Tracking the decline of the world’s largest seabream against policy adjustments
- Authors: Kerwath, Sven E , Parker, Denham , Winker, A Henning , Potts, Warren M , Mann, Bruce Q , Wilke, Christopher , Attwood, Colin G
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/131433 , vital:36571 , https://doi.org/10.3354/meps12853
- Description: For most rare marine species, abundance trends are poorly estimated. This uncertainty often translates into disagreement on management regulations, impeding conservation efforts when they are most urgently required. The world’s largest sea bream, the red steenbras Petrus rupestris, has undergone a substantial and widely acknowledged decline during the 20th century. Standardised probability of encounter over the last 3 decades was used to track red steenbras abundance trajectories in 2 regions, which together represent the species’ distribution. The results predicted a reduction in abundance of 44% in the East region and 96% in the South-West region, from what was already considered to be a collapsed population at the start of the time series. The species is now largely confined to areas in the centre of its historical abundance. Content analysis of a recreational angling magazine revealed a concurrent 50% decrease in reported size between 1984 and 2012. Shore-based observer data (2009-2010) indicate that the impact of recreational fishers on this species far exceeded that of commercial fishers at the time. Regulations in the form of progressively more stringent catch and effort restrictions appear to have been largely ineffective, too lenient, implemented too late or were unsuitable to control fishing mortality for this species. This study highlights 2 fundamental challenges in management of rare marine fish species: (1) providing decision makers with a credible measure of abundance for species whose rarity limits data availability and (2) implementing effective policy changes before the specific measures become ineffective and obsolete.
- Full Text:
- Date Issued: 2019
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.
- Full Text:
- Date Issued: 2014
New possibilities for research on reef fish across the continental shelf of South Africa
- Authors: Bernard, Anthony T F , Götz, Albrecht , Parker, Daniel M , Heyns, Elodie R , Halse, Sarah J , Riddin, N A , Smith, M K S , Paterson, Angus W , Winker, A Henning , Fullwood, L , Langlois, T J , Harvey, E S
- Date: 2014
- Language: English
- Type: Article
- Identifier: vital:6971 , http://hdl.handle.net/10962/d1014566
- Description: [From introduction] Subtidal research presents numerous challenges that restrict the ability to answer fundamental ecological questions related to reef systems. These challenges are closely associated with traditional monitoring methods and include depth restrictions (e.g. safe diving depths for underwater visual census), habitat destruction (e.g. trawling), mortality of target species (e.g. controlled angling and fish traps), and high operating costs (e.g. remotely operated vehicles and large research vessels. Whereas many of these challenges do not apply or are avoidable in the shallow subtidal environment, the difficulties grow as one attempts to sample deeper benthic habitats. This situation has resulted in a paucity of knowledge on the structure and ecology of deep water reef habitats around the coast of South Africa and in most marine areas around the world. Furthermore, the inability to effectively survey deep water benthic environments has limited the capacity of researchers to investigate connectivity between shallow and deep water habitats in a standardised and comparable fashion.
- Full Text:
- Date Issued: 2014
Life history strategy and population characteristics of an unexploited riverine cyprinid, Labeo capensis, in the largest impoundment in the Orange River Basin
- Authors: Winker, A Henning , Weyl, Olaf L F , Booth, Anthony J , Ellender, Bruce R
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124910 , vital:35709 , https://doi.10.3377/004.047.0124
- Description: Common carp (Cyprinus carpio) is one of the world’s most widely introduced and established freshwater fishes (Casal 2006). The species is considered to be one of the eight most invasive freshwater fishes (Lowe et al. 2000) and worldwide, it accounts for most of the records of successful establishments and adverse ecological effects (Casal 2006; Kulhanek et al. 2011). This invasive success suggests that feral C. carpio is equipped with a set of adaptable life history attributes that allow it to successfully colonise a wide range of habitats (Koehn 2004; Zambrano et al. 2006; Britton et al. 2007). Where feral C. carpio occurs in high densities, it is often perceived as an invasive pest species (Sivakumaran et al. 2003; Brown and Walker 2004; Koehn 2004) because it can have severe impacts on habitat heterogeneity and biodiversity by increasing water turbidity through its bottom feeding behaviour, increasing nutrient availability, decreasing benthic and macrophyte density and diversity, altering zooplankton assemblages and decreasing endemic fish abundance (Zambrano et al. 2001; Khan 2003; Kulhanek et al. 2011). Within south-east Australia, for example, C. carpio comprises the largest proportion of the ichthyobiomass in the continent’s largest river system – the Murray–Darling Basin (Gehrke et al. 1995). As a consequence, serious concerns about its threat to endemic freshwater species (Koehn 2004) have prompted several of the most recent investigations into its life history (e.g. Sivakumaran et al. 2003; Smith and Walker 2004; Brown et al. 2005). Other potential threats posed also include competition with indigenous species and the spread of diseases and parasites (Dudgeon et al. 2006). In South Africa, for example, Asian tapeworm Bothriocephalus acheilognathi is now widely distributed in seven river systems and has infected eight novel cyprinid hosts due to the translocation of infected by C. carpio from a centralized aquaculture facility (Stadtlander et al. 2011).
- Full Text:
- Date Issued: 2012
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: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124921 , vital:35710 , https://doi.10.3377/004.048.0225
- Description: African sharptooth catfish Clarias gariepinus (Burchell, 1822) is a widely distributed fish that has now invaded water bodies in South America, Eastern Europe, Asia and South Africa (Cambray 2003). In South Africa it is native as far south as the Orange-Vaal river system, but inter-basin water transfer schemes (IBWTs), illegal stocking by anglers and from aquaculture has resulted in the establishment of extralimital populations in almost all river systems (van Rensburg et al. 2011). Within the Eastern Cape Province, C. gariepinus has invaded the Great Fish and Sundays rivers through IBWTs, that connect the Orange River to the Great Fish River and then to the Sundays River system which flows directly into Darlington Dam (Kadye & Booth 2013a) (Fig. 1). Soon after the completion of the IBWTs sharptooth catfish were recorded in Grassridge Dam in 1976 (Laurenson & Hocutt 1985), and later from Darlington Dam in 1981 (Scott et al. 2006). Although Cambray & Jubb (1977) are of the opinion that the species was translocated prior to the IBWT connection, there is now a permanent corridor between the Orange River and its receiving river systems that can facilitate the continued introduction of non-native Orange River fishes and other aquatic biota.
- Full Text:
- Date Issued: 2012
Life history and population dynamics of invasive common carp, Cyprinus carpio, within a large turbid African impoundment
- Authors: Winker, A Henning , Weyl, Olaf L F , Booth, Anthony J , Ellender, Bruce R
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124898 , vital:35708 , https://doi.10.1071/MF11054
- Description: Common carp (Cyprinus carpio) is one of the world’s most widely introduced and established freshwater fishes (Casal 2006). The species is considered to be one of the eight most invasive freshwater fishes (Lowe et al. 2000) and worldwide, it accounts for most of the records of successful establishments and adverse ecological effects (Casal 2006; Kulhanek et al. 2011). This invasive success suggests that feral C. carpio is equipped with a set of adaptable life history attributes that allow it to successfully colonise a wide range of habitats (Koehn 2004; Zambrano et al. 2006; Britton et al. 2007). Where feral C. carpio occurs in high densities, it is often perceived as an invasive pest species (Sivakumaran et al. 2003; Brown and Walker 2004; Koehn 2004) because it can have severe impacts on habitat heterogeneity and biodiversity by increasing water turbidity through its bottom feeding behaviour, increasing nutrient availability, decreasing benthic and macrophyte density and diversity, altering zooplankton assemblages and decreasing endemic fish abundance (Zambrano et al. 2001; Khan 2003; Kulhanek et al. 2011). Within south-east Australia, for example, C. carpio comprises the largest proportion of the ichthyobiomass in the continent’s largest river system – the Murray–Darling Basin (Gehrke et al. 1995). As a consequence, serious concerns about its threat to endemic freshwater species (Koehn 2004) have prompted several of the most recent investigations into its life history (e.g. Sivakumaran et al. 2003; Smith and Walker 2004; Brown et al. 2005). Other potential threats posed also include competition with indigenous species and the spread of diseases and parasites (Dudgeon et al. 2006). In South Africa, for example, Asian tapeworm Bothriocephalus acheilognathi is now widely distributed in seven river systems and has infected eight novel cyprinid hosts due to the translocation of infected by C. carpio from a centralized aquaculture facility (Stadtlander et al. 2011).
- Full Text:
- Date Issued: 2011
Quantifying the annual fish harvest from South Africa’s largest freshwater reservoir
- Authors: Ellender, Bruce R , Weyl, Olaf L F , Winker, A Henning , Booth, Anthony J
- Date: 2010
- Language: English
- Type: Article
- Identifier: vital:7149 , http://hdl.handle.net/10962/d1011852
- Description: South African inland fisheries are poorly developed and their contribution to near-shore communities is poorly understood. This study is the first comprehensive assessment of recreational and subsistence angling undertaken in an inland fishery in South Africa. The study was conducted on the 360 km2 Lake Gariep, South Africa’s largest freshwater reservoir. A total of 508 anglers were interviewed between February 2007 and January 2008. Of those interviewed, 67% were subsistence anglers and 33% recreational anglers. Catch per unit effort (CPUE) did not differ significantly between sectors. CPUE fluctuated seasonally, ranging between 0.37 (95% CI= 0.26 to 0.51) kg·angler-1·h-1 in winter and 0.88 (0.67 to 1.17) kg·angler- 1·h-1 in summer. The duration of a fishing day ranged from 5.99 (5.24 to 6.74) h in mid-winter to 7.26 (6.88 to 7.63) h in early summer. Expected end-of-day catch (CPUE × fishing-trip duration) ranged from 2.2 to 6.4 kg·angler-1·d-1 depending on the season. The number of anglers ranged from 22 (8 to 53) anglers·d-1 in June/July to 74 (25 to 176) anglers·d-1 in April. Total annual catch from the roving creel survey was estimated at 71.4 (57.4 to 91.4) t·yr-1. Another 7.5 t∙yr-1 were landed during recreational angling competitions. The resultant total catch divided by the lakeshore population equated to a per capita fish supply of 11.1 kg·yr-1. More than 70% of the catch was the alien invasive carp Cyprinus carpio and there was no evidence of overfishing. The fish resource of Lake Gariep is of significant recreational and subsistence value. As a result of the low fish price (ZAR5.72 ± 2.60·kg-1) subsistence fishing was considered a low-revenue activity that mainly augmented food security in lakeshore communities. The relatively high CPUE indicated that the fishery may be an important safety-net during periods when alternate sources of livelihoods are limited. Consequently, we recommend that the importance of angling to local communities needs to be taken into account when planning fisheries development and developing an inland fisheries policy
- Full Text:
- Date Issued: 2010
Validation of growth zone deposition in otoliths of two large endemic cyprinids in Lake Gariep, South Africa
- Authors: Winker, A Henning , Ellender, Bruce R , Weyl, Olaf L F , Booth, Anthony J
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/446812 , vital:74562 , https://doi.org/10.1080/15627020.2010.11657263
- Description: We tested the hypothesis that growth zones in the astericus otoliths of smallmouth yellowfish (Labeobarbus aeneus) and Orange River mudfish (Labeo capensis) were deposited annually. Two methods, fluorochrome marking and edge analysis of otoliths were used. For fluorochrome marking, specimens of both species were injected with 60 mg/kg fish mass oxytetracycline hydrochloride (OTC) and released into large earthen ponds under ambient conditions adjacent to Lake Gariep. Twenty-three L. aeneus and one L. capensis were recaptured 10–14 months later. Edge analysis was based on the optical interpretation of L. aeneus (n = 342) and L. capensis (n = 512) otolith margins collected between November 2006 and May 2008 from Lake Gariep. The frequency distribution of opaque margins over time was fitted using a binomial periodic regression. The estimated cycle length was not significantly different from a hypothesized 12 months for both species. The number of growth zones distal to the OTC mark was consistent with findings from the edge analysis, providing evidence that growth zones in astericus otoliths of both species can be interpreted as annuli.
- Full Text:
- Date Issued: 2010
A tropical/subtropical biogeographic disjunction in southeastern Africa separates two evolutionarily significant units of an estuarine prawn
- Authors: Teske, Peter R , Winker, A Henning , McQuaid, Christopher D , Barker, Nigel P
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/445407 , vital:74383 , https://doi.org/10.1007/s00227-009-1168-3
- Description: Recent phylogeographic research has indicated that biodiversity in the sea may be considerably greater than previously thought. However, the majority of phylogeographic studies on marine invertebrates have exclusively used a single locus (mitochondrial DNA), and it is questionable whether the phylogroups identified can be considered distinct species. We tested whether the mtDNA phylogroups of the southern African sandprawn Callianassa kraussi Stebbing (Decapoda: Thalassinidea) are also recovered using nuclear sequence data. Four mtDNA phylogroups were recovered that were each associated with one of South Africa’s four major biogeographic provinces. Three of these were poorly differentiated, but the fourth (tropical) group was highly distinct. The nuclear phylogeny recovered two major clades, one present in the tropical region and the other in the remainder of South Africa. Congruence between mitochondrial and nuclear DNA indicates that the species comprises two Evolutionarily Significant Units sensu Moritz (1994). In conjunction with physiological data from C. kraussi and morphological, ecological and physiological data from other species, this result supports the notion that at least some of the mtDNA phylogroups of coastal invertebrates whose distributions are limited.
- Full Text:
- Date Issued: 2009
Who uses the fishery resources in South Africa’s largest impoundment? Characterising subsistence and recreational fishing sectors on Lake Gariep
- Authors: Ellender, Bruce R , Weyl, Olaf L F , Winker, A Henning
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6778 , http://hdl.handle.net/10962/d1008088
- Description: The African Union’s prioritisation of inland fisheries as an investment area for poverty alleviation and regional economic development will require the development of management plans. These should be based on sound knowledge of the social dynamics of the resource users. In South Africa the social dynamics of resource users of inland fisheries have never been assessed. The purpose of this study was to assess the human dimensions of the anglers utilising the fishery in Lake Gariep, South Africa’s largest impoundment. The study was based on 357 first-time interviews conducted on the lakeshore between October 2006 and December 2007. Anglers were categorised as recreational (39%) or subsistence (61%) based on their residency, occupation, primary motivation for angling, mode of transport and gear use. Subsistence anglers were local (99%), residing within 10 km of the place where they were interviewed, while recreational anglers included both local resident and non-resident members. The racial composition of anglers was dependent on user group and differed significantly (p ≤ 0.05) from the demographic composition of the regional population. Recreational anglers were predominantly White (≥ 60% of interviews) and Coloured (≥ 25%), while 84% of subsistence anglers were Coloured and 16% Black African. Most recreational anglers had permanent employment or were pensioners while <30% of subsistence anglers were permanently employed. Most recreational users (82%) accessed the lake with their own vehicle while subsistence anglers mainly walked (63%) or used a bicycle (28%). Recreational interviewees either consumed (59%), sold (11%), gave away (10%) or released (20%) some of their catch. Subsistence anglers either ate their catch (53%) and/or sold (41%) their catch. Within the subsistence sector no anglers released fish after capture or gave some of the catch away. We conclude that this inland fishery contributes to the livelihood of the rural poor who use the lake on a subsistence basis and that recreational-angler based tourism may contribute to increased income and employment opportunities through related service industries.
- Full Text:
- Date Issued: 2009