A retrospective assessment of the Port Alfred linefishery with respect to the changes in the South African fisheries management environment
- Authors: Donovan, Bruce
- Date: 2013-07-18
- Subjects: Fishery management -- South Africa -- Port Alfred , Fisheries -- South Africa -- Port Alfred , South Africa. Marine & Coastal Management , Coastal zone management -- South Africa -- Port Alfred , Fishing -- South Africa -- Port Alfred , Fisheries -- Environmental aspects -- South Africa -- Port Alfred , Fish stock assessment -- South Africa -- Port Alfred , Fishing surveys -- South Africa -- Port Alfred , Marine fishes -- South Africa -- Port Alfred
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5353 , http://hdl.handle.net/10962/d1008298 , Fishery management -- South Africa -- Port Alfred , Fisheries -- South Africa -- Port Alfred , South Africa. Marine & Coastal Management , Coastal zone management -- South Africa -- Port Alfred , Fishing -- South Africa -- Port Alfred , Fisheries -- Environmental aspects -- South Africa -- Port Alfred , Fish stock assessment -- South Africa -- Port Alfred , Fishing surveys -- South Africa -- Port Alfred , Marine fishes -- South Africa -- Port Alfred
- Description: Since the study on the Port Alfred/Kenton-on-Sea/Boknes linefishery by Hecht and Tilney (1989) there have been substantive changes to the linefish management environment in South Africa. Using the Port Alfred linefishery as a model, the aim of this study was to evaluate the effectiveness of the linefish management regulations that were implemented by Marine and Coastal Management (MCM) since 1992, and to assess the behaviour and 'status' of the fishery in response to these changes. Changes to both the licensing structure and catch regulations have had a significant effect on the functioning of many aspects of the Port Alfred linefishery (fishing effort, catch composition, cpue) as well as on the structure of the fishery and its socio-economic profile. Overall commercial cpue decreased from 1985 to 1998. Since 1998 there has been a significant increase in cpue (from 2.3 Kg.fisher⁻¹ hour⁻¹ to a peak of 4.8 Kg.fisher⁻¹.hour⁻¹ in 2005. This was attributed to good catches of geelbek, particularly in 2005, 2007 and 2008 (during these years geelbek contributed an average of 35% to the total landings in comparison to a mean contribution of II % between 1985 and 2004). However, size spectra analysis suggests that the increase in overall cpue since 1998 misrepresents the actual status of the fishery. If geelbek is excluded from the analysis on the grounds that it is the only species in the fishery that is highly migratory, susceptible to recruitment fluctuations and it does not contribute to the catches on a year round basis, then the results suggest that the fishery is still in a declining phase despite the 80% reduction in commercial effort and numerous stricter catch regulations (e.g. size/bag limits). Furthermore, the cpue of silver kob, which has been the "mainstay" species of the fishery, has consistently declined over the last 23 year period (from 1.69 Kg.fisher⁻1 .hour1 in 1986 to 0.86 Kg.fisher⁻1.hour⁻1in 2007). The substantial reduction in commercial effort in the fishery from 33 vessels in 2001 to 13 in 2002 resulted in a shift from commercial to recreational fishing. The number of active commercial vessels in Port Alfred alone decreased from 29 in 1989 (Hecht 1993) to four in 2008. During the same timeframe, the number of regularly active recreational vessels had almost doubled (16 in 1989 to 26 in 2008). Despite the greater number of recreational boats in the fishery they only landed approximately half the average yearly tonnage of the commercial vessels (21,5 and 44,7 tonnes,annum-I , respectively) between 2006 and 2008, This was ascribed to the differences in catch regulations for the two sectors, Furthermore, it was speculated that increasing operating costs and narrowing profit margins have contributed to lower levels of compliance in both the commercial and recreational sectors since 2006, For example, 16% of silver kob landed during 2006-08 were under the minimum size, Despite the changes made to the regulations since 1998 and the 60,6% reduction In legislated commercial effort in the fishery between 2001 and 2002 it was concluded that the fishery has continued to decline, Except for the good recruitment of geelbek (which may be due to regulatory changes made in 1992) the changes in the management environment have had no measurable positive effect on this fishery, It is recommended that commercial effort should not be allowed to increase beyond the current number of active boats, that there should be an area restriction on all commerciallinefish vessels, that the current recreational bag limit for silver kob should be re-assessed, there should also be a concerted and nationally funded effort to educate recreational anglers about the merits of catch and release, and the frequency of catch inspections of both sectors should be increased, , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
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An investigation into the captive spawning, egg characteristics and egg quality of the mud crab (Scylla serrata) in South Africa
- Authors: Churchill, Giles John
- Date: 2004
- Subjects: Scylla serrata , Crabs -- South Africa , Scylla serrata -- South Africa , Crabs -- Eggs -- Incubation , Crabs -- Spawning
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5376 , http://hdl.handle.net/10962/d1015963
- Description: The source of a reliable supply of seed is one of the most important factors determining the success of aquaculture. At present mud crab culture is reliant on wild caught juveniles, which limits the expansion of mud crab farming globally. This, coupled with the paucity of knowledge of the spawning and egg characteristics of mud crabs, prompted the investigation into the captive spawning, incubation and egg quality of Scylla serrata in South Africa. A total of 112 mature females were caught from three estuaries in northern KwaZulu Natal and acclimated to captive conditions. Mature females were present in the estuaries throughout the year and ranged from 90 to 200 mm carapace width. Except for 40 crabs all the females spawned in captivity. On average spawning took place 38 ± 23 days after capture but was not dependent on crab size. Fecundity was significantly correlated to crab size (p = 0.026), with larger females producing more eggs. The average fecundity per batch was 5.79 ± 2.07 million eggs. Hatch success rate for all egg batches was high averaging 84 ± 6 %. Egg dropping occurred in all egg batches during incubation. On average 6.5 % of the egg mass was dropped during incubation. At the average temperature of 27⁰C eggs in the incubation system hatched within 292 ± 12 hours after extrusion. In-vitro incubation of eggs proved to be an ineffective means of incubating Scylla serrata eggs with a hatch success rate of only 25 ± 5 %. Egg quality was assessed both directly, using variables such as hatch success rate and hatch synchronicity and retrospectively by using stress tests and comparing survival of larvae from different coloured egg batches. Lipid class composition and fatty acid methyl ester content for 28 batches of eggs and 16 batches of larvae were analyzed. The biochemical composition of the egg was correlated to survival of larvae in the stress tests to ascertain if the lipid content of the eggs determines their quality. Stress tests were used to retrospectively assess egg quality. Four stressors were administered to newly hatched larvae and the LD50 values recorded. An average LD50 of 64 hours was recorded for the starvation tests, 40% for the salinity tests, 37 ppm for the formalin tests and 39.7 mg/l NH3 for the ammonia stress tests was recorded. Egg colour ranged from pale yellow to orange-red. Egg colour was not influenced by female size or the time the females spent in captivity prior to spawning. Egg colour can therefore not be used as an indicator of quality. The lipid profiles of newly extruded eggs had no effect on hatch synchronicity or hatch success rate. However, the stress tests identified female size (p ≤ 0.02), DHA content of the egg (p ≤ 0.02), Σ omega-3 fatty acids of eggs (p ≤ 0.02) and EPA content of eggs (p ≤ 0.007) as possible determinants of egg quality. Larger crabs tended to produce poorer quality eggs. Egg quality also decreased as the amount of DHA, EPA and the Σ omega-3 fatty acids decreased in the eggs. To summarize, the results of this study indicated that the following parameters affect egg quality - crab size, DHA, EPA and Σ omega-3 fatty acid content of eggs.
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Aspects of the biology of the doublesash butterflyfish, Chaetodon marleyi (Pisces: Chaetodontidae)
- Authors: Vine, Niall Gordon
- Date: 1998
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:21103 , http://hdl.handle.net/10962/6396
- Description: The doublesash butterflyfish, Chaetodon marleyi, indigenous to South Africa, is popular amongst marine aquarists. To provide a basis for the management of the species and assess its suitability for aquaculture, aspects of its biology were investigated. Specimens were collected between February 1996 and November 1997 from localities along the eastern Cape coastline of South Africa and from specimens in the RUSI fish collection. The dentition of C.marleyi is typical of non-coraline, benthic invertebrate feeding chaetodontids. The teeth are long, inwardly hooked and spatulate which allow easy grasping and manipulation of the prey. Stomach content analysis showed that the species fed predominantly on the tentacles of terebellid polychaetes with other polychaetes, crustaceans, hydro ids and ascideans contributing to the remainder of the diet. Juveniles had a larger volume of terebellid tentacles compared to adults which preyed more upon other polychaetes. The proximate composition (64.25% protein, 4.76% fat, 4.84% carbohydrate and 24.3 kJ/g total energy content) of the terebellid tentacles was determined suggesting a high energetic requirement of the fish or maximisation of feeding profit rates.
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A comparative study of the life histories of the sister species, Pseudobarbus afer and Pseudobarbus asper, in the Gamtoos River system, South Africa
- Authors: Cambray, James Alfred
- Date: 1993
- Subjects: Barbus -- Life cycles , Barbus -- Ecology -- South Africa -- Gamtoos River , Cyprinidae -- Life cycles , Cyprinidae -- Ecology -- South Africa -- Gamtoos River , Minnows -- Life cycles , Minnows -- Ecology -- South Africa -- Gamtoos River
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5375 , http://hdl.handle.net/10962/d1015730
- Description: This thesis explores the biology, ecology, and life-history styles of two closely-related redfin minnows, Pseudobarbus afer and P. asper (pisces; Cyprinidae), which both occur in the Gamtoos River system of South Africa. Five of the seven species of flexible-rayed redfin minnows are in the South African Red Data Book - Fishes. This investigation was designed to provide the data which would enable conservation authorities to manage the remaining populations of the Pseudobarbus species. A thorough understanding of the Gamtoos River system was necessary to properly interpret the findings of this study. The palaeo river systems and the changing climates since the break-up of Gondwanaland are discussed so that the present day environments could be considered as well as the past environmental changes. P. afer and P. asper occur in the Gamtoos River system with no physical barrier separating the two species. P. afer only occurs in the clear mountain streams of the Cape Fold Mountain Belt whereas P. asper occurs in the highly saline and turbid Karoo section of the system. P. afer were found to be the more precocial form of the sister species. They had bigger eggs, lower relative fecundity, shorter breeding season, lower gonadosomatic indices, larger first feeding larval fish, matured later and had a longer life-span than did P. asper, which had more altricial life-history attributes. They differ in their tradeoffs with P. asper devoting more resources earlier to reproduction and having a shorter lifespan. The improvement in the one aspect of fitness (early maturity) leads to the deterioration in another, namely lifespan. Both species undertake breeding migrations to riffle areas where they spawn in mid-channel immediately above a pool after an increase in water flow. P. afer and P. asper are non-guarders of their non-adhesive eggs and young, open substrate spawners on coarse substrates (rocks) and have photophobic free embryos. The breeding season is shorter for P. afer whereas P. asper can spawn as late as April and impoundment releases can induce them to spawn. A study of comparative neuroecology revealed that of the four groups of fish analyzed (males and females of both species) male P. afer had the largest brains, especially the optic lobes and cerebellum. P. asper females had the smallest brains. No neural compensation in the external gustatory centre, the facial lobe, was found for P. asper inhabiting the turbid waters. P. afer also had significantly larger eyes and longer barbels. P. afer males were also found to have the highest density and largest nuptial tubercles as well as the most pronounced breeding colouration. It was concluded that P. asper is the more derived of the sister species pair with regard to life-history attributes. It is further suggested that investment per offspring is important in determining the life-history trajectories. Paedomorphosis has occurred and by this mechanism variability has been restored to the redfin minnows in the Groot River which enables them to survive in the highly variable, intermittent Karoo stream. The more precocial P. afer do not require this variability in the more constant and predictable environment of the Wit River.
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A study of coeval sibling cannibalism in larval and juvenile fishes and its control under culture conditions
- Authors: Pienaar, Anthony Graham
- Date: 1990
- Subjects: Fishes -- Behavior , Fishes -- Larvae , Fish culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5781 , http://hdl.handle.net/10962/d1005469 , Fishes -- Behavior , Fishes -- Larvae , Fish culture
- Description: The primary objective of this study was to examine environmental parameters thought to affect cannibalism in certain fish species. It was found that environmental, behavioural, genetic and physiological factors all affect cannibalism in the species exhibiting the phenomenon. The diversity of factors nfluencing cannibalism served to illustrate the complexity of this behaviour pattern. Feeding to satiation was found to suppress cannibalism in catfish, trout and koi carp. High population densities were found to increase the rate of cannibalism, thereby acting as a population regulation mechanism for catfish, trout and the common and koi carps. Live food, as compared with dry pelletized feed was found to significantly suppress cannibalistic aggression. Catfish grown in total darkness, provided with refuges and living in turbid conditions were found to exhibit lowered cannibalistic and territorial aggression. Various lines of evidence suggested that cannibalism has a genetic basis, as was shown by the differences in cannibalistic behaviour of the two strains of Cyprinus carpio, viz. common and koi carp, with cannibalism being higher in the latter. This finding substantiates the hypothesis that cannibalism is genetically controlled and therefore open to evolutionary change. It is concluded that cannibalism is adaptive in times of food limitation, but that it is merely a by-product of normal feeding behaviour when food is abundant. Since cannibalism is advantageous and thus adaptive, the question arises ai to whether selection is occurring at the individual or the population level (or both). It was concluded that it is acting at the individual level, and that any benefits accruing at the population level iv were simply the effect of the initial cause, viz. individual selection. One of the aims of this study was to determine whether cannibalistic tendencies in fish are influenced by differing life history style trajectories. Based on the results of this study it is hypothesized that cannibalism is an r-selected trait. wi th the understanding gained from the knowl edge of the fundamental principles governing cannibalism, certain recommendations for its control in fish culture could be made. It is, however, imperative that further intensive studies be carried out to understand more fully this complex subject. General "rules" for regulating cannibalism could be helpful for any given cannibalistic species. However, in considering the differing life-history styles of each species, it becomes evident that species-specific guidelines need to be worked out. Until then, any suggestions for cannibalistic control offered to the aquaculturist can only serve as unrefined tools.
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