The Energetic Ecology of Larval Cod (Gadus morhua): Integrating Bioenergetics and Behavior

James Ruzicka, Ph.D., 2004
Scott Gallager, Advisor

How do larval cod, Gadus morhua, balance foraging effort against the high cost of swimming in a viscous hydrodynamic regime? A respirometry system was developed to measure the activity metabolism of individual larvae. The cost of swimming was modeled as a power-performance relationship (energy expenditure as a function of swimming speed) and as the cost of transport (the cost to travel a given distance). The cost of transport was high relative to adult fish, but larvae swam more efficiently as they grew and became better able to overcome viscous drag.

A large-volume observation system was developed to record foraging behavior in three dimensions. There are two phases of the saltatory search cycle used by larval cod: the burst which serves to position larvae within a new search volume and the pause when larvae search for prey. Larvae spent more time in the pause phase when searching when prey were absent, perhaps reflecting more thorough visual processing of each search volume or conserving energy until conditions improve. Comparison of observed behavior and cost of swimming measurements to simulation modeling of alternative saltatory foraging strategies suggests that cod larvae use a prey encounter maximization strategy rather than an energy conservation strategy.