Reproductive biology of a riverine cyprinid, Labeo umbratus (Teleostei: Cyprinidae), in small South African reservoirs
- Potts, Warren M, Booth, Anthony J, Hecht, Thomas, Andrew, Timothy G
- Authors: Potts, Warren M , Booth, Anthony J , Hecht, Thomas , Andrew, Timothy G
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125854 , vital:35826 , https://doi.10.2989/16085910509503849
- Description: The reproductive and recruitment characteristics of moggel, Labeo umbratus, populations were examined in four small South African reservoirs. Reproduction, characterised by an extended spawning season, high fecundity, short incubation time and rapid larval development, appears to be ideally suited to the highly variable environment of small reservoirs. Evidence suggested that L. umbratus spawns in the reservoirs. In two reservoirs where samples were conducted monthly, GSI (gonado-somatic index) was positively correlated with both water temperature and day length, whilst the CPUE (catch per unit effort) of juveniles was not related to any environmental variable. The success of moggel spawning appeared to increase when there was early spring and consistent summer rainfall.
- Full Text:
- Date Issued: 2010
- Authors: Potts, Warren M , Booth, Anthony J , Hecht, Thomas , Andrew, Timothy G
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125854 , vital:35826 , https://doi.10.2989/16085910509503849
- Description: The reproductive and recruitment characteristics of moggel, Labeo umbratus, populations were examined in four small South African reservoirs. Reproduction, characterised by an extended spawning season, high fecundity, short incubation time and rapid larval development, appears to be ideally suited to the highly variable environment of small reservoirs. Evidence suggested that L. umbratus spawns in the reservoirs. In two reservoirs where samples were conducted monthly, GSI (gonado-somatic index) was positively correlated with both water temperature and day length, whilst the CPUE (catch per unit effort) of juveniles was not related to any environmental variable. The success of moggel spawning appeared to increase when there was early spring and consistent summer rainfall.
- Full Text:
- Date Issued: 2010
Shark fishing effort and catch of the ragged-tooth shark Carcharias taurus in the South African competitive shore-angling fishery
- Dicken, Matthew L, Booth, Anthony J, Smale, Malcolm J
- Authors: Dicken, Matthew L , Booth, Anthony J , Smale, Malcolm J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/126944 , vital:35937 , https://doi.10.2989/18142320609504209
- Description: In South Africa, Carcharias taurus is commonly known as the ragged-tooth shark or raggie. The species is also referred to as the sand-tiger shark in North America and as the grey-nurse shark in Australia. It is a long-lived species with an estimated longevity of up to 40 years (Goldman 2002). Female sharks reach sexual maturity at approximately 10 years (Goldman 2002), and they exhibit a biennial reproductive cycle (Branstetter and Musick 1994, Lucifora et al. 2002, G Cliff, Natal Sharks Board, unpublished data). Intra-uterine cannibalisation results in a maximum fecundity of two pups per litter after a gestation period of approximately 9–12 months (Bass et al. 1975, Gilmore et al. 1983). These life-history characteristics make this species particularly susceptible to overexploitation.
- Full Text:
- Date Issued: 2010
- Authors: Dicken, Matthew L , Booth, Anthony J , Smale, Malcolm J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/126944 , vital:35937 , https://doi.10.2989/18142320609504209
- Description: In South Africa, Carcharias taurus is commonly known as the ragged-tooth shark or raggie. The species is also referred to as the sand-tiger shark in North America and as the grey-nurse shark in Australia. It is a long-lived species with an estimated longevity of up to 40 years (Goldman 2002). Female sharks reach sexual maturity at approximately 10 years (Goldman 2002), and they exhibit a biennial reproductive cycle (Branstetter and Musick 1994, Lucifora et al. 2002, G Cliff, Natal Sharks Board, unpublished data). Intra-uterine cannibalisation results in a maximum fecundity of two pups per litter after a gestation period of approximately 9–12 months (Bass et al. 1975, Gilmore et al. 1983). These life-history characteristics make this species particularly susceptible to overexploitation.
- Full Text:
- Date Issued: 2010
Spatial and seasonal distribution patterns of the ragged-tooth shark Carcharias taurus along the coast of South Africa
- Dicken, Matthew L, Booth, Anthony J, Smale, Malcolm J
- Authors: Dicken, Matthew L , Booth, Anthony J , Smale, Malcolm J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127008 , vital:35943 , https://doi.10.2989/18142320609504210
- Description: Off South Africa, the ragged-tooth shark Carcharias Taurus has been occasionally reported from the West Coast, but it is more commonly found along the East and South coasts from Cape Town to northern KwaZulu-Natal (KZN) (Bass et al. 1975, Smale 2002). Mating is thought to occur off the south coast of KZN from October to late November (G Cliff, Natal Sharks Board, unpublished data). Pregnant females then move northward to spend the early part of their gestation in the warmer waters of northern KZN and possibly southern Moçambique. During July and August, the near-term pregnant females begin to move southwards towards the cooler waters of the Eastern Cape (Wallett 1973, Bass et al. 1975, G Cliff, unpublished data), where they give birth from September to November (Smale 2002). After parturition, many of the females migrate back to KZN. The whereabouts of mature males outside of the mating season is unclear. These broadscale distribution and migratory habits for C. taurus have been inferred from limited catch records obtained for only parts of its range along the South African coast.
- Full Text:
- Date Issued: 2010
- Authors: Dicken, Matthew L , Booth, Anthony J , Smale, Malcolm J
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127008 , vital:35943 , https://doi.10.2989/18142320609504210
- Description: Off South Africa, the ragged-tooth shark Carcharias Taurus has been occasionally reported from the West Coast, but it is more commonly found along the East and South coasts from Cape Town to northern KwaZulu-Natal (KZN) (Bass et al. 1975, Smale 2002). Mating is thought to occur off the south coast of KZN from October to late November (G Cliff, Natal Sharks Board, unpublished data). Pregnant females then move northward to spend the early part of their gestation in the warmer waters of northern KZN and possibly southern Moçambique. During July and August, the near-term pregnant females begin to move southwards towards the cooler waters of the Eastern Cape (Wallett 1973, Bass et al. 1975, G Cliff, unpublished data), where they give birth from September to November (Smale 2002). After parturition, many of the females migrate back to KZN. The whereabouts of mature males outside of the mating season is unclear. These broadscale distribution and migratory habits for C. taurus have been inferred from limited catch records obtained for only parts of its range along the South African coast.
- Full Text:
- Date Issued: 2010
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, Rob W
- Authors: Fairweather, T P , Booth, Anthony J , Sauer, Warwick H H , Leslie, Rob 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, Rob 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
Establishment of translocated populations of smallmouth yellowfish, Labeobarbus aeneus (Pisces: Cyprinidae), in lentic and lotic habitats in the Great Fish River system, South Africa
- Weyl, Olaf L F, Stadtlander, Timo, Booth, Anthony J
- Authors: Weyl, Olaf L F , Stadtlander, Timo , Booth, Anthony J
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124418 , vital:35607 , https://doi.org/10.3377/004.044.0109
- Description: As a result of numerous introductions and translocations of fishes, South Africa has recently been identified as a fish invasion hotspot (Leprieur et al. 2008). In freshwater ecosystems invasion by alien species is considered a leading mechanism driving environmental change (Clavero & Garcia- Berthou 2005; Garcia-Berthou et al. 2005). In South Africa, documented effects of fish invasions include the extirpation of indigenous fishes through predation (Cambray 2003), changes in invertebrate community structure (Lowe et al. 2008) and hybridization (Canonico et al. 2005). As a result, the management of alien species is a high national priority (National Environmental Management: Biodiversity Act 2004). Such management requires an understanding of the biology, ecology and establishment success of fishes outside their native range.
- Full Text:
- Date Issued: 2009
- Authors: Weyl, Olaf L F , Stadtlander, Timo , Booth, Anthony J
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124418 , vital:35607 , https://doi.org/10.3377/004.044.0109
- Description: As a result of numerous introductions and translocations of fishes, South Africa has recently been identified as a fish invasion hotspot (Leprieur et al. 2008). In freshwater ecosystems invasion by alien species is considered a leading mechanism driving environmental change (Clavero & Garcia- Berthou 2005; Garcia-Berthou et al. 2005). In South Africa, documented effects of fish invasions include the extirpation of indigenous fishes through predation (Cambray 2003), changes in invertebrate community structure (Lowe et al. 2008) and hybridization (Canonico et al. 2005). As a result, the management of alien species is a high national priority (National Environmental Management: Biodiversity Act 2004). Such management requires an understanding of the biology, ecology and establishment success of fishes outside their native range.
- Full Text:
- Date Issued: 2009
Rapid biological assessment of the fishery potential of Xonxa Dam, near Queenstown, South Africa
- Richardson, T J, Booth, Anthony J, Weyl, Olaf L F
- Authors: Richardson, T J , Booth, Anthony J , Weyl, Olaf L F
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125798 , vital:35818 , https://doi.10.2989/AJAS.2009.34.1.9.734
- Description: In Africa, the harvesting of fish from small reservoirs has been identified as an important food resource for small rural communities, particularly those living close to waterbodies (Kapetsky and Petr 1984, Marshall and Maes 1994, van der Knaap 1994). Development of fisheries to utilize these resources has recently been identified by the African Union as a priority investment area for poverty alleviation and regional economic development (NEPAD 2005). Within a South African context, it is suspected that there will be increased interest in developing these fisheries to address major national policy objectives, which include food security, economic empowerment, optimal economic benefit from water, and poverty eradication (RSA 1998a, 1998b). South Africa, however, presents a somewhat anomalous situation. The lack of a fishing history in communities, the lack of species with a high fisheries potential, inadequate inland fisheries policy and a lack of directed fisheries development have resulted in low utilisation levels of fish resources in South African reservoirs (Weyl et al. 2007).
- Full Text:
- Date Issued: 2009
- Authors: Richardson, T J , Booth, Anthony J , Weyl, Olaf L F
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125798 , vital:35818 , https://doi.10.2989/AJAS.2009.34.1.9.734
- Description: In Africa, the harvesting of fish from small reservoirs has been identified as an important food resource for small rural communities, particularly those living close to waterbodies (Kapetsky and Petr 1984, Marshall and Maes 1994, van der Knaap 1994). Development of fisheries to utilize these resources has recently been identified by the African Union as a priority investment area for poverty alleviation and regional economic development (NEPAD 2005). Within a South African context, it is suspected that there will be increased interest in developing these fisheries to address major national policy objectives, which include food security, economic empowerment, optimal economic benefit from water, and poverty eradication (RSA 1998a, 1998b). South Africa, however, presents a somewhat anomalous situation. The lack of a fishing history in communities, the lack of species with a high fisheries potential, inadequate inland fisheries policy and a lack of directed fisheries development have resulted in low utilisation levels of fish resources in South African reservoirs (Weyl et al. 2007).
- 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
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
Spatial and seasonal distribution patterns of juvenile and adult raggedtooth sharks (Carcharias taurus) tagged off the east coast of South Africa
- Dicken, Matthew L, Booth, Anthony J, Smale, Malcolm J, Cliff, G
- Authors: Dicken, Matthew L , Booth, Anthony J , Smale, Malcolm J , Cliff, G
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/126997 , vital:35942 , https://doi.10.1071/MF06018
- Description: Crucial to effective fisheries management is a thorough understanding of the stock structure of a population. Understanding the spatial and seasonal distribution patterns of a species is necessary to define habitat use and evaluate the potential effects of exploitation and anthropogenic activities. This is particularly important for a species such as the raggedtooth shark (Carcharias Taurus Rafinesque, 1810), whose life-history characteristics make it particularly susceptible to over-exploitation (Pollard et al. 1996; Smith et al. 1998; Compagno 2001). Exploitation, even at low levels for a slow-growing, late-maturing species that only produces two pups every other year, could reduce the population growth rate, could reduce the population growth rate to values of λ<1.0, resulting in severe population declines in a very short time period (Baum et al. 2003).
- Full Text:
- Date Issued: 2007
- Authors: Dicken, Matthew L , Booth, Anthony J , Smale, Malcolm J , Cliff, G
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/126997 , vital:35942 , https://doi.10.1071/MF06018
- Description: Crucial to effective fisheries management is a thorough understanding of the stock structure of a population. Understanding the spatial and seasonal distribution patterns of a species is necessary to define habitat use and evaluate the potential effects of exploitation and anthropogenic activities. This is particularly important for a species such as the raggedtooth shark (Carcharias Taurus Rafinesque, 1810), whose life-history characteristics make it particularly susceptible to over-exploitation (Pollard et al. 1996; Smith et al. 1998; Compagno 2001). Exploitation, even at low levels for a slow-growing, late-maturing species that only produces two pups every other year, could reduce the population growth rate, could reduce the population growth rate to values of λ<1.0, resulting in severe population declines in a very short time period (Baum et al. 2003).
- Full Text:
- Date Issued: 2007
Spatial patterns in the biology of the chokka squid, Loligo reynaudii on the Agulhas Bank, 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: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127053 , vital:35947 , https://doi.10.1007/s11160-006-9027-5
- Description: Although migration patterns for various life history stages of the chokka squid (Loligo reynaudii) have been previously presented, there has been limited comparison of spatial variation in biological parameters. Based on data from research surveys; size ranges of juveniles, subadults and adults on the Agulhas Bank were estimated and presented spatially. The bulk of the results appear to largely support the current acceptance of the life cycle with an annual pattern of squid hatching in the east, migrating westwards to offshore feeding grounds on the Central and Western Agulhas Bank and the west coast and subsequent return migration to the eastern inshore areas to spawn. The number of adult animals in deeper water, particularly in autumn in the central study area probably represents squid spawning in deeper waters and over a greater area than is currently targeted by the fishery. The distribution of life history stages and different feeding areas does not rule out the possibility that discrete populations of L. reynaudii with different biological characteristics inhabit the western and eastern regions of the Agulhas Bank. In this hypothesis, some mixing of the populations does occur but generally squid from the western Agulhas Bank may occur in smaller numbers, grow more slowly and mature at a larger size. Spawning occurs on the western portion of the Agulhas Bank, and juveniles grow and mature on the west coast and the central Agulhas Bank. Future research requirements include the elucidation of the age structure of chokka squid both spatially and temporally, and a comparison of the statolith chemistry and genetic characterization between adults from different spawning areas across the Agulhas Bank.
- Full Text:
- Date Issued: 2007
- Authors: Olyott, L J H , Sauer, Warwick H H , Booth, Anthony J
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127053 , vital:35947 , https://doi.10.1007/s11160-006-9027-5
- Description: Although migration patterns for various life history stages of the chokka squid (Loligo reynaudii) have been previously presented, there has been limited comparison of spatial variation in biological parameters. Based on data from research surveys; size ranges of juveniles, subadults and adults on the Agulhas Bank were estimated and presented spatially. The bulk of the results appear to largely support the current acceptance of the life cycle with an annual pattern of squid hatching in the east, migrating westwards to offshore feeding grounds on the Central and Western Agulhas Bank and the west coast and subsequent return migration to the eastern inshore areas to spawn. The number of adult animals in deeper water, particularly in autumn in the central study area probably represents squid spawning in deeper waters and over a greater area than is currently targeted by the fishery. The distribution of life history stages and different feeding areas does not rule out the possibility that discrete populations of L. reynaudii with different biological characteristics inhabit the western and eastern regions of the Agulhas Bank. In this hypothesis, some mixing of the populations does occur but generally squid from the western Agulhas Bank may occur in smaller numbers, grow more slowly and mature at a larger size. Spawning occurs on the western portion of the Agulhas Bank, and juveniles grow and mature on the west coast and the central Agulhas Bank. Future research requirements include the elucidation of the age structure of chokka squid both spatially and temporally, and a comparison of the statolith chemistry and genetic characterization between adults from different spawning areas across the Agulhas Bank.
- Full Text:
- Date Issued: 2007
Maximum likelihood and Bayesian approaches to stock assessment when data are questionable
- Booth, Anthony J, Quinn II, T J
- Authors: Booth, Anthony J , Quinn II, T J
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6764 , http://hdl.handle.net/10962/d1007962
- Description: This study examines the use of age-structured maximum likelihood and Bayesian approaches for stock assessment of the Namibian monkfish, Lophius vomerinus, resource with questionable data, in which time series are short, abundance indices are variable, and research data conflict with commercial data. Bayesian approaches with both noninformative and informative priors are investigated to determine if they enhance estimation stability. Three data scenarios are assessed: commercial and research survey data, research survey data only, and commercial data only. Both statistical approaches show that resource abundance has decreased with exploitable biomass estimated at approximately 44% of pristine levels. The maximum likelihood and the Bayesian approach with noninformative priors result in similar estimates. As the abundance data contained little information pertaining to possible density dependence within the stock–recruit relationship, only a Bayesian approach with informative priors reduces uncertainty in the steepness parameter h. Estimated management quantities are sensitive both to the set of data sources and whether prior information was informative or not. The strengths of the Bayesian approach include the integration of prior information with uncertain data, the exploration of data conflicts, and the ability to show the uncertainty in estimates of management parameters. Its weakness is that estimation stability is dependent on the choice of priors, which alters some posterior distributions of management quantities.
- Full Text:
- Date Issued: 2006
- Authors: Booth, Anthony J , Quinn II, T J
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6764 , http://hdl.handle.net/10962/d1007962
- Description: This study examines the use of age-structured maximum likelihood and Bayesian approaches for stock assessment of the Namibian monkfish, Lophius vomerinus, resource with questionable data, in which time series are short, abundance indices are variable, and research data conflict with commercial data. Bayesian approaches with both noninformative and informative priors are investigated to determine if they enhance estimation stability. Three data scenarios are assessed: commercial and research survey data, research survey data only, and commercial data only. Both statistical approaches show that resource abundance has decreased with exploitable biomass estimated at approximately 44% of pristine levels. The maximum likelihood and the Bayesian approach with noninformative priors result in similar estimates. As the abundance data contained little information pertaining to possible density dependence within the stock–recruit relationship, only a Bayesian approach with informative priors reduces uncertainty in the steepness parameter h. Estimated management quantities are sensitive both to the set of data sources and whether prior information was informative or not. The strengths of the Bayesian approach include the integration of prior information with uncertain data, the exploration of data conflicts, and the ability to show the uncertainty in estimates of management parameters. Its weakness is that estimation stability is dependent on the choice of priors, which alters some posterior distributions of management quantities.
- Full Text:
- Date Issued: 2006
Predictor variables for moggel (Labeo umbratus) biomass and production in small South African reservoirs
- Potts, Warren M, Booth, Anthony J, Hecht, Thomas, Andrew, Timothy G
- Authors: Potts, Warren M , Booth, Anthony J , Hecht, Thomas , Andrew, Timothy G
- Date: 2006
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125763 , vital:35815 , https://doi.10.2989/16085910609503877
- Description: South Africa has approximately 3 100 registered reservoirs, ranging in size from 1–1 000 hectares, with a surface area totalling 84 439 hectares (SADC Surface Water Body Database, unpublished data). Within southern and eastern Africa, Lindqvist (1994) estimated the number of small reservoirs to be between 50 000 and 100 000. Given Bernacsek’s (1986) estimate of the total fishery potential of small reservoirs in Africa at between 1 and 2.3 million tons, this number of reservoirs clearly could provide fishery opportunities for rural communities.
- Full Text:
- Date Issued: 2006
- Authors: Potts, Warren M , Booth, Anthony J , Hecht, Thomas , Andrew, Timothy G
- Date: 2006
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125763 , vital:35815 , https://doi.10.2989/16085910609503877
- Description: South Africa has approximately 3 100 registered reservoirs, ranging in size from 1–1 000 hectares, with a surface area totalling 84 439 hectares (SADC Surface Water Body Database, unpublished data). Within southern and eastern Africa, Lindqvist (1994) estimated the number of small reservoirs to be between 50 000 and 100 000. Given Bernacsek’s (1986) estimate of the total fishery potential of small reservoirs in Africa at between 1 and 2.3 million tons, this number of reservoirs clearly could provide fishery opportunities for rural communities.
- Full Text:
- Date Issued: 2006
Preliminary observations of tag shedding, tag reporting, tag wounds, and tag biofouling for raggedtooth sharks (Carcharias taurus) tagged off the east coast of South Africa
- Dicken, Matthew Laurence, Booth, Anthony J, Smale, Malcolm John
- Authors: Dicken, Matthew Laurence , Booth, Anthony J , Smale, Malcolm John
- Date: 2006
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125774 , vital:35816 , https://doi.10.1016/j.icesjms.2006.06.009
- 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: 2006
- Authors: Dicken, Matthew Laurence , Booth, Anthony J , Smale, Malcolm John
- Date: 2006
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125774 , vital:35816 , https://doi.10.1016/j.icesjms.2006.06.009
- 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: 2006
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.
- Full Text:
- Date Issued: 2006
Marine Reserves: a guide to science, design, and use
- Authors: Booth, Anthony J
- Date: 2005
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124965 , vital:35714 , https://doi.10.2989/16085910509503862
- Description: With the considerable pressures that are being placed on our marine resources, there is an urgent need to find alternative strategies to ensure their long-term sustainability. One measure that has been proposed, and which is rapidly gaining popularity, is the designation of Marine Protected Area (MPA). These are demarcated areas that prohibit (or at least restrict) consumptive or extractive uses, such that human interferences and impacts are minimised. In this edited collection of papers, most of which have been written or co-written by the authors themselves, Sobel and Dahlgren have presented an excellent synopsis of the rationale behind, and the scientific basis underpinning, the use of marine reserves as a management tool. In addition, they have devoted half the book to the provision of case studies.
- Full Text:
- Date Issued: 2005
- Authors: Booth, Anthony J
- Date: 2005
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124965 , vital:35714 , https://doi.10.2989/16085910509503862
- Description: With the considerable pressures that are being placed on our marine resources, there is an urgent need to find alternative strategies to ensure their long-term sustainability. One measure that has been proposed, and which is rapidly gaining popularity, is the designation of Marine Protected Area (MPA). These are demarcated areas that prohibit (or at least restrict) consumptive or extractive uses, such that human interferences and impacts are minimised. In this edited collection of papers, most of which have been written or co-written by the authors themselves, Sobel and Dahlgren have presented an excellent synopsis of the rationale behind, and the scientific basis underpinning, the use of marine reserves as a management tool. In addition, they have devoted half the book to the provision of case studies.
- Full Text:
- Date Issued: 2005
Reproductive biology of ningu, Labeo victorianus (pisces: cyprinidae), in the kagera and Sio rivers, Uganda
- Rutaisire, Justus, Booth, Anthony J
- Authors: Rutaisire, Justus , Booth, Anthony J
- Date: 2005
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125864 , vital:35827 , https://doi.10.1007/s10641-004-5564-8
- Description: We investigated aspects of the reproductive biology of the cyprinid fish, Labeo victorianus, locally known as ningu, in the Kagera and Sio Rivers, Uganda. These rivers represent the last remaining refuges for this species within Uganda. L. victorianus is a highly fecund, potamodrometic fish that migrates upstream to spawn. Spawning is generally synchronised with the bimodal water level maxima observed within the rivers. There were, however, some deviations from this pattern. We caught sexually mature fish throughout the year in the Sio River, and noticed that spawing started before the second rainfall peak. Fish from the Kagera matured at significantly larger sizes than fish from the Sio River. Male and female fish, from both rivers, fed intensively during the non-breeding months accumulating significant fat reserves; a probable energy storage mechanism prior to their spawning migrations. The differences between the populations is probably a phenotypic response to differing abiotic factors such as river size, flow velocity and food availability.
- Full Text:
- Date Issued: 2005
- Authors: Rutaisire, Justus , Booth, Anthony J
- Date: 2005
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125864 , vital:35827 , https://doi.10.1007/s10641-004-5564-8
- Description: We investigated aspects of the reproductive biology of the cyprinid fish, Labeo victorianus, locally known as ningu, in the Kagera and Sio Rivers, Uganda. These rivers represent the last remaining refuges for this species within Uganda. L. victorianus is a highly fecund, potamodrometic fish that migrates upstream to spawn. Spawning is generally synchronised with the bimodal water level maxima observed within the rivers. There were, however, some deviations from this pattern. We caught sexually mature fish throughout the year in the Sio River, and noticed that spawing started before the second rainfall peak. Fish from the Kagera matured at significantly larger sizes than fish from the Sio River. Male and female fish, from both rivers, fed intensively during the non-breeding months accumulating significant fat reserves; a probable energy storage mechanism prior to their spawning migrations. The differences between the populations is probably a phenotypic response to differing abiotic factors such as river size, flow velocity and food availability.
- Full Text:
- Date Issued: 2005
Evolution of Labeo victorianus predates the Pleistocene desiccation of Lake Victoria: evidence from mitochondrial DNA sequence variation
- Rutaisire, Justus, Booth, Anthony J, Masembe, C, Nyakaana, S, Muwanika, V B
- Authors: Rutaisire, Justus , Booth, Anthony J , Masembe, C , Nyakaana, S , Muwanika, V B
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6762 , http://hdl.handle.net/10962/d1007924
- Description: Geological data show that Lake Victoria dried out some 15 000 years ago. These data suggest that the entire faunal diversity within the lake has evolved since this time. However, mitochondrial DNA sequence diversity in the endemic cyprinid fish, Labeo victorianus, was high (24 haplotypes in 38 individuals; percentage sequence divergence of 0.74%), suggesting that the evolution of this species predates this Late Pleistocene climatological event. This finding is consistent with what has been reported earlier for cichlid fishes in the lake.
- Full Text:
- Date Issued: 2004
- Authors: Rutaisire, Justus , Booth, Anthony J , Masembe, C , Nyakaana, S , Muwanika, V B
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6762 , http://hdl.handle.net/10962/d1007924
- Description: Geological data show that Lake Victoria dried out some 15 000 years ago. These data suggest that the entire faunal diversity within the lake has evolved since this time. However, mitochondrial DNA sequence diversity in the endemic cyprinid fish, Labeo victorianus, was high (24 haplotypes in 38 individuals; percentage sequence divergence of 0.74%), suggesting that the evolution of this species predates this Late Pleistocene climatological event. This finding is consistent with what has been reported earlier for cichlid fishes in the lake.
- Full Text:
- Date Issued: 2004
Induced ovulation, spawning, egg incubation, and hatching of the cyprinid fish Labeo victorianus in captivity
- Rutaisire, Justus, Booth, Anthony J
- Authors: Rutaisire, Justus , Booth, Anthony J
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124789 , vital:35697 , https://doi.10.1111/j.1749-7345.2004.tb00102.x
- Description: Ningu Lubeo victorianus is the only labeine fish within Lake Victoria and its catchment (Greenwood 1966; Reid 1985). This species, once widely distributed in the Lake Victoria basin and supporting a commercial fishery until the late 195Os, has declined due to overfishing (Cadwalladr 1965; Ogutu-Ohwayo 1990; Seehausen 1996). The L. victorianus fishery has not only collapsed but the species has also disappeared from some of its former habitats. Recent surveys in Uganda have only found two distant populations-one in the Sio River on the Uganda-Kenya border (0” I3’53”N, 34”00’30’E), and the second in the Kagera River on the Uganda-Tanzania border (0°56’28.1”S, 3 1’46’ 18”E) (Rutaisire 2003) (Fig. 1). Currently, there is growing interest to breed the fish for wild stock enhancement and culture as a food fish.
- Full Text:
- Date Issued: 2004
- Authors: Rutaisire, Justus , Booth, Anthony J
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124789 , vital:35697 , https://doi.10.1111/j.1749-7345.2004.tb00102.x
- Description: Ningu Lubeo victorianus is the only labeine fish within Lake Victoria and its catchment (Greenwood 1966; Reid 1985). This species, once widely distributed in the Lake Victoria basin and supporting a commercial fishery until the late 195Os, has declined due to overfishing (Cadwalladr 1965; Ogutu-Ohwayo 1990; Seehausen 1996). The L. victorianus fishery has not only collapsed but the species has also disappeared from some of its former habitats. Recent surveys in Uganda have only found two distant populations-one in the Sio River on the Uganda-Kenya border (0” I3’53”N, 34”00’30’E), and the second in the Kagera River on the Uganda-Tanzania border (0°56’28.1”S, 3 1’46’ 18”E) (Rutaisire 2003) (Fig. 1). Currently, there is growing interest to breed the fish for wild stock enhancement and culture as a food fish.
- Full Text:
- Date Issued: 2004
Spatial aspects of the reproductive and feeding biology of the striped robber, Brycinus lateralis (Pisces: Characidae), in the Okavango Delta, Botswana
- Booth, Anthony J, McKinlay, Bruce W
- Authors: Booth, Anthony J , McKinlay, Bruce W
- Date: 2001
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127020 , vital:35944 , https://doi.10.1080/15627020.2001.11657111
- Description: The Okavango Delta is a vast inland wetland system situated in northern Botswana. High rainfall is received in early summer in the southern Angolan highlands and throughout the Delta with the flood waters reaching the upper riverine floodplain between March and May where it percolates through to the lower drainage rivers between July and September. Aspects of the reproductive and feeding biology of two allopatric populations of the striped robber, Brycinus lateralis, a small characin species inhabiting the northern riverine floodplain and southern drainage rivers, were investigated. Both populations were similar in the biological aspects studied, with the flood cycle having little influence on the timing of reproduction, sexual maturity and dietary composition. Female fish from both populations matured sexually at 57mmSL, breeding over a protracted period during the warm, summer months. In both populations, the sex ratio was female-dominated at 4.8:1 (riverine floodplain) and 2.2:1 (drainage rivers). The striped robber is an opportunistic micro-carnivore with immature fish feeding predominantly on Daphnia spp. and adults being largely insectivorous.
- Full Text:
- Date Issued: 2001
- Authors: Booth, Anthony J , McKinlay, Bruce W
- Date: 2001
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127020 , vital:35944 , https://doi.10.1080/15627020.2001.11657111
- Description: The Okavango Delta is a vast inland wetland system situated in northern Botswana. High rainfall is received in early summer in the southern Angolan highlands and throughout the Delta with the flood waters reaching the upper riverine floodplain between March and May where it percolates through to the lower drainage rivers between July and September. Aspects of the reproductive and feeding biology of two allopatric populations of the striped robber, Brycinus lateralis, a small characin species inhabiting the northern riverine floodplain and southern drainage rivers, were investigated. Both populations were similar in the biological aspects studied, with the flood cycle having little influence on the timing of reproduction, sexual maturity and dietary composition. Female fish from both populations matured sexually at 57mmSL, breeding over a protracted period during the warm, summer months. In both populations, the sex ratio was female-dominated at 4.8:1 (riverine floodplain) and 2.2:1 (drainage rivers). The striped robber is an opportunistic micro-carnivore with immature fish feeding predominantly on Daphnia spp. and adults being largely insectivorous.
- Full Text:
- Date Issued: 2001
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, Alan K
- Authors: Maree, R C , Booth, Anthony J , Whitfield, Alan 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, Alan 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