment or were pensioners while <30% of subsistence anglers were permanently employed. Most recreational users (82%) accessed the lake with their own vehicle while subsistence anglers mainly walked (63%) or used a bicycle (28%). Recreational interviewees either consumed (59%), sold (11%), gave away (10%) or released (20%) some of their catch. Subsistence anglers either ate their catch (53%) and/or sold (41%) their catch. Within the subsistence sector no anglers released fish after capture or gave some of the catch away. We conclude that this inland fishery contributes to the livelihood of the rural poor who use the lake on a subsistence basis and that recreational-angler based tourism may contribute to increased income and employment opportunities through related service industries.
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Juvenile population dynamics of Oreochromis mossambicus in an intermittently open estuary at the limit of its natural distribution
- Ellender, Bruce R, Weyl, Olaf L F, Shanyengange, M K, Cowley, Paul D
- Authors: Ellender, Bruce R , Weyl, Olaf L F , Shanyengange, M K , Cowley, Paul D
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446893 , vital:74568 , https://doi.org/10.1080/15627020.2008.11657245
- Description: Juvenile Oreochromis mossambicus in the 25 ha, temperate, intermittently open, East Kleinemonde Estuary in the Eastern Cape, South Africa (33°32’S, 27°03’E), showed a seasonal shift in distribution, occupying all areas of the estuary in summer and, subsequently, being limited to the upper reaches in winter. The young of the year in the littoral zone were rapidly depleted and resultant estimates of the instantaneous rate of total mortality (Z) ranged from 5.4/yr to 6.9/yr. High annual rates of juvenile mortality and small adult populations imply that stock recovery after a reduction in adult population numbers, through activities such as fishing, may be slow. This work adds to the knowledge base of O. mossambicus ecology and population dynamics in temperate estuaries at the limit of its natural distribution.
- Full Text:
- Authors: Ellender, Bruce R , Weyl, Olaf L F , Shanyengange, M K , Cowley, Paul D
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446893 , vital:74568 , https://doi.org/10.1080/15627020.2008.11657245
- Description: Juvenile Oreochromis mossambicus in the 25 ha, temperate, intermittently open, East Kleinemonde Estuary in the Eastern Cape, South Africa (33°32’S, 27°03’E), showed a seasonal shift in distribution, occupying all areas of the estuary in summer and, subsequently, being limited to the upper reaches in winter. The young of the year in the littoral zone were rapidly depleted and resultant estimates of the instantaneous rate of total mortality (Z) ranged from 5.4/yr to 6.9/yr. High annual rates of juvenile mortality and small adult populations imply that stock recovery after a reduction in adult population numbers, through activities such as fishing, may be slow. This work adds to the knowledge base of O. mossambicus ecology and population dynamics in temperate estuaries at the limit of its natural distribution.
- Full Text:
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