Spatial description of hake-directed fishing activity off the west coast of South Africa
- Fairweather, T P, Booth, Anthony J, Sauer, Warwick H H, Leslie, R W
- Authors: Fairweather, T P , Booth, Anthony J , Sauer, Warwick H H , Leslie, R W
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127031 , vital:35945 , https://doi.10.2989/18142320609504129
- Description: Historically, the two species of Cape hakes Merluccius capensis and M. paradoxus off South Africa were commercially exploited exclusively by demersal trawling. In 1994, hake-directed demersal longline was introduced on an experimental basis, and in 1998 was initiated as a commercial fishing sector. The effect of a combined fleet composed of both trawlers and longliners on the Cape hake resource is not fully understood. Analysis of fishing intensity and catch-rate data revealed that the highest catch rates were found around the 400m and 500m isobaths for the trawl and longline fisheries respectively. Catch rates from both fishing sectors were also noted to be higher over sediments with a sand component. Differences between areas of the highest fishing intensity and highest catch rates were noted. In addition to other factors, it is suggested that a ‘friction of distance’ effect applies — vessels will trade-off higher catch rates with the increased costs associated with fishing in deeper waters.
- Full Text:
- Date Issued: 2010
- Authors: Fairweather, T P , Booth, Anthony J , Sauer, Warwick H H , Leslie, R W
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127031 , vital:35945 , https://doi.10.2989/18142320609504129
- Description: Historically, the two species of Cape hakes Merluccius capensis and M. paradoxus off South Africa were commercially exploited exclusively by demersal trawling. In 1994, hake-directed demersal longline was introduced on an experimental basis, and in 1998 was initiated as a commercial fishing sector. The effect of a combined fleet composed of both trawlers and longliners on the Cape hake resource is not fully understood. Analysis of fishing intensity and catch-rate data revealed that the highest catch rates were found around the 400m and 500m isobaths for the trawl and longline fisheries respectively. Catch rates from both fishing sectors were also noted to be higher over sediments with a sand component. Differences between areas of the highest fishing intensity and highest catch rates were noted. In addition to other factors, it is suggested that a ‘friction of distance’ effect applies — vessels will trade-off higher catch rates with the increased costs associated with fishing in deeper waters.
- Full Text:
- Date Issued: 2010
Indicators of sustainable fishing for South African sardine Sardinops sagax and anchovy Engraulis encrasicolus
- Fairweather, T P, Van der Lingen, C D, Booth, Anthony J, Drapeau, L, Van Der Westhuizen, J J
- Authors: Fairweather, T P , Van der Lingen, C D , Booth, Anthony J , Drapeau, L , Van Der Westhuizen, J J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124778 , vital:35691 , https://doi.10.2989/18142320609504215
- Description: Six indicators were investigated for South African sardine Sardinops sagax and anchovy Engraulis encrasicolus: mean length of catch, length-at-50% maturity, total mortality, exploitation rate, ratio of bycatch, and centre of gravity of commercial catches. Sardine length-at-50% maturity is the most promising as a descriptive indicator because it is positively correlated with population size for an extensive time period (1953–2005). The remaining indicators were limited by shorter data-series (1984–2005). However, mean length of catch, ratio of bycatch and exploitation rate were found to be useful when considered in conjunction with other indicators. The centre of gravity of commercial sardine catches has shown a significant eastward shift from the West Coast, whereas that of anchovy has remained off that coast. Ratio of bycatch indicates that school composition is a reliable descriptive indicator of relative abundance in the two species. Fewer indicators for anchovy were useful, which is attributed to this species’ flexible life-history pattern.
- Full Text:
- Date Issued: 2010
- Authors: Fairweather, T P , Van der Lingen, C D , Booth, Anthony J , Drapeau, L , Van Der Westhuizen, J J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124778 , vital:35691 , https://doi.10.2989/18142320609504215
- Description: Six indicators were investigated for South African sardine Sardinops sagax and anchovy Engraulis encrasicolus: mean length of catch, length-at-50% maturity, total mortality, exploitation rate, ratio of bycatch, and centre of gravity of commercial catches. Sardine length-at-50% maturity is the most promising as a descriptive indicator because it is positively correlated with population size for an extensive time period (1953–2005). The remaining indicators were limited by shorter data-series (1984–2005). However, mean length of catch, ratio of bycatch and exploitation rate were found to be useful when considered in conjunction with other indicators. The centre of gravity of commercial sardine catches has shown a significant eastward shift from the West Coast, whereas that of anchovy has remained off that coast. Ratio of bycatch indicates that school composition is a reliable descriptive indicator of relative abundance in the two species. Fewer indicators for anchovy were useful, which is attributed to this species’ flexible life-history pattern.
- Full Text:
- Date Issued: 2010
Retrospective stock assessment of the Emperor red snapper (Lutjanus sebae) on the Seychelles Bank between 1977 and 2006
- Grandcourt, E M, Hecht, Thomas, Booth, Anthony J, Robinson, J
- Authors: Grandcourt, E M , Hecht, Thomas , Booth, Anthony J , Robinson, J
- Date: 2008
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125887 , vital:35829 , https://doi.10.1093/icesjms/fsn064
- Description: The Emperor red snapper, Lutjanus sebae, known as “Bourzwa” in the Seychelles, is distributed throughout the Indo-West Pacific from the southern Red Sea and East Africa to New Caledonia, north to Japan and south to Australia. It occurs near coral or rocky reefs and also over adjacent sand flats and gravel patches between 5 and 180 m deep (Allen, 1985; Anderson, 1986). Juveniles are frequently commensal with sea urchins (Kuiter and Tonozuka, 2001), and are found in nearshore, turbid waters (Williams and Russ, 1992), mangrove areas (Allen, 1985), and around coastal and offshore reefs (Williams and Russ, 1992). Larger L. sebae are generally found deeper, although they are also known to move into shallower water during winter (McPherson et al., 1988; Williams and Russ, 1992). Prey items include fish, crabs, other benthic crustaceans, and cephalopods. Lutjanus sebae is a large, long-lived species, attaining a maximum size of 116 cm fork length (McPherson and Squire, 1992) and maximum age of 34 years (Newman and Dunk, 2002). Despite an absence of data on its population structure, mixing, and identity, the population on the Seychelles Bank has been considered to be a unit stock for assessment purposes because of its remote location (e.g. Lablache and Carrara, 1988; Mees, 1992).
- Full Text:
- Date Issued: 2008
- Authors: Grandcourt, E M , Hecht, Thomas , Booth, Anthony J , Robinson, J
- Date: 2008
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125887 , vital:35829 , https://doi.10.1093/icesjms/fsn064
- Description: The Emperor red snapper, Lutjanus sebae, known as “Bourzwa” in the Seychelles, is distributed throughout the Indo-West Pacific from the southern Red Sea and East Africa to New Caledonia, north to Japan and south to Australia. It occurs near coral or rocky reefs and also over adjacent sand flats and gravel patches between 5 and 180 m deep (Allen, 1985; Anderson, 1986). Juveniles are frequently commensal with sea urchins (Kuiter and Tonozuka, 2001), and are found in nearshore, turbid waters (Williams and Russ, 1992), mangrove areas (Allen, 1985), and around coastal and offshore reefs (Williams and Russ, 1992). Larger L. sebae are generally found deeper, although they are also known to move into shallower water during winter (McPherson et al., 1988; Williams and Russ, 1992). Prey items include fish, crabs, other benthic crustaceans, and cephalopods. Lutjanus sebae is a large, long-lived species, attaining a maximum size of 116 cm fork length (McPherson and Squire, 1992) and maximum age of 34 years (Newman and Dunk, 2002). Despite an absence of data on its population structure, mixing, and identity, the population on the Seychelles Bank has been considered to be a unit stock for assessment purposes because of its remote location (e.g. Lablache and Carrara, 1988; Mees, 1992).
- Full Text:
- Date Issued: 2008
Growth and longevity of Exosphaeroma hylocoetes (Isopoda) under varying conditions of salinity and temperature
- Henninger, Tony O, Froneman, P William, Booth, Anthony J, Hodgson, Alan N
- Authors: Henninger, Tony O , Froneman, P William , Booth, Anthony J , Hodgson, Alan N
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124571 , vital:35630 , https://doi.org/10.3377/004.045.0118
- Description: Numerous studies have documented the importance of both temperature and salinity in influencing aquatic crustacean metabolic processes such as respiration and growth. For example, increased water temperatures have been shown to increase respiration rates in various species of shrimp (Chen & Nan 1993; Spanonopoulos-Hernándeza et al. 2005; Allan et al. 2006), and copepods (Isla & Perissinotto 2004). The response of invertebrates to changes in salinity is more complex, largely reflecting their evolutionary origins (Kinne 1966). For example, juvenile blue swimming crabs, Portunus pelagicus, displayed significantly faster growth and higher survival in response to increasingsalinity (Romano & Zeng 2006). Additional factors that may influence the growth rates of crustaceans include photoperiod (Gambardella et al. 1997), food availability (Shuster & Guthrie 1999) and sex (Newman et al. 2007).
- Full Text:
- Date Issued: 2010
- Authors: Henninger, Tony O , Froneman, P William , Booth, Anthony J , Hodgson, Alan N
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124571 , vital:35630 , https://doi.org/10.3377/004.045.0118
- Description: Numerous studies have documented the importance of both temperature and salinity in influencing aquatic crustacean metabolic processes such as respiration and growth. For example, increased water temperatures have been shown to increase respiration rates in various species of shrimp (Chen & Nan 1993; Spanonopoulos-Hernándeza et al. 2005; Allan et al. 2006), and copepods (Isla & Perissinotto 2004). The response of invertebrates to changes in salinity is more complex, largely reflecting their evolutionary origins (Kinne 1966). For example, juvenile blue swimming crabs, Portunus pelagicus, displayed significantly faster growth and higher survival in response to increasingsalinity (Romano & Zeng 2006). Additional factors that may influence the growth rates of crustaceans include photoperiod (Gambardella et al. 1997), food availability (Shuster & Guthrie 1999) and sex (Newman et al. 2007).
- Full Text:
- Date Issued: 2010
Some life-history parameters of the non-native amphipod Platorchestia platensis (Talitridae) in a warm temperate South African estuary
- Hodgson, Alan N, Booth, Anthony J, David-Engelbrecht, Viginia, Henninger, Tony O
- Authors: Hodgson, Alan N , Booth, Anthony J , David-Engelbrecht, Viginia , Henninger, Tony O
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/126976 , vital:35940 , https://doi.10.1080/0035919X.2014.941961
- Description: Density, population structure, growth, mortality and aspects of reproduction of the non-native amphipod Platorchestia platensis were studied for 20 consecutive months (October 2008 to May 2010) in the supralittoral wrack of the Knysna Estuary, South Africa. Amphipod density varied over the sampling period with the lowest numbers recorded in summer (January and February). Ovigerous females with embryos, and juveniles were found in most months with peaks in recruitment found in both April and October, suggesting that in Knysna this species is a biannual breeder. Average female size was significantly greater in winter, with larger females tending to brood more embryos. The largest adults (13.5 mm total length) were always male although the monthly sex ratio was nearly always female biased. Growth rate estimated from a cohort analysis was about 1 mm per month and monthly survival about 69%. The ability to reproduce all year round may be one reason why this introduced species has become established within this warm temperate estuary.
- Full Text:
- Date Issued: 2014
- Authors: Hodgson, Alan N , Booth, Anthony J , David-Engelbrecht, Viginia , Henninger, Tony O
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/126976 , vital:35940 , https://doi.10.1080/0035919X.2014.941961
- Description: Density, population structure, growth, mortality and aspects of reproduction of the non-native amphipod Platorchestia platensis were studied for 20 consecutive months (October 2008 to May 2010) in the supralittoral wrack of the Knysna Estuary, South Africa. Amphipod density varied over the sampling period with the lowest numbers recorded in summer (January and February). Ovigerous females with embryos, and juveniles were found in most months with peaks in recruitment found in both April and October, suggesting that in Knysna this species is a biannual breeder. Average female size was significantly greater in winter, with larger females tending to brood more embryos. The largest adults (13.5 mm total length) were always male although the monthly sex ratio was nearly always female biased. Growth rate estimated from a cohort analysis was about 1 mm per month and monthly survival about 69%. The ability to reproduce all year round may be one reason why this introduced species has become established within this warm temperate estuary.
- Full Text:
- Date Issued: 2014
Pessimistic assessment of white shark population status in South Africa: comment on Andreotti et al.(2016)
- Irion, Dylan T, Noble, Leslie R, Kock, Alison A, Gennari, Enrico, Dicken, Matthew L, Hewitt, Adrian M, Towner, Alison V, Booth, Anthony J, Smale, Malcolm J, Cliff, Geremy
- Authors: Irion, Dylan T , Noble, Leslie R , Kock, Alison A , Gennari, Enrico , Dicken, Matthew L , Hewitt, Adrian M , Towner, Alison V , Booth, Anthony J , Smale, Malcolm J , Cliff, Geremy
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/${Handle} , vital:35799 , https://doi.10.3354/meps12283
- Description: Andreotti et al. (2016; Mar Ecol Prog Ser 552:241−253) estimate an abundance (N) of 438 white sharks Carcharodon carcharias and a contemporary effective population size (CNe) of 333 individuals along the South African coast. N was estimated by using a mark-recapture analysis of photographic identification records from a single aggregation site (Gansbaai). CNe was calculated based on the levels of pairwise linkage disequilibrium of genetic material collected from 4 aggregation sites across approximately 965 km of South African coastline. However, due to the complex stock structure of white sharks and the model assumptions made by Andreotti et al. (2016), the conclusions drawn cannot be supported by their methods and data.
- Full Text:
- Date Issued: 2017
- Authors: Irion, Dylan T , Noble, Leslie R , Kock, Alison A , Gennari, Enrico , Dicken, Matthew L , Hewitt, Adrian M , Towner, Alison V , Booth, Anthony J , Smale, Malcolm J , Cliff, Geremy
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/${Handle} , vital:35799 , https://doi.10.3354/meps12283
- Description: Andreotti et al. (2016; Mar Ecol Prog Ser 552:241−253) estimate an abundance (N) of 438 white sharks Carcharodon carcharias and a contemporary effective population size (CNe) of 333 individuals along the South African coast. N was estimated by using a mark-recapture analysis of photographic identification records from a single aggregation site (Gansbaai). CNe was calculated based on the levels of pairwise linkage disequilibrium of genetic material collected from 4 aggregation sites across approximately 965 km of South African coastline. However, due to the complex stock structure of white sharks and the model assumptions made by Andreotti et al. (2016), the conclusions drawn cannot be supported by their methods and data.
- Full Text:
- Date Issued: 2017
An invader within an altered landscape: one catfish, two rivers and an inter-basin water transfer scheme
- Kadye, Wilbert T, Booth, Anthony J
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123776 , vital:35494 , https://doi.10.1002/rra.2599
- Description: African sharptooth catfish Clarias gariepinus has become established as a non-native invasive species in Eastern Cape, South Africa, where it was translocated primarily through an inter-basin water transfer scheme into the Great Fish and Sundays rivers. This study examined the patterns in catfish distribution and abundance, and compared trophic niches in relation to the ichthyofauna of the two rivers. Correspondence analysis revealed upstream to downstream gradients associated with the spatial distribution in species richness for most species within the mainstream and mainstream to tributary gradients that were associated mostly with the spatial distribution of native minnows in both rivers. Catfish was predicted to occur widely within the mainstream habitats and to decrease progressively from mainstreams to tributaries. Based on classification and regression trees, the physico-chemical environment was found to be a good proxy for predicting the occurrence and abundance of catfish. Although non-significant relationships were observed between catfish and other native fish species abundances, the study suggests potential impact due to predation and interference in habitats where the invader co-occurs with other fishes. Comparisons of trophic niches indicated higher trophic diversity for the mainstream ichthyofauna than the tributary communities in both rivers, suggesting an upstream to downstream continuum in community structure and resource availability. Catfish within the invaded mainstream had comparable trophic niches and similar dispersion patterns among individuals for both rivers, but indicated differences in shapes of scatter. This suggests that the catfish exhibited a differential response, probably in relation to resource availability, that may be indicative of its dietary plasticity. The study suggests the proliferation of catfish and its probable impact within the mainstream flow-altered habitats where invasion resistance was possibly reduced. Comparisons of trophic niches provided information on its probable impact at different scales and the potential risk of invasion of tributaries inhabited by native minnow species.
- Full Text:
- Date Issued: 2013
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123776 , vital:35494 , https://doi.10.1002/rra.2599
- Description: African sharptooth catfish Clarias gariepinus has become established as a non-native invasive species in Eastern Cape, South Africa, where it was translocated primarily through an inter-basin water transfer scheme into the Great Fish and Sundays rivers. This study examined the patterns in catfish distribution and abundance, and compared trophic niches in relation to the ichthyofauna of the two rivers. Correspondence analysis revealed upstream to downstream gradients associated with the spatial distribution in species richness for most species within the mainstream and mainstream to tributary gradients that were associated mostly with the spatial distribution of native minnows in both rivers. Catfish was predicted to occur widely within the mainstream habitats and to decrease progressively from mainstreams to tributaries. Based on classification and regression trees, the physico-chemical environment was found to be a good proxy for predicting the occurrence and abundance of catfish. Although non-significant relationships were observed between catfish and other native fish species abundances, the study suggests potential impact due to predation and interference in habitats where the invader co-occurs with other fishes. Comparisons of trophic niches indicated higher trophic diversity for the mainstream ichthyofauna than the tributary communities in both rivers, suggesting an upstream to downstream continuum in community structure and resource availability. Catfish within the invaded mainstream had comparable trophic niches and similar dispersion patterns among individuals for both rivers, but indicated differences in shapes of scatter. This suggests that the catfish exhibited a differential response, probably in relation to resource availability, that may be indicative of its dietary plasticity. The study suggests the proliferation of catfish and its probable impact within the mainstream flow-altered habitats where invasion resistance was possibly reduced. Comparisons of trophic niches provided information on its probable impact at different scales and the potential risk of invasion of tributaries inhabited by native minnow species.
- Full Text:
- Date Issued: 2013
Inter-seasonal persistence and size-structuring of two minnow species within headwater streams in the Eastern Cape, South Africa
- Kadye, Wilbert T, Booth, Anthony J
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124866 , vital:35705 , https://doi.10.1111/j.1439-0426.2012.02027.x
- Description: This study examined temporal variation in population dynamics and size structuring of two cyprinid minnows, Pseudobarbus afer and Barbus anoplus, in relation to their proximate physical habitats. Population estimates were determined using three-pass depletion sampling during both summer and winter. The habitats were characterised by seasonal variation in all physico-chemical conditions and spatial variation in substrata compositions. Whereas significant differences in population size were noted between seasons for B. anoplus, no differences were found between seasons for density and capture probability for either species. An increase in boulders was associated with increase in population size and density for P. afer; for B. anoplus, increased percentages of bedrock and bank vegetation were associated with an increase in population size and probability of capture, respectively. According to Canonical Correspondence Analysis, size structuring in P. afer was explained predominantly by seasonality, with smaller length classes associated with the seasonal variable of summer, while larger length classes were associated with pH that was higher in winter. By comparison, for B. anoplus, the habitat variables – bank vegetation and bedrock – accounted for much of the explained variance for size structuring. Recruitment appeared to be the major driver of size structuring for the two species; refugia, especially boulders and bank vegetation, also appeared to be important. Overall, the two species were adapted to the headwater streams that were generally variable in environmental conditions. Potential invasions by non-native invasive fishes that occur within the mainstream habitats threaten these two species. Efforts should continue to protect these minnows from such invasions by constructing barriers to upstream migration of non-native fishes into these headwater habitats.
- Full Text:
- Date Issued: 2012
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124866 , vital:35705 , https://doi.10.1111/j.1439-0426.2012.02027.x
- Description: This study examined temporal variation in population dynamics and size structuring of two cyprinid minnows, Pseudobarbus afer and Barbus anoplus, in relation to their proximate physical habitats. Population estimates were determined using three-pass depletion sampling during both summer and winter. The habitats were characterised by seasonal variation in all physico-chemical conditions and spatial variation in substrata compositions. Whereas significant differences in population size were noted between seasons for B. anoplus, no differences were found between seasons for density and capture probability for either species. An increase in boulders was associated with increase in population size and density for P. afer; for B. anoplus, increased percentages of bedrock and bank vegetation were associated with an increase in population size and probability of capture, respectively. According to Canonical Correspondence Analysis, size structuring in P. afer was explained predominantly by seasonality, with smaller length classes associated with the seasonal variable of summer, while larger length classes were associated with pH that was higher in winter. By comparison, for B. anoplus, the habitat variables – bank vegetation and bedrock – accounted for much of the explained variance for size structuring. Recruitment appeared to be the major driver of size structuring for the two species; refugia, especially boulders and bank vegetation, also appeared to be important. Overall, the two species were adapted to the headwater streams that were generally variable in environmental conditions. Potential invasions by non-native invasive fishes that occur within the mainstream habitats threaten these two species. Efforts should continue to protect these minnows from such invasions by constructing barriers to upstream migration of non-native fishes into these headwater habitats.
- Full Text:
- Date Issued: 2012
Environmental niche patterns of native and non-native fishes within an invaded African river system
- Kadye, Wilbert T, Booth, Anthony J
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124407 , vital:35605 , https://doi.10.1111/jfb.13988
- Description: To test ecological niche theory, this study investigated the spatial patterns and the environmental niches of native and non-native fishes within the invaded Great Fish River system, South Africa. For the native fishes, there were contrasting environmental niche breadths that varied from being small to being large and overlapped for most species, except minnows that were restricted to headwater tributaries. In addition, there was high niche overlap in habitat association among fishes with similar distribution. It was therefore inferred that habitat filtering-driven spatial organization was important in explaining native species distribution patterns. In comparison, most non-native fishes were found to have broad environmental niches and these fishes showed high tolerance to environmental conditions, which generally supported the niche opportunity hypothesis. The proliferation of multiple non-native fishes in the mainstem section suggest that they form a functional assemblage that is probably facilitated by the anthropogenic modification of flow regimes through inter-basin water transfer. Based on the distribution patterns observed in the study, it was inferred that there was a likelihood of negative interactions between native and nonnative fishes. Such effects are likely to be exacerbated by altered flow regime that was likely to have negative implications for native ichthyofauna.
- Full Text:
- Date Issued: 2019
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124407 , vital:35605 , https://doi.10.1111/jfb.13988
- Description: To test ecological niche theory, this study investigated the spatial patterns and the environmental niches of native and non-native fishes within the invaded Great Fish River system, South Africa. For the native fishes, there were contrasting environmental niche breadths that varied from being small to being large and overlapped for most species, except minnows that were restricted to headwater tributaries. In addition, there was high niche overlap in habitat association among fishes with similar distribution. It was therefore inferred that habitat filtering-driven spatial organization was important in explaining native species distribution patterns. In comparison, most non-native fishes were found to have broad environmental niches and these fishes showed high tolerance to environmental conditions, which generally supported the niche opportunity hypothesis. The proliferation of multiple non-native fishes in the mainstem section suggest that they form a functional assemblage that is probably facilitated by the anthropogenic modification of flow regimes through inter-basin water transfer. Based on the distribution patterns observed in the study, it was inferred that there was a likelihood of negative interactions between native and nonnative fishes. Such effects are likely to be exacerbated by altered flow regime that was likely to have negative implications for native ichthyofauna.
- Full Text:
- Date Issued: 2019
Integrating stomach content and stable isotope analyses to elucidate the feeding habits of non-native sharptooth catfish Clarias gariepinus
- Kadye, Wilbert T, Booth, Anthony J
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124843 , vital:35703 , https://doi.10.1007/s10530-011-0116-6
- Description: Sharptooth catfish Clarias gariepinus was introduced into the Eastern Cape Province, South Africa, in 1976 and there are concerns about its possible negative impacts on native biota. This study investigated its trophic impact by examining its feeding habits. Stomach content and stable isotope analyses were compared from three localities—the Great Fish River, Sundays River and Glen Melville Dam. Stomach content analysis indicated a catholic diet dominated by fish particularly in all localities.Spatially, however, the diets revealed differences based on the dominance of macrophytes that were only present in the rivers, and aquatic invertebrates that appeared more diverse within the Great Fish River compared to other localities. By contrast, stable isotopes revealed a more generalised feeding pattern with no clear dominance of particular prey. Stable isotopes further showed that the catfish was a complex predator, with large catfish being top predators whereas smaller size groups appeared to feed lower in the food chain. An ontogenetic shift in diet was evident, with small fish predominantly consuming aquatic invertebrates and shifting towards fish with increasing size. High dietary overlap suggests the potential risk associated catfish feeding, especially the potential of piscivory by small catfish that are more likely to persist in shallow and marginal where endangered indigenous minnows occur. The alteration of environmental conditions, especially flow by inter basin water transfer (IBWT) schemes, was inferred to have had a probable influence its invasion success. Occurrence of other invaders, which was facilitated by the IBWT together with the catfish, posits the risk of invasion meltdown within the study systems.
- Full Text:
- Date Issued: 2012
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124843 , vital:35703 , https://doi.10.1007/s10530-011-0116-6
- Description: Sharptooth catfish Clarias gariepinus was introduced into the Eastern Cape Province, South Africa, in 1976 and there are concerns about its possible negative impacts on native biota. This study investigated its trophic impact by examining its feeding habits. Stomach content and stable isotope analyses were compared from three localities—the Great Fish River, Sundays River and Glen Melville Dam. Stomach content analysis indicated a catholic diet dominated by fish particularly in all localities.Spatially, however, the diets revealed differences based on the dominance of macrophytes that were only present in the rivers, and aquatic invertebrates that appeared more diverse within the Great Fish River compared to other localities. By contrast, stable isotopes revealed a more generalised feeding pattern with no clear dominance of particular prey. Stable isotopes further showed that the catfish was a complex predator, with large catfish being top predators whereas smaller size groups appeared to feed lower in the food chain. An ontogenetic shift in diet was evident, with small fish predominantly consuming aquatic invertebrates and shifting towards fish with increasing size. High dietary overlap suggests the potential risk associated catfish feeding, especially the potential of piscivory by small catfish that are more likely to persist in shallow and marginal where endangered indigenous minnows occur. The alteration of environmental conditions, especially flow by inter basin water transfer (IBWT) schemes, was inferred to have had a probable influence its invasion success. Occurrence of other invaders, which was facilitated by the IBWT together with the catfish, posits the risk of invasion meltdown within the study systems.
- Full Text:
- Date Issued: 2012
Movement patterns and habitat selection of invasive African sharptooth catfish
- Kadye, Wilbert T, Booth, Anthony J
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125276 , vital:35767 , http://dx.doi.10.1111/j.1469-7998.2012.00960.x
- Description: Information on the movement behaviour and habitat use by non-native invasive African catfish Clarias gariepinus is crucial in understanding and possibly mitigating its potential impacts. The aim of this study was to examine catfish movement and habitat selection within an invaded impoundment in the Eastern Cape, South Africa. Acoustic telemetry data for 10 tagged catfish were analyzed to identify spatial patterns in home ranges and seasonal changes in habitat associations. Long-distance movements were observed for most catfish from common central release point, whereas short-distance movements defined their home ranges and utilization distributions that were categorized as localized within single or multiple habitats. Habitat selection was non-random with most catfish utilizing the shallow river mouth and upper section of the reservoir that were dominated by a rocky substratum interspersed with submerged trees. These localities were likely to be preferred for spawning and/or feeding. Utilization of these habitats by catfish is likely to be associated with probable impact due to predation and interference competition for feeding and breeding grounds with other species. Although most catfish maintained their home ranges throughout the study, seasonal shifts in habitat use, which was reflected by the utilization of deep and silt-dominated habitats, were also observed for some catfish. Non-random habitat use and homing behaviour within single and multiple habitats by non-native sharptooth catfish suggests that its impact within the invaded habitats may be associated with particular habitats both at broad spatial and temporal scales. Protection of habitats from catfish invasion should be considered as a management option to conserve native biota.
- Full Text:
- Date Issued: 2013
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125276 , vital:35767 , http://dx.doi.10.1111/j.1469-7998.2012.00960.x
- Description: Information on the movement behaviour and habitat use by non-native invasive African catfish Clarias gariepinus is crucial in understanding and possibly mitigating its potential impacts. The aim of this study was to examine catfish movement and habitat selection within an invaded impoundment in the Eastern Cape, South Africa. Acoustic telemetry data for 10 tagged catfish were analyzed to identify spatial patterns in home ranges and seasonal changes in habitat associations. Long-distance movements were observed for most catfish from common central release point, whereas short-distance movements defined their home ranges and utilization distributions that were categorized as localized within single or multiple habitats. Habitat selection was non-random with most catfish utilizing the shallow river mouth and upper section of the reservoir that were dominated by a rocky substratum interspersed with submerged trees. These localities were likely to be preferred for spawning and/or feeding. Utilization of these habitats by catfish is likely to be associated with probable impact due to predation and interference competition for feeding and breeding grounds with other species. Although most catfish maintained their home ranges throughout the study, seasonal shifts in habitat use, which was reflected by the utilization of deep and silt-dominated habitats, were also observed for some catfish. Non-random habitat use and homing behaviour within single and multiple habitats by non-native sharptooth catfish suggests that its impact within the invaded habitats may be associated with particular habitats both at broad spatial and temporal scales. Protection of habitats from catfish invasion should be considered as a management option to conserve native biota.
- Full Text:
- Date Issued: 2013
Detecting impacts of invasive non-native sharptooth catfish, Clarias gariepinus, within invaded and non-invaded rivers.
- Kadye, Wilbert T, Booth, Anthony J
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124100 , vital:35539 , https://doi.10.1007/s10531-012-0291-5
- Description: In aquatic ecosystems, impacts by invasive introduced fish can be likened to press disturbances that persistently influence communities. This study examined invasion disturbances by determining the relationship between non-native sharptooth catfish Clarias gariepinus and aquatic macroinvertebrates in the Eastern Cape, South Africa. A Multiple Before–After Control–Impact (MBACI) experimental design was used to examine macroinvertebrate communities within two rivers: one with catfish and another one without catfish. Within the invaded river, macroinvertebrates showed little response to catfish presence, whereas predator exclusion appeared to benefit community structure. This suggests that the macroinvertebrate community within the invaded river was adapted to predation impact because of the dominance of resilient taxa, such as Hirudinea, Oligochaeta and Chironomidae that were abundant in the Impact treatment relative to the Control treatment. High macroinvertebrate diversity and richness that was observed in the Control treatment, which excluded the predator, relative to the Impact treatment suggests predator avoidance behaviour within the invaded river. By comparison, within the uninvaded river, catfish introduction into the Impact treatment plots indicated negative effects on macroinvertebrate community that was reflected by decrease in diversity, richness and biomass. A community level impact was also reflected in the multivariate analysis that indicated more variation in macroinvertebrate composition within the Impact treatment relative to the Control in the uninvaded river. Catfish impact within the uninvaded river suggests the dominance of vulnerable taxa, such as odonates that were less abundant in the Impact treatment plots after catfish introduction. From a disturbance perspective, this study revealed different macroinvertebrate responses to catfish impact, and suggests that within invaded habitats, macroinvertebrates were less responsive to catfish presence, whereas catfish introduction within uninvaded habitats demonstrated invasion impact that was shown by a decrease in the abundance of vulnerable taxa. The occurrence of non-native sharptooth catfish within many Eastern Cape rivers is a concern because of its predation impact and potential to influence trophic interrelationships, and efforts should be taken to protect uninvaded rivers, and, where possible, eradicate the invader.
- Full Text:
- Date Issued: 2012
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124100 , vital:35539 , https://doi.10.1007/s10531-012-0291-5
- Description: In aquatic ecosystems, impacts by invasive introduced fish can be likened to press disturbances that persistently influence communities. This study examined invasion disturbances by determining the relationship between non-native sharptooth catfish Clarias gariepinus and aquatic macroinvertebrates in the Eastern Cape, South Africa. A Multiple Before–After Control–Impact (MBACI) experimental design was used to examine macroinvertebrate communities within two rivers: one with catfish and another one without catfish. Within the invaded river, macroinvertebrates showed little response to catfish presence, whereas predator exclusion appeared to benefit community structure. This suggests that the macroinvertebrate community within the invaded river was adapted to predation impact because of the dominance of resilient taxa, such as Hirudinea, Oligochaeta and Chironomidae that were abundant in the Impact treatment relative to the Control treatment. High macroinvertebrate diversity and richness that was observed in the Control treatment, which excluded the predator, relative to the Impact treatment suggests predator avoidance behaviour within the invaded river. By comparison, within the uninvaded river, catfish introduction into the Impact treatment plots indicated negative effects on macroinvertebrate community that was reflected by decrease in diversity, richness and biomass. A community level impact was also reflected in the multivariate analysis that indicated more variation in macroinvertebrate composition within the Impact treatment relative to the Control in the uninvaded river. Catfish impact within the uninvaded river suggests the dominance of vulnerable taxa, such as odonates that were less abundant in the Impact treatment plots after catfish introduction. From a disturbance perspective, this study revealed different macroinvertebrate responses to catfish impact, and suggests that within invaded habitats, macroinvertebrates were less responsive to catfish presence, whereas catfish introduction within uninvaded habitats demonstrated invasion impact that was shown by a decrease in the abundance of vulnerable taxa. The occurrence of non-native sharptooth catfish within many Eastern Cape rivers is a concern because of its predation impact and potential to influence trophic interrelationships, and efforts should be taken to protect uninvaded rivers, and, where possible, eradicate the invader.
- Full Text:
- Date Issued: 2012
Growth, reproduction and population structure of Diplotaxodon limnothrissa in the southeast arm of Lake Malawi
- Kanyerere, Geoffrey Z, Weyl, Olaf L F, Booth, Anthony J
- Authors: Kanyerere, Geoffrey Z , Weyl, Olaf L F , Booth, Anthony J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124583 , vital:35633 , https://doi.org/10.2989/16085910509503832
- Description: With a surface area of ca 28 800km2, Lake Malawi (9°30’S–14°30’S) is the second largest of the African Rift Valley lakes, supporting at least 500, and possibly 2 000, fish species (Turner 1995). The ichthyofauna is dominated by haplochomine cichlids, most of which are confined to the demersal and littoral zones. As a result of over-fishing, the abundance of many of these species has declined (Turner 1994a, 1995, Bulirani et al. 1999, Allison et al. 2002). In contrast, the lake’s offshore fish stocks are considered to be unexploited or only lightly exploited (Thompson and Allison 1997, Turner et al. 2000) and the redirection of fishing effort to these stocks is a high priority (Thompson and Allison 1997, Turner et al. 2000, Allison et al. 2002). Consequently, the Malawi government is currently collaborating with the African Development Bank to develop the deepwater/ offshore fishery in order to increase yields by an estimated 11 000 tons (MC Banda, National Research co-ordinator, pers. comm.). The most abundant cichlid species in the pelagic zone is the small (<210mm TL) zooplanktivorous Diplotaxodon limnothrissa (Turner 1994, Thompson and Allison 1997). It has been recorded throughout the lake at depths ranging from 20 metres down to the anoxic zone at ca 220 metres (Turner 1994b, Thompson et al. 1996, Duponchelle et al. 2000a) and it makes up ca 52% to the total fish biomass (Thompson and Allison 1997). Diplotaxodon limnothrissa will therefore be a major target species in the pelagic fishery, and already comprises in excess of 50% of the mid-water trawl fishery in the southeast arm (SEA) of the lake (Turner 1996).
- Full Text:
- Date Issued: 2010
- Authors: Kanyerere, Geoffrey Z , Weyl, Olaf L F , Booth, Anthony J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124583 , vital:35633 , https://doi.org/10.2989/16085910509503832
- Description: With a surface area of ca 28 800km2, Lake Malawi (9°30’S–14°30’S) is the second largest of the African Rift Valley lakes, supporting at least 500, and possibly 2 000, fish species (Turner 1995). The ichthyofauna is dominated by haplochomine cichlids, most of which are confined to the demersal and littoral zones. As a result of over-fishing, the abundance of many of these species has declined (Turner 1994a, 1995, Bulirani et al. 1999, Allison et al. 2002). In contrast, the lake’s offshore fish stocks are considered to be unexploited or only lightly exploited (Thompson and Allison 1997, Turner et al. 2000) and the redirection of fishing effort to these stocks is a high priority (Thompson and Allison 1997, Turner et al. 2000, Allison et al. 2002). Consequently, the Malawi government is currently collaborating with the African Development Bank to develop the deepwater/ offshore fishery in order to increase yields by an estimated 11 000 tons (MC Banda, National Research co-ordinator, pers. comm.). The most abundant cichlid species in the pelagic zone is the small (<210mm TL) zooplanktivorous Diplotaxodon limnothrissa (Turner 1994, Thompson and Allison 1997). It has been recorded throughout the lake at depths ranging from 20 metres down to the anoxic zone at ca 220 metres (Turner 1994b, Thompson et al. 1996, Duponchelle et al. 2000a) and it makes up ca 52% to the total fish biomass (Thompson and Allison 1997). Diplotaxodon limnothrissa will therefore be a major target species in the pelagic fishery, and already comprises in excess of 50% of the mid-water trawl fishery in the southeast arm (SEA) of the lake (Turner 1996).
- Full Text:
- Date Issued: 2010
Quantifying commercial catch and effort of monkfish Lophius vomerinus and L. vaillanti off Namibia
- Maartens, Lima, Booth, Anthony J
- Authors: Maartens, Lima , Booth, Anthony J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125786 , vital:35817 , https://doi.10.2989/025776101784528999
- Description: Mark-recapture models do not distinguish how ‘‘deaths’’ accrue to marked animals in the population. If animals lose their tags, then recaptures will be fewer than expected and estimates of survival will be underestimated (Arnason and Mills, 1981; McDonald et al., 2003). Similarly, if the non-reporting rate is unknown and assumed to be negligible, as is the case in some tagging studies (e.g. Cliff et al., 1996, for white sharks Carcharodon carcharias), the probability of capture can be underestimated. The effects of both these problems, inherent in cooperative tagging programmes, lead to too few tagged fish being recovered, with a positive bias on the estimation of population size. These effects are most pronounced when capture probability is low and fewer tags are available for recapture (McDonald et al., 2003).
- Full Text:
- Date Issued: 2010
- Authors: Maartens, Lima , Booth, Anthony J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125786 , vital:35817 , https://doi.10.2989/025776101784528999
- Description: Mark-recapture models do not distinguish how ‘‘deaths’’ accrue to marked animals in the population. If animals lose their tags, then recaptures will be fewer than expected and estimates of survival will be underestimated (Arnason and Mills, 1981; McDonald et al., 2003). Similarly, if the non-reporting rate is unknown and assumed to be negligible, as is the case in some tagging studies (e.g. Cliff et al., 1996, for white sharks Carcharodon carcharias), the probability of capture can be underestimated. The effects of both these problems, inherent in cooperative tagging programmes, lead to too few tagged fish being recovered, with a positive bias on the estimation of population size. These effects are most pronounced when capture probability is low and fewer tags are available for recapture (McDonald et al., 2003).
- Full Text:
- Date Issued: 2010
Assessment of the monkfish Lophius vomerinus resource off Namibia
- Maartens, Lima, Booth, Anthony J
- Authors: Maartens, Lima , Booth, Anthony J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123863 , vital:35509 , https://doi.10.2989/025776101784528926
- Description: Monkfish (Lophius vomerinus and L. vaillanti) constitute a commercially important resource off Namibia. During 1998, the Lophius resource was the fourth most important commercial resource in terms of landed mass (c. 17 000 tons) and the fifth most important commercial resource in terms of export value (U$19.8 million) of the Namibian fishing sector (Ministry of Fisheries and Marine Resources, Namibia, unpublished data). Historically, monkfish constituted an important bycatch in the trawl fishery directed at hake (Merluccius spp.), but due to increasing market demand since the early 1990s, a fishery directed at monkfish and sole (Austroglossus microlepis) has developed. The Namibian Ministry of Fisheries and Marine Resources has identified the need to develop a management plan to ensure the resource’s medium and longterm sustainability (Maartens et al. 1999). Long-term resource management plans include the identification of an assessment model to represent reality so that the implications of managing the resource in future under a range of assumptions about its present status and its future dynamics (Cochrane et al. 1998) can be examined. The aim of this study was, therefore, to assess the status of at least part of the monkfish resource using a length-based cohort assessment (Jones 1979, 1984, Sparre and Venema 1998) and an age structured production model (Punt 1994, Punt and Japp 1994, Booth and Punt 1998).
- Full Text:
- Date Issued: 2010
- Authors: Maartens, Lima , Booth, Anthony J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123863 , vital:35509 , https://doi.10.2989/025776101784528926
- Description: Monkfish (Lophius vomerinus and L. vaillanti) constitute a commercially important resource off Namibia. During 1998, the Lophius resource was the fourth most important commercial resource in terms of landed mass (c. 17 000 tons) and the fifth most important commercial resource in terms of export value (U$19.8 million) of the Namibian fishing sector (Ministry of Fisheries and Marine Resources, Namibia, unpublished data). Historically, monkfish constituted an important bycatch in the trawl fishery directed at hake (Merluccius spp.), but due to increasing market demand since the early 1990s, a fishery directed at monkfish and sole (Austroglossus microlepis) has developed. The Namibian Ministry of Fisheries and Marine Resources has identified the need to develop a management plan to ensure the resource’s medium and longterm sustainability (Maartens et al. 1999). Long-term resource management plans include the identification of an assessment model to represent reality so that the implications of managing the resource in future under a range of assumptions about its present status and its future dynamics (Cochrane et al. 1998) can be examined. The aim of this study was, therefore, to assess the status of at least part of the monkfish resource using a length-based cohort assessment (Jones 1979, 1984, Sparre and Venema 1998) and an age structured production model (Punt 1994, Punt and Japp 1994, Booth and Punt 1998).
- Full Text:
- Date Issued: 2010
Aspects of the reproductive biology of monkfish Lophius vomerinus off Namibia
- Maartens, Lima, Booth, Anthony J
- Authors: Maartens, Lima , Booth, Anthony J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123831 , vital:35504 , https://doi.10.2989/18142320509504090
- Description: Aspects of the reproductive biology of monkfish Lophius vomerinus are described from material collected during hake Merluccius spp. biomass surveys and from commercial monkfish and sole Austroglossus microlepis vessels between January 1996 and June 2000 off Namibia at depths between 97m and 686m. Length-at-50% sexual maturity for males and females were estimated at 39.9cm and 58.2cm respectively, males maturing faster than females. The adult sex ratio of fish >50cm total length was strongly biased towards females. There was reproductive activity throughout the year, peaking slightly between autumn and spring.
- Full Text:
- Date Issued: 2010
- Authors: Maartens, Lima , Booth, Anthony J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123831 , vital:35504 , https://doi.10.2989/18142320509504090
- Description: Aspects of the reproductive biology of monkfish Lophius vomerinus are described from material collected during hake Merluccius spp. biomass surveys and from commercial monkfish and sole Austroglossus microlepis vessels between January 1996 and June 2000 off Namibia at depths between 97m and 686m. Length-at-50% sexual maturity for males and females were estimated at 39.9cm and 58.2cm respectively, males maturing faster than females. The adult sex ratio of fish >50cm total length was strongly biased towards females. There was reproductive activity throughout the year, peaking slightly between autumn and spring.
- Full Text:
- Date Issued: 2010
Effect of water temperature on the biogeography of South African estuarine fishes associated with the subtropical/warm temperate subtraction zone
- Maree, R C, Booth, Anthony J, Whitfield, A K
- Authors: Maree, R C , Booth, Anthony J , Whitfield, A K
- Date: 2000
- Language: English
- Type: text , Article
- Identifier: vital:7133 , http://hdl.handle.net/10962/d1011776
- Description: Estuarine biogeographical regions along the southeastern coast of South Africa were investigated in terms of fish distribution and abundance patterns, with particular emphasis on the role of water temperature in influencing these patterns. Qualitative and quantitative analyses were conducted upon the ichthyofaunal assemblages to determine whether the location of the subtropical/warm temperate boundary corresponds to that proposed by Whitfield.(n1) Analyses included the distribution ranges of species associated with estuaries according to presence/absence data, cluster analysis of gill net catches in eight estuaries along the southeastern coast and the relative proportion of tropical to temperate marine species within these eight systems. Quantitative analysis indicated that the ichthyofaunal biogeographical regions are indeed a reflection of water temperature regimes and that the subtropical/warm temperate boundary is located between the Great Kei and Mbashe estuaries. A strong negative correlation was found between the number of temperate fish species and the mean of the minimum monthly temperatures recorded in the systems studied. Qualitative analysis revealed that a barrier appears to exist in the vicinity of the Swartkops estuary, which prevents the westward migration of tropical 'vagrants'. The influence of the Agulhas Current along the east coast and its divergence from the coastline in the Algoa Bay region, as well as upwelling phenomena on the southeast and south coasts are identified as major factors that influence marine and estuarine temperature regimes and therefore the ichythyofauna of this region.
- Full Text: false
- Date Issued: 2000
- Authors: Maree, R C , Booth, Anthony J , Whitfield, A K
- Date: 2000
- Language: English
- Type: text , Article
- Identifier: vital:7133 , http://hdl.handle.net/10962/d1011776
- Description: Estuarine biogeographical regions along the southeastern coast of South Africa were investigated in terms of fish distribution and abundance patterns, with particular emphasis on the role of water temperature in influencing these patterns. Qualitative and quantitative analyses were conducted upon the ichthyofaunal assemblages to determine whether the location of the subtropical/warm temperate boundary corresponds to that proposed by Whitfield.(n1) Analyses included the distribution ranges of species associated with estuaries according to presence/absence data, cluster analysis of gill net catches in eight estuaries along the southeastern coast and the relative proportion of tropical to temperate marine species within these eight systems. Quantitative analysis indicated that the ichthyofaunal biogeographical regions are indeed a reflection of water temperature regimes and that the subtropical/warm temperate boundary is located between the Great Kei and Mbashe estuaries. A strong negative correlation was found between the number of temperate fish species and the mean of the minimum monthly temperatures recorded in the systems studied. Qualitative analysis revealed that a barrier appears to exist in the vicinity of the Swartkops estuary, which prevents the westward migration of tropical 'vagrants'. The influence of the Agulhas Current along the east coast and its divergence from the coastline in the Algoa Bay region, as well as upwelling phenomena on the southeast and south coasts are identified as major factors that influence marine and estuarine temperature regimes and therefore the ichythyofauna of this region.
- Full Text: false
- Date Issued: 2000
Effect of water temperature on the biogeography of South African estuarine fishes associated with the subtropical/warm temperate subtraction zone
- Maree, R C, Booth, Anthony J, Whitfield, A K
- Authors: Maree, R C , Booth, Anthony J , Whitfield, A K
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6766 , http://hdl.handle.net/10962/d1008043
- Description: Estuarine biogeographical regions along the southeastern coast of South Africa were investigated in terms of fish distribution and abundance patterns, with particular emphasis on the role of water temperature in influencing these patterns. Qualitative and quantitative analyses were conducted upon the ichthyofaunal assemblages to determine whether the location of the subtropical/warm temperate boundary corresponds to that proposed by Whitfield.(n1) Analyses included the distribution ranges of species associated with estuaries according to presence/absence data, cluster analysis of gill net catches in eight estuaries along the southeastern coast and the relative proportion of tropical to temperate marine species within these eight systems. Quantitative analysis indicated that the ichthyofaunal biogeographical regions are indeed a reflection of water temperature regimes and that the subtropical/warm temperate boundary is located between the Great Kei and Mbashe estuaries. A strong negative correlation was found between the number of temperate fish species and the mean of the minimum monthly temperatures recorded in the systems studied. Qualitative analysis revealed that a barrier appears to exist in the vicinity of the Swartkops estuary, which prevents the westward migration of tropical 'vagrants'. The influence of the Agulhas Current along the east coast and its divergence from the coastline in the Algoa Bay region, as well as upwelling phenomena on the southeast and south coasts are identified as major factors that influence marine and estuarine temperature regimes and therefore the ichythyofauna of this region.
- Full Text: false
- Date Issued: 2000
- Authors: Maree, R C , Booth, Anthony J , Whitfield, A K
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6766 , http://hdl.handle.net/10962/d1008043
- Description: Estuarine biogeographical regions along the southeastern coast of South Africa were investigated in terms of fish distribution and abundance patterns, with particular emphasis on the role of water temperature in influencing these patterns. Qualitative and quantitative analyses were conducted upon the ichthyofaunal assemblages to determine whether the location of the subtropical/warm temperate boundary corresponds to that proposed by Whitfield.(n1) Analyses included the distribution ranges of species associated with estuaries according to presence/absence data, cluster analysis of gill net catches in eight estuaries along the southeastern coast and the relative proportion of tropical to temperate marine species within these eight systems. Quantitative analysis indicated that the ichthyofaunal biogeographical regions are indeed a reflection of water temperature regimes and that the subtropical/warm temperate boundary is located between the Great Kei and Mbashe estuaries. A strong negative correlation was found between the number of temperate fish species and the mean of the minimum monthly temperatures recorded in the systems studied. Qualitative analysis revealed that a barrier appears to exist in the vicinity of the Swartkops estuary, which prevents the westward migration of tropical 'vagrants'. The influence of the Agulhas Current along the east coast and its divergence from the coastline in the Algoa Bay region, as well as upwelling phenomena on the southeast and south coasts are identified as major factors that influence marine and estuarine temperature regimes and therefore the ichythyofauna of this region.
- Full Text: false
- Date Issued: 2000
Reproductive and feeding biology of the Natal mountain catfish, Amphilius natalensis (Siluriformes: Amphiliidae)
- Marriott, Michael S, Booth, Anthony J, Skelton, Paul H (Paul Harvey)
- Authors: Marriott, Michael S , Booth, Anthony J , Skelton, Paul H (Paul Harvey)
- Date: 1997
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125837 , vital:35823 , https://doi.10.1023/A:1007361511052
- Description: The family Amphiliidae comprises nine genera and about 60 species. Only five species are found in southern Africa, three of which belong to the genus Amphilius (Skelton 1993). These soft-bodied catlets inhabit clear, fast flowing mountain streams where they live amongst cobbles, feeding predominantly on benthic invertebrates (Crass 1964, Skelton 1993). The Natal mountain catfish, A. natalensis Boulenger, 1917, is a small, nocturnal species with a restricted distribution along the eastern seaboard of southern Africa. It occurs in mountain streams from the Umkomaas River north to the Limpopo system in South Africa. It is also present in the Marozi River, a tributary of the Zambezi River in Zimbabwe and in the Ruo River, Malawi (Skelton 1984, 1993). Skelton (1993) suggested that predation by introduced trout species has led to scarcity of A. natalensis in many streams. In spite of this, no studies on the biology of this catfish species have been published. This study presents the first quantitative information on the biology of an amphiliid catfish, A. natalensis including gametogenesis, spawning seasonality, size-at-maturity, adult sex ratio and diet.
- Full Text:
- Date Issued: 1997
- Authors: Marriott, Michael S , Booth, Anthony J , Skelton, Paul H (Paul Harvey)
- Date: 1997
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125837 , vital:35823 , https://doi.10.1023/A:1007361511052
- Description: The family Amphiliidae comprises nine genera and about 60 species. Only five species are found in southern Africa, three of which belong to the genus Amphilius (Skelton 1993). These soft-bodied catlets inhabit clear, fast flowing mountain streams where they live amongst cobbles, feeding predominantly on benthic invertebrates (Crass 1964, Skelton 1993). The Natal mountain catfish, A. natalensis Boulenger, 1917, is a small, nocturnal species with a restricted distribution along the eastern seaboard of southern Africa. It occurs in mountain streams from the Umkomaas River north to the Limpopo system in South Africa. It is also present in the Marozi River, a tributary of the Zambezi River in Zimbabwe and in the Ruo River, Malawi (Skelton 1984, 1993). Skelton (1993) suggested that predation by introduced trout species has led to scarcity of A. natalensis in many streams. In spite of this, no studies on the biology of this catfish species have been published. This study presents the first quantitative information on the biology of an amphiliid catfish, A. natalensis including gametogenesis, spawning seasonality, size-at-maturity, adult sex ratio and diet.
- Full Text:
- Date Issued: 1997
Spatio-temporal patterns in maturation of the chokka squid (Loligo vulgaris reynaudii) off the coast of South Africa
- Olyott, L J H, Sauer, Warwick H H, Booth, Anthony J
- Authors: Olyott, L J H , Sauer, Warwick H H , Booth, Anthony J
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6763 , http://hdl.handle.net/10962/d1007930
- Description: Knowledge of the temporal and spatial characteristics of chokka squid (Loligo vulgaris reynaudii) biology in South African waters is limited, so the possibility of there being a geographically fragmented stock was examined by investigating the distribution of maturity patterns for the species, covering all known spawning areas and using both historical and recent data. Gonadosomatic indices (GSI) varied between year-round consistency and apparent seasonal peaks in both summer and winter; there was no clear spatial pattern. Monthly percentage maturity provided further evidence for two peak reproductive periods each year, although mature squid were present throughout. Sex ratios demonstrated great variability between different areas and life history stages. Male-biased sex ratios were only apparent on the inshore spawning grounds and ranged between 1.118:1 and 4.267:1. Size at sexual maturity was also seasonal, squid maturing smaller in winter/spring than in summer/autumn. Also, squid in the east matured smaller than squid in the west. Although the results from the present study do not provide conclusive evidence of distinct geographic populations, squid likely spawn over a significantly larger area of the Agulhas Bank than previously estimated, and squid on the west coast of South Africa may return to spawn on the western portion of the Agulhas Bank. It remains likely, however, that the east and west coast populations are a single stock and that migration of juveniles to the west coast and their subsequent return as sub-adults is an integral but non-essential and variable part of the life history.
- Full Text:
- Date Issued: 2006
- Authors: Olyott, L J H , Sauer, Warwick H H , Booth, Anthony J
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6763 , http://hdl.handle.net/10962/d1007930
- Description: Knowledge of the temporal and spatial characteristics of chokka squid (Loligo vulgaris reynaudii) biology in South African waters is limited, so the possibility of there being a geographically fragmented stock was examined by investigating the distribution of maturity patterns for the species, covering all known spawning areas and using both historical and recent data. Gonadosomatic indices (GSI) varied between year-round consistency and apparent seasonal peaks in both summer and winter; there was no clear spatial pattern. Monthly percentage maturity provided further evidence for two peak reproductive periods each year, although mature squid were present throughout. Sex ratios demonstrated great variability between different areas and life history stages. Male-biased sex ratios were only apparent on the inshore spawning grounds and ranged between 1.118:1 and 4.267:1. Size at sexual maturity was also seasonal, squid maturing smaller in winter/spring than in summer/autumn. Also, squid in the east matured smaller than squid in the west. Although the results from the present study do not provide conclusive evidence of distinct geographic populations, squid likely spawn over a significantly larger area of the Agulhas Bank than previously estimated, and squid on the west coast of South Africa may return to spawn on the western portion of the Agulhas Bank. It remains likely, however, that the east and west coast populations are a single stock and that migration of juveniles to the west coast and their subsequent return as sub-adults is an integral but non-essential and variable part of the life history.
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- Date Issued: 2006