Egg and larval ecology of anchovy (Engraulis capensis) and sardine (Sardinops sagax) in the Southern Benguela ecosystem

 

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dc.contributor.advisor Gibbons, M J en_ZA
dc.contributor.advisor Field, John G en_ZA
dc.contributor.author Fowler, Justine Lindsay en_ZA
dc.date.accessioned 2016-05-13T09:34:57Z
dc.date.available 2016-05-13T09:34:57Z
dc.date.issued 1998 en_ZA
dc.identifier.citation Fowler, J. 1998. Egg and larval ecology of anchovy (Engraulis capensis) and sardine (Sardinops sagax) in the Southern Benguela ecosystem. University of Cape Town. en_ZA
dc.identifier.uri http://hdl.handle.net/11427/19645
dc.description Bibliography: pages 118-131. en_ZA
dc.description.abstract Temporal and spatial changes in the abundance and distribution of anchovy and sardine eggs and larvae in the southern Benguela ecosystem were investigated during 14 cruises over 2 consecutive summer upwelling seasons as part of the South African Sardine and Anchovy Recruitment programme (SA-SARP). Cruises were conducted each month between August 1993 and March 1994 (SARP I) and September 1994 and March 1995 (SARP II). Anchovy spawning was largely confined to the western Agulhas Bank, reaching a definite peak during spring (October and November). Sardine ·spawning extended up the west coast ·duiing·periods when anchovy spawning reached a peak on the western Agulhas Bank. However, sardine eggs were dense on the western Agulhas Bank during peak spawning activity which appears to be bimodal, reaching a peak in the early spring (August/September) and again in late summer (February). · Although the midshelf region on the W AB appeared to be the centre of both anchovy and ·sardine spawning in the southern Benguela ecosystem, these data suggest that anchovy and sardine spawning activity may be both spatially, and temporally separated to some extent. Mean anchovy egg densities on the W AB decreased by 53 % from 1993/94 to 1994/95 while a slight increase in mean sardine egg density (16 %) over the entire region was observed from one season to the next. Lloyd's Patchiness Index was used to investigate the distribution patterns of spawning products and the results showed that the distribution of both anchovy and sardine eggs and larvae was extremely patchy, but that the eggs of both species were more patchy than their larvae. Anchovy eggs were most abundant at sea surface temperatures ranging from 16-20°C. Changes in the extent of 16-l 9°C water (as a measure of spawning habitat) and the abundance of large copepods within this region reflect intra-annual changes in the intensity of anchovy spawning activity. Sardine eggs were found predominantly in water of between 14.5-21.5°C. The seasonal intensity of sardine spawning appears to vary independently of the area of 16-19°C water, but· a positive correlation between the spawning activity of sardine and the monthly chlorophyll a concentrations on the W AB suggests that spawning may be related to their feeding conditions. A comparison of egg and larval distributions with current features from selected months during SARP supports previous studies which indicate that the frontal jet plays an important role in the transport of the early life history stages of anchovy and sardine but that the position of such transport can vary between the 200 m and 500 m isobaths. Areas of possible egg loss included the W AB, the offshore currents which can develop west of the Cape Peninsula and the outer branch of the jet off Cape Columbine. However, there is evidence that onshore currents further north may transport the eggs back to the region of the jet. The monthly estimates of anchovy egg mortality were highly variable and imprecise and these results were probably due to a combination of small sample sizes and reduced egg abundances, usually encountered at the start and end of the anchovy spawning season. The annual estimates of anchovy egg mortality during November between 1984 and 1994 were positively correlated with the patchiness of anchovy eggs during the same cruises. The effect of cannibalism in areas where eggs are particularly dense was invoked as a possible explanation for this result. It was concluded that the spawning behaviour of anchovy and sardine may be influenced by sea surface temperatures, feeding conditions for adult fish and advective processes in the southern Benguela ecosystem and these factors were discussed in terms of their possible impact on recruitment. en_ZA
dc.language.iso eng en_ZA
dc.subject.other Zoology en_ZA
dc.title Egg and larval ecology of anchovy (Engraulis capensis) and sardine (Sardinops sagax) in the Southern Benguela ecosystem en_ZA
dc.type Master 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 Masters
dc.type.qualificationname MSc en_ZA
uct.type.filetype Text
uct.type.filetype Image
dc.identifier.apacitation Fowler, J. L. (1998). <i>Egg and larval ecology of anchovy (Engraulis capensis) and sardine (Sardinops sagax) in the Southern Benguela ecosystem</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Biological Sciences. Retrieved from http://hdl.handle.net/11427/19645 en_ZA
dc.identifier.chicagocitation Fowler, Justine Lindsay. <i>"Egg and larval ecology of anchovy (Engraulis capensis) and sardine (Sardinops sagax) in the Southern Benguela ecosystem."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 1998. http://hdl.handle.net/11427/19645 en_ZA
dc.identifier.vancouvercitation Fowler JL. Egg and larval ecology of anchovy (Engraulis capensis) and sardine (Sardinops sagax) in the Southern Benguela ecosystem. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 1998 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/19645 en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Fowler, Justine Lindsay AB - Temporal and spatial changes in the abundance and distribution of anchovy and sardine eggs and larvae in the southern Benguela ecosystem were investigated during 14 cruises over 2 consecutive summer upwelling seasons as part of the South African Sardine and Anchovy Recruitment programme (SA-SARP). Cruises were conducted each month between August 1993 and March 1994 (SARP I) and September 1994 and March 1995 (SARP II). Anchovy spawning was largely confined to the western Agulhas Bank, reaching a definite peak during spring (October and November). Sardine ·spawning extended up the west coast ·duiing·periods when anchovy spawning reached a peak on the western Agulhas Bank. However, sardine eggs were dense on the western Agulhas Bank during peak spawning activity which appears to be bimodal, reaching a peak in the early spring (August/September) and again in late summer (February). · Although the midshelf region on the W AB appeared to be the centre of both anchovy and ·sardine spawning in the southern Benguela ecosystem, these data suggest that anchovy and sardine spawning activity may be both spatially, and temporally separated to some extent. Mean anchovy egg densities on the W AB decreased by 53 % from 1993/94 to 1994/95 while a slight increase in mean sardine egg density (16 %) over the entire region was observed from one season to the next. Lloyd's Patchiness Index was used to investigate the distribution patterns of spawning products and the results showed that the distribution of both anchovy and sardine eggs and larvae was extremely patchy, but that the eggs of both species were more patchy than their larvae. Anchovy eggs were most abundant at sea surface temperatures ranging from 16-20°C. Changes in the extent of 16-l 9°C water (as a measure of spawning habitat) and the abundance of large copepods within this region reflect intra-annual changes in the intensity of anchovy spawning activity. Sardine eggs were found predominantly in water of between 14.5-21.5°C. The seasonal intensity of sardine spawning appears to vary independently of the area of 16-19°C water, but· a positive correlation between the spawning activity of sardine and the monthly chlorophyll a concentrations on the W AB suggests that spawning may be related to their feeding conditions. A comparison of egg and larval distributions with current features from selected months during SARP supports previous studies which indicate that the frontal jet plays an important role in the transport of the early life history stages of anchovy and sardine but that the position of such transport can vary between the 200 m and 500 m isobaths. Areas of possible egg loss included the W AB, the offshore currents which can develop west of the Cape Peninsula and the outer branch of the jet off Cape Columbine. However, there is evidence that onshore currents further north may transport the eggs back to the region of the jet. The monthly estimates of anchovy egg mortality were highly variable and imprecise and these results were probably due to a combination of small sample sizes and reduced egg abundances, usually encountered at the start and end of the anchovy spawning season. The annual estimates of anchovy egg mortality during November between 1984 and 1994 were positively correlated with the patchiness of anchovy eggs during the same cruises. The effect of cannibalism in areas where eggs are particularly dense was invoked as a possible explanation for this result. It was concluded that the spawning behaviour of anchovy and sardine may be influenced by sea surface temperatures, feeding conditions for adult fish and advective processes in the southern Benguela ecosystem and these factors were discussed in terms of their possible impact on recruitment. DA - 1998 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1998 T1 - Egg and larval ecology of anchovy (Engraulis capensis) and sardine (Sardinops sagax) in the Southern Benguela ecosystem TI - Egg and larval ecology of anchovy (Engraulis capensis) and sardine (Sardinops sagax) in the Southern Benguela ecosystem UR - http://hdl.handle.net/11427/19645 ER - en_ZA


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