The energetics and evolution of intraspecific predation (egg cannibalism) in the anchovy Engraulis capensis

Anchovy feeding activity (based on samples collected around the South African coast between 1986 and 1988) seems to peak twice daily, with the major peak between 17:00 and 19:00 hrs. Mean daily consumption in the field was estimated at 3.45% of body wt d^-1. Since the various food types available to anchovy differ in their caloric values, this figure might be expected to vary according to the type of diet available to the fish. To obtain a diet energetically equivalent to that measured in the field anchovy feeding exclusively on phytoplankton would need to consume the equivalent of 5.8% of their body wt d^-1 and those feeding on zooplankton 3.5 to 4.5% of the body wt, while fish feeding on their own eggs would require only 2.5% of their body wt daily. Feeding on eggs at peak spawning on the spawning grounds —where there is limited alternative food (i.e., zooplankton) available — seems adequate to support reproduction. In selection at the population level, cannibalistic fish benefit from homeostatic self-regulation.