Predation by a carnivorous marine copepod, Euchaeta elongata Esterly, on eggs and larvae of the Pacific hake, Merluccius productus

Abstract

The predatory behavior of the carnivorous marine copepod, adult female Euchaeta elongata Esterly, feeding on eggs and larvae of the Pacific hake, Merluccius productus, was examined in the laboratory and in a natural setting. E. elongata did not feed on eggs. Predation on larvae is believed to depend on larval swimming behavior: (1) predation rates were low on early stage yolk-sac larvae which are inactive swimmers and are relatively undetected by the predator; (2) rates were high on middle stage yolk-sac larvae which are more active swimmers yet have a poorly developed escape response; and (3) rates were low on larger larvae which are able to escape the predator effectively. Starved hake larvae were more vulnerable to predation due to a poor escape ability although they were less active and not easily detected. The presence of naturally occurring alternative prey, Pseudocalanus sp., depressed the rate of E. elongata predation on hake larvae. In an analysis of field data, hake larvae and E. elongata were found to occupy the same depths in Dabob Bay. A high percentage of E. elongata collected had apparently been feeding on hake larvae, as indicated by the presence of pigments in their guts. Survival of hake larvae in late spring appears to be relatively poor compared with early spring; poorer survival in late spring may be due partly to an increase in the abundance of invertebrate predators, such as E. elongata.