https://vital.seals.ac.za/vital/access/manager/Index ${session.getAttribute("locale")} 5 https://vital.seals.ac.za/vital/access/manager/Repository/vital:49976 Wed 31 Aug 2022 15:12:45 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:65371 Wed 26 Jul 2023 15:48:20 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:65370 Wed 26 Jul 2023 15:13:29 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:65772 Wed 19 Jul 2023 14:31:11 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28096 Wed 12 May 2021 23:37:56 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20676 Wed 12 May 2021 23:07:18 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20011 Wed 12 May 2021 23:04:31 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38538 Wed 12 May 2021 23:00:38 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:25450 Wed 12 May 2021 22:39:29 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28476 Wed 12 May 2021 22:36:15 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:37991 Wed 12 May 2021 22:19:41 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:39507 0.05). The HRAP produced more biomass (317.18±27.76 g/m3) than the AS (83.12±64.91 g/m3), which resulted in a significantly greater downstream production of biogas and fertiliser per volume of effluent treated. According to the LCA, this also resulted in the HRAP system having a higher terrestrial ecotoxicity, due to the greater volume of solids and thus heavy metals applied to the soil. This interpretation can be misleading, because the mass of heavy metals released into the environment is the same for both systems, with a greater portion being applied to the land in the HRAP scenario and discharged into fresh water in the case of AS. Future LCA models should clarify if these biomasses are going to be applied to a single piece of land or multiple sites as this will influence the risk of contamination via pollutant build up in the soil. The application of sludge or algae on soil increased the soil’s sodium concentration and sodium absorption ratio from 774.80±13.66 mg/kg to 952.17±34.89 mg/kg and 2.91±0.04 to 3.53±0.13, respectively. Regulations on the application of algae or sludge on agricultural soils should be altered to consider the limit values for sodium and future LCA’s associated with effluent treatment facilities should incorporate the possibility of soil contamination through sodium build-up. This work also conceptualised the importance of reporting water emissions in wastewater treatment LCA in as much detail as possible, because this had a significant influence on the eutrophication impacts on water systems. Reporting water emissions as total nitrogen underestimated downstream eutrophication impacts compared with those using nitrogen-species concentration (ammonia, nitrite, nitrate etc). A marine eutrophication sensitivity co-efficient should be included in future LCA models which accounts for the probability of nitrogen and phosphorus emissions entering the coastal environment as well as the vulnerability of the marine environment to eutrophication. Activated sludge systems are favourable for situations where space is limited, were there are inadequate options for biomass disposal (biomass not be used in agriculture or AD) and were electricity is generated from a renewable source; whereas, HRAP are more suitable under circumstances where electricity production relies on fossil fuel that carries a high environmental impact and where options are available to use the biomass for economic gain such as biogas and fertiliser production. This thesis contributes towards a zero-waste brewery effluent treated process. The HRAP and AS treated effluent for reuse in the brewery or in agricultural irrigation. The solids were anaerobically digested, and the carbon was recovered as a biogas, while the digestate was applied as an agricultural fertiliser. This allowed for the recovery of water, nutrients and carbon.]]> Wed 12 May 2021 20:28:34 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38336 Wed 12 May 2021 20:11:48 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38253 0.05) results when temperature was analysed by t-test between 2002 and 2015. There was also a weak correlation between length frequency and the total squid catch in a given year (F Statistic (df = 1; 13) is 3.686 and 5.394 for males and females respectively, R² is 0.221 for males and 0.293 for females), but too weak to interpret, given the lack of other supporting data and the short time series. The ML_TW relationship showed no significant trends between the years for either sex. There was also no correlation between the ML_TW and total squid catch or temperature. A white caecum occurred significantly more often in males than in females (dof = 1; p < 0.05) from General Linear Model (GLM), indicating that the presence of non-feeding males in the spawning grounds may be linked to the behaviour of spawning squid.]]> Wed 12 May 2021 19:49:49 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:21184 Wed 12 May 2021 19:47:48 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38424 Wed 12 May 2021 19:09:42 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:25532 Wed 12 May 2021 19:09:05 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:31197 0.05). However, there were differences in water quality; with the municipal treatment having the lowest pH, EC and nitrate concentration (p<0.05); but all water quality parameters remained in a range suitably for fish production. Due to the tidal CW having the highest plant harvest and lowest frequency of chlorosis and mortality; it was the most suitable CW technology to clean the brewery effluent, and to produce B. vulgaris and water that could be used downstream in aquaculture.]]> Wed 12 May 2021 18:43:57 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28098 Wed 12 May 2021 18:19:49 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20702 50% of the samples), most were seen at similar abundances in samples using lighting and in those without lighting. No significant differences were observed in fish length data between samples collected with and samples collected without lighting. This suggests that standardised stereo-BRUVs sampling across photic zones on the continental shelf of South Africa can be collected without blue lighting when ambient light levels are sufficient to see the survey area.]]> Wed 12 May 2021 18:04:12 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38448 20 m) and rocky habitats were most important in explaining Chambo abundance and detection probability. The size-structure of Chambo in Lake Malawi/Niassa reflects size-specific depth and habitat migrations. Larger Chambo were observed aggregating in waters deeper than 20 m and a broader size range of individuals were observed utilising structured habitat. The effects of fishing are apparent in the size-structure of Chambo in the areas sampled. In study areas exposed to greater levels of fishing pressure – such as Malawi, the BRUVS detected significantly fewer individuals within sexually mature size classes, and the average size was smaller than in areas with less exploitation.]]> Wed 12 May 2021 17:47:05 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:21276 Wed 12 May 2021 17:11:02 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:30048 Wed 12 May 2021 16:38:09 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:24014 Wed 12 May 2021 16:35:23 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29446 Wed 12 May 2021 16:01:45 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38411 Wed 12 May 2021 15:56:48 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41462 Wed 12 May 2021 15:10:41 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:42024 Wed 12 May 2021 14:54:44 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41276 Wed 12 May 2021 14:47:27 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41499 Wed 12 May 2021 14:45:58 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:42133 Wed 12 May 2021 14:36:35 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41506 Wed 12 May 2021 14:11:40 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41357 Wed 12 May 2021 14:00:51 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:41436 Wed 12 May 2021 13:45:25 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:45147 Wed 11 May 2022 12:11:11 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:45203 Wed 06 Jul 2022 10:04:40 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:45063 Wed 02 Mar 2022 16:47:09 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:65773 Tue 30 Jan 2024 21:24:39 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:42814 0.05; df = 2). However, mortalities were high and growth rates low, indicating that the rearing conditions were sub-optimal, possibly masking genetic differences. No significant differences were observed in oxygen consumption rates (ANOVA, P = 0.18; df = 2), and CTM (t-Test, P = 0.31; df = 3) between the two populations. The CTM for both populations was between 29 - 30℃. The farm trial yielded no significant differences in growth rate during the Nursery phase (t-Test, P = 0.25; df = 2), however significant differences in growth rate were observed during the grow out phase with the Central region abalone offspring growing faster than the Eastern edge population (t-Test, P = 0.04; df = 4) indicating the possibility of a genetic difference between the two populations. Further experiments will be required to determine whether the differences observed in the growth trial were genetically or environmentally induced.]]> Tue 18 May 2021 14:45:49 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:56823 Thu 29 Sep 2022 15:26:40 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:45054 0.05), with the overall population growth curve being best described as L(t) = 697.15(1-e-0.06(t-6.30)). Males matured at a slightly larger size than females, however, no significant differences were observed (LRT, p > 0.05). The length- and age- at-50% maturity was 330 mm (FL) and 5.73 years for the full population, respectively. Histological analyses showed that Oplegnathus conwayi are asynchronous spawners with a gonochoristic reproductive style. Macroscopic staging and gonadosomatic index results indicated a protracted spawning season for Oplegnathus conwayi, with a peak in spring. A survey was designed and disseminated to collect FEK on the biology and population status of Oplegnathus conwayi and human dimension information on South Africa’s spearfishery. A total of 103 survey responses were received, of which 94 were regarded as specialised (spearfishers who had greater experience, skill and avidity, and maintained spearfishing as an important component of their lifestyle) spearfishers. Based on the responses of the specialist spearfishers, the top four main species caught by spearfishers from this survey were Seriola lalandi (13.9%), Pachymetopon grande (11.7%), Oplegnathus conwayi (11.4%) and Sparodon durbanensis (11%), and the majority of respondents indicated that there had been no changes in abundance, size and catches of these species in the years that they had been spearfishing. Respondents indicated that Oplegnathus conwayi are most commonly targeted in the Eastern Cape and are found at depths of up to 40 m. Respondents also indicated that there may be a seasonal onshore (Summer/Winter) and offshore (Summer/Winter) migration with year-round spawning and a peak in November, December and January. The incorporation of spearfishers into the data collection, both through the collection of specimens and their FEK, was beneficial to this study. Besides providing samples from a broader geographical range than the primary collection area, the collaboration with spearfishers has promoted the inclusion of this group into the management system. The findings of this study also suggest that FEK data can be more reliable if the concept of recreational specialisation is incorporated into data collection. While the FEK suggested that the population was stable, a stock assessment is necessary to fully understand the population status and implement management strategies. Nevertheless, the key life history characteristics (slow growth and late maturation) observed in this study are characteristic of species that is vulnerable to overexploitation, and thus the precautionary approach should be applied. The reproductive information collected in this study has provided information for the implementation of an appropriate size limit regulation for Oplegnathus conwayi. Here, a minimum size limit of 400 mm TL, which corresponds approximately with the length-at-50% maturity of 330 mm FL, would be appropriate to allow fish to mature and spawn, and reduce the likelihood of recruitment overfishing. Reduction in the bag limit from five to two fish per person per day may also be appropriate as a precautionary measure until a stock assessment has been completed. Finally, the incorporation of stakeholder into biological collection and the use of FEK may be a useful approach for other data deficient species and in countries with limited resources for ecological research.]]> Thu 29 Sep 2022 14:29:54 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:30597 100 km) behaviour, respectively. Further behavioural diversity was observed with ‘resident’, ‘roaming’ and ‘embayment’ contingents identified based on varying levels of affinity to certain habitats. The presence of both resident and migratory individuals within the northernmost study during June and July, combined with available biological information, suggested that area-specific spawning may take place. While PAT, CPUE and CT largely aligned in determining area specific high-area use, results from network analyses and mixed effects models conducted on the PAT data supported the spawning hypothesis, with anomalous behaviour around specific receivers during the spawning season. All fish, regardless of behavioural contingent, displayed similar movement behaviour during the spawning season and this was driven by factors generally associated with reproduction, such as lunar illumination. Interestingly, these drivers were different from those that determined the area specific use of individuals outside of the spawning season. The environmental drivers of longshore migration into the northern study site were identified as a decline in water temperature and shorter day lengths. The results of this study highlight the importance of using a multi-method approach in determining migratory movement behaviour, area specific area use, and stock structure of key fisheries species. The identification of different behavioural contingents highlights the importance of acknowledging individual variation in movement and habitat-use patterns. This is particularly relevant as future climate change and spatiotemporal variation in fishing effort may artificially skew natural selection processes to favour certain behavioural groups. This study also highlighted the importance of scientists forming relationships with resource-users, such as recreational angling lodges in areas where limited research has been conducted. This is particularly relevant within the West African context where little is known about many of the fish species that are being increasingly targeted by tourism angling ventures.]]> Thu 29 Sep 2022 14:25:47 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:31213 Thu 29 Sep 2022 14:24:30 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:30599 Thu 29 Sep 2022 14:23:25 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:26094 Thu 29 Sep 2022 14:21:25 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:25988 Thu 29 Sep 2022 14:20:40 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5389 Thu 29 Sep 2022 14:19:59 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:27799 Thu 29 Sep 2022 14:18:31 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29924 0.05), development or the active metabolic (P > 0.05) or metabolic scope (P > 0.05) of fish in the three treatments throughout the study. However, the standard metabolic rate was significantly higher in the year 2068 treatment but only at the flexion/post-flexion stage which could be attributed to differences in developmental rates (including the development of the gills) between the 2068 and the other two treatments. Overall, the metabolic scope was narrowest in the 2090 treatment, but varied according to life stage. Although not significantly different, metabolic scope in the 2090 treatment was noticeably lower at the flexion stage compared to the other two treatments, and the development appeared slower, suggesting that this could be the stage most prone to OA. The study concluded that, in isolation, OA levels predicted to occur between 2050 and 2090 will not negatively affect size-at-hatch, growth, development, and metabolic responses of larval A. japonicus up to 22 DAH (flexion/post-flexion stage). Taken together with the previous studies of the same species, the tipping point of tolerance (where negative impacts will begin) in larvae of the species appears to be between the years 2090 and 2100.]]> Thu 29 Sep 2022 12:56:05 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:44744 250 m) for the 2001–2018 time series. Comparison of the contemporary (2015–2019) proportions of developing, ripe and spent gonads to the historical study data (1996 – 2000) show minimal differences. Ripe ovaries capable of spawning (Stage IV) were dominant in July (23.8%) and August (26.2%), while ripe testes were prevalent in April (52.5%) and November (28.5%). The discovery of the veil (a gelatinous, flat ribbon structure containing individual eggs) off Namibia for the first time (during this study) is a significant because this result provides important reproduction activities information of this species, which were never recorded off Namibia. The location where the veil was discovered, off Swakopmund (22⁰30'S, 13⁰25'E), provides further evidence of the identified spawning hotspot areas, this location is also identified as a monkfish consecutive hotspot fishing area. The ages, growth rates, and length-weight relationships were compared between fish collected during monkfish commercial fishing activities between 1996 and 1998 (Period 1) and during monkfish routine monitoring surveys from 2014 to 2016 (Period 2). A total of 607 (size range: 9–96 cm total length (TL)) and 852 (size range: 9–96 cm TL) Cape monkfish were aged by reading sectioned illicia, during Periods 1 and 2, respectively. The length-weight relationships were W = 0.012L3.035 (r2 = 0.98) and W = 0.014L 2.989 (r2 = 0.98) for females and males, respectively, during Period 1, and W = 0.01L2.97 (r2 = 0.98) and W = 0.01L 3.03 (r2 = 0.98) for females and males, respectively, in Period 2. The growth of Cape monkfish (in cm) for combined sexes was described by Lt = 94(1 − e(−0.10(t−(-0.31))) in Period 1 and Lt = 98(1 − e(−0.10(t−(-0.33))) in Period 2. Females grew significantly faster during Period 1 (LRT results from Maartens et al., 1999), while male and female growth was not significantly different during Period 2 (F = 0.65, p = 0.58). There were no significant differences between the male and female growth curve in Period 2 (F = 0.65, p = 0.58). Although the growth curves are similar between Period 1 and Period 2, the larger fish are in Period 2 are lighter than those in Period 1. This finding is important to the monkfish fishing industry because fish is sold by weight. This finding may suggest that although the fish grow similarly by length, changes in the environmental conditions may have resulted in a reduced condition of the fish. In terms of mean age, the historical Period 1 had a slightly lower mean age of 4.40 compared with a mean age of 5.49 during Period 2. Slight differences were also observed in the age structure between the two periods, with 2-year-olds (20.3%) the most abundant age class in the historical period while 5-year-old fish (18.3%) were most abundant in Period 2. Although the spatial distribution of the catch was not available for Period 1, 0-year-old fish were distributed from 22⁰ to 24⁰S, and 25⁰ to 26⁰S in shallower waters of 166–290 m during Period 2. Only fish between 5 and 16 years old were found off the documented historical nursery area off 28º S. The similar growth curves and spatial overlap of nursery habitats between Period 1 and Period 2 suggest that Cape monkfish may be fairly resilient to the rapid environmental change reported in this region and to the extensive levels of exploitation for the species. However, the recent spatial shifts in the nursery areas are sensitive to disturbance and may indicate that these changes could be having an impact on the early life stages of the species. Continued monitoring may be necessary to understand the consequences of these spatial shifts for the age and growth and resilience of the species. Analysis of the overall spatial and temporal catches of monkfish (both Cape monkfish and shortspine African monkfish) off Namibia between 1998 and 2018 identified noticeable spatio-temporal trends. The pattern of fishing activities for Cape monkfish is heterogeneous, with identified ‘hotspots’ in specific areas. Of particular importance is the consecutive hotspot, between 1998 to 2018 for monkfish fishing activities between 25⁰ and 26⁰ S. The kernel density analysis indicated that the area around 24⁰S, and between 26º and 27 ⁰S, between Walvis Bay and Lüderitz, had the highest total catch densities (~300 kg/km2), suggesting that this is the core of the stock abundance. Annual monkfish catches have fluctuated since the inception of the fishery in 1994, with a drastic decline in the catch recorded after 2003 through to 2018. Generally, there has been an underutilisation of the total allowable catch (TAC) for most of the years. The decrease in catches and the underutilisation of the TAC might be indicative of the reduction in the stock abundance. However, external factors such as lack of capacity of the fishing industry and the administration can contribute to underutilisation of TAC. Basic regression analysis between total monthly catches and monthly sea surface temperature (SST) yielded low r-squared values indicate that in all three grids, only ~ 1% of the variation is explained between SST and total monkfish catches in these areas. The most prominent points to consider from this study are the results of the comparative feeding study (Chapter 3), reproductive indicators (Chapter 4) and age and growth (Chapter 5). Certainly, there have been changes in feeding, demography, and distribution of the species in the last two decades – climate-driven changes were recorded in the feeding habits of Cape monkfish, spatially and temporally – but despite the changes in prey species composition, distribution and abundance in various habits and periods, Cape monkfish was able to switch prey species, reflecting wide trophic adaptability. The dominance of M. paradoxus at all size classes in all analysed habitats is a significant result because. The peak spawning period has remained the same between July and September, as previously reported in Period 1. The consecutive spawning hotspots were identified in the areas between 22º and 25ºS. From a fisheries management perspective, the spawning ground and spawning season should be protected (by means of closure). The evidence of changes in length at 50% maturity presented in this study hints at both climate change and extensive exploitation pressure. The discovery of the veil for the first time in this study is very important; however, it might be sampling related and not driven by climate or exploitation pressure. Finally, the change in the Cape monkfish distribution discussed in Chapter 6 may be attributed to a shift in the distribution or fishing effort as a consequence of shallow water depletion.]]> Thu 29 Sep 2022 12:49:29 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:42759 10 m depth) and inshore sites (intertidal surf zones). Many sites in the bay, especially the atypical site at Cape Recife, exhibit higher than the average pH levels (>8.04), suggesting that pH variability may be biologically driven. This is further evidenced by high diurnal variability in pH (~0.55 pH units). Although the specific drivers of the high pH variability in Algoa Bay could not be identified, baseline carbonate chemistry conditions were identified, which is necessary information to design and interpret biological experiments. Long-term, continuous monitoring is required to improve understanding of the drivers of pH variability in understudied coastal regions, like Algoa Bay. A local fisheries species, D. capensis, was selected as a model species to assess the impacts of future OA scenarios in Algoa Bay. It was hypothesized that this temperate, coastally distributed species would be adapted to naturally variable pH conditions and thus show some tolerance to low pH, considering that they are exposed to minimum pH levels of 7.77 and fluctuations of up to 0.55 pH units. Laboratory perturbation experiments were used to expose early postflexion stage of D. capensis to a range of pH treatments that were selected based on the measured local variability (~8.0–7.7 pH), as well as future projected OA scenarios (7.6–7.2 pH). Physiological responses were estimated using intermittent flow respirometry by quantifying routine and active metabolic rates as well as relative aerobic scope at each pH treatment. The behavioural responses of the larvae were also assessed at each pH treatment, as activity levels, by measuring swimming distance and speed in video-recording experiments, as well as feeding rates. D. capensis had sufficient physiological capacity to maintain metabolic performance at pH levels as low as 7.27, as evidenced by no changes in any of the measured metabolic rates (routine metabolic rate, active metabolic rate, and relative aerobic scope) after exposure to the range of pH treatments (8.02–7.27). Feeding rates of D. capensis were similarly unaffected by pH treatment. However, it appears that subtle increases in activity level (measured by swimming distance and swimming speed experiments) occur with a decrease in pH. These changes in activity level were a consequence of a change in behaviour rather than metabolic constraints. This study concludes, however, that based on the parameters measured, there is no evidence for survival or fitness related consequences of near future OA on D. capensis. OA research is still in its infancy in South Africa, and the potential impacts of OA to local marine resources has not yet been considered in local policy and resource management strategies. Integrating field monitoring and laboratory perturbation experiments is emerging as best practice in OA research. This is the first known study on the temperate south coast of South Africa to quantify local pH variability and to use this information to evaluate the biological response of a local species using relevant local OA scenarios as treatment levels for current and near future conditions. Research on local conditions in situ and the potential impacts of future OA scenarios on socio-economically valuable species, following the model developed in this study, is necessary to provide national policy makers with relevant scientific data to inform climate change management policies for local resources.]]> Thu 29 Sep 2022 12:42:34 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28707 Thu 13 May 2021 16:40:45 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:31194 Thu 13 May 2021 08:55:46 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:25445 Thu 13 May 2021 08:50:20 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28153 Thu 13 May 2021 08:34:59 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:25449 Thu 13 May 2021 08:12:15 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:24013 Thu 13 May 2021 06:58:11 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5387 Thu 13 May 2021 06:57:30 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20786 Thu 13 May 2021 06:43:19 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:26992 Thu 13 May 2021 06:38:26 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29391 Thu 13 May 2021 06:19:50 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20023 Thu 13 May 2021 06:09:34 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38548 Thu 13 May 2021 05:39:40 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:31196 Thu 13 May 2021 05:17:47 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38102 Thu 13 May 2021 04:58:25 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:20754 Thu 13 May 2021 04:50:09 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28154 Thu 13 May 2021 02:39:01 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38658 Thu 13 May 2021 02:30:12 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:5385 Thu 13 May 2021 01:52:29 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28082 Thu 13 May 2021 01:50:35 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:29249 Thu 13 May 2021 00:55:36 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:27798 500 km) and modelled with an ordinal logistic regression. Species, life-stage (juvenile/adult) and time- at-liberty were included as predictor variables. Model coefficients were then included in a cluster analysis, which produced two primary groupings of species (Category I and II), with two sub-groupings (Category IIa and IIb). Category I species were characterised by wide-ranging movements, greatest median recapture length and highest trophic levels. Category II species were characterised by residency, lower median recapture length and lower trophic levels. These findings have implications for fisheries management. Exploitation of resident species may lead to localised depletion, but their diffuse spatial distribution may offer some resilience. In contrast, even localised targeting of migratory species may pose a population level risk if individuals are known to aggregate. Life-cycle diversity or intra-population variability describes the existence of alternative strategies or tactics among coexisting individuals within an animal population (Chapter 5). Partial migration is a specific case of life-cycle diversity where coexisting groups exhibit either resident or migratory (wide-ranging) behaviour within a single population. Mark- recapture data collected under the auspices of the ORICFTP were used to investigate the occurrence and nature of life-cycle diversity in the movement behaviour of five non- diadromous fish species around the coastline of southern Africa. Among the five species were three teleosts (Category I and IIa) and two elasmobranchs (Category I). A fish was considered to have remained resident if recaptured within 0-5 km after 365 days at liberty. A fish was considered to have undertaken a wide-ranging movement if recaptured more than 50 km away from the release site in 365 days or less. A total of 1848 individuals from the five study species were recaptured during the study, of which 73% of the observations were classified as being resident. Binomial logistic regression confirmed that species, life-stage (juvenile/adult) and ecoregion were significant (p < 0.001) predictors of the probability of wide-ranging behaviour. A Gaussian model confirmed that species and ecoregion were also significant (p < 0.001) predictors of direction and distance of wide-ranging movement. However, the direction and distance of wide-ranging movements in juveniles did not differ significantly (p > 0.05) to that of adults. The median growth rate was mostly greater in wide- ranging individuals; however, this was only statistically significant (p < 0.05) in two cases. These findings provide unequivocal evidence of life-cycle diversity in five fish species, with vastly different life-histories. This ecological phenomenon may provide species resilience at the population level and needs to be considered in fisheries management initiatives. The movement of fishes is a fundamental aspect to consider when designing fishery management regimes. Unfortunately, traditional management strategies have often disregarded movement behaviour to the detriment of fish populations (Chapter 6). As a case study, the management of Lichia amia (Category I: wide-ranging) was evaluated in the context of its movement behaviour. Long-term catch-per-unit-effort (CPUE) datasets were examined for three South African recreational fishery sectors. The CPUE was standardised using generalized linear models (delta-Gamma/hurdle approach) to reduce the effect of factors other than abundance. Factors that were available for this purpose were year, month and locality/zone. Year was included in every model as the primary objective was to detect trends in abundance over time. Although standardised CPUE for all sectors showed an overall long-term decline, there was considerable variability in trends between the different recreational sectors and between datasets. Contrasting trends between competitive shore angling and general shore angling datasets were ascribed to hyperstability in competitive CPUE data. Hyperstability in this case was mostly influenced by rapidly improving technology, techniques and communication networks amongst competitive anglers. Month and locality were significant factors explaining the probability of catching L. amia. This suggests that the predictable aggregatory behaviour of this species could further compound the observed CPUE hyperstability. Although the CPUE responded positively for six years after implementation of the first minimum size and bag limits, and for one year after the decommercialisation of the species, these regulations and their amendments failed to arrest a long-term decline in the CPUE despite the ample evidence for hyperstability. It is clear from this case study that the predictable nature of wide-ranging behaviour in L. amia has made the population vulnerable to exploitation. This has led to the demise in the population, which could have been worse if not for the occurrence of intra-population variability in its movement behaviour, which may provide some measure of resilience.]]> Thu 13 May 2021 00:49:53 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:65763 200 km). These characteristics provide opportunities for high levels of connectivity, and as such, the stock structure is not well understood. We applied an integrated, multidisciplinary approach to provide an improved understanding of the complex stock structure dynamics for Patagonian toothfish on the Patagonian Shelf, specifically in relation to the shelf, slope, and deep-sea plains around the Falkland Islands. Research results were focused on aspects pertaining to (1) geographic variation in phenotypic characters (otolith shape); (2) a description of the spatial-temporal distribution patterns; (3) the active movements of deep-sea adults (tag-recapture study); and (4) the identification of early life-history dispersal through otolith microstructure and microchemical chronologies. Results from the study indicate high regional connectivity during the early life-history stages derived from at least two spawning contingents into spatially discrete nursery areas (cohort groups) on the Falklands Shelf. Fish followed distinct ontogenetic pathways into deeper waters adjacent to the areas wherein juvenile settlement into a demersal habitat occurred. There is little to no evidence of mixing among cohort groups during their ontogenetic migration into deep-sea adult habitats, reflecting a mixed population based on oceanographically defined egg and larval dispersal. The majority of the adult component of the population continue to display high site fidelity. However, between 9 and 25% of the population, consisting predominantly of larger reproductively capable adults undertake long-distance dispersal behaviour, identified as home-range relocations from the adult deep-sea habitats towards three of the known southern spawning grounds in the region. Results are suggestive of a requirement for improved collaborative efforts for regionally-based management approaches with careful consideration of local stock contingents. Future monitoring and research priorities should focus on the identification of reproductive potential, dispersal pathways and settlement patterns of stock contingents to inform the dynamics of mixed stock origins across the Patagonian region. While many aspects regarding the stock structure remain unresolved, results derived from the current studies can be used to inform the development of management measures to ensure the continued recovery and sustainable management of Patagonian toothfish within the region.]]> Thu 11 Jan 2024 18:07:47 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:71932 Thu 04 Apr 2024 19:04:28 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:71930 Thu 04 Apr 2024 18:57:36 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:71929 Thu 04 Apr 2024 18:50:26 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:71928 Thu 04 Apr 2024 17:34:04 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:45038 Thu 02 Dec 2021 15:59:51 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:57236 Sun 09 Oct 2022 18:49:45 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:72146 Sat 20 Apr 2024 16:17:00 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:72145 Sat 20 Apr 2024 16:09:35 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:72144 Sat 20 Apr 2024 15:55:54 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:72143 Sat 20 Apr 2024 15:48:55 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:71961 Sat 06 Apr 2024 14:42:26 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:71955 Sat 06 Apr 2024 12:42:05 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:38741 Sat 04 Dec 2021 12:41:27 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:44792 Mon 25 Oct 2021 10:25:42 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:57235 Mon 24 Oct 2022 09:15:55 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:28660 Mon 24 Apr 2023 08:33:54 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:45340 Mon 22 Nov 2021 15:55:03 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:21262 Mon 12 Jun 2023 12:17:56 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:50004 Mon 10 Oct 2022 08:02:20 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:65667 Mon 10 Jul 2023 19:25:05 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:31344 Mon 06 May 2019 15:28:07 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:27629 Mon 03 Jul 2023 14:13:59 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:56834 Fri 30 Sep 2022 11:21:50 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:26997 Fri 23 Jul 2021 11:15:06 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:45051 Fri 18 Feb 2022 11:43:00 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:65363 Fri 07 Jul 2023 14:24:16 SAST ]]> https://vital.seals.ac.za/vital/access/manager/Repository/vital:45064 1 relative to the native crab irrespective of region, which were higher for the summer than the winter season, suggesting greater impact of the invaders compared to the native species. This study further estimated the socioeconomic losses due to catch spoilage by C. quadricarinatus which are up to 1500 t per year in the invaded Kafue River Basin, which translates to an annual income loss of US$ 2 million. Information provided in this study is vital for conservation management and to compel policymakers to develop appropriate conservation management tools within regulatory frameworks, which could stop or minimise the spread of crayfish species and protect Africa from further losing aquatic biodiversity.]]> Fri 06 May 2022 11:07:38 SAST ]]>