The last two remaining populations of the critically endangered estuarine pipefish are inbred and not genetically distinct
- Weiss, Sven-Erick, Emami-Khoyi, Arsalan, Kaiser, Horst, Cowley, Paul D, James, Nicola C, Jansen van Vuuren, Bettine, Whitfield, Alan K, Teske, Peter R
- Authors: Weiss, Sven-Erick , Emami-Khoyi, Arsalan , Kaiser, Horst , Cowley, Paul D , James, Nicola C , Jansen van Vuuren, Bettine , Whitfield, Alan K , Teske, Peter R
- Date: 2022
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/445101 , vital:74347 , https://doi.org/10.3389/fmars.2021.756595
- Description: Temporary wetland ecosystems are common in arid and semi‐arid envi-ronments, and are inhabited by diverse invertebrate communities. Little is known about the dynamics of genetic connectivity in the geograph-ically scattered populations of these wetland specialists. The current study investigated the spatial genetic structure and dispersal history of a recently described calanoid copepod, Lovenula raynerae, reported from temporary wetlands in the Eastern Cape province of South Africa. We tested whether the species represents a single, well-connected population or comprises different regional genetic groups, some of which may be rare or endangered.
- Full Text:
- Date Issued: 2022
- Authors: Weiss, Sven-Erick , Emami-Khoyi, Arsalan , Kaiser, Horst , Cowley, Paul D , James, Nicola C , Jansen van Vuuren, Bettine , Whitfield, Alan K , Teske, Peter R
- Date: 2022
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/445101 , vital:74347 , https://doi.org/10.3389/fmars.2021.756595
- Description: Temporary wetland ecosystems are common in arid and semi‐arid envi-ronments, and are inhabited by diverse invertebrate communities. Little is known about the dynamics of genetic connectivity in the geograph-ically scattered populations of these wetland specialists. The current study investigated the spatial genetic structure and dispersal history of a recently described calanoid copepod, Lovenula raynerae, reported from temporary wetlands in the Eastern Cape province of South Africa. We tested whether the species represents a single, well-connected population or comprises different regional genetic groups, some of which may be rare or endangered.
- Full Text:
- Date Issued: 2022
High genetic diversity and limited spatial structure in an endangered, endemic South African sparid, the red steenbras Petrus rupestris:
- Gouws, Gavin, Kerwath, S E, Potts, Warren M, James, Nicola C, Vine, Niall G, Cowley, Paul D
- Authors: Gouws, Gavin , Kerwath, S E , Potts, Warren M , James, Nicola C , Vine, Niall G , Cowley, Paul D
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/160379 , vital:40440 , DOI: 10.2989/1814232X.2020.1788640
- Description: The red steenbras Petrus rupestris is endemic to South Africa, occurring from False Bay in the Western Cape Province to St Lucia in the province of KwaZulu-Natal. This species, the largest member of the family Sparidae, has undergone a substantial stock decline as a result of overfishing and is considered to be collapsed. Various aspects of its life history, including high residency, predictable migrations, late maturity and longevity, have made it vulnerable to overexploitation. This study analysed the diversity and genetic structure of red steenbras across seven sampling regions, using mitochondrial (control region) and nuclear (S7 intron 1) DNA markers.
- Full Text:
- Date Issued: 2020
- Authors: Gouws, Gavin , Kerwath, S E , Potts, Warren M , James, Nicola C , Vine, Niall G , Cowley, Paul D
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/160379 , vital:40440 , DOI: 10.2989/1814232X.2020.1788640
- Description: The red steenbras Petrus rupestris is endemic to South Africa, occurring from False Bay in the Western Cape Province to St Lucia in the province of KwaZulu-Natal. This species, the largest member of the family Sparidae, has undergone a substantial stock decline as a result of overfishing and is considered to be collapsed. Various aspects of its life history, including high residency, predictable migrations, late maturity and longevity, have made it vulnerable to overexploitation. This study analysed the diversity and genetic structure of red steenbras across seven sampling regions, using mitochondrial (control region) and nuclear (S7 intron 1) DNA markers.
- Full Text:
- Date Issued: 2020
Movement and predation: a catch-and-release study on the acoustic tracking of bonefish in the Indian Ocean
- Moxham, Emily Jeanne, Cowley, Paul D, Bennett, Rhett H, von Brandis, Rainer G
- Authors: Moxham, Emily Jeanne , Cowley, Paul D , Bennett, Rhett H , von Brandis, Rainer G
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/103946 , vital:32325 , https://doi.org/10.1007/s10641-019-00850-1
- Description: Tourism generated through bonefish (Albula spp.) fishing contributes to the economies of many isolated tropical islands and atolls. However, little research has been conducted on bonefish in the Indian Ocean. This study aimed to contribute to the understanding of bonefish ecology in the Indian Ocean by quantifying the spatial and temporal movements of Albula glossodonta at a near-pristine and predator-rich atoll in the Seychelles; however, to achieve this, an analysis to identify the occurrence of possible post-release predation bias was first necessary. An acoustic telemetry study was initiated at the remote St. Joseph Atoll, within an array of 88 automated data-logging acoustic receivers. Thirty bonefish were surgically implanted with Vemco V13 acoustic transmitters and tracked for one year. Only 10% of the tagged bonefish were detected for longer than two weeks. A comparison of the final 100 h of movement data from fish detected for less than two weeks to the movement data of the fish detected for longer periods revealed distinct differences in area use and significant differences in the average daily distance moved, speed of movement and frequency of detections. This suggested that mortality in the form of post-release predation was at least 43% of tagged fish. The three surviving bonefish were tracked for 210 to 367 days. These individuals remained in the atoll and showed high use of the marginal habitats between the shallow sand flats and the lagoon. A generalised linear mixed model identified that water temperature, diel cycle and tide were significant predictors of bonefish presence in the lagoon. The high post-release mortality highlights that catch-and-release is likely not as benign as previously believed and management and policy should be adjusted accordingly.
- Full Text:
- Date Issued: 2019
- Authors: Moxham, Emily Jeanne , Cowley, Paul D , Bennett, Rhett H , von Brandis, Rainer G
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/103946 , vital:32325 , https://doi.org/10.1007/s10641-019-00850-1
- Description: Tourism generated through bonefish (Albula spp.) fishing contributes to the economies of many isolated tropical islands and atolls. However, little research has been conducted on bonefish in the Indian Ocean. This study aimed to contribute to the understanding of bonefish ecology in the Indian Ocean by quantifying the spatial and temporal movements of Albula glossodonta at a near-pristine and predator-rich atoll in the Seychelles; however, to achieve this, an analysis to identify the occurrence of possible post-release predation bias was first necessary. An acoustic telemetry study was initiated at the remote St. Joseph Atoll, within an array of 88 automated data-logging acoustic receivers. Thirty bonefish were surgically implanted with Vemco V13 acoustic transmitters and tracked for one year. Only 10% of the tagged bonefish were detected for longer than two weeks. A comparison of the final 100 h of movement data from fish detected for less than two weeks to the movement data of the fish detected for longer periods revealed distinct differences in area use and significant differences in the average daily distance moved, speed of movement and frequency of detections. This suggested that mortality in the form of post-release predation was at least 43% of tagged fish. The three surviving bonefish were tracked for 210 to 367 days. These individuals remained in the atoll and showed high use of the marginal habitats between the shallow sand flats and the lagoon. A generalised linear mixed model identified that water temperature, diel cycle and tide were significant predictors of bonefish presence in the lagoon. The high post-release mortality highlights that catch-and-release is likely not as benign as previously believed and management and policy should be adjusted accordingly.
- Full Text:
- Date Issued: 2019
Should I stay or should I go?: Intra-population variability in movement behaviour of wide-ranging and resident coastal fishes
- Maggs, Jade Q, Cowley, Paul D, Porter, S N, Childs, Amber-Robyn
- Authors: Maggs, Jade Q , Cowley, Paul D , Porter, S N , Childs, Amber-Robyn
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/158290 , vital:40170 , https://doi.org/10.3354/meps12953
- Description: Life-cycle diversity is the existence of alternative strategies among coexisting individuals within the same population and is an important factor in the structuring and connectivity of fish stocks. Mark-recapture data, collected along the coastline of southern Africa from 1984-2015, were used to investigate the occurrence of different movement behaviours (resident vs. wide-ranging) in 5 fishery species with contrasting life histories. A total of 88245 individuals was tagged, with recapture rates ranging from 4-27% for the 5 species. Individuals were considered resident if recaptured within 0-5 km of the release site after 365 d at liberty or wide-ranging if recaptured more than 50 km from the release site within 365 d.
- Full Text:
- Date Issued: 2019
- Authors: Maggs, Jade Q , Cowley, Paul D , Porter, S N , Childs, Amber-Robyn
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/158290 , vital:40170 , https://doi.org/10.3354/meps12953
- Description: Life-cycle diversity is the existence of alternative strategies among coexisting individuals within the same population and is an important factor in the structuring and connectivity of fish stocks. Mark-recapture data, collected along the coastline of southern Africa from 1984-2015, were used to investigate the occurrence of different movement behaviours (resident vs. wide-ranging) in 5 fishery species with contrasting life histories. A total of 88245 individuals was tagged, with recapture rates ranging from 4-27% for the 5 species. Individuals were considered resident if recaptured within 0-5 km of the release site after 365 d at liberty or wide-ranging if recaptured more than 50 km from the release site within 365 d.
- Full Text:
- Date Issued: 2019
Birds as major predators of fishes in the East Kleinemonde Estuary
- Cowley, Paul D, Whitfield, Alan K, Terörde, Anja I
- Authors: Cowley, Paul D , Whitfield, Alan K , Terörde, Anja I
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443271 , vital:74104 , https://hdl.handle.net/10520/EJC-c2893c53c
- Description: This study provides a quantitative account of fish predation by piscivorous birds in the temporarily open/closed East Kleinemonde Estuary and represents the first global attempt to simultaneously relate such consumption to production by a fish community in the same estuary. Cormorants and herons were the dominant predators and seasonal variations in the avifaunal community composition were noted. Based on comprehensive counts over three years, the piscivorous bird population was estimated to have consumed a maximum of 4 414 kg of fish in 1994, 2 400 kg in 1995/96 and 2 960 kg in 2004/05. In 1995/96 fish production in the East Kleinemonde Estuary (55.89 g m−2 a−1) was estimated at 9 780 kg and maximum bird predation amounted to 25% of annual fish production within the system over the same period, assuming that all birds counted on the estuary foraged there and that the diet of these birds comprised only fish. The above 1995/96 figures, together with an estimate of fish predation by the dominant piscivorous fish Lichia amia of 696 kg suggests that birds are probably the single most important natural predator of fishes within this estuary. An unusual mass invasion by marine Cape Cormorants Phalacrocorax capensis during July 1994 was responsible for large-scale predation of fish (2 155 kg) and resulted in the population of estuary-associated marine fishes declining from approximately 63 300 to about 18 600 individuals during the 1994 closed phase. Given that little or no marine fish recruitment was possible while the estuary mouth was closed, piscivorous birds are likely to have a higher predatory impact on populations of juvenile marine fishes in small temporarily closed estuaries than in larger permanently open systems.
- Full Text:
- Date Issued: 2017
- Authors: Cowley, Paul D , Whitfield, Alan K , Terörde, Anja I
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443271 , vital:74104 , https://hdl.handle.net/10520/EJC-c2893c53c
- Description: This study provides a quantitative account of fish predation by piscivorous birds in the temporarily open/closed East Kleinemonde Estuary and represents the first global attempt to simultaneously relate such consumption to production by a fish community in the same estuary. Cormorants and herons were the dominant predators and seasonal variations in the avifaunal community composition were noted. Based on comprehensive counts over three years, the piscivorous bird population was estimated to have consumed a maximum of 4 414 kg of fish in 1994, 2 400 kg in 1995/96 and 2 960 kg in 2004/05. In 1995/96 fish production in the East Kleinemonde Estuary (55.89 g m−2 a−1) was estimated at 9 780 kg and maximum bird predation amounted to 25% of annual fish production within the system over the same period, assuming that all birds counted on the estuary foraged there and that the diet of these birds comprised only fish. The above 1995/96 figures, together with an estimate of fish predation by the dominant piscivorous fish Lichia amia of 696 kg suggests that birds are probably the single most important natural predator of fishes within this estuary. An unusual mass invasion by marine Cape Cormorants Phalacrocorax capensis during July 1994 was responsible for large-scale predation of fish (2 155 kg) and resulted in the population of estuary-associated marine fishes declining from approximately 63 300 to about 18 600 individuals during the 1994 closed phase. Given that little or no marine fish recruitment was possible while the estuary mouth was closed, piscivorous birds are likely to have a higher predatory impact on populations of juvenile marine fishes in small temporarily closed estuaries than in larger permanently open systems.
- Full Text:
- Date Issued: 2017
Life-histories explain the conservation status of two estuary-associated pipefishes
- Whitfield, Alan K, Mkare, Thomas K, Teske, Peter R, James, Nicola C, Cowley, Paul D
- Authors: Whitfield, Alan K , Mkare, Thomas K , Teske, Peter R , James, Nicola C , Cowley, Paul D
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/445087 , vital:74346 , https://doi.org/10.1016/j.biocon.2017.06.024
- Description: Two endemic southern African pipefish species (Teleostei: Syngnathidae) co-occur in estuaries on the southeast coast of South Africa. The larger longsnout pipefish, Syngnathus temminckii, is abundant and has a wide range that comprises coastal and estuarine habitats in all three of the region's marine biogeographic provinces. In contrast, the smaller estuarine pipefish S. watermeyeri is critically endangered, and confined to a few warm-temperate estuaries. Here, we explore reasons for these considerable differences in conservation status.
- Full Text:
- Date Issued: 2017
- Authors: Whitfield, Alan K , Mkare, Thomas K , Teske, Peter R , James, Nicola C , Cowley, Paul D
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/445087 , vital:74346 , https://doi.org/10.1016/j.biocon.2017.06.024
- Description: Two endemic southern African pipefish species (Teleostei: Syngnathidae) co-occur in estuaries on the southeast coast of South Africa. The larger longsnout pipefish, Syngnathus temminckii, is abundant and has a wide range that comprises coastal and estuarine habitats in all three of the region's marine biogeographic provinces. In contrast, the smaller estuarine pipefish S. watermeyeri is critically endangered, and confined to a few warm-temperate estuaries. Here, we explore reasons for these considerable differences in conservation status.
- Full Text:
- Date Issued: 2017
Movement behaviour of alien largemouth bass Micropterus salmoides in the estuarine headwater region of the Kowie River, South Africa
- Murray, Taryn S, Magoro, Mandla L, Whitfield, Alan K, Cowley, Paul D
- Authors: Murray, Taryn S , Magoro, Mandla L , Whitfield, Alan K , Cowley, Paul D
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443194 , vital:74087 , https://doi.org/10.1080/15627020.2015.1079141
- Description: The movement behaviour of largemouth bass Micropterus salmoides in the estuarine headwater region of the Kowie River, South Africa, was investigated using passive acoustic telemetry. Ten adult fish were tagged and released in four discrete pools below a weir that precluded possible upriver migration. Their residency and movement patterns were monitored using 27 moored acoustic receivers spanning both riverine and estuarine habitats between January and November 2013. Small-scale movements ranging from 50 to 400 m occurred between pools in the headwater region, where tagged fish remained resident (did not leave their tagging pool) during the warmer (summer) months. The onset of autumn and winter correlated with declining water temperatures and half of the tagged largemouth bass made downstream excursions into the slightly warmer upper reaches of the estuary. The penetration of these alien piscivores into estuarine headwaters potentially provide additional predator pressure on the juveniles of migratory estuary-associated native marine fish species, which utilise these areas as nurseries. The presence of the alien fish in South African estuarine headwaters may impair the migration of juvenile fishes between the estuarine and freshwater environments.
- Full Text:
- Date Issued: 2015
- Authors: Murray, Taryn S , Magoro, Mandla L , Whitfield, Alan K , Cowley, Paul D
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443194 , vital:74087 , https://doi.org/10.1080/15627020.2015.1079141
- Description: The movement behaviour of largemouth bass Micropterus salmoides in the estuarine headwater region of the Kowie River, South Africa, was investigated using passive acoustic telemetry. Ten adult fish were tagged and released in four discrete pools below a weir that precluded possible upriver migration. Their residency and movement patterns were monitored using 27 moored acoustic receivers spanning both riverine and estuarine habitats between January and November 2013. Small-scale movements ranging from 50 to 400 m occurred between pools in the headwater region, where tagged fish remained resident (did not leave their tagging pool) during the warmer (summer) months. The onset of autumn and winter correlated with declining water temperatures and half of the tagged largemouth bass made downstream excursions into the slightly warmer upper reaches of the estuary. The penetration of these alien piscivores into estuarine headwaters potentially provide additional predator pressure on the juveniles of migratory estuary-associated native marine fish species, which utilise these areas as nurseries. The presence of the alien fish in South African estuarine headwaters may impair the migration of juvenile fishes between the estuarine and freshwater environments.
- Full Text:
- Date Issued: 2015
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
Movement patterns of Lichia amia (Teleostei Carangidae) results from a long-term cooperative tagging project in South Africa
- Dunlop, Stuart W, Mann, Bruce Q, Cowley, Paul D, Murray, Taryn S, Maggs, Jade Q
- Authors: Dunlop, Stuart W , Mann, Bruce Q , Cowley, Paul D , Murray, Taryn S , Maggs, Jade Q
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443970 , vital:74175 , https://doi.org/10.1080/15627020.2015.1058724
- Description: Understanding fish movement patterns and migrations is important for fisheries management as well as the identification and conservation of critical habitats. Data collected by the Oceanographic Research Institute's Cooperative Fish Tagging Project (ORI-CFTP) were used to describe the large-scale movement patterns of Lichia amia along the South African coastline. A total of 10 762 L. amia were tagged between 1984 and 2012, of which 744 (7%) were recaptured. Most tagging effort, mainly on juvenile and subadult individuals, took place along the south-eastern (i.e. Eastern Cape) and south-western (i.e. Western Cape) regions of the country during summer. Conversely, more L. amia were tagged and recaptured (mostly adults) during winter and spring (July to November) along the north-east coast (i.e. KwaZulu-Natal). Movements (dispersal distance in kilometres) by juveniles were restricted and largely confined to estuaries within the south-eastern and south-western regions of the country. There was a significant effect of fish size on distance moved (ANOVA: p0.001), with evidence of a distinct seasonal (winter) longshore migration by adults to KwaZulu-Natal. The consequences of juvenile residency in estuarine habitats and high recapture rate of adults during a directed, seasonal spawning migration are discussed in light of improving current fisheries management.
- Full Text:
- Date Issued: 2015
- Authors: Dunlop, Stuart W , Mann, Bruce Q , Cowley, Paul D , Murray, Taryn S , Maggs, Jade Q
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443970 , vital:74175 , https://doi.org/10.1080/15627020.2015.1058724
- Description: Understanding fish movement patterns and migrations is important for fisheries management as well as the identification and conservation of critical habitats. Data collected by the Oceanographic Research Institute's Cooperative Fish Tagging Project (ORI-CFTP) were used to describe the large-scale movement patterns of Lichia amia along the South African coastline. A total of 10 762 L. amia were tagged between 1984 and 2012, of which 744 (7%) were recaptured. Most tagging effort, mainly on juvenile and subadult individuals, took place along the south-eastern (i.e. Eastern Cape) and south-western (i.e. Western Cape) regions of the country during summer. Conversely, more L. amia were tagged and recaptured (mostly adults) during winter and spring (July to November) along the north-east coast (i.e. KwaZulu-Natal). Movements (dispersal distance in kilometres) by juveniles were restricted and largely confined to estuaries within the south-eastern and south-western regions of the country. There was a significant effect of fish size on distance moved (ANOVA: p0.001), with evidence of a distinct seasonal (winter) longshore migration by adults to KwaZulu-Natal. The consequences of juvenile residency in estuarine habitats and high recapture rate of adults during a directed, seasonal spawning migration are discussed in light of improving current fisheries management.
- Full Text:
- Date Issued: 2015
Residency patterns and migration dynamics of adult bull sharks (Carcharhinus leucas) on the east coast of southern Africa:
- Daly, Ryan, Smale, Malcolm J, Cowley, Paul D, Froneman, P William
- Authors: Daly, Ryan , Smale, Malcolm J , Cowley, Paul D , Froneman, P William
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/143235 , vital:38213 , doi:10.1371/journal.pone.0109357
- Description: Bull sharks (Carcharhinus leucas) are globally distributed top predators that play an important ecological role within coastal marine communities. However, little is known about the spatial and temporal scales of their habitat use and associated ecological role. In this study, we employed passive acoustic telemetry to investigate the residency patterns and migration dynamics of 18 adult bull sharks (195–283 cm total length) tagged in southern Mozambique for a period of between 10 and 22 months. The majority of sharks (n = 16) exhibited temporally and spatially variable residency patterns interspersed with migration events. Ten individuals undertook coastal migrations that ranged between 433 and 709 km (mean = 533 km) with eight of these sharks returning to the study site.
- Full Text:
- Date Issued: 2014
- Authors: Daly, Ryan , Smale, Malcolm J , Cowley, Paul D , Froneman, P William
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/143235 , vital:38213 , doi:10.1371/journal.pone.0109357
- Description: Bull sharks (Carcharhinus leucas) are globally distributed top predators that play an important ecological role within coastal marine communities. However, little is known about the spatial and temporal scales of their habitat use and associated ecological role. In this study, we employed passive acoustic telemetry to investigate the residency patterns and migration dynamics of 18 adult bull sharks (195–283 cm total length) tagged in southern Mozambique for a period of between 10 and 22 months. The majority of sharks (n = 16) exhibited temporally and spatially variable residency patterns interspersed with migration events. Ten individuals undertook coastal migrations that ranged between 433 and 709 km (mean = 533 km) with eight of these sharks returning to the study site.
- Full Text:
- Date Issued: 2014
Residency and small-scale movement behaviour of three endemic sparid fishes in their shallow rocky subtidal nursery habitat, South Africa
- Watt-Pringle, Peter A, Cowley, Paul D, Götz, Albrecht
- Authors: Watt-Pringle, Peter A , Cowley, Paul D , Götz, Albrecht
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443584 , vital:74135 , https://hdl.handle.net/10520/EJC137608
- Description: The residency and small-scale movements of early juveniles (175 mm fork length) of three sparid fish species were examined in the shallow subtidal zone along a 500 m stretch of rocky coastline near Schoenmakerskop (Eastern Cape Province, South Africa). A total of 12 blacktail (Diplodus capensis), 12 zebra (Diplodus hottentotus) and six white musselcracker (Sparodon durbanensis) were tagged using visible implant elastomer (VIE) tags. Underwater observations in four shallow rocky subtidal gullies and adjacent areas were made using snorkelling gear on a total of 37 days spanning 13 field trips over spring low tide periods between January and August 2006. The VIE tagging method was well suited to individually tag small juvenile fish with minimum disturbance. In general, the degree of residency of juveniles in the shallow rocky subtidal zone was species specific and dependent on the size of individuals. Juvenile zebra displayed the highest degree of residency followed by white musselcracker and blacktail, with re-sightings recorded on 53%, 40% and 10% of observation days, respectively. The high degree of residency by early juvenile sparids renders them vulnerable to localized coastal perturbations and climate change.
- Full Text:
- Date Issued: 2013
- Authors: Watt-Pringle, Peter A , Cowley, Paul D , Götz, Albrecht
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443584 , vital:74135 , https://hdl.handle.net/10520/EJC137608
- Description: The residency and small-scale movements of early juveniles (175 mm fork length) of three sparid fish species were examined in the shallow subtidal zone along a 500 m stretch of rocky coastline near Schoenmakerskop (Eastern Cape Province, South Africa). A total of 12 blacktail (Diplodus capensis), 12 zebra (Diplodus hottentotus) and six white musselcracker (Sparodon durbanensis) were tagged using visible implant elastomer (VIE) tags. Underwater observations in four shallow rocky subtidal gullies and adjacent areas were made using snorkelling gear on a total of 37 days spanning 13 field trips over spring low tide periods between January and August 2006. The VIE tagging method was well suited to individually tag small juvenile fish with minimum disturbance. In general, the degree of residency of juveniles in the shallow rocky subtidal zone was species specific and dependent on the size of individuals. Juvenile zebra displayed the highest degree of residency followed by white musselcracker and blacktail, with re-sightings recorded on 53%, 40% and 10% of observation days, respectively. The high degree of residency by early juvenile sparids renders them vulnerable to localized coastal perturbations and climate change.
- Full Text:
- Date Issued: 2013
Effects of altered estuarine submerged macrophyte bed cover on the omnivorous Cape stumpnose Rhabdosargus holubi
- Sheppard, Jill N, Whitfield, Alan K, Cowley, Paul D, Hill, Jaclyn M
- Authors: Sheppard, Jill N , Whitfield, Alan K , Cowley, Paul D , Hill, Jaclyn M
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/444676 , vital:74259 , https://doi.org/10.1111/j.1095-8649.2011.03197.x
- Description: The ecological importance of submerged macrophyte beds to fishes within estuaries was investigated through the example of the ubiquitous Cape stumpnose Rhabdosargus holubi, an omnivorous, vegetation and estuary‐dependent species, using stable‐isotope techniques and long‐term abundance (catch‐per‐unit‐effort) data from the East Kleinemonde Estuary, South Africa. Outputs from a Bayesian mixing model using δ13C and δ15N signatures indicated that the submerged macrophytes Ruppia cirrhosa and Potamogeton pectinatus were not a primary source of nutrition for R. holubi, confirming previous work that revealed that macrophytes are consumed but not digested. Long‐term seine netting data showed reduced abundance of R. holubi during a prolonged period of macrophyte senescence, suggesting that submerged macrophyte habitats provide shelter that reduces mortality (predation risk) and a food‐rich foraging area.
- Full Text:
- Date Issued: 2012
- Authors: Sheppard, Jill N , Whitfield, Alan K , Cowley, Paul D , Hill, Jaclyn M
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/444676 , vital:74259 , https://doi.org/10.1111/j.1095-8649.2011.03197.x
- Description: The ecological importance of submerged macrophyte beds to fishes within estuaries was investigated through the example of the ubiquitous Cape stumpnose Rhabdosargus holubi, an omnivorous, vegetation and estuary‐dependent species, using stable‐isotope techniques and long‐term abundance (catch‐per‐unit‐effort) data from the East Kleinemonde Estuary, South Africa. Outputs from a Bayesian mixing model using δ13C and δ15N signatures indicated that the submerged macrophytes Ruppia cirrhosa and Potamogeton pectinatus were not a primary source of nutrition for R. holubi, confirming previous work that revealed that macrophytes are consumed but not digested. Long‐term seine netting data showed reduced abundance of R. holubi during a prolonged period of macrophyte senescence, suggesting that submerged macrophyte habitats provide shelter that reduces mortality (predation risk) and a food‐rich foraging area.
- Full Text:
- Date Issued: 2012
First assessment of estuarine space use and home range of juvenile white steenbras, Lithognathus lithognathus
- Bennett, Rhett H, Childs, Amber-Robyn, Cowley, Paul D, Næsje, T F, Thorstad, Eva B, Økland, F
- Authors: Bennett, Rhett H , Childs, Amber-Robyn , Cowley, Paul D , Næsje, T F , Thorstad, Eva B , Økland, F
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447517 , vital:74653 , https://doi.org/10.1080/15627020.2011.11407476
- Description: The spatial dynamics and home range sizes of early juvenile white steenbras (Lithognathus lithognathus Cuvier, 1829) in the permanently open Great Fish Estuary, South Africa, were assessed using acoustic telemetry. Seven individuals (154–184 mm fork length) tagged with acoustic transmitters spent the majority of their time in the mesohaline to oligohaline regions of the estuary, between five and seven kilometres from the mouth. Mean home range size was small (97 399 ± 22 557 m2, mean ± S.D.) relative to the size of the estuary (approx. 1 360 000m2). Mean length of the estuary used by an individual was 1707m(±S.D.=1663 m). The fish were highly resident within the estuary, and showed fidelity towards their site of capture.
- Full Text:
- Date Issued: 2011
- Authors: Bennett, Rhett H , Childs, Amber-Robyn , Cowley, Paul D , Næsje, T F , Thorstad, Eva B , Økland, F
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447517 , vital:74653 , https://doi.org/10.1080/15627020.2011.11407476
- Description: The spatial dynamics and home range sizes of early juvenile white steenbras (Lithognathus lithognathus Cuvier, 1829) in the permanently open Great Fish Estuary, South Africa, were assessed using acoustic telemetry. Seven individuals (154–184 mm fork length) tagged with acoustic transmitters spent the majority of their time in the mesohaline to oligohaline regions of the estuary, between five and seven kilometres from the mouth. Mean home range size was small (97 399 ± 22 557 m2, mean ± S.D.) relative to the size of the estuary (approx. 1 360 000m2). Mean length of the estuary used by an individual was 1707m(±S.D.=1663 m). The fish were highly resident within the estuary, and showed fidelity towards their site of capture.
- Full Text:
- Date Issued: 2011
Connectivity between marine reserves and exploited areas in the philopatric reef fish Chrysoblephus laticeps (Teleostei: Sparidae)
- Teske, Peter R, Forget, Fabian R G, Cowley, Paul D, von der Heyden, Sophie, Beheregaray, Luciano B
- Authors: Teske, Peter R , Forget, Fabian R G , Cowley, Paul D , von der Heyden, Sophie , Beheregaray, Luciano B
- Date: 2010
- Language: English
- Type: Article
- Identifier: vital:6776 , http://hdl.handle.net/10962/d1008086
- Description: "No-take‟ Marine Protected Areas (MPAs) are successful in protecting populations of many exploited fish species, but it is often unclear whether networks of MPAs are adequately spaced to ensure connectivity among reserves, and whether spillover occurs into adjacent exploited areas. Such issues are particularly important in species with low dispersal potential, many of which exist as genetically distinct regional stocks.The roman, Chrysoblephus laticeps, is an overexploited, commercially important fishery species endemic to South Africa. Post-recruits display resident behavior and occupy small home ranges, making C. laticeps a suitable model species to investigate connectivity in marine teleosts with potentially low dispersal ability. We used multilocus data from two types of highly variable genetic markers (mitochondrial DNA control region and microsatellites) to clarify patterns of genetic connectivity and population structure in C. laticeps using samples from two MPAs and several moderately or severely exploited regions. Despite using analytical tools that are sensitive to detect even subtle genetic structure, we found that this species exists as a single, well-mixed stock throughout its core distribution. This finding lends supports to the status of MPAs as an adequate tool for managing overexploited marine teleosts. Even though adult dispersal out of MPAs is limited, the fact that the large adults in these reserves produce exponentially more offspring than their smaller counterparts in exploited areas makes MPAs a rich source of recruits. We nonetheless caution against concluding that the lack of structure identified in C. laticeps and several other southern African teleosts can be considered to be representative of marine teleosts in this region in general. Many such species are represented in more than one marine biogeographic province and may be comprised of regionally-adapted stocks that need to be managed individually.
- Full Text:
- Date Issued: 2010
- Authors: Teske, Peter R , Forget, Fabian R G , Cowley, Paul D , von der Heyden, Sophie , Beheregaray, Luciano B
- Date: 2010
- Language: English
- Type: Article
- Identifier: vital:6776 , http://hdl.handle.net/10962/d1008086
- Description: "No-take‟ Marine Protected Areas (MPAs) are successful in protecting populations of many exploited fish species, but it is often unclear whether networks of MPAs are adequately spaced to ensure connectivity among reserves, and whether spillover occurs into adjacent exploited areas. Such issues are particularly important in species with low dispersal potential, many of which exist as genetically distinct regional stocks.The roman, Chrysoblephus laticeps, is an overexploited, commercially important fishery species endemic to South Africa. Post-recruits display resident behavior and occupy small home ranges, making C. laticeps a suitable model species to investigate connectivity in marine teleosts with potentially low dispersal ability. We used multilocus data from two types of highly variable genetic markers (mitochondrial DNA control region and microsatellites) to clarify patterns of genetic connectivity and population structure in C. laticeps using samples from two MPAs and several moderately or severely exploited regions. Despite using analytical tools that are sensitive to detect even subtle genetic structure, we found that this species exists as a single, well-mixed stock throughout its core distribution. This finding lends supports to the status of MPAs as an adequate tool for managing overexploited marine teleosts. Even though adult dispersal out of MPAs is limited, the fact that the large adults in these reserves produce exponentially more offspring than their smaller counterparts in exploited areas makes MPAs a rich source of recruits. We nonetheless caution against concluding that the lack of structure identified in C. laticeps and several other southern African teleosts can be considered to be representative of marine teleosts in this region in general. Many such species are represented in more than one marine biogeographic province and may be comprised of regionally-adapted stocks that need to be managed individually.
- Full Text:
- Date Issued: 2010
Estuarine use by spotted grunter Pomadasys commersonnii in a South African estuary, as determined by acoustic telemetry
- Childs, Amber-Robyn, Cowley, Paul D, Næsje, T F, Booth, Anthony J, Potts, Warren M, Thorstad, Eva B, Økland, F
- Authors: Childs, Amber-Robyn , Cowley, Paul D , Næsje, T F , Booth, Anthony J , Potts, Warren M , Thorstad, Eva B , Økland, F
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124428 , vital:35612 , https://doi.org/10.2989/A JMS.2008.30.1.12.462
- Description: Estuaries are important in the life history and the maintenance of the diversity of coastal fish species because of their function as nursery areas for juveniles as well as feeding grounds for adults (Cyrus 1991). The dependence of many fish species on estuaries is well documented (e.g. Wallace et al. 1984, Lenanton and Potter 1987, Blaber et al. 1989, Whitfield 1990, Hoss and Thayer 1993). Spotted grunter Pomadasys commersonnii (Haemulidae) (Lacepède 1801) is an estuarine-dependent species which spawns in the KwaZulu-Natal inshore coastal waters, between August and December (Wallace 1975b, Wallace and van der Elst 1975, Harris and Cyrus 1997, 1999). The eggs and larvae are transported southwards by the Agulhas Current, and juveniles between 20 mm and 50 mm TL recruit into the KwaZulu-Natal and south-eastern Cape estuaries (Wallace and van der Elst 1975, Whitfield 1990). Juvenile spotted grunter make use of the abundant food resources in estuaries, where they grow rapidly and remain for a period of 1–3 years (Wallace and Schleyer 1979, Day et al. 1981). Upon attaining sexual maturity (at between 300 mm and 400 mm TL), they return to the marine environment (Wallace 1975b). Some adults, however, return to estuaries to feed and to regain condition after spawning (Wallace 1975b, Whitfield 1994). The return of post-spawning fish coincides with increased catches by fishers in estuaries between July and January. These events are known as ‘grunter runs’ (Wallace 1975a, Marais and Baird 1980, Marais 1988, Pradervand and Baird 2002). It is suggested that adults spend up to several months in estuaries, before moving back to sea where they undergo gonadal development and ultimately spawn (Wallace 1975b, Wallace and van der Elst 1975). It is believed that adult fish also enter estuaries in a prespawning state to gain condition en route to their spawning grounds in KwaZulu-Natal (Webb 2002).
- Full Text:
- Date Issued: 2010
- Authors: Childs, Amber-Robyn , Cowley, Paul D , Næsje, T F , Booth, Anthony J , Potts, Warren M , Thorstad, Eva B , Økland, F
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124428 , vital:35612 , https://doi.org/10.2989/A JMS.2008.30.1.12.462
- Description: Estuaries are important in the life history and the maintenance of the diversity of coastal fish species because of their function as nursery areas for juveniles as well as feeding grounds for adults (Cyrus 1991). The dependence of many fish species on estuaries is well documented (e.g. Wallace et al. 1984, Lenanton and Potter 1987, Blaber et al. 1989, Whitfield 1990, Hoss and Thayer 1993). Spotted grunter Pomadasys commersonnii (Haemulidae) (Lacepède 1801) is an estuarine-dependent species which spawns in the KwaZulu-Natal inshore coastal waters, between August and December (Wallace 1975b, Wallace and van der Elst 1975, Harris and Cyrus 1997, 1999). The eggs and larvae are transported southwards by the Agulhas Current, and juveniles between 20 mm and 50 mm TL recruit into the KwaZulu-Natal and south-eastern Cape estuaries (Wallace and van der Elst 1975, Whitfield 1990). Juvenile spotted grunter make use of the abundant food resources in estuaries, where they grow rapidly and remain for a period of 1–3 years (Wallace and Schleyer 1979, Day et al. 1981). Upon attaining sexual maturity (at between 300 mm and 400 mm TL), they return to the marine environment (Wallace 1975b). Some adults, however, return to estuaries to feed and to regain condition after spawning (Wallace 1975b, Whitfield 1994). The return of post-spawning fish coincides with increased catches by fishers in estuaries between July and January. These events are known as ‘grunter runs’ (Wallace 1975a, Marais and Baird 1980, Marais 1988, Pradervand and Baird 2002). It is suggested that adults spend up to several months in estuaries, before moving back to sea where they undergo gonadal development and ultimately spawn (Wallace 1975b, Wallace and van der Elst 1975). It is believed that adult fish also enter estuaries in a prespawning state to gain condition en route to their spawning grounds in KwaZulu-Natal (Webb 2002).
- Full Text:
- Date Issued: 2010
Microsatellite markers for the roman, Chrysoblephus laticeps (Teleostei: Sparidae), an overexploited seabream from South Africa
- Teske, Peter R, Cowley, Paul D, Forget, Fabian R, Beheregaray, Luciano B
- Authors: Teske, Peter R , Cowley, Paul D , Forget, Fabian R , Beheregaray, Luciano B
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/445690 , vital:74414 , https://doi.org/10.1111/j.1755-0998.2009.02595.x
- Description: Eleven polymorphic microsatellite loci were developed from an enrichment library of the roman, Chrysoblephus laticeps, and characterized for 40 individuals collected in Africa's largest and oldest Marine Protected Area (MPA), the Tsitsikamma National Park. The number of alleles per locus ranged from three to 19, and heterozygosities ranged from 0.20 to 0.85. A significant departure from Hardy–Weinberg equilibrium was detected for one locus, and linkage disequilibrium was identified among three pairs of loci. The markers will be useful to detect whether populations resident in MPAs along the South African coast are genetically connected, and whether there is spillover of recruits into adjacent exploited areas.
- Full Text:
- Date Issued: 2009
- Authors: Teske, Peter R , Cowley, Paul D , Forget, Fabian R , Beheregaray, Luciano B
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/445690 , vital:74414 , https://doi.org/10.1111/j.1755-0998.2009.02595.x
- Description: Eleven polymorphic microsatellite loci were developed from an enrichment library of the roman, Chrysoblephus laticeps, and characterized for 40 individuals collected in Africa's largest and oldest Marine Protected Area (MPA), the Tsitsikamma National Park. The number of alleles per locus ranged from three to 19, and heterozygosities ranged from 0.20 to 0.85. A significant departure from Hardy–Weinberg equilibrium was detected for one locus, and linkage disequilibrium was identified among three pairs of loci. The markers will be useful to detect whether populations resident in MPAs along the South African coast are genetically connected, and whether there is spillover of recruits into adjacent exploited areas.
- Full Text:
- Date Issued: 2009
Do environmental factors influence the movement of estuarine fish? A case study using acoustic telemetry
- Childs, Amber-Robyn, Cowley, Paul D, Næsje, T F, Booth, Anthony J, Thorstad, Eva B, Økland, F
- Authors: Childs, Amber-Robyn , Cowley, Paul D , Næsje, T F , Booth, Anthony J , Thorstad, Eva B , Økland, F
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6772 , http://hdl.handle.net/10962/d1008070
- Description: Telemetry methods were used to investigate the influence of selected environmental variables on the position and movement of an estuarine-dependent haemulid, the spotted grunter Pomadasys commersonnii (Lacepède 1801), in the Great Fish Estuary, South Africa. Forty individuals (263–698 mm TL) were surgically implanted with acoustic coded transmitters and manually tracked during two periods (7 February to 24 March 2003; n = 20 and 29 September to 15 November 2003; n = 20). Real-time data revealed that spotted grunter are euryhaline (0–37) and are able to tolerate large variations in turbidity (4–356 FTU) and temperature (16–30 °C). However, the fish altered their position in response to large fluctuations in salinity, temperature and turbidity, which are characteristic of tidal estuarine environments. Furthermore, tidal phase had a strong influence on the position of spotted grunter in the estuary.
- Full Text:
- Date Issued: 2008
- Authors: Childs, Amber-Robyn , Cowley, Paul D , Næsje, T F , Booth, Anthony J , Thorstad, Eva B , Økland, F
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6772 , http://hdl.handle.net/10962/d1008070
- Description: Telemetry methods were used to investigate the influence of selected environmental variables on the position and movement of an estuarine-dependent haemulid, the spotted grunter Pomadasys commersonnii (Lacepède 1801), in the Great Fish Estuary, South Africa. Forty individuals (263–698 mm TL) were surgically implanted with acoustic coded transmitters and manually tracked during two periods (7 February to 24 March 2003; n = 20 and 29 September to 15 November 2003; n = 20). Real-time data revealed that spotted grunter are euryhaline (0–37) and are able to tolerate large variations in turbidity (4–356 FTU) and temperature (16–30 °C). However, the fish altered their position in response to large fluctuations in salinity, temperature and turbidity, which are characteristic of tidal estuarine environments. Furthermore, tidal phase had a strong influence on the position of spotted grunter in the estuary.
- Full Text:
- Date Issued: 2008
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
A survey of selected Eastern Cape estuaries with particular reference to the ichthyofauna
- Vorwerk, Paul D, Whitfield, Alan K, Cowley, Paul D, Paterson, Angus W
- Authors: Vorwerk, Paul D , Whitfield, Alan K , Cowley, Paul D , Paterson, Angus W
- Date: 2001
- Language: English
- Type: Text
- Identifier: vital:15032 , http://hdl.handle.net/10962/d1019908 , ISSN 0073-4381 , Ichthyological Bulletin J.L.B. Smith Institute of Ichthyology; No. 72
- Description: The physical environment and ichthyofauna of 10 estuaries, the East Kleinemonde, Klein Palmiet, Great Fish, Mtati, Mpekweni, Mgwalana, Bira, Gqutywa, Ngculura and Keiskamma, was sampled over a four year period. The ichthyofauna of each estuary was sampled once during winter and once during summer in that period, with the physical environment being sampled on two occasions per season. This investigation provides baseline ichthyofaunal and physical information for these estuaries, the majority of which have never been studied before. The fish data presented for these systems includes species composition, relative abundance, richness and diversity, longitudinal distributions and length frequency data. Descriptions of the physical environment within each estuary are also presented. The permanently open estuaries had a greater proportion of marine and freshwater species relative to the temporarily open/closed systems which were dominated by marine species dependent on estuaries and estuarine resident species. The permanently open estuaries had a higher Margalef's species richness index relative to the temporarily open/closed systems but the Shannon-Wiener species diversity index did not follow any discernible trend. There were minor longitudinal distribution trends when analysing the community as a whole, with patterns for individual species being more pronounced. The length frequency histograms for estuarine resident species differed between estuary types, while those for the marine migrant species were similar in the different estuary types.\ , Rhodes University Libraries (Digitisation)
- Full Text:
- Date Issued: 2001
- Authors: Vorwerk, Paul D , Whitfield, Alan K , Cowley, Paul D , Paterson, Angus W
- Date: 2001
- Language: English
- Type: Text
- Identifier: vital:15032 , http://hdl.handle.net/10962/d1019908 , ISSN 0073-4381 , Ichthyological Bulletin J.L.B. Smith Institute of Ichthyology; No. 72
- Description: The physical environment and ichthyofauna of 10 estuaries, the East Kleinemonde, Klein Palmiet, Great Fish, Mtati, Mpekweni, Mgwalana, Bira, Gqutywa, Ngculura and Keiskamma, was sampled over a four year period. The ichthyofauna of each estuary was sampled once during winter and once during summer in that period, with the physical environment being sampled on two occasions per season. This investigation provides baseline ichthyofaunal and physical information for these estuaries, the majority of which have never been studied before. The fish data presented for these systems includes species composition, relative abundance, richness and diversity, longitudinal distributions and length frequency data. Descriptions of the physical environment within each estuary are also presented. The permanently open estuaries had a greater proportion of marine and freshwater species relative to the temporarily open/closed systems which were dominated by marine species dependent on estuaries and estuarine resident species. The permanently open estuaries had a higher Margalef's species richness index relative to the temporarily open/closed systems but the Shannon-Wiener species diversity index did not follow any discernible trend. There were minor longitudinal distribution trends when analysing the community as a whole, with patterns for individual species being more pronounced. The length frequency histograms for estuarine resident species differed between estuary types, while those for the marine migrant species were similar in the different estuary types.\ , Rhodes University Libraries (Digitisation)
- Full Text:
- Date Issued: 2001
Ichthyofaunal characteristics of a typical temporarily open/closed estuary on the southeast coast of South Africa
- Cowley, Paul D, Heemstra, Phillip C
- Authors: Cowley, Paul D , Heemstra, Phillip C
- Date: 2001
- Subjects: Estuarine fishes -- Ecology -- Indian Ocean , Estuarine ecology -- South Africa , Fish communities -- South Africa , Fish communities -- Indian Ocean
- Language: English
- Type: Text
- Identifier: vital:15021 , http://hdl.handle.net/10962/d1019862 , ISSN 0073-4381 , Ichthyological Bulletin J.L.B. Smith Institute of Ichthyology; No. 71
- Description: The present study was undertaken to describe the species composition, size composition and distribution of the fish fauna associated with the temporarily open/closed East Kleinemonde Estuary on the southeast coast of South Africa. Data collected on the estuary mouth condition from March 1993 to August 1997 indicated that this system was predominantly closed, while open mouth conditions were unseasonal and prevailed for only a short duration following periods of high rainfall. Fishes were sampled throughout the estuary between April 1993 and January 1997 using seine and gill nets. A total of 30 species belonging to 17 families were recorded, including the critically endangered estuarine pipefish Syngnathus watermeyeri. Besides the estuarine pipefish, an additional five species capable of completing their life cycle within the estuary were recorded. The ichthyofaunal community was dominated by 18 marine-spawning species with varying degrees of dependence on estuaries as nursery areas. The marine species that are not dependent on estuaries as nursery areas were represented by three species, while the euryhaline freshwater species, obligate catadromous species and facultative catadromous species were each represented by one species. The dominant members of the estuarine-spawning group were well represented by all post-larval life-history stages, whereas the mean size of each marine-spawning species indicated that juvenile size classes dominated this group. Classification and ordination of both the small- and large-mesh seine net fish assemblages revealed a high degree of similarity throughout the estuary, with the exception of a distinct grouping associated with sandy substrata in the lower reaches of the system. Catch per unit effort (CPUE) data provided evidence of spatial segregation by several species as well as within some families (e.g. Gobiidae). , Rhodes University Libraries (Digitisation)
- Full Text:
- Date Issued: 2001
- Authors: Cowley, Paul D , Heemstra, Phillip C
- Date: 2001
- Subjects: Estuarine fishes -- Ecology -- Indian Ocean , Estuarine ecology -- South Africa , Fish communities -- South Africa , Fish communities -- Indian Ocean
- Language: English
- Type: Text
- Identifier: vital:15021 , http://hdl.handle.net/10962/d1019862 , ISSN 0073-4381 , Ichthyological Bulletin J.L.B. Smith Institute of Ichthyology; No. 71
- Description: The present study was undertaken to describe the species composition, size composition and distribution of the fish fauna associated with the temporarily open/closed East Kleinemonde Estuary on the southeast coast of South Africa. Data collected on the estuary mouth condition from March 1993 to August 1997 indicated that this system was predominantly closed, while open mouth conditions were unseasonal and prevailed for only a short duration following periods of high rainfall. Fishes were sampled throughout the estuary between April 1993 and January 1997 using seine and gill nets. A total of 30 species belonging to 17 families were recorded, including the critically endangered estuarine pipefish Syngnathus watermeyeri. Besides the estuarine pipefish, an additional five species capable of completing their life cycle within the estuary were recorded. The ichthyofaunal community was dominated by 18 marine-spawning species with varying degrees of dependence on estuaries as nursery areas. The marine species that are not dependent on estuaries as nursery areas were represented by three species, while the euryhaline freshwater species, obligate catadromous species and facultative catadromous species were each represented by one species. The dominant members of the estuarine-spawning group were well represented by all post-larval life-history stages, whereas the mean size of each marine-spawning species indicated that juvenile size classes dominated this group. Classification and ordination of both the small- and large-mesh seine net fish assemblages revealed a high degree of similarity throughout the estuary, with the exception of a distinct grouping associated with sandy substrata in the lower reaches of the system. Catch per unit effort (CPUE) data provided evidence of spatial segregation by several species as well as within some families (e.g. Gobiidae). , Rhodes University Libraries (Digitisation)
- Full Text:
- Date Issued: 2001
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