Egg cannibalism by anchovy in the Southern Benguela Current Region

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dc.contributor.advisorGriffiths, Charles Len_ZA
dc.contributor.advisorField, John Gen_ZA
dc.contributor.authorRodriguez, Edy Sylvia Valdesen_ZA
dc.date.accessioned2016-02-29T12:06:06Z
dc.date.available2016-02-29T12:06:06Z
dc.date.issued1986en_ZA
dc.description.abstractSamples of adult anchovy and plankton were collected on Sea Fisheries Research Institute R.S. Africana 1984-1985 anchovy spawner biomass estimation cruises. A total of 40 sets of anchovy samples of 30 fish each and 40 plankton samples were taken roughly at the same time within an area of intensive spawning over the Agulhas Bank, using an Engels 308 midwater trawl and a CalVET net respectively. Fish samples were frozen in a deep freeze at 20° C shortly after capture. Plankton samples were stored in formaldehyde solution. Fish were measured (total length), weighed (total and ovary mass) and de-stomached. Weight of the stomach contents were determined and anchovy eggs in the stomach were counted. Anchovy eggs in CalVET net samples were counted and staged. Frequency distributions of densities of eggs in the plankton on the Agulhas Bank and off the West Coast were plotted to compare egg density in the two areas. Approximately 53% of the eggs caught over Agulhas Bank occurred in only 25% of samples, indicating a patchy distribution. A frequency distribution was plotted of abundance of eggs in the stomachs of fish. Egg patchiness caused a skewed frequency distribution of egg abundance in anchovy stomachs. Feeding time was estimated from an examination of the relationship between weight of stomach contents versus time of day, taking into account time for gut evacuation. Based upon a developmental stage/temperature/age key, mortality rates of eggs in the sea were calculated, and it was estimated that 44% of anchovy eggs were lost daily. Taking into account estimated rates of egg mortality, egg production, gastric evacuation rate, number of eggs eaten and feeding time, cannibalism was estimated to account for about 62%-70% of the egg mortality. The rate of cannibalism was shown to be consistent with a density-dependent functional response.en_ZA
dc.identifier.apacitationRodriguez, E. S. V. (1986). <i>Egg cannibalism by anchovy in the Southern Benguela Current Region</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Biological Sciences. Retrieved from http://hdl.handle.net/11427/17363en_ZA
dc.identifier.chicagocitationRodriguez, Edy Sylvia Valdes. <i>"Egg cannibalism by anchovy in the Southern Benguela Current Region."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 1986. http://hdl.handle.net/11427/17363en_ZA
dc.identifier.citationRodriguez, E. 1986. Egg cannibalism by anchovy in the Southern Benguela Current Region. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Rodriguez, Edy Sylvia Valdes AB - Samples of adult anchovy and plankton were collected on Sea Fisheries Research Institute R.S. Africana 1984-1985 anchovy spawner biomass estimation cruises. A total of 40 sets of anchovy samples of 30 fish each and 40 plankton samples were taken roughly at the same time within an area of intensive spawning over the Agulhas Bank, using an Engels 308 midwater trawl and a CalVET net respectively. Fish samples were frozen in a deep freeze at 20° C shortly after capture. Plankton samples were stored in formaldehyde solution. Fish were measured (total length), weighed (total and ovary mass) and de-stomached. Weight of the stomach contents were determined and anchovy eggs in the stomach were counted. Anchovy eggs in CalVET net samples were counted and staged. Frequency distributions of densities of eggs in the plankton on the Agulhas Bank and off the West Coast were plotted to compare egg density in the two areas. Approximately 53% of the eggs caught over Agulhas Bank occurred in only 25% of samples, indicating a patchy distribution. A frequency distribution was plotted of abundance of eggs in the stomachs of fish. Egg patchiness caused a skewed frequency distribution of egg abundance in anchovy stomachs. Feeding time was estimated from an examination of the relationship between weight of stomach contents versus time of day, taking into account time for gut evacuation. Based upon a developmental stage/temperature/age key, mortality rates of eggs in the sea were calculated, and it was estimated that 44% of anchovy eggs were lost daily. Taking into account estimated rates of egg mortality, egg production, gastric evacuation rate, number of eggs eaten and feeding time, cannibalism was estimated to account for about 62%-70% of the egg mortality. The rate of cannibalism was shown to be consistent with a density-dependent functional response. DA - 1986 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1986 T1 - Egg cannibalism by anchovy in the Southern Benguela Current Region TI - Egg cannibalism by anchovy in the Southern Benguela Current Region UR - http://hdl.handle.net/11427/17363 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/17363
dc.identifier.vancouvercitationRodriguez ESV. Egg cannibalism by anchovy in the Southern Benguela Current Region. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 1986 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/17363en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Biological Sciencesen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherZoologyen_ZA
dc.titleEgg cannibalism by anchovy in the Southern Benguela Current Regionen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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