Using action cameras to estimate the abundance and habitat use of threatened fish in clear headwater streams:
- Hannweg, B, Marr, S M, Bloy, Lesley E, Weyl, Olaf L F
- Authors: Hannweg, B , Marr, S M , Bloy, Lesley E , Weyl, Olaf L F
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/148911 , vital:38785 , DOI: 10.2989/16085914.2019.1701404
- Description: Snorkel and electrofishing surveys are the traditional baseline methods for fish surveys in clear headwater streams. However, action cameras provide a non-harmful alternative to monitor freshwater fish populations to develop informed conservation management initiatives. In this paper, estimates from photographs and videos from action cameras are compared with snorkel survey estimates of the density of a threatened endemic minnow species in a headwater stream, Eastern Cape, South Africa. Photograph-based relative abundances of fish summed over five microhabitats in each pool returned equivalent results to snorkel surveys, whereas the equivalent video-based abundance estimates were approximately 50% greater than the snorkel estimates. Therefore, photograph-derived estimates could be used as an alternative to snorkel surveys for fish population monitoring and habitat use studies in clear headwater streams.
- Full Text:
- Date Issued: 2020
- Authors: Hannweg, B , Marr, S M , Bloy, Lesley E , Weyl, Olaf L F
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/148911 , vital:38785 , DOI: 10.2989/16085914.2019.1701404
- Description: Snorkel and electrofishing surveys are the traditional baseline methods for fish surveys in clear headwater streams. However, action cameras provide a non-harmful alternative to monitor freshwater fish populations to develop informed conservation management initiatives. In this paper, estimates from photographs and videos from action cameras are compared with snorkel survey estimates of the density of a threatened endemic minnow species in a headwater stream, Eastern Cape, South Africa. Photograph-based relative abundances of fish summed over five microhabitats in each pool returned equivalent results to snorkel surveys, whereas the equivalent video-based abundance estimates were approximately 50% greater than the snorkel estimates. Therefore, photograph-derived estimates could be used as an alternative to snorkel surveys for fish population monitoring and habitat use studies in clear headwater streams.
- Full Text:
- Date Issued: 2020
The abundance of an invasive freshwater snail Tarebia granifera (Lamarck, 1822) in the Nseleni River, South Africa
- Jones, Roy W, Hill, Jaclyn M, Coetzee, Julie A, Hill, Martin P, Avery, T S, Weyl, Olaf L F
- Authors: Jones, Roy W , Hill, Jaclyn M , Coetzee, Julie A , Hill, Martin P , Avery, T S , Weyl, Olaf L F
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69077 , vital:29382 , https://doi.org/10.2989/16085914.2017.1298984
- Description: The invasive freshwater snail Tarebia granifera (Lamarck, 1822) was first reported in South Africa in 1999 and it has become widespread across the country, with some evidence to suggest that it reduces benthic macroinvertebrate biodiversity. The current study aimed to identify the primary abiotic drivers behind abundance patterns of T. granifera, by comparing the current abundance of the snail in three different regions, and at three depths, of the highly modified Nseleni River in KwaZulu-Natal, South Africa. Tarebia granifera was well established throughout the Nseleni River system, with an overall preference for shallow waters and seasonal temporal patterns of abundance. Although it is uncertain what the ecological impacts of the snail in this system are, its high abundances suggest that it should be controlled where possible and prevented from invading other systems in the region.
- Full Text: false
- Date Issued: 2017
- Authors: Jones, Roy W , Hill, Jaclyn M , Coetzee, Julie A , Hill, Martin P , Avery, T S , Weyl, Olaf L F
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69077 , vital:29382 , https://doi.org/10.2989/16085914.2017.1298984
- Description: The invasive freshwater snail Tarebia granifera (Lamarck, 1822) was first reported in South Africa in 1999 and it has become widespread across the country, with some evidence to suggest that it reduces benthic macroinvertebrate biodiversity. The current study aimed to identify the primary abiotic drivers behind abundance patterns of T. granifera, by comparing the current abundance of the snail in three different regions, and at three depths, of the highly modified Nseleni River in KwaZulu-Natal, South Africa. Tarebia granifera was well established throughout the Nseleni River system, with an overall preference for shallow waters and seasonal temporal patterns of abundance. Although it is uncertain what the ecological impacts of the snail in this system are, its high abundances suggest that it should be controlled where possible and prevented from invading other systems in the region.
- Full Text: false
- Date Issued: 2017
Validation of the periodicity of growth zone formation in the otoliths of four fish species from the Upper Zambezi ecoregion, southern Africa
- Taylor, Geraldine C, Peel, Richard A, Weyl, Olaf L F, Hay, Clinton J
- Authors: Taylor, Geraldine C , Peel, Richard A , Weyl, Olaf L F , Hay, Clinton J
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443414 , vital:74116 , https://hdl.handle.net/10520/EJC196537
- Description: In the Upper Zambezi and Okavango ecoregions, Brycinus lateralis, Hepsetus cuvieri, Schilbe intermedius and Serranochromis macrocephalus are important in subsistence fisheries, while S. intermedius and S. macrocephalus are often caught in commercial catches. Despite their importance, there is little information on their age and growth and age validation. Growth zone deposition rate in otoliths of B. lateralis, H. cuvieri, S. intermedius and S. macrocephalus was validated as annual using edge analysis in this study. Annual deposition of growth zones was corroborated by a fluorochrome marking experiment. Both methods demonstrated that one growth zone was deposited annually. Edge analysis demonstrated that the highest proportion of opaque zones was detected between August and December, most likely as a result of slow growth during lower temperature water during the preceding winter. With growth zone deposition validated as annual, future research should focus on determining the growth, maturity and mortality rates of these species, parameters which are important for their management.
- Full Text:
- Date Issued: 2016
- Authors: Taylor, Geraldine C , Peel, Richard A , Weyl, Olaf L F , Hay, Clinton J
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443414 , vital:74116 , https://hdl.handle.net/10520/EJC196537
- Description: In the Upper Zambezi and Okavango ecoregions, Brycinus lateralis, Hepsetus cuvieri, Schilbe intermedius and Serranochromis macrocephalus are important in subsistence fisheries, while S. intermedius and S. macrocephalus are often caught in commercial catches. Despite their importance, there is little information on their age and growth and age validation. Growth zone deposition rate in otoliths of B. lateralis, H. cuvieri, S. intermedius and S. macrocephalus was validated as annual using edge analysis in this study. Annual deposition of growth zones was corroborated by a fluorochrome marking experiment. Both methods demonstrated that one growth zone was deposited annually. Edge analysis demonstrated that the highest proportion of opaque zones was detected between August and December, most likely as a result of slow growth during lower temperature water during the preceding winter. With growth zone deposition validated as annual, future research should focus on determining the growth, maturity and mortality rates of these species, parameters which are important for their management.
- Full Text:
- Date Issued: 2016
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
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
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
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:
- Date Issued: 2008
- 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:
- Date Issued: 2008
- «
- ‹
- 1
- ›
- »