The biology of Tilapia rendalli and Oreochromis mossambicus (Pisces: Cichlidae) in a subtropical lake in Mozambique

This study of age and growth, reproduction and juvenile recruitment of Tilapia rendalli and Oreochromis mossambicus was undertaken in Lake Chicamba, a large, clear subtropical lake in central Mozambique. Sectioned otoliths were used to estimate age. Marginal zone analysis showed that annulus formation occurred during winter, in July and August. Maximum age estimates for T. rendalli and O. mossambicus were 16 and 10 years, respectively. Growth was described by the 3 parameter von Bertalanffy model as Lt = 238.74 (1-e-0,636(1 + 00905)) mm TL for T. rendalli and Lt = 266.06 (1-e-0 70904(1 + 0269)) mm TL for O. mossambicus. The length-at-50% maturity (Lm50) of male T. rendalli was 218 mm total lenglh (TL) and 205 mm TL in females. In O. mossambicus the Lm50 for males was 251 mm TL and for females 223 mm TL. Both species spawned throughout summer. Lake level was found to have no effect on spawning periodicity although recruitment was flood dependent

An assessment of recreational bank angling in the Free State Province, South Africa, using licence sale and tournament data

Recreational angling is an important form of utilisation of inland fisheries in South Africa but there is little information on this sector. The objective of this study was to provide an assessment of recreational bank angling in the Free State Province using licence sale and tournament data. During 2013 and 2014, 8 256 and 7 710 angling licences were sold, respectively. This represents a decline of 76% compared to the total licence sales in the Province in 1971. Tournament catch and effort data were obtained for 4 796 tournaments that were held on 17 dams from 1974 to 2014. Reported tournament effort decreased by 67% from 8 548 tournament days in 1998 to 2 828 days in 2014. Tournament catch composition was dominated by alien common carp Cyprinus carpio. Overall, this species comprised 81% of the weight and 77% of the number of fish landed during tournaments making it the most important angling species. The recent observed increase in subsistence angling could not be included in the analysis as participants are mostly not licensed. Alternative methods are therefore required if total catch and effort are to be estimated.Keywords: recreational, fisheries, catch, effort, participatio

Reconstructing the introduction history of an invasive fish predator in South Africa

The Largemouth Bass (Micropterus salmoides) is a global invader with demonstrated ecological impacts on native fish communities. Introductions of fishes in freshwater ecosystems are often characterized as complex processes, yet an understanding of the nature of the introduction can inform management and conservation actions. Early in the twentieth century, two introductions of Largemouth Bass were made into South Africa for the establishment of a recreational fishery, and subsequent translocations have expanded their distribution to include much of southern Africa. In this study we quantified neutral genetic variation, modelled potential introduction scenarios, and identified potential source regions from within the native range. We documented limited levels of genetic diversity in nuclear microsatellite genotypes across populations (mean allelic richness = 1.80 and mean observed heterozygosity = 0.16) and observed low levels of genetic differentiation among four of the five focal populations (mean pairwise fixation index = 0.09), with a fifth population displaying greater levels of genetic divergence (mean pairwise fixation index = 0.27). A total of three cytochrome b haplotypes were recovered from South Africa samples and the single most common haplotype (93% of individuals) was identical to a haplotype from a population of Largemouth Bass in Maryland, USA. Using limited available stocking data along with outputs from Principal Component Analysis and approximate Bayesian evaluation of competing introduction scenarios we confirm the presence of multiple introductions. Despite evidence for multiple introductions, Largemouth Bass in South African water bodies harbor extremely low neutral genetic diversity, suggesting that even a very limited number of propagules can experience a high likelihood of success in invading nonnative waters

A qualitative and quantitative analysis of historic commercial fisheries in the Free State Province in South Africa

There is a general lack of information on inland commercial fisheries in South Africa. The primary objective of this study was to provide a retrospective assessment of commercial fisheries in the Free State Province based on the assessment of catch data from fisheries operating for the period 1979–2014. Permits were issued for commercial operators on 11 dams but catch data were only available for Bloemhof, Kalkfontein, Gariep, Vaal, Erfenis, Rustfontein and Koppies Dams. A total of 9 036 t of fish were harvested over the 35-year period, equating to an average (± SE) of 282 ± 185 t·yr-1. Catch composition differed between dams but comprised mainly of common carp Cyprinus carpio and the Labeos, Labeo capensis and Labeo umbratus. Based on an assessment of the available catch data, the only successful fisheries that were sustained for more than 10 years were on Bloemhof Dam (mean ± S.E.: 201 ± 25 t·yr-1 since 1981) and Kalkfontein Dam, where 127 ± 30 t·yr-1 was harvested (by an operator from Bloemhof Dam). All other fisheries appear to have failed with individual enterprises lasting between 1 and 10 years and generally yielding less than 25 t·yr-1 when operational. Success at Bloemhof Dam appears to have been dependent on the ability to harvest > 100 t·yr-1 and the long-term fisheries experience of the operators.Keywords: commercial, fisheries, catch, rates, composition, qualitative, quantitative, analysi

Trophic interactions in an austral temperate ephemeral pond inferred using stable isotope analysis

Ephemeral ponds are vulnerable aquatic habitats which are difficult to protect given their dynamic nature and sensitivity to degradation during dry periods. Little information is available on these habitats in austral regions, with almost no information on food-web structure and complexity. The study aimed to assess trophic interactions among dominant organisms in an ephemeral pond food web, and investigate the importance of autochthonous and allochthonous carbon, using 13C and 15N isotopes. Results of the investigation suggest that the food web comprised four trophic levels, with the top predators being Notonectids (Notonecta sp.) and diving beetles (Cybister tripunctatus (Olivier)). Intermediary trophic levels comprised zooplankton (daphniids and copepodids), macroinvertebrates (e.g. micronectids and molluscs) and tadpoles. Generalist feeders dominated the higher trophic levels (>3) with specialists comprising the lower trophic levels (≤3). The consumers preferred autochthonous fine particulate organic matter, epiphyton and submerged macrophyte organic matter sources over allochthonous sources. Autochthonous organic matter was transferred to the food web via zooplankton and select macroinvertebrates including Micronecta sp. and Physa sp. The food-web structure within the pond appeared to reflect the secondary stage of trophic structural complexity in the evolution of ephemeral ponds over the course of their hydro-period

An assessment of the reproductive biology of the Marico barb Barbus motebensis from the upper Groot Marico catchment, South Africa

Barbus motebensis is endemic to the Groot Marico River catchment in the North West province, South Africa, and is considered of particular conservation importance due to being Red-Listed as Vulnerable. Due to its vulnerable conservation status, the aim of this study was to provide information on its condition factor, breeding season, gonadosomatic index, fecundity range and length at maturity from specimens collected by means of electrofishing and seine-netting between November 2012 and May 2014 from the Draaifonteinspruit and Kaaloog se Loop. Length at maturity was estimated as 37.5 mm TL for males and 44.5 mm TL for females. Microscopic gonad staging and gonadosomatic index demonstrated that B. motebensis has an extended breeding season from spring to summer. Relative (578 eggs g−1) and absolute (3 728 eggs) fecundity were relatively high for small barbs

Unexpected survival of sharptooth catfish Clarias gariepinus (Burchell 1822) during acute rotenone toxicity trials will complicate management of invasions

The sharptooth catfish Clarias gariepinus is an emerging global invader for which control strategies might include the use of piscicides such as rotenone. Experimental exposure demonstrated that C. gariepinus was less susceptible to rotenone than most other fish species, with unexpected survival observed at rotenone concentrations of 87.5 and 100 lg L-1. C. gariepinus were also observed exhibiting avoidance behaviour to rotenone treated water and were found to be capable of recovering from rotenone exposure. As such, effective eradication might not be attainable even at a dose exceeding 100 lg L-1 with exposures of longer than 24 h. This exposure scenario may pose an unacceptable risk to non-target fauna and highlights the difficulty associated with managing current and future invasions

Occupancy dynamics of rare cyprinids after invasive fish eradication

The eradication of invasive species is a management strategy implemented to eliminate adverse impacts of invaders on native species communities. After eradications, follow-up studies are done to confirm eradication of the invasive species and the short-term recovery of the native species, but long-term monitoring to confirm full population recovery and stability is often not completed. In this study, long-term monitoring of native fishes was carried out over 5 years after the eradication of an invasive fish from the Rondegat River, South Africa. Forty-six sites distributed along four river sections were sampled for presence/absence using underwater cameras and snorkel surveys. Density data were collected by snorkel surveys. Using multi-season occupancy models, the annual probability of colonization and local extinction of the native fishes and annual rate of change in occupancy along the river were estimated. Changes in native fish densities across time and across the control and treatment sections were analysed using Kruskal-Wallis analysis, followed by Dunn's post-hoc test. Probability of colonization and local extinction differed for each native fish species and may have been affected by extrinsic factors, such as rainfall, and intrinsic density-dependent factors, hypothesized from the density data. The occupancy rates of change revealed that the two Near Threatened fish species have reached an occupancy dynamic equilibrium but the Endangered fish has not, suggesting that other conservation efforts may be needed. Long-term monitoring of native fishes after an eradication programme has confirmed the successful removal of the invader and the recovery and stability of the community. However, successful eradication was not sufficient for full recovery of all species; additional conservation management strategies are needed to secure the population stability and persistence of endangered fishes. We recommend that eradication programmes, regardless of locality, should employ long-term monitoring to ensure full recovery of a native fish community

The abundance of an invasive freshwater snail Tarebia granifera (Lamarck, 1822) in the Nseleni River, South Africa

The invasive freshwater snail Tarebia granifera (Lamarck, 1822) was first reported in South Africa in 1999 and it has become widespread across the country, with some evidence to suggest that it reduces benthic macroinvertebrate biodiversity. The current study aimed to identify the primary abiotic drivers behind abundance patterns of T. granifera, by comparing the current abundance of the snail in three different regions, and at three depths, of the highly modified Nseleni River in KwaZulu-Natal, South Africa. Tarebia granifera was well established throughout the Nseleni River system, with an overall preference for shallow waters and seasonal temporal patterns of abundance. Although it is uncertain what the ecological impacts of the snail in this system are, its high abundances suggest that it should be controlled where possible and prevented from invading other systems in the region

Optimising invasive fish management in the context of invasive species legislation in South Africa

South Africa hosts a large number of non-native freshwater fishes that were introduced for various industries. Many of these species are now listed under the National Environmental Management: Biodiversity Act (NEM:BA) Alien and Invasive Species (A&IS) lists and regulations, though the practical options available to conservation agencies to effectively manage these fishes vary greatly among species and regions. Objectives & methods: We assessed the history and status of national legislation pertaining to invasive freshwater fishes, and the practical implications of the legislation for managing different species with contrasting distributions, impacts and utilisation value. Results: The smallmouth bass, despite being a potential conflict-generating species, is fairly straightforward to manage based on current legislation. Two species of trout, which remain absent from the NEM:BA A&IS lists because of ongoing consultation with stakeholders, continue to be managed in regions like the Western Cape province using existing provincial legislation. To maximise the limited capacity for management within conservation agencies, we proposed a decision-support tool that prioritises invasive fish populations that represent high environmental risk and low potential for conflict with stakeholders. Using three case studies, we demonstrated how the tool can be used to set management goals of 'eradicate', 'manage against impacts and further spread' and 'continue to monitor population' as the most pragmatic solutions given the state of an invasion, its socio-economic impact and the capacity of the responsible agency to act. Conclusion: By choosing a pragmatic management strategy, conservation agencies can maximise the effective deployment of limited resources, while minimising avoidable conflicts with stakeholders.EM201