Browsing by Author "Arendse, Clement"

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    Does the implementation of a closed Fishing Season during the breeding Season benefit a Species? A per-recruit-based approach using Cymbula Granatina as an Illustration
    (2004) Arendse, Clement; Govender, Anesh; Branch, George
    Closed seasons are generally implemented on the presumption that they increase reproductive output of fished populations. This is.based on the assumption that the imposition of a closed season during the breed~· season allows more individuals to reproduce, as they are not being harvested.I evaluated the validity of imposing closed seasons during the breeding season creating a simulation model using the limpet Cymbula granatina as a test case and the compared following four scenarios: 1) an unharvested population; 2) no closed season imposed; 3) a closed season imposed during the breeding season; and 4) a closed season imposed outside the breeding season, to determine the effects of the latter three situations on the reproductive output and yield. From the outputs of the model it was determined that closed seasons do not significantly affect the reproductive output of the population and that the timing of closed seasons made no difference to the reproductive output of the population, as the output was the same for populations with closed seasons during the breeding season or outside the breeding season. Survivors, catch in numbers and yield in biomass were affected by the timing of closed seasons, with higher outputs for each obtained when the closed season was closer to the month when individuals become of harvestable size. It was thus concluded that the imposition of a closed season at any time of the year is an effective management measure if imposing the closed season can reduce annual fishing, but the imposition of a closed season specifically during the breeding season with a view to increase reproductive output brings no benefits relative to closure at any other time of the year. Moreover, any closure will be ineffective if it does not also bring about a reduction of annual fishing effort. The reasons for advocating closure of a fishery during the breeding season are thus based on false ground.
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    On the phylogenetic relationship of South African species of Cladophora (Chlorophyta) based on the 26S (LSU) gene region
    (2004) Arendse, Clement; Bolton, John J; Nowell, Tracey L
    In order to delineate the genus Cladophora in South Africa, several sites along the Cape peninsula were sampled and sequences for the partial26S region of the rRNA were obtained and a phylogram was constructed. The aims of this study were to provide a robust phylogenetic tree describing the relationship between members of the genus Cladophora and related taxa and to determine the origins of South Africa's estuarine species of Cladophora. After DNA extraction and cycle sequencing of products, sequences were aligned and compared to several east coast species (obtained from GENBANK) and a phylogram was constructed. The results yielded several clades within Cladophora; Clad. capensis grouping with Clad. isaacii, Clad sericea and Clad. dalmatica; Cheatomorpha forming a polyphyletic group within Cladophora; and Clad. vagabunda and Clad. laetevirens grouping with the estuarine species. As no Clad. vagabunda or Clad. laetevirens are found along the coast of South Africa, the origins of its estuarine species still remain a mystery and needs further investigation.