Optimal foraging and density-dependent competition in marine fish larvae

Abstract

ABSTRACT. Ontogenetic migrations of fish larvae were studied in relation to vertical distribution of their prey and their predators at a single, unstratified, 60 m deep, station off Plymouth, UK. The vertical distribution of fish larvae was highly stratified. Die1 migrations were weak. Marked ontogenetic migrations reflected a size-related shlft in the equilibrium between predation and starvation risks. Yolksac larvae concentrated in the top half of the water column where planktonic predators were the least abundant. As size increased, the overlap between the vertical distribution of the postlarvae and that of potential predators increased. Postlarval stages of species feeding on copepods were distributed in direct proportion to resource availability. This suggested an optimization of postlarval foraging behaviour in response to density-dependent competition for food. Calculations showed that the larvae themselves had little impact on their resource, but indications were found that the abundance of larval fish food was affected by other planktivorous predators. We conclude that the density-dependent competition for food suggested by the observed patterns of postlarval distribution could only be generated at the level of the entire assemblage of planktonic predators.

Diel and vertical movements of preflexion fish larvae assemblage associated with <i>Posidonia oceanica</i> beds

“…Callionymidae, Scorpaenidae, Bleniidae, Labridae and Serranidae) remained in the entire water column during both the day and night. This suggests that they have not reached the development stage necessary to use the demersal habitat, given that vertical migrations of these taxa could be carried out by larger larvae (Fortier and Leggett, 1983;Fortier and Harris, 1989). This interpretation agrees in this respect with several other studies that have determined specific vertical distributions for larger larvae of certain species in offshore open waters (Leis et al, 1996;Olivar and Sabatés, 1997).…”

Small-scale patterns in distribution and feeding of Atlantic mackerel ( Scomber scombrus L.) larvae in the Celtic Sea with special regard to intra-cohort cannibalism

“…Thus, to be less aggregated in the water column might be a strategy to avoid being eaten by conspecifics. Predation avoidance, by selecting depth strata of low predator abundance, has been discussed as motivation for vertical migration (Ohman et al 1983;Gliwicz 1986;Ohman 1990) and has been reported for fish larvae with respect to invertebrate predators (e.g., Yamashita et al 1985;Fortier and Harris 1989). However, nothing is known about predator avoidance with respect to conspecifics.…”

Intra- and interspecific variability in prey size and niche breadth of myctophiform fish larvae

“…Studies on foraging patterns and the diet of multi-specific natural assemblages of fish larvae have indicated that the degree of prey-overlap can vary (e.g. Govoni et al 1983, Jenkins 1987, Fortier & Harris 1989, Economu 1991, Gaughan & Potter 1997. Because of the high degree of morphological and behavioural variability in fish larvae, it would seem reasonable to assume that interspecific differences would have an adaptive value for the fitness of the larvae under the environmental conditions of their particular habitat.…”