Marine fish foraging strategy in relation to behavioral thermoregulation

Abstract

The thermal environment of the ocean changes drastically with depth, and fish can actively regulate their body temperatures through short-term vertical migrations. The larger a fish’s body size, the greater its thermal inertia, and the longer it can remain outside its preferred temperature range. In this paper, foraging strategies used by fish to catch prey in environments outside their preferred temperature range are discussed in terms of thermoregulation, using the example of the ocean sunfish Mola mola, which makes deep dives to feed on deep-sea jellyfish. With variations in dive duration, the proportion of time spent moving increased when the dive was short, and the proportion of time spent in body temperature recovery increased when the dive was long. Thus, there is a dive duration that maximizes foraging time. This dive duration was estimated to increase with prey depth and fish body size. This may be an example of the optimal foraging theory whereby foraging time is increased through the efficient use of thermal resources rather than food resources.