Abstract
The allocation of time and energy to different behaviours can impact survival and fitness, and ultimately influence population dynamics. Intrinsically, the rate at which animals expend energy is a key component in understanding how they interact with surrounding environments. Activity, derived through locomotion and basic metabolism, represents the principal energy cost for most animals, although it is rarely quantified in the field. We examined some abiotic drivers of variability in locomotor activity of a free-ranging freshwater predatory fish, Murray cod (Maccullochella peelii), for six months using tri-axial accelerometers. Murray cod (n = 20) occupied discrete river reaches and generally exhibited small-scale movements (<5 km). Activity was highest during crepuscular and nocturnal periods when water temperatures were warmest (19–30°C; January–March). As water temperatures cooled (9–21°C; April–June) Murray cod were active throughout the full diel cycle and dormant periods were rarely observed. Light level, water temperature and river discharge all had a significant, non-linear effect on activity. Activity peaked during low light levels, at water temperatures of ~20°C, and at discharge rates of ~400 ML d-1. The temporal changes observed in the behaviour of Murray cod likely reflect the complex interactions between physiological requirements and prey resource behaviour and availability in driving activity, and highlight the importance of empirical field data to inform bioenergetics models.
Highlights
The time animals allocate to different behaviours has evolved around the principle of maximising energy gain whilst minimising predation risk [1]
Distinct nocturnal activity patterns were evident during warmer water temperatures (January– March) which are consistent with studies of congeneric trout cod (M. macquariensis [16]) and eastern freshwater cod (M. ikei [17])
We propose that unquantified biotic factors including seasonal prey availability and behaviour may be influencing Murray cod activity
Summary
The time animals allocate to different behaviours has evolved around the principle of maximising energy gain whilst minimising predation risk [1]. Behaviours are rhythmic, typically consistent within species, are determined by a combination of biotic and abiotic stimuli, and are expressed as a trait that enables the optimal exploitation of a particular resource [2]. Plasticity in activity is a key behavioural trait that enables individuals to regulate responses to stochastic changes as well as predictable seasonal progression in abiotic and biotic stimuli [3].
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