Fish spawning strategies in the variable southern Benguela Current region

 

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dc.contributor.advisor Field, John G en_ZA
dc.contributor.author Shelton, Peter Anthony en_ZA
dc.date.accessioned 2016-11-02T09:09:01Z
dc.date.available 2016-11-02T09:09:01Z
dc.date.issued 1986 en_ZA
dc.identifier.citation Shelton, P. 1986. Fish spawning strategies in the variable southern Benguela Current region. University of Cape Town. en_ZA
dc.identifier.uri http://hdl.handle.net/11427/22418
dc.description Bibliography: pages 320-327. en_ZA
dc.description.abstract A 120 station grid was surveyed at monthly intervals in the southern Benguela. Current system between August 1977 and August 1978. Plankton was collected at each station by means of a double oblique tow behind the ship at 2 knots down to 100m or 5m off the bottom. Plankton displaced volume was determined and all fish eggs and larvae were removed and identified to the lowest possible taxon. Water samples were collected at each·station by means of 5 litre bottles from 5 depths down to a maximum depth of 75m. Microplankton (37-100 μm fraction) particle concentration, chlorophyll concentration and salinity were determined from the samples. A vertical temperature profile was obtained at each station using a bathythermograph. Twenty plastic drift cards were released at each station and recoveries plotted. Wind measurements were made on board the ship and also obtained after the cruise from land sites at Cape Point and Cape Columbine. After August 1978, the CELP grid was resurveyed in November 1978, November 1981 and November 1982. In November 1979 and November 1980 a number of stations were sampled in the vicinity of the Cape Peninsula. to determine the vertical abundance pattern of anchovy eggs. In November 1983, 1984 and 1985 a much larger portion of the southern Benguela Current system was surveyed to determine the spawner biomass of anchovy using the egg production and acoustic methods. In these surveys anchovy eggs were sampled by means of a vertical tow with a CalVET net and at some stations on the Agulhas Bank the vertical abundance of anchovy eggs was sampled using a multiple opening and closing RMT sampler. The ichthyoplankton and environmental data were interpreted to reveal any similarity in pattern. Anchovy, hake and laternfish were selected for special attention because of their different spawning strategies, and were shown to have seasonal and spatial patterns of egg and larval abundance which could be related to the environment. The major environmental process influencing ichthyoplankton abundance patterns appeared to be the seasonal advection of warm western boundary current water into the system from late spring to early autumn, causing the development of a temperature front along the west coast and a thermocline over the Agulhas Bank. Plankton standing stocks were elevated between the front and the coast and in the thermocline. In order to place their spawning strategies into perspective, a simulation model was used to explore the performance of anchovy, hake and lanternfish life history strategies in filtering out environmental variability. Results suggested that anchovy and hake are adapted to cope with variability whereas lanternfish are less well adpated, and therefore spawn in winter when the system is most homogeneous. Conclusions are drawn as to the kinds of environmental anomalies likely to cause poor year class strength in the three species. en_ZA
dc.language.iso eng en_ZA
dc.subject.other Zoology en_ZA
dc.title Fish spawning strategies in the variable southern Benguela Current region en_ZA
dc.type Doctoral Thesis
uct.type.publication Research en_ZA
uct.type.resource Thesis en_ZA
dc.publisher.institution University of Cape Town
dc.publisher.faculty Faculty of Science en_ZA
dc.publisher.department Department of Biological Sciences en_ZA
dc.type.qualificationlevel Doctoral
dc.type.qualificationname PhD en_ZA
uct.type.filetype Text
uct.type.filetype Image
dc.identifier.apacitation Shelton, P. A. (1986). <i>Fish spawning strategies in the variable southern Benguela Current region</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Biological Sciences. Retrieved from http://hdl.handle.net/11427/22418 en_ZA
dc.identifier.chicagocitation Shelton, Peter Anthony. <i>"Fish spawning strategies in the variable southern Benguela Current region."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 1986. http://hdl.handle.net/11427/22418 en_ZA
dc.identifier.vancouvercitation Shelton PA. Fish spawning strategies in the variable 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/11427/22418 en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Shelton, Peter Anthony AB - A 120 station grid was surveyed at monthly intervals in the southern Benguela. Current system between August 1977 and August 1978. Plankton was collected at each station by means of a double oblique tow behind the ship at 2 knots down to 100m or 5m off the bottom. Plankton displaced volume was determined and all fish eggs and larvae were removed and identified to the lowest possible taxon. Water samples were collected at each·station by means of 5 litre bottles from 5 depths down to a maximum depth of 75m. Microplankton (37-100 μm fraction) particle concentration, chlorophyll concentration and salinity were determined from the samples. A vertical temperature profile was obtained at each station using a bathythermograph. Twenty plastic drift cards were released at each station and recoveries plotted. Wind measurements were made on board the ship and also obtained after the cruise from land sites at Cape Point and Cape Columbine. After August 1978, the CELP grid was resurveyed in November 1978, November 1981 and November 1982. In November 1979 and November 1980 a number of stations were sampled in the vicinity of the Cape Peninsula. to determine the vertical abundance pattern of anchovy eggs. In November 1983, 1984 and 1985 a much larger portion of the southern Benguela Current system was surveyed to determine the spawner biomass of anchovy using the egg production and acoustic methods. In these surveys anchovy eggs were sampled by means of a vertical tow with a CalVET net and at some stations on the Agulhas Bank the vertical abundance of anchovy eggs was sampled using a multiple opening and closing RMT sampler. The ichthyoplankton and environmental data were interpreted to reveal any similarity in pattern. Anchovy, hake and laternfish were selected for special attention because of their different spawning strategies, and were shown to have seasonal and spatial patterns of egg and larval abundance which could be related to the environment. The major environmental process influencing ichthyoplankton abundance patterns appeared to be the seasonal advection of warm western boundary current water into the system from late spring to early autumn, causing the development of a temperature front along the west coast and a thermocline over the Agulhas Bank. Plankton standing stocks were elevated between the front and the coast and in the thermocline. In order to place their spawning strategies into perspective, a simulation model was used to explore the performance of anchovy, hake and lanternfish life history strategies in filtering out environmental variability. Results suggested that anchovy and hake are adapted to cope with variability whereas lanternfish are less well adpated, and therefore spawn in winter when the system is most homogeneous. Conclusions are drawn as to the kinds of environmental anomalies likely to cause poor year class strength in the three species. DA - 1986 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1986 T1 - Fish spawning strategies in the variable southern Benguela Current region TI - Fish spawning strategies in the variable southern Benguela Current region UR - http://hdl.handle.net/11427/22418 ER - en_ZA


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