Ecological niche modeling of the invasive potential of Nile tilapia Oreochromis niloticus in African river systems: concerns and implications for the conservation of indigenous congenerics
- Authors: Zengeya, Tsungai A , Robertson, Mark P , Booth, Anthony J , Chimimba, Christian T
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124341 , vital:35596 , https://doi.10.1007/s10530-012-0386-7
- Description: This study applied ecological niche models to determine the potential invasive range of Nile tilapia, Oreochromis niloticus, with a particular focus on river systems in southern Africa where it is now established and spreading. Computational tools such as niche models are useful in predicting the potential range of invasive species, but there are limitations to their application. In particular, models trained on native records may fail to predict the full extent of an invasion. This failure is often attributed to changes in either the niche of the invading species or the variables used to develop the models. In this study, we therefore evaluated the differences in the predictive power of models trained with different environmental variables, the effect of species range (native vs. introduced) on model performance and assessed whether or not there is evidence suggestive of a niche shift in Nile tilapia following its introduction. Niche models were constructed using Maxent and the degree of niche similarity was assessed using Schoener‘s index. Null models were used to test for significance. Model performance and niche conservatism varied significantly with variable selection and species range. This indicates that the environmental conditions available to Nile tilapia in its native and introduced ranges are not congruent. Nile tilapia exhibited broad invasive potential over most of southern Africa that overlaps the natural range of endemic congenerics. Of particular concern are areas which are free of exotic species but are now vulnerable due to the promotion of fish introductions mainly for aquaculture and sport fishing.
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- Date Issued: 2013
Movement patterns and habitat selection of invasive African sharptooth catfish
- 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.
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- Date Issued: 2013
Life-history characteristics of an age-validated established invasive African sharptooth catfish, Clarias gariepinus, population in a warm-temperate African impoundment
- Authors: Wartenberg, Reece , Weyl, Olaf L F , Booth, Anthony J , Winker, A Henning
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443542 , vital:74130 , https://hdl.handle.net/10520/EJC145790
- Description: It has been suggested that the invasive, omnivorous Clarias garipienus is capable of rapid invasions and long-term persistence in recently inhabited freshwater systems. To test this hypothesis, the life history of the established, extralimital Darlington Dam (33°10'31"S, 25°09'13"E) population was investigated. By counting post-fluorescent mark increments on otoliths from 21 chemically tagged wild fish recaptured 244-537 days later, the deposition of growth zones, comprising alternating opaque and translucent bands, was validated as annual. Examination of sectioned otoliths from 175 fish revealed that the oldest fish, two males of 840 and 1074 mm total length (TL), were 25 years old - 10 years older than previously described for any C. gariepinus population. The oldest female was 885 mm TL and 21 years old. Length-at-age was subsequently described using the von Bertalanffy growth model. Combined-sex growth was best described as Lt = 931.7 ( 1 - exp(-0.15(t +2.43))) mm TL. Total mortality (Z) was calculated using catch curve analysis and the Chapman and Robson estimator to be 0.35/yr. The presence of specimens 15 years and older indicates that these fish established quickly and supports the finding that mortality rates are low, which, in turn, suggests likely long-term population persistence.
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- Date Issued: 2014
Occurrence of larval fishes in a rocky shore-associated nursery area in temperate South Africa, with emphasis on temperature-related growth in dominant Sparidae
- Authors: Strydom, Nadine A , Booth, Anthony J , McLachlan, A
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125342 , vital:35774 , https://doi.10.2989/1814232X.2014.899269
- Description: Larval fishes were studied in Shark Bay on the warm, temperate south-east coast of South Africa. The bay is a small, shallow, subtidal area associated with a rocky shore. Sampling took place fortnightly for a period of one year (September 2004–August 2005) to assess composition, abundance and growth of fishes. The objectives of the study were to assess the extent of use of this habitat type by larvae throughout the year and to ascertain what temperature advantages this relatively warm habitat could have on growth of dominant species. A total of 10 fish families, represented by 16 taxa, was collected using a specially modified beach seine net (mesh aperture 500 μm). Shark Bay was utilised extensively by Diplodus capensis and Sarpa salpa and to a lesser extent by Clinus supercilious, Liza spp. and Mugil cephalus. Mean catch per unit effort (CPUE) of larvae was high (>500 larvae per net haul), peaking at ~7 500 larvae in a single haul that consisted mostly of postflexion-stage Sparidae. There was a weak, negative correlation (−0.24) between temperature and overall CPUE, which reflected either the seasonality or protracted nature of spawning by the species occurring in the bay. There was no significant difference in CPUE between the moon phases sampled on the spring tides in this study. Shark Bay was dominated by postflexionstage larvae, consisting in particular of species common to tide pools during the juvenile stage. Certain species were sampled for only short periods during the year. The year-round occurrence and high abundance of the two dominant species indicate that Shark Bay represents an important nursery habitat for the completion of the larval phase. These species exhibited exponential growth that lagged behind small increases in temperature, highlighting the importance of access to shallow, warm habitat that allows larval growth to increase, leading to earlier settlement into juvenile habitat and thereby reducing the pelagic larval duration.
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- Date Issued: 2014
Ocean warming affects the distribution and abundance of resident fishes by changing their reproductive scope
- Authors: Potts, Warren M , Booth, Anthony J , Richardson, Timothy J , Sauer, Warwick H H
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125352 , vital:35775 , https://doi.10.1007/s11160-013-9329-3
- Description: With ocean warming predicted globally, one of the mechanisms driving distributional shifts and changes in the abundance of resident fishes is reproductive output. The relationship between sea surface temperature and the reproductive activity of a eurythermic, resident coastal species, blacktail seabream Diplodus sargus capensis, was examined in the ‘‘ocean warming’’ hotspot of the northern Benguela. Reproductive activity was found to be restricted to periods when the water temperature dropped below 20 _C. A metadata analysis conducted on the D. sargus sub-species complex similarly showed that reproductive activity was restricted to temperatures between 15 and 20 _C, regardless of the range in ambient water temperature. Based on these findings and using satellite derived SST information, we examined D. s. capensis’s total and seasonal ‘‘reproductive scope’’ that is defined as either the area suitable for spawning each year or the duration of its potential spawning season at a fixed geographical locality, respectively. Trends were examined over the last three decades. Reproductive scope by area was found to be shrinking at a rate of 7 % per decade in southern Angola and expanding at a rate of 6 % per decade in northern Namibia. Reproductive scope by season decreased by 1.05 months per decade in Namibe, southern Angola and increased by 0.76 months per decade in Hentiesbaai, northern Namibia. Changes in reproductive scope may be a driving mechanism of distributional shifts in resident fishes, although the rate of the shifts is likely to be slow. More importantly, changes in reproductive scope will not be uniform throughout fish distributions and will most likely result in heterogeneous variations in fish abundance.
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- Date Issued: 2014
Ocean warming, a rapid distributional shift, and the hybridization of a coastal fish species
- Authors: Potts, Warren M , Henriques, Romina , Santos, Carmen V D , Munnik, Kate , Ansorge, Isabelle J , Dufois, Francois , Sauer, Warwick H H , Booth, Anthony J , Kirchner, Carola , Sauer, Warwick , Shaw, Paul W
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125375 , vital:35777 , https://doi.10.1111/gcb.12612
- Description: Despite increasing awareness of large-scale climate-driven distribution shifts in the marine environment, no study has linked rapid ocean warming to a shift in distribution and consequent hybridization of a marine fish species. This study describes rapid warming (0.8 °C per decade) in the coastal waters of the Angola-Benguela Frontal Zone over the last three decades and a concomitant shift by a temperature sensitive coastal fish species (Argyrosomus coronus) southward from Angola into Namibia. In this context, rapid shifts in distribution across Economic Exclusive Zones will complicate the management of fishes, particularly when there is a lack of congruence in the fisheries policy between nations. Evidence for recent hybridization between A. coronus and a congener, A. inodorus, indicate that the rapid shift in distribution of A. coronus has placed adults of the two species in contact during their spawning events. Ocean warming may therefore revert established species isolation mechanisms and alter the evolutionary history of fishes. While the consequences of the hybridization on the production of the resource remain unclear, this will most likely introduce additional layers of complexity to their management.
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- Date Issued: 2014
Some life-history parameters of the non-native amphipod Platorchestia platensis (Talitridae) in a warm temperate South African estuary
- 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.
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- Date Issued: 2014
A description of gametogenesis in the panga Pterogymnus laniarius (Pisces: Sparidae) with comments on changes in maturity patterns over the past two decades
- Authors: Booth, Anthony J , Hecht, Thomas
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123542 , vital:35452 , https://doi.org/10.1080/02541858.1997.11448428
- Description: A description of gametogenesis in the panga Pferogymnus laniarius, a common endemic seabream species inhabiting the Agulhas Bank, South Africa, is presented. After sexual maturity, oogenesis and spermatogenesis continued throughout the year and were found to be similar to these processes in other seabream species and teleosts in general. Analysis of maturity data over the past two decades revealed a significant change in both age and size-at-maturity, a response to fishing pressure.
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- Date Issued: 2015
Aspects of the biology and life history of largespot pompano, Trachinotus botla, in South Africa
- Authors: Parker, Daniel M , Booth, Anthony J
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123798 , vital:35499 , https://doi.10.1071/MF14029
- Description: Trachinotus botla is an important recreational surf zone-dependent fish species distributed in the Indo-west Pacific from South Africa to Australia. In South Africa it is restricted to the northern KwaZulu-Natal coast. Biological investigations revealed that it is a fast growing species that attains a maximum age of, 7 years. Males and females sexually matured in their third year. It has a protracted summer spawning season with evidence of serial spawning behaviour. T. botla is an opportunistic predator with a generalist diet, with fish feeding on a wide variety of prey items particularly those that are temporally ‘superabundant’. Small fish fed predominantly on copepods and terrestrial insects, whereas larger fish consumed bivalves and crabs. Teleosts, primarily engraulids, were important components to the diet of fish of all sizes. An ontogenetic dietary shift was observed just after sexual maturity (300-mm fork length) that is possibly linked to a change in habitat preference with larger fish foraging on deeper reefs.
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- Date Issued: 2015
Seasonality, behaviour and philopatry of spotted ragged tooth sharks Carcharias taurus in Eastern Cape nursery areas, South Africa
- Authors: Smale, Malcolm J , Dicken, Matthew L , Booth, Anthony J
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/126672 , vital:35910 , https://doi.10.2989/1814232X.2015.1043342
- Description: Spotted ragged-tooth sharks Carcharias taurus occur along the southern and eastern coasts of South Africa. We report on movements of juveniles and adults within a known nursery area on the Eastern Cape coast using acoustic telemetry. The focus area of the study was Algoa Bay, where six VEMCO VR2 ultrasonic receivers were placed at known shark aggregation sites. An additional receiver was placed at Thunderbolt Reef, approximately 2 km southwest of Cape Recife, the south-western tip of Algoa Bay. Single receivers were also deployed at Port Alfred and East London, some 45 and 170 km north-east of Algoa Bay, respectively. VEMCO acoustic V16 tags were either surgically implanted (n = 37) or attached externally using dart heads (n = 6) between January 2003 and March 2006. Surgically implanted tags were recorded over multiple months and years, whereas external tags were probably lost shortly after tagging because they were detected for very short periods. Sharks moved extensively between the sites and revisited monitored reefs over time-periods of months and years, demonstrating philopatry. Departures from and arrivals at reefs were more frequently recorded at sunset and sunrise, respectively. Sharks were detected throughout the year but they spent more time at aggregation sites during summer and autumn, indicating seasonal abundance in agreement with previous findings. Movements away from study reefs were attributed to either foraging or movements to other reefs. Despite extensive movements around the bay and beyond, both juveniles and adults exhibited philopatry to the study area over multiple years.
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- Date Issued: 2015
Pessimistic assessment of white shark population status in South Africa: comment on Andreotti et al.(2016)
- 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.
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- Date Issued: 2017
An endangered seahorse selectively chooses an artificial structure
- Authors: Claassens, Louw , Booth, Anthony J , Hodgson, Alan N
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123718 , vital:35486 , https://doi.10.1007/s10641-018-0732-4
- Description: The development of a residential marina estate within the Knysna estuary, South Africa, introduced Reno mattresses (horizontal wire cages filled with rocks) as a novel habitat for the endangered Knysna seahorse Hippocampus capensis. Consistently high seahorse densities on these artificial structures, despite the availability of seagrass habitat, begged the question of whether this habitat was chosen by the seahorse in preference to natural vegetation. An in situ habitat choice experiment was conducted which focused on the choice made by adult H. capensis between natural vegetation (Zostera capensis) and artificial (Reno mattress) habitat within a choice chamber. Seahorses were significantly more likely to move away from Z. capensis onto a Reno mattress structure or remain on this structure. This study concludes that higher H. capensis densities on Reno mattresses within Thesen Islands Marina are owing to some positive feature of this habitat and the underlying processes responsible for the choice made by this species (additional food, holdfasts, protection) can now be investigated.
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- Date Issued: 2018
Environmental niche patterns of native and non-native fishes within an invaded African river system
- 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.
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- Date Issued: 2019