Comparison of the metabolic physiology of exploited and unexploited populations of red roman (Chrysoblephus laticeps) along the south coast of South Africa
- Authors: Nabani, Xolani Prince
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424358 , vital:72146
- Description: Anthropogenic-induced climate change and exploitation pose threat to many marine fishes on which a vast majority of people around the world depend. Rapid changes in sea surface temperature have a direct impact on the physiology of ectothermic organisms such as fish, potentially resulting in changes to population distribution, abundance, and demographics. In the face of climate change, the impacts of increasing temperature variability on fish populations may be exacerbated by exploitation. Understanding how the resilience of exploited populations is affected by climate change is critical to predict how fishes will respond in the future. This study aimed to augment our knowledge on the impact of exploitation and thermal variability on fishes by comparing the thermal physiology of an exploited and unexploited population of the resident, reef-dwelling, Chrysoblephus laticeps. Twenty live fish were collected from the exploited, Cape St Francis and 18 fish from the unexploited, Goukamma Marine Protected Area and transported to the laboratory. The metabolic performance, in terms of standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope (AS) of individual C. laticeps were estimated repeatedly at 10 ℃, 16 °C and 21 °C. Linear mixed effects models were used to examine the relationship between temperature, population, and metabolic rate and a ‘cvequality’ test analysis was used to compare the variance structure of the metabolic rate regression model for each population. Overall, the findings of this study show that Chrysoblephus laticeps from the unexploited population maintains a significantly higher aerobic scope (AS) across all temperature treatments (10, 16 and 21 ℃) when compared with those from the exploited population. In addition, the maximum metabolic rate (MMR) of individuals from the unexploited population was significantly higher than that of individuals from the exploited population, but there was no evidence to suggest that variability was significantly different between the populations. On the other hand, the individuals from an exploited population had a significantly higher standard metabolic rate (SMR) at high temperatures of 21 ℃, while the unexploited population had a low SMR at these high temperatures, but a high SMR at 10 ℃. Despite these differences there was no significant variation in the SMR between the two populations. The findings of this study confirm previous work on different exploited and unexploited populations of C. laticeps and together these findings suggest that hook and line exploitation lead to reduced physiological phenotypic diversity and reduced physiological performance in exploited fish populations. These findings emphasise the importance of incorporating the iii physiological information to develop viable fisheries management tools in the context of climate change. This study also highlights the effectiveness of MPAs in conserving highperformance physiological phenotypes to maintain phenotypic diversity in fish populations. Future research should aim to evaluate the efficacy of existing MPAs in preserving the physiological diversity of important hook and line fisheries species, while fisheries managers should consider augmenting their approaches through the incorporation of well-designed MPA’s to promote physiological diversity. This will be critical to advance the development of sustainable management practices, not only in a South African context but globally, where oceanic and coastal environmental conditions are expected to rapidly change in the future. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
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- Date Issued: 2023-10-13
Exploring the drivers of co-occurring multiple non-native fish assemblages within an invaded and flow-modified African river system
- Authors: Mpopetsi, Pule Peter
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/431871 , vital:72810 , DOI 10.21504/10962/431871
- Description: Globally, there is growing concern on the negative impacts of species invasions and habitat disturbance because these have been shown to have the potential to disrupt native community structure and function. In some instances, these two stressors can occur in concert, such as in river systems associated with inter-basin water transfer (IBWT) schemes. The Great Fish River in the Eastern Cape, South Africa, is an example of a system affected by both habitat modification and multiple fish invasions largely because of an IBWT scheme. The opening of the Orange-Fish IBWT, which transfers water from the Orange River to the Great Fish River, modified the latter’s natural flow regime from irregular seasonal to perennial. In addition, the IBWT facilitated translocations of five fish species from the Gariep Dam (Orange River system) into the Great Fish River system. Proliferation of these non-native fish species, along with that of other fish species introduced for angling and biological control, raise questions on the mechanisms facilitating their existence within this highly modified river system. This thesis explored mechanisms associated with co-occurrences of these multiple non-native fishes within the Great Fish River. A comparison of historical and contemporary records on the ichthyofauna of the Great Fish River revealed that, of the 11 non-native fishes reported in this system, seven have established successfully, three have failed to establish and the status of one was uncertain. The Orange-Fish IBWT and angling were the main vectors of these invasions, accounting for 36% and 46%, respectively. The study also found that most established non-native fish species were large sized, had high longevity and wide habitat tolerance. Trait-based approaches were employed to investigate the role of functional diversity of non-native and native fishes in relation to their composition, distribution and environmental relationships. Although considerable interspecific variation in body morphology-related functional traits among species were observed, there was no clear distinction in these traits between native and non-native fish assemblages on a trait-ordination space. Furthermore, there were weak species-trait-environment relationships, suggesting that environmental filtering was less plausible in explaining the occurrence patterns of these fishes. Stable isotope-based trophic relationships were evaluated in three invaded sections: the upper (UGFR) mainstem sections of the Great Fish River; and lower (LGFR) mainstem sections of the Great Fish River; and its tributary, the Koonap River. It was observed that native and non-native fish assemblages exhibited variation in isotopic diversity typified by low isotopic diversity overlaps in UGFR and Koonap River, whereas the LGFR was characterised by high isotopic diversity overlap. Within the invaded sections, non-native fishes were found to have isotopic niches characterised by variable isotopic niche sizes and were more isotopically dissimilar with propensity towards trophic differentiation within the UGFR and Koonap River but were mostly characterised by high isotope niche overlaps in the LGFR. Overall, these results provided evidence of trophic niche differentiation as a probable mechanism associated with the co-occurrences of the non-native fishes. However, mechanisms facilitating these co-occurrences within the invaded sections appears to be complex, context-specific and, in some cases, unclear. Lastly, machine learning techniques, boosted (BRT) and multivariate (MRT) regression trees, revealed that the flow-disturbed habitats were invaded by multiple non-native species, whereas the non-disturbed headwaters remained invasion free. In addition, non-native species were predicted to co-occur with native species within the mainstem and large tributary sections of the Great Fish River system. Thus, the IBWT-disturbed mainstem sections were predicted to be more prone to multiple invasions compared to undisturbed headwater tributaries. , Tlhaselo ka mefuta ya diphoofolo-tsa-matswantle (non-native species), ha mmoho le phetolo/tsenyehelo ya bodulo ba diphoofolo-tsa-lehae (native species), di nkuwa ele tse pedi tsa tse kgolo ka ho fetisisa hara ditshoso tse kgahlanong le paballo kapa tshireletso ya diphoofolo-tsa-lehae tse phelang dinokeng kapa metsing. Maemong a mang, dikgatello tsena tse pedi dika etsahala ka nako e le nngwe, jwalo ka dinokeng tseo di amanang le maano a ho fetisa/tsamaisa metsi pakeng tsa dinoka tse fapa-fapaneng (IBWT). Enngwe ya dinoka tse jwalo, ke noka e bitswang ka Great Fish River, e fumanehang Kapa-Botjabela (Eastern Cape) ka hara naha ya Afrika Borwa (South Africa). Noka ena ya Great Fish River e angwa ke tshenyehelo ya bodulo ba ditlhapi-tsa-lehae, ha mmoho le tlhaselo ya tsona ka ditlhapi-tsa-matswantle. Tsena di etsahala hahololo ka lebaka la morero kapa leano la phepelo ya metsi le bitswang Orange-Fish IBWT, leo lona le ileng la fetola phallo ya tlhaho ya metsi a Great Fish River. Ho feta moo, leano lena la phephelo yametsi, Orange-Fish IBWT, le entse hore ho be bonolo ho fetisetswa ha mefuta e mehlano ya ditlhapi-tsa-matswantle ho tloha letamong le bitswang Gariep Dam, hoya kena ka hara noka ya Great Fish River. Ditla morao tsa tsena tsohle, ebile ho ata ha mefuta e mengata ya ditlhapi-tsa-matswantle ka hara noka ya Great Fish River. Ho ata hona ha ditlapi-tsa-matswantle ka hara noka ena ya Great Fish River, ho hlahisa dipotso mabapi le mekgwa e bebofatsang ho phela ha ditlhapi tsena tsa matswantle ka hara noka ena; hore ana ebe diphela jwang ka hara noka ya Great Fish River? Ka hona, sepheo le merero wa thuto ena ke ho phuputsa mekgwa e bebofatsang ho phela ha mefuta ena e fapaneng ya ditlhapi-tsa-matswantle ka hara noka ya Great Fish River. Dipheto tsa diphuputso di hlalosa hore, ha jwale, ka hara noka ena ya Great Fish River, hona le ditlhapi-tsa-matswantle tse leshome le motso o mong (11). Bosupa (7) ba tsona di phela ka katleho, ha tse tharo di hlolehile ho theha (3), mme e le nngwe (1) boemo ba teng ha bo hlake. Hare lekola hore ke efeng mekgwa e amanang le ho ata ha ditlhapi-tsa-matswantle ka hara Great Fish River, re fumana hore leano la phephelo ya metsi la Orange-Fish IBWT ka 36%, ha mmoho le boithapollo ba ho tshwasa ditlhapi (angling) ka 46%, ene ele tsona tsela tsa ho kena ha ditlhapi-tsa-matswantle ka hara Great Fish River, tse ka sehlohong. Re fumantsha hape hore katleho ya ditlhapi-tsa-matswantle e amahangwa le hore di boholo bo bokae, le hore diphela nako e ka kang. Mohlala, ditlhapi tse kgolo tse phelang nako etelele ka tlhaho ya tsona, di amahangwa le katleho ya ho theha ka hara noka ena. Ha tseo tse phelang nako e kgutshwanyane tsona disa amahangwe leho atleha ka hara noka ena. Tse ding tsa dipheto di hlalosa hore, ditlhapi-tsa-lehae le ditlhapi-tsa-matswantle, ka karolelano, hadi fapane haholo ka dibopeho tsa mmele, dihlopa tsena tse pedi diya tshwana. Re fumantsha hape hore dihlopa tsena tse pedi tsa ditlapi dija mefuta e fapaneng ya dijo. Eleng engwe ya dintho tse netefatsang katleho ya ditlhapi-tsa-matswantle ka hara noka ena ya Great fish river. Hona keka lebaka la hore, dihlopa tsena tse pedi hadi bakisane dijo, empa di phela ka mefuta e fapaneng ya dijo. Hare phethela, re fumantsha hore mefuta e fapafapaneng ya ditlhapi-tsa-matswantle e fumaneha feela ka hara madulo a amahangwang le phethoho ya phallo ya metsi (flow alteration), madulo asa amahangwang le phetoho ya phallo ya metsi ona ane a hloka ditlhapi-tsa-matswantle. Sena se bolela hore phetolo ya phallo ya metsi ya Great Fish River, ka lebaka la Orange-Fish IBWT, e fokoditse matla a noka ena ho lwantsha tlhaselo ya ditlhapi-tsa-matswantle. Ka hona, ho bobebe hore ditlhapi-tsa-matswantle di thehe ka katleho ka hara noka ena. Tsena tsohle keka baka la phetolo ya phallo ya metsi a Great Fish River e bakilweng ke leano la phephelo ya metsi la Orange-Fish IBWT. , Thesis (PhD) -- Faculty of Science, Faculty of Science, Ichthyology and Fisheries Science, 2023
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- Date Issued: 2023-10-13
Movement ecology of a West African sciaenid fish, Argyrosomus coronus, in southern Angola
- Authors: Parkinson, Matthew Cameron
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/432203 , vital:72851 , DOI 10.21504/10962/432203
- Description: Argyrosomus coronus is a large sciaenid species with a primary distribution between Cape Frio, in Namibia, and Luanda, in Angola, where it exists as a panmictic stock. Early juveniles (< 300 mm TL) occur on muddy offshore substrata (50–80 m deep) and at one year of age they recruit into the inshore zone. Adults are thought to predominantly occur inshore. Spawning occurs in the species during late spring. The species is heavily targeted by the recreational, subsistence, artisanal and commercial fisheries as juveniles through to adults and there are signs of population decline with declines in catch per unit effort (CPUE) and maximum size. A basic understanding of their movement ecology has emerged from previous studies, based on conventional tagging (mark-recapture) and CPUE monitoring from a shore-based recreational fishery. Juveniles were thought to be resident, with larger fish undertaking long distance migration southward in the austral summer and returning during the austral winter. In addition to the fishery-related threats faced by the species, the southern Angolan region has been identified to be an ocean warming hotspot, and this has been linked to a southward distribution shift and the recent hybridisation of A. coronus with its congener A. inodorus, in Namibia. This study aims to expand the knowledge of the movement ecology of A. coronus and to interrogate our current understanding of the movement patterns of the species using passive acoustic telemetry. Passive acoustic receivers were deployed at three study sites, Flamingo, where all tagging occurred, which lies ~ 200 km north of the Angolan border with Namibia, is a relatively exposed stretch of coastline; Tombua Bay, which lies 30 km south of Flamingo, is a small, sheltered natural embayment; and Baia dos Tigres, which lies 100 km south of Tombua Bay, is a sheltered lagoon in the lee of an island ~ 10 km from the mainland. Tagging occurred in two batches, one year apart. In the first batch, sub-adults (n = 3) and adults (n = 17) were tagged and monitored for two years. In the second batch, juveniles (n = 7) and sub-adults (n = 3) were tagged and monitored for one year. The first objective of this thesis (Chapter 3) was to examine the spatio-temporal dynamics of A. coronus at a regional-level (across study sites, to investigate the prevalence of the longshore migration), and at a local-level (within a study site), and to categorise the movement behaviour of juveniles, sub-adults and adults. Traditional seasons were not used in this thesis, as the study region alternates between ‘warm’ periods (up to ~ 26 °C mean daily water temperature), when Angola Current water covers the area, and ‘cold’ periods (down to ~ 15 °C mean daily water temperature), when Benguela Current water covers the area. A high degree of residency of tagged fish to the Flamingo study site, where tagging was conducted, was found, with juveniles and sub-adults never being detected outside of the Flamingo study site. Five adults (29 %) were detected haphazardly for between one and 36 days at Tombua Bay, following which they were typically detected again at the Flamingo study site. No fish were ever detected at the southernmost site, Baia dos Tigres, suggesting that none migrated to Namibia. Within the Flamingo study site, adults were found to group at the inshore mid-region of the study site during ‘cold’ periods, dispersing again during ‘warm’ periods, when there was a concomitant offshore shift in their area use. This explained the absence of the species from catches in the shore-based recreational fishery during ‘warm’ periods. These results challenge previous migration hypotheses for the species. Therefore, longshore return migrations which were evident from previously conducted conventional tagging, are probably not the norm for the species, but likely occur at a low frequency. The species exhibited a high degree of residency to their tagging site, despite the drastic seasonal changes in water temperatures and station-keeping was the dominant behaviour across all life stages. The constrained area-use noted in this study, relative to the known distribution of the species, suggests that A. coronus exists as a metapopulation, consisting of a network of subpopulations interconnected by gene flow that is most likely facilitated during their pelagic egg and larval phase. The second objective of this thesis was to examine the group formation observed at the Flamingo study site during ‘cold’ periods (Chapter 4). While this grouping of individuals was found to be correlated with water temperature, it was unlikely to be a causal relationship, as the water temperature was not dissimilar to adjacent areas. The area where individuals were concentrated is known to frequently attract large shoals of their dominant prey, Sardinella aurita. While the timing of this group formation aligns with a pre-spawning period, no studies have assessed the existence of local spawning. A. coronus were, however, likely utilising an abundant prey source, during the important pre-spawning period, in order to build up energy reserves. Group formation is a common feature of sciaenids, but literature on the subject is restricted to spawning congregations. Fish are not only more vulnerable to capture during these periods but may also be disturbed during these potentially important social periods. The third objective of this thesis was to investigate the presence of sociality in the species (Chapter 5). Evidence for sociality during and outside the seasonal group formation was explored using network analyses. There was evidence for sociality, with several groups, characterized by co-locations among individuals, identified. While these groups were fluid through time, there was evidence of persistent sociality, with two individuals in particular being consistently co-located over the entire study period. Due to the persistent nature of sociality, group foraging is suggested as an explanation for this, with anecdotal evidence of coordinated hunting supporting this. Acoustic telemetry vastly improved the knowledge of the movement ecology of A. coronus. Despite their panmictic population genetic structure, they were found to be largely resident, likely occurring as a metapopulation across their distribution, with egg and larval dispersal likely the primary mechanism for maintaining panmixia. Evidence for sociality was also found, which was previously unexplored in the species. The persistent nature of social groupings throughout the year, suggests that it may be linked with group foraging and is supported by anecdotal evidence of coordinated hunting by the species. While this study highlights the value of acoustic telemetry in studying movement ecology, it also shows the importance of drawing on multiple methods to fully understand a species’ spatial ecology, including mark-recapture, population genetics, and fishery catch and effort data. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
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- Date Issued: 2023-10-13
Spatial analysis of littoral and demersal fish assemblages within the Knysna Estuary system
- Authors: Meiklejohn, Andrew Keith
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424334 , vital:72144
- Description: The Knysna Estuary is a unique system as it is the only “estuarine bay” system in the warm-temperate region of South Africa and is the largest estuary system on the southern coastline of South Africa. The Knysna Estuary has been identified as the estuary with the highest conversation priority in South Africa. The volume of research undertaken on the Knysna Estuary has led to it being rated “excellent” in terms of research productivity. However, despite this, surprisingly little work has been undertaken and published around the dynamics of fish assemblages occurring in the system, with little to no research assessing the demersal fish assemblage. The last widespread fish sampling effort that has been published was conducted in 1994, highlighting the need for an updated fish assessment with a focused sampling effort targeting both the littoral and demersal fish populations. The identification of key habitats for estuarine fish assemblages is essential for addressing estuarine conservation needs. Despite the importance of spatial data in addressing conservation planning, few estuarine studies have used spatial analyses in Geographic Information Systems (GIS) to identify conservation priority areas. Such information is critical for effective estuarine management plans. The aim of this project was to identify juvenile fish density hotspots to inform future systematic conservation planning. This study made use of two methods of sampling, seine netting to target the littoral fish assemblage and beam trawling to target demersal fish species. Two dedicated sampling trips for each sampling method were undertaken in June 2021 and March 2022 for Seine net sampling and November 2021 and March 2022 for Beam trawl sampling. Fish were identified to species level, measured (mm TL) and categorised into life history stages (i.e. settlement stage, juvenile and adult) and thereafter assigned into their various estuarine association guilds. A total of 47 species were recorded, with 42 species were caught in the seine net sampling and 24 species in the beam trawl sampling. The results from this study showed the vast extent of marine dominance in the Knysna Estuary, with marine estuarine-opportunist (MEO) species dominating catches (richness) from both sampling methods. The spatial analysis highlighted the importance of the lower “marine bay” region of the system, with the majority of estuarine guilds showing a high abundance in this region. Key fishery species and dominant fish species were identified during this study, the dominant species during the sampling effort were identified as ecologically important fish species and were dominated by adult specimens. The key fishery species sampled during this study were dominated by juvenile specimens. This highlights the role of the Knysna Estuary as a nursery area for juvenile fishery species and the contribution of the estuary to the estuarine and adjacent coastal fisheries. Key hotspots were identified for fishery species, these being the “Ashmead Channel” in the marine bay region and the “Belvidere” section of the lagoon region. Ashmead channel is sheltered backwater area while the Belvidere section is some distance from the main river channel, reducing the anthropogenic impact on these areas. The low anthropogenic utilization of these areas along with weaker water current in these regions was linked to the usage of these region by key fishery species. These areas were highlighted as important conservation hotspots with both currently not adequately protected under the current habitat sensitivity management model. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
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- Date Issued: 2023-10-13
Spatiotemporal ecology and potential displacement of white sharks in southern Africa
- Authors: Towner, Alison
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/432275 , vital:72857
- Description: Restricted access. Expected release date in 2025. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
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- Date Issued: 2023-10-13
Species diversity and distribution patterns of three freshwater fish genera in southern Africa
- Authors: Mutizwa, Tadiwa Isaac
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/431896 , vital:72813
- Description: Access restricted. Expected release in 2025. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
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- Date Issued: 2023-10-13
The androgenic and anabolic effects of pine pollen on Nile tilapia (Oreochromis niloticus)
- Authors: Abaho, Ivan
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/431615 , vital:72790
- Description: Access restricted. Expected release date in 2025 , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
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- Date Issued: 2023-10-13
The effects of exploitation on the activity of Chrysoblephus laticeps in a thermally variable environment
- Authors: Mlotshwa, Nonhle Thubelihle
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424346 , vital:72145
- Description: Embargoed. Expected release date 2025. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
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- Date Issued: 2023-10-13
Thermal physiology of juvenile red roman seabream, Chrysoblephus laticeps after long-term exposure to low pH conditions
- Authors: Allison, Caitlin
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424323 , vital:72143
- Description: Climate change has caused a combination of effects on the physiology of fishes. Of particular concern are the effects of thermal variability and ocean acidification. Organismal energy budgets change throughout ontogeny and research into the metabolic scope during early life stages is particularly useful in identifying potential bottlenecks. The first part of this thesis aimed to assess the absolute aerobic scope (AAS, described as the difference between the maximum and standard metabolic rates) of individual juveniles from a protected population of the endemic, commercially important seabream, Chrysoblephus laticeps, across a range of ecologically relevant temperatures (T = 11, 14, 18, 22˚C) under present-day conditions (pH = 8.03, pCO2 ≈ 420 μatm) using intermittent flow respirometry. The second component sought to investigate how long-term exposure (from fertilisation to juvenile, ~100 days exposure) to high-pCO2/hypercapnic conditions (pH = 7.63, pCO2 ≈ 1400 μatm), would affect the AAS of juvenile C. laticeps over a range of temperatures. Lower pH conditions were predicted to cause a decrease in the AAS of treatment animals due to additional energetic costs of acid-base regulation. The findings of the first data chapter demonstrated that juvenile C. laticeps reared under current CO2 conditions are tolerant to a wide range of thermal conditions, and individuals with a broad aerobic scope will be the best suited to coping with enhanced thermal variability. In contrast to the expected outcomes of the second data chapter, juvenile C. laticeps reared under high pCO2 conditions displayed greater AAS at high and low temperatures when compared with specimens from high pH conditions. Whilst a high degree of individual phenotypic variation was observed in the metabolic response of both groups, this was reduced at the lower and upper extreme temperatures for high pH and low pH animals respectively. Notably, the variation in treatment animal’s SMR was significantly diminished across all temperatures tested, compared to only a localised reduction in the SMR of high pH animals at cold temperatures. This may be indicative of compensatory pathways affecting energy restructuring and thermally-governed physiological trade-offs under hypercapnia. Given these results, juvenile C. laticeps appear to be more resilient to ocean acidification than anticipated, potentially owing to intrapopulation metabolic phenotypic diversity. This is likely attributed to the parental lineage originating in the Tsitsikamma MPA, which is thought to boast greater phenotypic diversity as a consequence of the refuge that these conservation areas offer from exploitation. Owing to the restriction imposed by the availability of surviving, captive-reared juveniles, the sample size used in this study was relatively low. However, owing to the repeated-measures nature of this research the sample size was sufficient to offer suitable statistical power for the polynomial mixed model used in the analysis. Future research should incorporate both physiological and behavioural responses to multiple environmental stressors to better understand covariation between these two traits, and to detect any behavioural trade-offs that might arise through compensation. In addition, these trials should be repeated using offspring from outside of the MPA to compare whether the same level of resilience and metabolic phenotypic diversity would be present in an exploited population. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
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- Date Issued: 2023-10-13
Towards a better understanding of small-scale fishing decisions and their consequences in Northern Mozambique
- Authors: Heckendorn, Katrina Ann
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/431797 , vital:72805 , DOI 10.21504/10962/431797
- Description: This study investigates the relationship between the interacting social and ecological systems within the Pemba Bay fishery, in Northern Mozambique, as mediated by fishing decisions. All ecosystems in the world are affected by human behaviours in some way. In many cases, human effects on ecosystems are detrimental to many other species and can cause shifts in the entire system. In fisheries, the connections between human behaviours and ecosystems are obvious, as fishers extract wild populations of marine species. Human behavioural plasticity and sometimes rapid cultural evolution allow human behaviours to change and adapt faster than many other species can respond which often allows fishers to overexploit marine ecosystems. Many fisheries in the world are fully, or over exploited. Managing these fisheries often focuses on changing those highly adaptable human behaviours. Fishers’ motivations for making different fishing decisions as well as attitudes towards the fishery can be used to understand human interactions with ecosystems when the dependence between the two is direct, as well as allowing managers to tailor interventions that account for fishers’ motivations and attitudes. Most fisheries’ management projects assume that behaviours are motivated by profit maximization. This study investigates this assumption by comparing the compatibility of interview responses and fishing behaviours with rational actor theory, which assumes profit maximization is the only goal. Responses are also compared with prospect theory, which emphasizes reliability of outcomes; descriptive norms, which focuses on social interactions; habitual behaviour, which assumes most decision are automatic based on habit; and theory of planned behaviour, which allows attitudes to be shaped by economic or non-economic motivations, as well as peer opinion and incorporates perceived behavioural control in making decisions. These behavioural theories span a variety of potential fisher motivations which could affect fishing decisions. The study then investigates the state of the social and ecological systems which have resulted, at least in part, from those fishing decisions, and makes recommendations on possible interventions to improve the system based on better understanding of fishers’ attitudes and motivations. The study tests the hypothesis that fishers are motivated primarily by profit maximization and, therefore, rational actor theory is most compatible with fishers’ stated motivations for fishing, or alternatively, that one of the other behavioural theories better explains fisher responses. This section used categorized interview responses based on their agreement, or not, with assumed responses if a particular behavioural theory were compatible. The results indicate that four of the five theories are most compatible with responses for at least one fisher, but that the theory of planned behaviour is the most consistent with the data overall, not rational actor theory. Specifically, fishers seem concerned with behavioural control as well as some non-catch related characteristics of the fishery, such as collective action and sustainability. The second hypothesis is that prospect theory is more compatible with current fishing behaviours than rational actor theory. Prospect theory states that people prefer more reliable outcomes, even if slightly less profitable, than outcomes which are more profitable on average, but also more variable. This section used catch data, and changes in relative use of different fishing methods to address this hypothesis. This hypothesis is confirmed for some aspects of fishery data, but not all. Fishers prefer methods which are more reliable and these methods are increasing in relative use. However, neither catch value nor reliability increases fishers’ opinions of their fishing method, but fisher characteristics which increase options do. This again indicates that behavioural control is important in determining fishers’ attitudes towards fishing. The third question addresses the social system within the fishery. It investigates whether fishing in Pemba Bay is a chosen profession or a livelihood of desperation from the poorest individuals. The study hypothesizes that fishers are as well-off as their non-fishing neighbours, and fishers who use more reliable or profitable methods are better off than those using less reliable/profitable methods and, as such, are more committed to fishing as a way of life. This section used fisher interview responses and household surveys to compare subjective and material wellbeing of fishers and non-fishers around Pemba Bay. The first part of the hypothesis is partly supported. Fishers using most methods have material standards of living comparable to non-fishers. However, they report lower subjective well-beings. Most measures of wellbeing are not affected by the reliability or profitability of the fishing method used, which does not support the second part of the hypothesis. Additionally, fishers using more profitable or reliable methods do not indicate more commitment to fishing as a way of life. The fourth and final section investigates the marine ecosystem. Based on conversations with fishers and local researchers, it is assumed that the Pemba fishery is overexploited. As such, the study hypothesizes that marine biomass, individual size of marine species, and functional diversity are lower in Pemba Bay than in other sites around Northern Mozambique, Vamizi Island, Situ Island, and Nuarro, due to high fishing pressure, and that direct removal of species by fishing has a dominant effect. This final section used baited remote underwater videos (BRUVs) to compare species composition and indices of abundance from the different locations. Again, there is support for part of this hypothesis. Marine species biomass and sizes are lower in Pemba Bay than other sites in Northern Mozambique; however, functional diversity is not different. In these data, changes in biomass and size are not correlated with amount of catch, so direct removal by fishing may not be the dominant source of change in the Pemba fishery. Together, these data indicate that the Pemba fishery may be unsustainable based on social and ecological indications. The importance of behavioural control in understanding fishing decisions indicates that any interventions to mitigate problems in the fishery will need to work with fishers to increase empowerment and allow experimentation to find locally relevant solutions to problems. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
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- Date Issued: 2023-10-13