Laboratory Analysis of Cannibalism by Larvae of the Cape Anchovy Engraulis capensis

Abstract
Recruitment of Cape anchovy in South African waters has been strong and consistent for nearly 20 years, despite year‐to‐year variability in the physical marine environment. This suggests an element of density‐dependent regulation in the population dynamics of this species. Cannibalism might be such a regulator, and laboratory experiments were conducted as a first step toward assessing the importance of cannibalism by larvae. Eggs and various sizes of larvae were added one at a time to tanks containing larger larvae and any approaches of potential predator and prey were observed. Some predator larvae between 15 and 35 mm standard length were capable of capturing and ingesting prey larvae as large as their mouth openings would permit, approaching half their own body length. Eggs and yolk‐sac larvae without pigmented eyes were less readily detected, and therefore less likely ingested, than early eyed larvae. Predation efficiencies (proportions of prey detected, struck at, or ingested) increased with increasing predator size and tended to decrease with increasing prey size. Cannibalism was markedly reduced when predators were pre‐fed copepods or when prey larvae were introduced at the same time as copepods. Thus, the potential exists for cannibalism among co‐occurring Cape anchovy larvae of different sizes, its extent being modified by predator and prey length and availability of alternative prey.

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