Vulnerability of late larval and early juvenile Atlantic herring, Clupea harengus, to predation by whiting,Merlangius merlangus

Laboratory experiments investigated changes in the vulnerability of herring to predation by whiting during growth from <34 to >80mm in length, Premetamorphic herring (<50mm) failed to react to c. 50% of attacks by the predator, but this was reduced to c. 20% in postmetamorphic fish. Premetamorphic herring failing to react had c. 30% probability of survival due to unforced errors by the predator (unsuccessful attacks that did not elicit a reaction by the prey), but these errors did not occur after herring metamorphosis. The loss of the advantage of lower conspicuousness following metamorphosis was counterbalanced by increased reactivity. Antipredator benefits should increase with schooling behaviour (first evident in experiments at c. 50 mm), so predation mortality should decrease in postmetamorphic herring in the sea. Metamorphosis itself would be associated with high predation risk since conspicuousness is enhanced but reactivity and schooling behaviour are still not fully developed.