Stock structure of Patagonian toothfish Dissostichus eleginoides (Smitt 1898, family Nototheniidae) in the Southwest Atlantic
- Authors: Lee, Brendon
- Date: 2022-10-14
- Subjects: Otoliths , Patagonian toothfish Geographical distribution , Fish tagging , Biogeography , Microstructure , Microchemistry
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365599 , vital:65763 , DOI https://doi.org/10.21504/10962/365599
- Description: The identification of discrete self-sustaining productive units in marine populations is essential for achieving sustainable fisheries objectives. Marine fish populations frequently exhibit dynamic characteristics across their life-histories, displaying variability in spatial structure and mixing patterns, both within and among populations. The incoherent application of management boundaries on biological populations can bias stock assessment results and have important implications on sustainable fisheries management. Patagonian toothfish (Dissostichus eleginoides) is a long-lived, slow-growing, late-maturing, deep-sea, benthopelagic species. It forms the basis of important and highly lucrative industrial and artisanal fisheries across its distribution. Patagonian toothfish have complex life-histories characterised by high dispersal potential during the egg and larval phase, a wide depth range because of their ontogenetic migratory behaviour, and large adult size that is capable of undertaking long-distance active movements (>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. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
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- Date Issued: 2022-10-14
The biology of Oreochromis mossambicus and vulnerability to the invasion of Oreochromis niloticus
- Authors: Mpanza, Nobuhle Phumzile
- Date: 2022-10-14
- Subjects: Ecomorphology , Mozambique tilapia , Nile tilapia , Introduced fishes , Predatory aquatic animals , Predation (Biology) , Otoliths , Von Bertalanffy function
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362983 , vital:65380
- Description: Mozambique tilapia, Oreochromis mossambicus, a native southern African species now co-occurs with invasive Nile tilapia, Oreochromis niloticus throughout much of the distribution of the former. The spread of O. niloticus in South Africa has been attributed to escapees from aquaculture facilities, placing O. mossambicus at risk through competition for habitat and food resources, as well as through hybridisation. To better manage invasions, a comprehensive understanding of the biology, ecology and behaviour of both native and invasive species is required. The aim of this research was to comparatively assess the biology of O. mossambicus and O. niloticus, their food resource use characteristics and potential competitive interactions to infer impact risks associated with O. niloticus invasion dynamics. In addition to lack of sufficient autecological knowledge on O. niloticus in general, the challenge in the Eastern Cape is that relatively little regional knowledge is available on the biology and ecology of the native O. mossambicus. To address this, a total of 101 O. mossambicus individuals (32 - 297 mm LT) were sampled from the Sunday River catchment and their age and growth determined using sectioned sagittal otoliths. The largest female was 288.8 mm with a parameter estimate of LT (mm) = 272 (1-e-0.331(t=0.772)) and the largest male was 297 mm described as LT (mm) = 331.9 (1-e-0.167(t=1.192)). The growth parameter estimate age for combined sexes was best described as LT (mm) = 322.5 (1-e-0.201(t=1.027)). The growth rate was initially rapid for O. mossambicus and the asymptotic length reached after four years. The length-at-50% maturity was reached at 106.45 mm LT (R2 = 0.57) for the entire population. There was a significant difference (ᵡ2 = 8,047, df = 1, p-value = 0.0045) in the sex ratio between males and females which was skewed towards males 1:1.89 (F:M). Comparisons with O. niloticus were based on literature and these showed that O. niloticus had faster growth rates than O. mossambicus. These results serve as a baseline study in predicting the potential impacts of O. niloticus if it was to be introduced in the Eastern Cape region. Furthermore, although these two species are known to share habitat and food resources, feeding dynamics within the context of relative impact on prey resources, and competition potential between the species, are largely lacking. I used experimental functional response procedures to contrast the food consumption dynamics of each species and to assess for any multiple predator effects (MPEs) between these two closely related fishes. This was done by contrasting functional responses between individual species under single predator scenarios, predicted multiple predator functional response dynamics based on the individual species outputs, and actually observed functional responses under multiple predator conditions. Results showed that both Nile tilapia and Mozambique tilapia depicted a destabilizing Type II functional response. In both single and conspecific pairing Nile tilapia had significantly greater functional responses than Mozambique tilapia, hence greater overall predatory potential than its native congeneric Mozambique tilapia. Attack rates were also greater for Nile tilapia than Mozambique tilapia with both species showing similar handling times in single trials. However, no evidence for MPEs were detected, given lack of differences between predicted and observed functional responses under heterospecific conditions. These results suggest that Nile tilapia do not adjust their food intake in the presence of heterospecific competitors, but do consume more than Mozambique tilapia and are better at finding food when it is present at low densities. Feeding-related morphological characteristics may influence predatory performance of a species and can further provide information on the species’ capacity to locate, attack and consume different prey items. The feeding capacities between O. mossambicus and O. niloticus were compared based on morphological traits in order to determine whether differences existed, and if these differences place the invasive O. niloticus at an advantageous position in terms of resource acquisition and consumption over its native congener. Principal component analysis for functional morphology traits showed overlap between O. niloticus and O. mossambicus. Oreochromis niloticus had distinctively larger lower jaw closing force, gill resistance and gill raker length which facilitated greater feeding capacities for the invasive species over the native O. mossambicus. Trophic profiles depicted high dietary overlap between the two species. Although O. niloticus had a greater feeding capacity towards phytoplankton, plants, fish (ambush), fish (pursuit) and larvae, while O. mossambicus only showed greater feeding capacity towards zooplankton. While dietary overlap and similarities in morphological traits between native and invasive species may result in exploitative competition between the species, O. niloticus seems to be more versatile in its feeding and capable of consuming food web components that O. mossambicus may not be able to handle. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
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- Date Issued: 2022-10-14
Age of squid Loligo reynaudii d’Orbigny, 1845, and its possible use to test effectiveness of the closed season in protecting this resource
- Authors: Mwanangombe, Collette Habani
- Date: 2020
- Subjects: Loliginidae -- Spawning -- South Africa , Loliginidae -- Age determination , Loligo fisheries -- South Africa , Fishery management -- South Africa , Otoliths , Loliginidae – Eggs -- Incubation , Loliginidae – Growth , Fish stock assessment -- South Africa , Recruitment (Population biology) -- South Africa , Loligo reynaudii d’Orbigny
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144333 , vital:38336
- Description: This study presents age distributions representing populations of adult Loligo reynaudii, together with the results of spawning and commercial catches to assist in understanding the beneficial role of the closed season. The results were based on 791 samples collected during three closed seasons (November: 2003, 2004 and 2005) and out of closed season during April/May 2005. Age and predicted growth were examined by counting daily rings on statolith microstructures. The age in days after hatching ranged from 168 to 484 days (71-425 mm) in males and from 125 to 478 days (83-263 mm) in females. Average age at spawning was found to be 323 days in males and 316 days in females. Population estimates of growth rates were best described by a linear growth model which revealed that males grew faster than females in length as they grew older with growth rate ranging between 0.63 to 0.83 mm per day for males and between 0.22 to 0.32 mm per day for females. Back-calculated hatch dates and later egg-laying events for parental populations were determined. Results from back calculated egg laying dates (presented as percentage of frequency of all laying dates) indicated a highest total of 36%, 39% and 15% of eggs from all samples were laid during the closed season and nine days after the closed season during year 2003, 2004 and 2005 respectively. Monthly commercial total catches (2002-2005) showed an increase from November soon after the fishery resumed, up until the month of January. Daily catches were highest in November (up to 290 tonnes) relative to the daily catches observed in December and January in all the years. Results led to the conclusion that the closed season (25 October to 22 November) is beneficial for both the chokka resource and the fishery. This is because: a) there is time for enough spawning biomass to accumulate, which subsequently results in high catches (good fishery), in the current year, best immediately after season opens in November; b) there is a link in the results between egg laying dates in the period of closed season and immediately afterwards, and the magnitude of catches in last nine days of November.
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- Date Issued: 2020
Biology and ecology of largemouth bass Micropterus salmoides in two temperate South African impoundments
- Authors: Taylor, Geraldine Claire
- Date: 2013 , 2013-03-19
- Subjects: Largemouth bass -- Ecology -- South Africa -- Eastern Cape , Largemouth bass -- Behavior -- South Africa -- Eastern Cape , Largemouth bass -- Growth -- South Africa -- Eastern Cape , Largemouth bass -- Reproduction -- South Africa -- Eastern Cape , Largemouth bass -- Food -- South Africa -- Eastern Cape , Largemouth bass -- Age determination -- South Africa -- Eastern Cape , Introduced fishes -- South Africa -- Eastern Cape , Fish populations -- South Africa -- Eastern Cape , Otoliths , Largemouth bass -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5181 , http://hdl.handle.net/10962/d1001668 , Largemouth bass -- Ecology -- South Africa -- Eastern Cape , Largemouth bass -- Behavior -- South Africa -- Eastern Cape , Largemouth bass -- Growth -- South Africa -- Eastern Cape , Largemouth bass -- Reproduction -- South Africa -- Eastern Cape , Largemouth bass -- Food -- South Africa -- Eastern Cape , Largemouth bass -- Age determination -- South Africa -- Eastern Cape , Introduced fishes -- South Africa -- Eastern Cape , Fish populations -- South Africa -- Eastern Cape , Otoliths
- Description: Globally largemouth bass Micropterus salmoides is one of the most widely introduced game fish species which has now become invasive in many countries. Well researched in its native North America, there are few studies on this species in its introduced range. This study aims to improve the understanding of the biology and ecology of M. salmoides in temperate southern Africa, where it threatens native biota and supports a popular recreational fishery. This aim was addressed by assessing the age, growth, maturity, reproductive seasonality, feeding, mortality and movement, of two M. salmoides populations from Wriggleswade (1000 ha, 723 m amsl, 32º35'S; 27º33'E) and Mankazana (35 ha, 66 m amsl, 33º09'S; 26º57'E) Dams in the Eastern Cape of South Africa. The most suitable structure for ageing M. salmoides was determined by comparing the accuracy and precision of otoliths and scales. Scales tended to underestimate the age of fish older than five years. Sectioned sagittal otoliths were the more precise structures for ageing (otoliths CV = 15.8 vs. scales CV = 21.9). The periodicity of growth zone formation was validated as annual for otoliths using both edge analysis (EA), and mark recapture of chemically tagged fish (MRCT). EA indicated one annual peak in the frequency of opaque margins between September and January using a periodic logistic regression and a binomial model linked with a von Mises distribution for circular data. MRCT showed the linear relationship between time at liberty and number of growth zones distal to the fluorescent band was not significantly different from one (slope = 0.89). Reproduction was similar to that in native and non-native populations with fish reaching age at 50% maturity at ca. two years, and length at 50% maturity at 259-290 mm FL depending on growth rate. Spawning season occurred in the spring months of August to October. The Wriggleswade Dam population reached similar ages (14 yrs) to populations in temperate North America. Growth was described using the von Bertalanffy growth equations of (Lt = 420(1-ᵉ⁻°·³³⁽ᵗ⁺°·²¹⁾) mm FL in Wriggleswade and (Lt = 641(1-ᵉ⁻°·²²⁽ᵗ⁺°·⁷⁶⁾) mm FL in Mankazana. Growth performance of both populations, described using the phi prime index, seemed to be correlated with temperature and the Wriggleswade Dam population (Φ’ = 2.8) grew similarly to those native temperate North American populations and the non-native populations of Japan and Italy. The Mankazana population had a higher growth performance (Φ’ = 2.9) compared to Wriggleswade and growth was comparable to other nonnative African populations. Both populations utilised all available food resources, with the Mankazana population being in better condition than the Wriggleswade population as a result of a more diverse diet, highly abundant food sources throughout the year, and potentially the adoption of a more conservative ambush feeding strategy. The Wriggleswade population, which was utilised by competitive anglers, showed low mortality rates (Z = 0.43 yr⁻¹), and translocated fish dispersed from the common release site, travelling an average distance of 4km over the study time of 494 days. These results indicated that M. salmoides are successful in these environments, growing at expected temperature dependant rates, maturing at two years, using all available food groups, and suffering from low mortality. It is therefore likely that they will persist in South Africa and establish where introduced.
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- Date Issued: 2013
The growth characteristics of sparid otoliths
- Authors: Lang, Judy Brenda
- Date: 1992
- Subjects: Fishes -- Age determination , Otoliths , Sparidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5285 , http://hdl.handle.net/10962/d1005129 , Fishes -- Age determination , Otoliths , Sparidae
- Description: The periodicity of formation of growth increments in the otoliths of South African sparids was validated by the oxytetracycline labelling technique. Intramuscular injections of oxytetracycline at a dosage of 250mg/kg marked the otoliths of laboratory held juvenile sparids, while a dosage range of 50 - 100mg/kg oxytetracycline, injected intramuscularly, marked adult sparids in the field. Laboratory held, larval sparid otoliths were marked by immersion for 24hrs a solution of 100-150mg/l alizarin complexone. Both daily (microstructural) and annual (macrostructural) growth increments were identified in the otoliths. The micro incremental pattern of deposition in the sparid otoliths conformed to the general pattern of otolith structure. Sparid otoliths consisted of a central opaque nucleus composed of multiple primordia. surrounding this nucleus were daily increments which decreased in width as the distance from the nucleus increased. Both check rings and subdaily increments were visible throughout the otolith. Minor environmental changes did not affect micro incremental deposition. Narrow opaque and wide hyaline annual growth zones were identified in sectioned sparid otoliths. Scanning electron microscope analysis of the annual growth zones revealed that microincrements within the opaque zone were narrowly spaced with prominent discontinuous phases. This resulted in the greater optical density and higher protein content of the zone. The hyaline zone was composed of widely spaced daily increments with prominent incremental phases accounting for the translucent nature of this zone. Opaque zone formation in the otoliths of many South African sparids was found to occur primarily during periods of reproductive activity and was shown to be indicative of slow otolith growth. The hyaline zone was formed after the spawning season, representative of fast otolith growth. The results of this study have resolved much of the controversy surrounding the rate of growth and time of formation of the opaque and hyaline growth zones in South African sparid otoliths.
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- Date Issued: 1992