The feeding ecology of and carbon and nitrogen budgets for Engraulis capensis in the southern Benguela ecosystem
Doctoral Thesis
1988
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University of Cape Town
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Abstract
The two main schools of thought regarding the diets of intermediate microphagous clupeids are: A) that they are herbivorous and B) that they are omnivorous, but consume mainly zooplankton. The former view has been employed to explain their abundance in upwelling areas, since their purported ability to efficiently utilise the primary producers shortens the pelagic food chain to 1 or 2 links. The literature concerning the trophic ecology of some commercially important clupeids is reviewed and it is concluded that few are true phytophagists. Most are omnivorous and derive the bulk of their energy from zooplankton. Results indicating that these fish are herbivorous are largely due to inadequate sampling strategies and analytical techniques. The results of field work show that Engraulis capensis feeds selectively upon meso- and macro-zooplankton. Laboratory experiments supported these findings. Prey are selected on the basis of size and particulate feeding is the dominant mode of intake when the' fish are presented with a mixed size assemblage of prey. Engraulis capensis cannot filter feed on particles less than 0.200mm maximum dimension, and there is a threshold size of approximately 0.700mm when feeding behaviour switches from filter to particulate feeding. Particulate feeding produced faster clearance rates than filtering, and the Cape anchovy feeds at maximum efficiency over most of their prey size spectrum.
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Bibliography: leaves 179-231.
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Reference:
James, A. 1988. The feeding ecology of and carbon and nitrogen budgets for Engraulis capensis in the southern Benguela ecosystem. University of Cape Town.