Diel vertical movements of a coastal predator, the roosterfish (Nematistius pectoralis)

Abstract

The roosterfish (Nematistius pectoralis) is a piscivorous predator targeted extensively in recreational fisheries throughout the eastern tropical Pacific; however, its biology is poorly understood. To address these shortcomings, we investigated vertical habitat use and behaviour of roosterfish in coastal Panama using pop-up satellite archival tags. Nearly 5000h of vertical movement data across 274 days from five fish showed that roosterfish largely used the upper 10m and 20m of the water column during the night-time and daytime respectively, and rarely left the mixed layer. Roosterfish diving behaviour showed a clear diurnal pattern, with oscillatory dives beginning during dawn and continuing through dusk. Accelerometer data showed that this period was also associated with a sharp increase in activity during dawn and a decrease around sunset. Whereas previous work in shallow systems (<20m) with limited structure showed that roosterfish were vertically active sporadically throughout the day and mostly during crepuscular periods, our study showed that in a habitat with continuous structure, roosterfish were continuously vertically active from dawn till dusk, possibly because foraging behaviours were limited by light levels rather than prey-congregating structure. Such changes in dive patterns illustrate how habitat influences behaviour and the importance of studying organisms throughout their range.