Occurrence of early stage fishes associated with Anaulus australis in a temperate South African surf zone, with notes on feeding ecology and incidental microplastic consumption in a dominant species
- Authors: McGregor, Steven
- Date: 2020
- Subjects: Estuarine fishes -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48489 , vital:40881
- Description: Surf zones are important fish nursery areas, however, microhabitats and threats to fishes within them remain understudied. Diatom accumulations in surf zones are a worldwide phenomenon on certain beach types and discolour the water, offering refuge from visual predators and feeding opportunities for fishes, thus providing a microhabitat for early stage fishes. Surf diatom accumulations require long lasting rip current-entrained gyres to occur, which also entrap buoyant microplastics. These microplastics may then be consumed by filter feeding fishes such as the Southern mullet Chelon richardsonii. This work aimed to assess the extent of association of early stage fishes with diatom Anaulus australis accumulations and the feeding ecology and incidence of microplastic ingestion in the commercially important and dominant surf zone mugilid C. richardsonii. Early stage fishes were sampled within and outside of A. australis accumulations in the Sundays Beach surf zone on the southeast coast of South Africa, using a 4.5 x 1.5 m modified larval seine net with 500 µm mesh. Later developmental stage C. richardsonii were captured using a cast net. A total of 338 replicate larval fish seine hauls were done, capturing 1074 fishes including 33 taxa from 19 families. To assess ontogenetic shifts in diet of the dominant species C. richardsonii, stomach contents of 150 fish were categorised and assessed by prey abundance, frequency of occurrence, volume, index of relative importance and dietary niche breadth and compared across all developmental stages, excluding flexion and preflexion. Dominant families of early stage fishes were Sparidae, Soleidae, Mugilidae and Clupeidae that comprised 93 % of the catch, with dominant species including Heteromycteris capensis, Rhabdosargus holubi, Solea turbynei, Diplodus capensis and Chelon richardsonii. Species diversity and catch per unit effort (CPUE) were significantly higher within accumulations compared to outside, as was the CPUE of postflexion larvae and early juveniles. Generalized Linear Models showed that temperature, dissolved oxygen (mg l-1 ), turbidity and A. australis biomass (µg Chl a l -1 ) were the most significant factors affecting the overall CPUE and that of dominant species. It was suggested that after reaching the postflexion stage of development, fishes utilise diatom accumulations opportunistically when and where they are present. A diet study of the dominant species showed an ontogenetic dietary shift in C. richardsonii using A. australis accumulations as a feeding area, with postflexion larvae feeding mostly on copepods and microplastic fibres, while later developmental stages consumed predominantly A. australis cells and sand. Microplastic fibres were present in 40 % of fish sampled and microplastic fragments in 5 %, with both types found in all developmental stages assessed. It was suggested that C. richardsonii were unable to distinguish microplastics from their natural prey and incidentally ingested them. This presents a conservation concern, because chemicals associated with microplastics could bioaccumulate and biomagnify up the food chain if key baitfish species such as C. richardsonii are ingesting plastic. This study was the first to assess the association of early stage fishes with surf diatom accumulations, and the first to record microplastic ingestion in C. richardsonii. Understanding the function of microhabitats for early stage fishes and threats within them is needed to understand the life history strategies and survival of fishes in key coastal nursery and feeding areas.
- Full Text:
- Date Issued: 2020
- Authors: McGregor, Steven
- Date: 2020
- Subjects: Estuarine fishes -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48489 , vital:40881
- Description: Surf zones are important fish nursery areas, however, microhabitats and threats to fishes within them remain understudied. Diatom accumulations in surf zones are a worldwide phenomenon on certain beach types and discolour the water, offering refuge from visual predators and feeding opportunities for fishes, thus providing a microhabitat for early stage fishes. Surf diatom accumulations require long lasting rip current-entrained gyres to occur, which also entrap buoyant microplastics. These microplastics may then be consumed by filter feeding fishes such as the Southern mullet Chelon richardsonii. This work aimed to assess the extent of association of early stage fishes with diatom Anaulus australis accumulations and the feeding ecology and incidence of microplastic ingestion in the commercially important and dominant surf zone mugilid C. richardsonii. Early stage fishes were sampled within and outside of A. australis accumulations in the Sundays Beach surf zone on the southeast coast of South Africa, using a 4.5 x 1.5 m modified larval seine net with 500 µm mesh. Later developmental stage C. richardsonii were captured using a cast net. A total of 338 replicate larval fish seine hauls were done, capturing 1074 fishes including 33 taxa from 19 families. To assess ontogenetic shifts in diet of the dominant species C. richardsonii, stomach contents of 150 fish were categorised and assessed by prey abundance, frequency of occurrence, volume, index of relative importance and dietary niche breadth and compared across all developmental stages, excluding flexion and preflexion. Dominant families of early stage fishes were Sparidae, Soleidae, Mugilidae and Clupeidae that comprised 93 % of the catch, with dominant species including Heteromycteris capensis, Rhabdosargus holubi, Solea turbynei, Diplodus capensis and Chelon richardsonii. Species diversity and catch per unit effort (CPUE) were significantly higher within accumulations compared to outside, as was the CPUE of postflexion larvae and early juveniles. Generalized Linear Models showed that temperature, dissolved oxygen (mg l-1 ), turbidity and A. australis biomass (µg Chl a l -1 ) were the most significant factors affecting the overall CPUE and that of dominant species. It was suggested that after reaching the postflexion stage of development, fishes utilise diatom accumulations opportunistically when and where they are present. A diet study of the dominant species showed an ontogenetic dietary shift in C. richardsonii using A. australis accumulations as a feeding area, with postflexion larvae feeding mostly on copepods and microplastic fibres, while later developmental stages consumed predominantly A. australis cells and sand. Microplastic fibres were present in 40 % of fish sampled and microplastic fragments in 5 %, with both types found in all developmental stages assessed. It was suggested that C. richardsonii were unable to distinguish microplastics from their natural prey and incidentally ingested them. This presents a conservation concern, because chemicals associated with microplastics could bioaccumulate and biomagnify up the food chain if key baitfish species such as C. richardsonii are ingesting plastic. This study was the first to assess the association of early stage fishes with surf diatom accumulations, and the first to record microplastic ingestion in C. richardsonii. Understanding the function of microhabitats for early stage fishes and threats within them is needed to understand the life history strategies and survival of fishes in key coastal nursery and feeding areas.
- Full Text:
- Date Issued: 2020
Sidumo revisited
- Authors: Boyens, Marthinus Johannes
- Date: 2015
- Subjects: Judicial review -- South Africa , Judgments -- South Africa , Labor courts -- South Africa
- Language: English
- Type: Thesis , Masters , LLM
- Identifier: vital:10249 , http://hdl.handle.net/10948/d1020117
- Description: The primary purpose of this treatise is to revisit and reconsider the development of the review test set out in the Constitutional Court judgment of Sidumo & another v Rustenburg Platinum Mines Ltd & Others (2007) 28 ILJ 2405 (CC) and consequently ascertain the correct approach to be adopted by our Labour Courts in the application of such test. The secondary purpose, entail the determination of the extent to which Labour Court judges interfere with the merits of awards and the resulting impact on the distinction between appeal and review. In order to establish whether the test for review was correctly developed and to determine whether our review proceedings deter recurrent interference by our judges, an edifying consideration of judicial review in South Africa, an extensive analysis of various judgements pertaining to such development, followed by a comprehensive comparison with the United Kingdom`s application of review proceedings and judicial composition are made. The research methodology is based on a contour of Sidumo, commencing with the Sidumo judgment, followed by three contentious Labour Appeal Court judgments and concluding with a Supreme Court of Appeal judgement, which clarifies the operation of the review test. The contour is interlinked with the notion of reasonableness. The primary research findings are identified in the judgment of Herholdt v Nedbank Ltd (2013) 34 ILJ 2795 (SCA). The judgment, concluding the Sidumo contour, underlines the current position in our law and consequent narrower approach. A comparison made with the United Kingdom, differentiate between such approach implemented by our courts and the strict gross unreasonableness approach applied by Employment Appeal Tribunals, recognising the finding, that our Labour Court judges ardently interfere with the merits of awards. In the conclusion it is submitted that our labour law jurisprudence will constantly evolve, dictated by our courts interpretation of lawfulness, reasonableness and fairness.
- Full Text:
- Date Issued: 2015
- Authors: Boyens, Marthinus Johannes
- Date: 2015
- Subjects: Judicial review -- South Africa , Judgments -- South Africa , Labor courts -- South Africa
- Language: English
- Type: Thesis , Masters , LLM
- Identifier: vital:10249 , http://hdl.handle.net/10948/d1020117
- Description: The primary purpose of this treatise is to revisit and reconsider the development of the review test set out in the Constitutional Court judgment of Sidumo & another v Rustenburg Platinum Mines Ltd & Others (2007) 28 ILJ 2405 (CC) and consequently ascertain the correct approach to be adopted by our Labour Courts in the application of such test. The secondary purpose, entail the determination of the extent to which Labour Court judges interfere with the merits of awards and the resulting impact on the distinction between appeal and review. In order to establish whether the test for review was correctly developed and to determine whether our review proceedings deter recurrent interference by our judges, an edifying consideration of judicial review in South Africa, an extensive analysis of various judgements pertaining to such development, followed by a comprehensive comparison with the United Kingdom`s application of review proceedings and judicial composition are made. The research methodology is based on a contour of Sidumo, commencing with the Sidumo judgment, followed by three contentious Labour Appeal Court judgments and concluding with a Supreme Court of Appeal judgement, which clarifies the operation of the review test. The contour is interlinked with the notion of reasonableness. The primary research findings are identified in the judgment of Herholdt v Nedbank Ltd (2013) 34 ILJ 2795 (SCA). The judgment, concluding the Sidumo contour, underlines the current position in our law and consequent narrower approach. A comparison made with the United Kingdom, differentiate between such approach implemented by our courts and the strict gross unreasonableness approach applied by Employment Appeal Tribunals, recognising the finding, that our Labour Court judges ardently interfere with the merits of awards. In the conclusion it is submitted that our labour law jurisprudence will constantly evolve, dictated by our courts interpretation of lawfulness, reasonableness and fairness.
- Full Text:
- Date Issued: 2015
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