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

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 5000 h of vertical movement data across 274 days from five fish showed that roosterfish largely used the upper 10 m and 20 m 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 (<20 m) 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.