The optimisation of transportation methods for abalone (Haliotis midae Linnaeus, 1758 (Mollusca: Gastropoda)) larvae
- Authors: Bajaba, Sharone
- Date: 2021-02
- Subjects: Abalone fisheries , Haliotis midae , Abalone culture
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/20561 , vital:46124
- Description: Sea ranching has been identified as a viable method for enhancing the natural stock of overexploited abalone (Haliotis midae). Currently, this process involves transporting live juvenile H. midae to the seeding site where they are released onto the reef however this is both costly and logistically problematic. Transportation of abalone larvae is another cost-effective option, as they are cheaper to produce and can be transported at high densities. A suitable larval transport method is required to minimise larval mortalities and stresses that might compromise settlement. A series of simulated experiments were conducted to optimise transportation systems of abalone (Haliotis midae) larvae. First, two potential transportation modes (Wet (W) and Dry (D) transportation) conducted at a cooler (14˚C) and average ambient (18˚C) temperatures with six replicates of each were compared with control treatments (six replicates) that were not subjected to transport, kept in water at 18˚C. Eighty hours post-initial settlement, the 14W treatment had significantly lower settlement (p=0.03) than the other three treatments (14D, 18W, 18D) and the Control. The Dry method was the prefered method to transport larvae as it is logistically simpler to employ. The second experiment investigated the effect of different stocking densities (200, 400 and 800 larvae cm-2) for the Dry method 18˚C over two transit periods (six and twelve hours) on post-transport settlement and post-settlement survival of H. midae larvae. Compared to the control, there was no difference in the number of settled larvae (p=0.368) and larvae still swimming (p=0.835) across all treatments. This suggested that H. midae larvae can be transported for twelve hours at 800 larvae cm-2 without compromising post-transport settlement or survival. This study’s results and recommendations can be used by abalone farms when there is a need to move abalone H. midae larvae between farms or to seeding sites for sea ranching. Furthermore, other researchers can use these results as a benchmark for larval transportation studies of H. midae and other abalone species. , Thesis (MSc) (Zoology) -- University of Fort Hare, 2021
- Full Text:
- Date Issued: 2021-02
- Authors: Bajaba, Sharone
- Date: 2021-02
- Subjects: Abalone fisheries , Haliotis midae , Abalone culture
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/20561 , vital:46124
- Description: Sea ranching has been identified as a viable method for enhancing the natural stock of overexploited abalone (Haliotis midae). Currently, this process involves transporting live juvenile H. midae to the seeding site where they are released onto the reef however this is both costly and logistically problematic. Transportation of abalone larvae is another cost-effective option, as they are cheaper to produce and can be transported at high densities. A suitable larval transport method is required to minimise larval mortalities and stresses that might compromise settlement. A series of simulated experiments were conducted to optimise transportation systems of abalone (Haliotis midae) larvae. First, two potential transportation modes (Wet (W) and Dry (D) transportation) conducted at a cooler (14˚C) and average ambient (18˚C) temperatures with six replicates of each were compared with control treatments (six replicates) that were not subjected to transport, kept in water at 18˚C. Eighty hours post-initial settlement, the 14W treatment had significantly lower settlement (p=0.03) than the other three treatments (14D, 18W, 18D) and the Control. The Dry method was the prefered method to transport larvae as it is logistically simpler to employ. The second experiment investigated the effect of different stocking densities (200, 400 and 800 larvae cm-2) for the Dry method 18˚C over two transit periods (six and twelve hours) on post-transport settlement and post-settlement survival of H. midae larvae. Compared to the control, there was no difference in the number of settled larvae (p=0.368) and larvae still swimming (p=0.835) across all treatments. This suggested that H. midae larvae can be transported for twelve hours at 800 larvae cm-2 without compromising post-transport settlement or survival. This study’s results and recommendations can be used by abalone farms when there is a need to move abalone H. midae larvae between farms or to seeding sites for sea ranching. Furthermore, other researchers can use these results as a benchmark for larval transportation studies of H. midae and other abalone species. , Thesis (MSc) (Zoology) -- University of Fort Hare, 2021
- Full Text:
- Date Issued: 2021-02
A holistic approach in understanding the effects of dietary protein sources on the growth and reproductive development of farmed abalone, Haliotis midae
- Wu, Yu
- Authors: Wu, Yu
- Date: 2020
- Subjects: Abalones -- Nutrition , Abalones -- Reproduction , Abalones -- Growth , Abalone culture , Haliotis midae -- Nutrition , Haliotis midae -- Reproduction , Haliotis midae -- Growth , Haliotis midae fisheries
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167719 , vital:41506
- Description: The combination of fishmeal and soya in the formulated feed of farmed South African abalone, Haliotis midae, not only improved abalone growth, but also the sustainability of the compound diets by reducing the reliance on fishmeal. However, the presence of soya produced larger gonads compared to those of abalone fed kelp or single-source protein diets. There is an increasing drive to control sexual maturation and reduce undesirable spawning events in farmed abalone. However, the reasons for the reported effects of soya inclusion on the reproductive development of farmed H. midae remain unresolved. The aim of this research was to use a combination of techniques to contribute to the understanding of the relationship between growth, reproductive and nutritional physiology of farmed H. midae fed diets of varying protein sources. These techniques included stable isotope analysis (SIA), fatty acid analysis, gonad histological assessments and haemolymph sexsteroid hormone analysis. The objectives were to examine the allocation of protein and nutritional components to somatic and reproductive tissues. This study also included the first attempt to investigate the role that sex steroid hormones play during gametogenesis. Abalone (40 – 50 g abalone-1) were fed one of four diets: either a single-source protein-based diet, i.e., (1) fishmeal-only (FM) or (2) soya-only (S), or a combination diet of (3) fishmeal-soya (FM S) or (4) fishmeal-sunflower meal (FM SM). Sampling occurred in 45-day intervals over one year. Dietary protein source had an effect on the growth of abalone, with enhancements in growth linked to the combination of fishmeal and a plant-protein source. The fishmeal ingredient was the most utilised protein source throughout the temporal changes in protein allocation into somatic and reproductive tissue, followed by soya and then sunflower meal. The mean whole- body mass of abalone was significantly influenced by an interaction between time and dietary treatment, with average whole-body mass changing differently over time between treatments (RM-ANOVA, F(24, 96) = 2.13, p = 0.005). Overall, abalone that were fed FM S had higher mean whole-body mass values than abalone that were fed the single-protein based diets, while abalone that were fed FM SM were similar to animals from all dietary treatments (RMANOVA, F(3, 12) = 5.75, p = 0.01). Male abalone had significantly higher gonad bulk index (GBI) values compared to females (RM-ANOVA, F(1, 24) = 49.03, p < 0.001) and this was independent of dietary treatment. Within each sex, female abalone fed the FM S diet (15.92 ± 1.88 mm3 g-1) had significantly higher GBI values than abalone fed S (9.76 ± 1.08 mm3 g-1), while abalone fed FM (11.96 ± 1.71 mm3 g-1) and FM SM (11.90 ± 0.80 mm3 g-1) were similar to abalone from all other dietary treatments (Tukey’s HSD, p < 0.05). Male abalone fed the FM S (21.59 ± 2.10 mm3 g-1) and FM SM diet (19.30 ± 2.63 mm3 g-1) had similar GBI values and they were significantly higher than in abalone fed the S diet (14.74 ± 1.27 mm3 g-1), while abalone fed FM S had significantly higher GBI values than abalone that consumed the FM diet (15.08 ±1.63mm3 g-1) ( Tukey’s HSD, p < 0.05). Although sunflower meal was poorly utilised, it produced similar overall growth to abalone that were fed the FM S diets. Yet, feed conversion ratio values were significantly lower for abalone fed FM S (1.30 ± 0.13) compared to those in the other three treatments, with ratios ranging from 1.65 – 1.72 over the one-year. The fatty acid compositions of the somatic and gonadal tissues were similar between treatments (PERMANOVA, p = 0.21), while fatty acid composition was influenced by sampling day, tissue type and abalone sex (PERMANOVA, p < 0.05). The essential fatty acids (EFAs) eicosadienoic acid and a-linolenic acid were present in abalone tissue, but they were not detected in the diets, suggesting the important role that an alternate food source (e.g. farmed abalone also had access to diatoms) may have played and the ability that H. midae may have in converting long-chain polyunsaturated fatty acids from C18 precursors. A change in the abundance of EFAs in the gonad tissue during highest and lowest GBI values suggested that arachidonic, eicosapentaenoic, g-linolenic and linoleic acid were important in females, while eicosapentaenoic, eicosadienoic and a-linolenic acid were important for male reproductive development. Dietary protein sources had an effect on the frequency distribution of maturity stages, where females that were fed FM S produced more ripe gonads and more males that were fed FM SM contained testes that showed signs of ripeness over the one-year study. Although dietary protein influenced the sex steroid concentrations in females and males, exhibiting fluctuations throughout the one-year period, no distinct pattern linked to gametogenesis were observed. The results from this study illustrate: (1) the importance of conducting laboratory studies when implementing SIA and mixing models in aquaculture nutrition; (2) conducting nutritional studies on mature, grow-out abalone; and (3) assessing the importance of naturally occurring diatoms in their diet and their contribution to growth and reproduction. The novel contribution of this research towards abalone nutritional physiology, the implications of these findings to industry as well as potential considerations for future studies were addressed.
- Full Text:
- Date Issued: 2020
- Authors: Wu, Yu
- Date: 2020
- Subjects: Abalones -- Nutrition , Abalones -- Reproduction , Abalones -- Growth , Abalone culture , Haliotis midae -- Nutrition , Haliotis midae -- Reproduction , Haliotis midae -- Growth , Haliotis midae fisheries
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167719 , vital:41506
- Description: The combination of fishmeal and soya in the formulated feed of farmed South African abalone, Haliotis midae, not only improved abalone growth, but also the sustainability of the compound diets by reducing the reliance on fishmeal. However, the presence of soya produced larger gonads compared to those of abalone fed kelp or single-source protein diets. There is an increasing drive to control sexual maturation and reduce undesirable spawning events in farmed abalone. However, the reasons for the reported effects of soya inclusion on the reproductive development of farmed H. midae remain unresolved. The aim of this research was to use a combination of techniques to contribute to the understanding of the relationship between growth, reproductive and nutritional physiology of farmed H. midae fed diets of varying protein sources. These techniques included stable isotope analysis (SIA), fatty acid analysis, gonad histological assessments and haemolymph sexsteroid hormone analysis. The objectives were to examine the allocation of protein and nutritional components to somatic and reproductive tissues. This study also included the first attempt to investigate the role that sex steroid hormones play during gametogenesis. Abalone (40 – 50 g abalone-1) were fed one of four diets: either a single-source protein-based diet, i.e., (1) fishmeal-only (FM) or (2) soya-only (S), or a combination diet of (3) fishmeal-soya (FM S) or (4) fishmeal-sunflower meal (FM SM). Sampling occurred in 45-day intervals over one year. Dietary protein source had an effect on the growth of abalone, with enhancements in growth linked to the combination of fishmeal and a plant-protein source. The fishmeal ingredient was the most utilised protein source throughout the temporal changes in protein allocation into somatic and reproductive tissue, followed by soya and then sunflower meal. The mean whole- body mass of abalone was significantly influenced by an interaction between time and dietary treatment, with average whole-body mass changing differently over time between treatments (RM-ANOVA, F(24, 96) = 2.13, p = 0.005). Overall, abalone that were fed FM S had higher mean whole-body mass values than abalone that were fed the single-protein based diets, while abalone that were fed FM SM were similar to animals from all dietary treatments (RMANOVA, F(3, 12) = 5.75, p = 0.01). Male abalone had significantly higher gonad bulk index (GBI) values compared to females (RM-ANOVA, F(1, 24) = 49.03, p < 0.001) and this was independent of dietary treatment. Within each sex, female abalone fed the FM S diet (15.92 ± 1.88 mm3 g-1) had significantly higher GBI values than abalone fed S (9.76 ± 1.08 mm3 g-1), while abalone fed FM (11.96 ± 1.71 mm3 g-1) and FM SM (11.90 ± 0.80 mm3 g-1) were similar to abalone from all other dietary treatments (Tukey’s HSD, p < 0.05). Male abalone fed the FM S (21.59 ± 2.10 mm3 g-1) and FM SM diet (19.30 ± 2.63 mm3 g-1) had similar GBI values and they were significantly higher than in abalone fed the S diet (14.74 ± 1.27 mm3 g-1), while abalone fed FM S had significantly higher GBI values than abalone that consumed the FM diet (15.08 ±1.63mm3 g-1) ( Tukey’s HSD, p < 0.05). Although sunflower meal was poorly utilised, it produced similar overall growth to abalone that were fed the FM S diets. Yet, feed conversion ratio values were significantly lower for abalone fed FM S (1.30 ± 0.13) compared to those in the other three treatments, with ratios ranging from 1.65 – 1.72 over the one-year. The fatty acid compositions of the somatic and gonadal tissues were similar between treatments (PERMANOVA, p = 0.21), while fatty acid composition was influenced by sampling day, tissue type and abalone sex (PERMANOVA, p < 0.05). The essential fatty acids (EFAs) eicosadienoic acid and a-linolenic acid were present in abalone tissue, but they were not detected in the diets, suggesting the important role that an alternate food source (e.g. farmed abalone also had access to diatoms) may have played and the ability that H. midae may have in converting long-chain polyunsaturated fatty acids from C18 precursors. A change in the abundance of EFAs in the gonad tissue during highest and lowest GBI values suggested that arachidonic, eicosapentaenoic, g-linolenic and linoleic acid were important in females, while eicosapentaenoic, eicosadienoic and a-linolenic acid were important for male reproductive development. Dietary protein sources had an effect on the frequency distribution of maturity stages, where females that were fed FM S produced more ripe gonads and more males that were fed FM SM contained testes that showed signs of ripeness over the one-year study. Although dietary protein influenced the sex steroid concentrations in females and males, exhibiting fluctuations throughout the one-year period, no distinct pattern linked to gametogenesis were observed. The results from this study illustrate: (1) the importance of conducting laboratory studies when implementing SIA and mixing models in aquaculture nutrition; (2) conducting nutritional studies on mature, grow-out abalone; and (3) assessing the importance of naturally occurring diatoms in their diet and their contribution to growth and reproduction. The novel contribution of this research towards abalone nutritional physiology, the implications of these findings to industry as well as potential considerations for future studies were addressed.
- Full Text:
- Date Issued: 2020
Morphometrics and reproduction of Terebrasabella heterouncinata (Polychaeta:Sabellidae), infesting abalone (Haliotis midae) from different culture environments
- Authors: Gray, Michael
- Date: 2003
- Subjects: Polychaeta , Sabellidae , Abalones -- Physiology , Abalones -- Nutrition , Abalone culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5384 , http://hdl.handle.net/10962/d1018231
- Description: In the late 1980's abalone culturalists noticed reduced growth rate and shell deformities in some abalone stocks. These problems were the result of infestations by a shell boring polychaete, Terebrasabella heterouncinata. Under intensive abalone culture conditions the level of infestation can reach epidemic proportions and there are often severe consequences for the host abalone. Heavy sabellid infestation levels have placed the economic viability of several South African farms under threat. This study formed part of an ongoing project that is aimed at investigating the basic biology of Terebrasabella heterouncinata. The majority of abalone farmers in South Africa feed their abalone either naturally occurring kelp (Ecklonia maxima) or the formulated abalone feed, Abfeed. Farmers have suggested that the use of Abfeed is associated with higher sabellid infestation levels and changing the abalone diet from Abfeed to kelp helps reduce sabellid infestation. Speculation has arisen indicating that older, slower growing abalone are more susceptible to sabellid infestation. The effect of host abalone diet history and their growth on sabellid settlement success, morphometries and reproduction was quantified. To better understand the plasticity of the expression of life history traits the variability of morphometric and reproductive characteristics was compared between different farm environments. And more...
- Full Text:
- Date Issued: 2003
- Authors: Gray, Michael
- Date: 2003
- Subjects: Polychaeta , Sabellidae , Abalones -- Physiology , Abalones -- Nutrition , Abalone culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5384 , http://hdl.handle.net/10962/d1018231
- Description: In the late 1980's abalone culturalists noticed reduced growth rate and shell deformities in some abalone stocks. These problems were the result of infestations by a shell boring polychaete, Terebrasabella heterouncinata. Under intensive abalone culture conditions the level of infestation can reach epidemic proportions and there are often severe consequences for the host abalone. Heavy sabellid infestation levels have placed the economic viability of several South African farms under threat. This study formed part of an ongoing project that is aimed at investigating the basic biology of Terebrasabella heterouncinata. The majority of abalone farmers in South Africa feed their abalone either naturally occurring kelp (Ecklonia maxima) or the formulated abalone feed, Abfeed. Farmers have suggested that the use of Abfeed is associated with higher sabellid infestation levels and changing the abalone diet from Abfeed to kelp helps reduce sabellid infestation. Speculation has arisen indicating that older, slower growing abalone are more susceptible to sabellid infestation. The effect of host abalone diet history and their growth on sabellid settlement success, morphometries and reproduction was quantified. To better understand the plasticity of the expression of life history traits the variability of morphometric and reproductive characteristics was compared between different farm environments. And more...
- Full Text:
- Date Issued: 2003
The potential of abalone stock enhancement in the Eastern Cape Province of South Africa
- Authors: Godfrey, Brian Peter
- Date: 2003
- Subjects: Abalones -- South Africa -- Eastern Cape , Abalone culture , Abalone fisheries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5312 , http://hdl.handle.net/10962/d1005157 , Abalones -- South Africa -- Eastern Cape , Abalone culture , Abalone fisheries -- South Africa -- Eastern Cape
- Description: The largest abalone in South Africa, the perlemoen, Haliotis midae, occurs along approximately two-thirds of the country's coastline, but has only been the target of an extensive commercial fishery in the south-western part of South Africa. Large-scale illegal fishing has however proliferated throughout its entire range over the last 10–15 years, which has had serious effects on stock abundance and once productive populations are facing economic collapse. Abalone stock enhancement has been put forward as an addition or alternative to traditional fisheries management practices, which can potentially rehabilitate overfished abalone populations and enhance natural production. The aim of this project was to investigate the potential of abalone stock enhancement for managing an area in the Eastern Cape Province, which was being subjected to intense illegal fishing pressure. A research approach was adopted to investigate the scale and effects of this poaching and to investigate the survival of artificially cultured abalone seed in the natural environment. A model of a commercial-scale ranching operation was investigated to assess the economic feasibility of such a scheme. Analysis of poaching cases and research samples from Cape Recife indicated high levels of fishing effort that appeared to be causing the observed declines in emergent abalone abundance and average size. Poaching cases from Cape Recife contributed 32% of the total number of cases of known origin in the Eastern Cape Province from 1998–2002, with the majority of the cases (82%) originating from within the Port Elizabeth metropole. There was an exponential increase in the number of poaching cases in the Eastern Cape Province (r²=0.967) and Port Elizabeth over this period but actual annual total catch stabilized, particularly at Cape Recife, where estimates of CPUE declined significantly from 2000–2002 (p<0.001). The annual proportion of emergent abalone under the MLS from Cape Recife was always >85% in confiscations and research collections, and did not change significantly over the period of examination. Comparison of illegal catches with an adjacent site indicated that the emergent abalone population at Cape Recife had a significantly higher proportion of undersized emergent animals (p<0.001) and they were significantly smaller than the abalone from the closest site, Noordhoek, and other areas in Port Elizabeth from 2000–2002 (p<0.001). The apparent declines in emergent abalone abundance indicated by the poaching data were corroborated by sampling of emergent abalone abundance at Cape Recife. Numbers of abalone declined significantly from 125.6 to 53.8 per 20min count (p<0.001), from April 1998–October 2001 and density declined from 1.3 to 0.8m⁻² over a similar period (p<0.001). Juvenile density did not change over this period, although there were significant differences in density observed between two different habitats (p<0.001). Initial releases of cultured juvenile abalone showed that they could be distinguished from their wild counterparts for at least a year after release, by their different shell colouration. Short-term, small-scale trials (7–10 days) using animals between 17 and 30mm SL had mean survival rates of 64–82% (mean 70.4%) and the effect of size on survival was not significant in most cases, although the power to detect differences was low. Attempts to measure the effect of habitat on survival were not conclusive, although refuges under sea urchins appeared to be favoured by both seed and wild abalone, although urchins were not an absolute requirement for survival. Similar medium-term trials (31–74 days) in sheltered sites yielded mean returns of 53.1% using 25mm SL animals and similar trials in a more exposed area had more variable survival rates of between 18.4 and 73.6%, after 25–27 days. A comparison between careful hand-seeding and surface-scattering seed release methods in the open-ocean habitat showed no significant differences in survival rate after 41 days. Larger seed survived significantly better than the smaller seed when scattered on the surface (p<0.0001) and the smaller seed survived significantly better when seeded carefully by hand onto the substrate (p<0.028). Further medium-term releases of large numbers of seed abalone, released using the surface-scattering method in open-ocean habitat, gave mean survival rates of 32.8% over periods of 83–114 days. Assessment of a seeding trial using release modules to seed juvenile animals in the open-ocean was hampered by poor sea conditions and difficult to search substrates, and a mean recovery rate of 3.1% was obtained for the sites that were sampled. Movement of seed was low in the more sheltered sites, and also appeared to be affected by the amount of available habitat. Growth of seed was measured using changes in shell colouration and there were significant differences between areas. An average growth of 1.6mm.month⁻¹ shell length was calculated for all areas. The potential for commercial scale abalone ranching to be used to enhance a territorial user right fishery was investigated using a model of economic feasibility. Internal rates of return of 30.3 and 36.9% were obtained from two harvest regimes using different harvest sizes. There was a high degree of risk associated with these figures owing to a lack of consistent seed survival rate estimates, and the input parameters, which are subject to variation, showed a significant effect on profitability. The operation of this type of ranching scheme is probably not economically feasible as a stand-alone operation but could probably be operated effectively in conjunction with an existing abalone farm. By adding a small wild catch component the profitability of a ranching scheme could be significantly improved. The results of the present study indicate that high levels of poaching at Cape Recife have led to declines in emergent abalone abundance, which will probably lead to stock collapse in the near future. This implies that fisheries managers have failed to fulfil the provisions of fisheries policy in South Africa. The present results from seeding trials show that cultured juveniles can survive and make a contribution to overall stock abundance. Furthermore, while there are obstacles to economic feasibility, commercial ranching has the potential to be a valuable addition to current abalone management strategy.
- Full Text:
- Date Issued: 2003
- Authors: Godfrey, Brian Peter
- Date: 2003
- Subjects: Abalones -- South Africa -- Eastern Cape , Abalone culture , Abalone fisheries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5312 , http://hdl.handle.net/10962/d1005157 , Abalones -- South Africa -- Eastern Cape , Abalone culture , Abalone fisheries -- South Africa -- Eastern Cape
- Description: The largest abalone in South Africa, the perlemoen, Haliotis midae, occurs along approximately two-thirds of the country's coastline, but has only been the target of an extensive commercial fishery in the south-western part of South Africa. Large-scale illegal fishing has however proliferated throughout its entire range over the last 10–15 years, which has had serious effects on stock abundance and once productive populations are facing economic collapse. Abalone stock enhancement has been put forward as an addition or alternative to traditional fisheries management practices, which can potentially rehabilitate overfished abalone populations and enhance natural production. The aim of this project was to investigate the potential of abalone stock enhancement for managing an area in the Eastern Cape Province, which was being subjected to intense illegal fishing pressure. A research approach was adopted to investigate the scale and effects of this poaching and to investigate the survival of artificially cultured abalone seed in the natural environment. A model of a commercial-scale ranching operation was investigated to assess the economic feasibility of such a scheme. Analysis of poaching cases and research samples from Cape Recife indicated high levels of fishing effort that appeared to be causing the observed declines in emergent abalone abundance and average size. Poaching cases from Cape Recife contributed 32% of the total number of cases of known origin in the Eastern Cape Province from 1998–2002, with the majority of the cases (82%) originating from within the Port Elizabeth metropole. There was an exponential increase in the number of poaching cases in the Eastern Cape Province (r²=0.967) and Port Elizabeth over this period but actual annual total catch stabilized, particularly at Cape Recife, where estimates of CPUE declined significantly from 2000–2002 (p<0.001). The annual proportion of emergent abalone under the MLS from Cape Recife was always >85% in confiscations and research collections, and did not change significantly over the period of examination. Comparison of illegal catches with an adjacent site indicated that the emergent abalone population at Cape Recife had a significantly higher proportion of undersized emergent animals (p<0.001) and they were significantly smaller than the abalone from the closest site, Noordhoek, and other areas in Port Elizabeth from 2000–2002 (p<0.001). The apparent declines in emergent abalone abundance indicated by the poaching data were corroborated by sampling of emergent abalone abundance at Cape Recife. Numbers of abalone declined significantly from 125.6 to 53.8 per 20min count (p<0.001), from April 1998–October 2001 and density declined from 1.3 to 0.8m⁻² over a similar period (p<0.001). Juvenile density did not change over this period, although there were significant differences in density observed between two different habitats (p<0.001). Initial releases of cultured juvenile abalone showed that they could be distinguished from their wild counterparts for at least a year after release, by their different shell colouration. Short-term, small-scale trials (7–10 days) using animals between 17 and 30mm SL had mean survival rates of 64–82% (mean 70.4%) and the effect of size on survival was not significant in most cases, although the power to detect differences was low. Attempts to measure the effect of habitat on survival were not conclusive, although refuges under sea urchins appeared to be favoured by both seed and wild abalone, although urchins were not an absolute requirement for survival. Similar medium-term trials (31–74 days) in sheltered sites yielded mean returns of 53.1% using 25mm SL animals and similar trials in a more exposed area had more variable survival rates of between 18.4 and 73.6%, after 25–27 days. A comparison between careful hand-seeding and surface-scattering seed release methods in the open-ocean habitat showed no significant differences in survival rate after 41 days. Larger seed survived significantly better than the smaller seed when scattered on the surface (p<0.0001) and the smaller seed survived significantly better when seeded carefully by hand onto the substrate (p<0.028). Further medium-term releases of large numbers of seed abalone, released using the surface-scattering method in open-ocean habitat, gave mean survival rates of 32.8% over periods of 83–114 days. Assessment of a seeding trial using release modules to seed juvenile animals in the open-ocean was hampered by poor sea conditions and difficult to search substrates, and a mean recovery rate of 3.1% was obtained for the sites that were sampled. Movement of seed was low in the more sheltered sites, and also appeared to be affected by the amount of available habitat. Growth of seed was measured using changes in shell colouration and there were significant differences between areas. An average growth of 1.6mm.month⁻¹ shell length was calculated for all areas. The potential for commercial scale abalone ranching to be used to enhance a territorial user right fishery was investigated using a model of economic feasibility. Internal rates of return of 30.3 and 36.9% were obtained from two harvest regimes using different harvest sizes. There was a high degree of risk associated with these figures owing to a lack of consistent seed survival rate estimates, and the input parameters, which are subject to variation, showed a significant effect on profitability. The operation of this type of ranching scheme is probably not economically feasible as a stand-alone operation but could probably be operated effectively in conjunction with an existing abalone farm. By adding a small wild catch component the profitability of a ranching scheme could be significantly improved. The results of the present study indicate that high levels of poaching at Cape Recife have led to declines in emergent abalone abundance, which will probably lead to stock collapse in the near future. This implies that fisheries managers have failed to fulfil the provisions of fisheries policy in South Africa. The present results from seeding trials show that cultured juveniles can survive and make a contribution to overall stock abundance. Furthermore, while there are obstacles to economic feasibility, commercial ranching has the potential to be a valuable addition to current abalone management strategy.
- Full Text:
- Date Issued: 2003
Aspects of the physiology of the South African abalone, Haliotis Midae L., and implications for intensive abalone culture
- Authors: Lyon, Robert Gary
- Date: 1996
- Subjects: Abalones -- Physiology , Abalone culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5226 , http://hdl.handle.net/10962/d1005069 , Abalones -- Physiology , Abalone culture
- Description: A physiological study was carried out to determine the effects of temperature, quantity of food fed, feeding activity and size class on the oxygen consumption and ammonia production of the South African abalone Haliotis midae L.. A set of intermittent flow respirometer chambers were used in a recirculating system to measure the oxygen consumption rates of fed (postprandial) and unfed (postabsorptive) abalone for three different size classes (15, 30, and 50mm) at three different temperatures (16°, 20° and 23°C) over a 24 hour period. Ammonia production rates and food consumption rates were simultaneously determined. Oxygen consumption and Ammonia production rates per gram abalone were linear functions of abalone size, temperature, and mass of food consumed. Oxygen consumption and ammonia production rates were found to increase proportionally to temperature and in inverse proportion to abalone size. These rates were significantly higher for fed as opposed to unfed abalone. Equations were derived to predict oxygen consumption and ammonia production for fed and unfed animals for a range of temperatures and size classes of abalone. A 96h LC50 lethal toxicity test for exposure to ammonia established 1.08mg.1⁻¹ of unionised ammonia as the lethal limit. A test on the long term effects on growth of acute exposure (12h) to various sublethal concentrations of ammonia showed no significant effects on growth for concentrations below 0.88 mg.1⁻¹. A safe chronic exposure level of 0.02 mg.1¹ NH₃-N was used to predict optimal flow rates required per kilogram of abalone in a rearing tank over a range of size classes and temperatures. The physiological and biological requirements of H. midae and the implications of this knowledge for rearing tank management and optimal design are discussed.
- Full Text:
- Date Issued: 1996
- Authors: Lyon, Robert Gary
- Date: 1996
- Subjects: Abalones -- Physiology , Abalone culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5226 , http://hdl.handle.net/10962/d1005069 , Abalones -- Physiology , Abalone culture
- Description: A physiological study was carried out to determine the effects of temperature, quantity of food fed, feeding activity and size class on the oxygen consumption and ammonia production of the South African abalone Haliotis midae L.. A set of intermittent flow respirometer chambers were used in a recirculating system to measure the oxygen consumption rates of fed (postprandial) and unfed (postabsorptive) abalone for three different size classes (15, 30, and 50mm) at three different temperatures (16°, 20° and 23°C) over a 24 hour period. Ammonia production rates and food consumption rates were simultaneously determined. Oxygen consumption and Ammonia production rates per gram abalone were linear functions of abalone size, temperature, and mass of food consumed. Oxygen consumption and ammonia production rates were found to increase proportionally to temperature and in inverse proportion to abalone size. These rates were significantly higher for fed as opposed to unfed abalone. Equations were derived to predict oxygen consumption and ammonia production for fed and unfed animals for a range of temperatures and size classes of abalone. A 96h LC50 lethal toxicity test for exposure to ammonia established 1.08mg.1⁻¹ of unionised ammonia as the lethal limit. A test on the long term effects on growth of acute exposure (12h) to various sublethal concentrations of ammonia showed no significant effects on growth for concentrations below 0.88 mg.1⁻¹. A safe chronic exposure level of 0.02 mg.1¹ NH₃-N was used to predict optimal flow rates required per kilogram of abalone in a rearing tank over a range of size classes and temperatures. The physiological and biological requirements of H. midae and the implications of this knowledge for rearing tank management and optimal design are discussed.
- Full Text:
- Date Issued: 1996
The effect of temperature and photoperiod on the digestive physiology of the South African abalone Haliotis midae
- Authors: Dixon, Mark Geoffrey
- Date: 1992
- Subjects: Abalone culture , Gastropoda -- Physiology , Gastropoda -- Food , Abalones -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5276 , http://hdl.handle.net/10962/d1005120 , Abalone culture , Gastropoda -- Physiology , Gastropoda -- Food , Abalones -- South Africa
- Description: Inadequate information of the nutritive physiology and the dietary requirements of abalone are the principle factors that currently limit the development of a formulated feed for the commercial culture of Haliotis midae. The need to develop a method to determine apparent digestibility co-efficient's for abalone in order to facilitate further applied nutritional research was identified. Animals between 50 and 80 mm were collected from natural stocks along the east Cape coast of South Africa at Port Alfred and Great Fish point, and acclimated to laboratory conditions. Initial trials demonstrated that H. midae accepted and preferred a semi-purified diet to the seaweed Plocamium corallorhiza, one of the main components of it's natural diet. A technique of determining apparent digestibility co-efficient's (ADC) using the indirect method with chromic oxide as an inert marker was developed. Digestibility trials yielded higher dry matter (DMADC) and crude protein apparent digestibility co-efficient's (CPADC) for the semi-purified diet than for two species of algae, Gelidium amanzii and P. corallorhiza (83.7% and 95.6%, 70.7% and 80.0%, and 29.9% and 57.3% respectively). The ability of the animals to utilize terrestrial animal and plant ingredients efficiently makes it feasible to use conventional feed ingredients in formulated feeds for H. midae. Trials to determine the effect of different temperatures (15°C, 18°C and 22°C) on DMADC and CPADC of the semipurified diet showed that peak digestibility occurred at 18°C. There was also a positive relationship between temperature and consumption rate. Although no enzyme studies with H. midae have been conducted, the peak ADC's at 18°C is attributed to an increase in enzyme activity at this temperature. Transit time, an inverse function of temperature and consumption, is considered to be responsible for the decrease in the ADC' s at 22°C in conjunction with a possible decrease in enzyme activity at this temperature. A photoperiod trial to investigate the effect of darkness on DMADC and CPADC of the semi-purified diet revealed that digestive efficiency decreased with increasing hours of darkness. There was also a positive relationship between duration of darkness and the rate of consumption. The decrease in ADC's is attributed to decreased transit times as the duration of darkness increased . The contribution of this project to the understanding of abalone nutrition, the development of a formulated abalone feed and systems design for abalone farms is discussed.
- Full Text:
- Date Issued: 1992
- Authors: Dixon, Mark Geoffrey
- Date: 1992
- Subjects: Abalone culture , Gastropoda -- Physiology , Gastropoda -- Food , Abalones -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5276 , http://hdl.handle.net/10962/d1005120 , Abalone culture , Gastropoda -- Physiology , Gastropoda -- Food , Abalones -- South Africa
- Description: Inadequate information of the nutritive physiology and the dietary requirements of abalone are the principle factors that currently limit the development of a formulated feed for the commercial culture of Haliotis midae. The need to develop a method to determine apparent digestibility co-efficient's for abalone in order to facilitate further applied nutritional research was identified. Animals between 50 and 80 mm were collected from natural stocks along the east Cape coast of South Africa at Port Alfred and Great Fish point, and acclimated to laboratory conditions. Initial trials demonstrated that H. midae accepted and preferred a semi-purified diet to the seaweed Plocamium corallorhiza, one of the main components of it's natural diet. A technique of determining apparent digestibility co-efficient's (ADC) using the indirect method with chromic oxide as an inert marker was developed. Digestibility trials yielded higher dry matter (DMADC) and crude protein apparent digestibility co-efficient's (CPADC) for the semi-purified diet than for two species of algae, Gelidium amanzii and P. corallorhiza (83.7% and 95.6%, 70.7% and 80.0%, and 29.9% and 57.3% respectively). The ability of the animals to utilize terrestrial animal and plant ingredients efficiently makes it feasible to use conventional feed ingredients in formulated feeds for H. midae. Trials to determine the effect of different temperatures (15°C, 18°C and 22°C) on DMADC and CPADC of the semipurified diet showed that peak digestibility occurred at 18°C. There was also a positive relationship between temperature and consumption rate. Although no enzyme studies with H. midae have been conducted, the peak ADC's at 18°C is attributed to an increase in enzyme activity at this temperature. Transit time, an inverse function of temperature and consumption, is considered to be responsible for the decrease in the ADC' s at 22°C in conjunction with a possible decrease in enzyme activity at this temperature. A photoperiod trial to investigate the effect of darkness on DMADC and CPADC of the semi-purified diet revealed that digestive efficiency decreased with increasing hours of darkness. There was also a positive relationship between duration of darkness and the rate of consumption. The decrease in ADC's is attributed to decreased transit times as the duration of darkness increased . The contribution of this project to the understanding of abalone nutrition, the development of a formulated abalone feed and systems design for abalone farms is discussed.
- Full Text:
- Date Issued: 1992
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