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Environmental determinants for repeatability of activity patterns in free-ranging elasmobranchs

Newsome, Rachel J. (2021) Environmental determinants for repeatability of activity patterns in free-ranging elasmobranchs. Honours thesis, Murdoch University.

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Repeatability of behaviour is the degree of behavioural variation attributed to differences between- or within- individuals in a population and may often be conceptualised as animal personality. Behaviour is often plastic in response to environmental challenges to maximise individual survival. In ectotherms, this may be expressed as changes in behaviours due to higher environmental temperatures increasing metabolic demand. Personality is thought to constrain this behavioural plasticity as individuals express behaviours within their personality type. Most studies in this field have been conducted under controlled or semi-controlled conditions, which control for confounding factors and hence remain limited in their applicability in the face of uncertain field conditions. To date, no field studies have focused on the environmental conditions that determine how repeatability of behaviour is exhibited. Here we use biotelemetry tag derived activity data to assess environmental factors influencing the repeatability of activity patterns (i.e., repeated behaviours) in two euryhaline free-ranging elasmobranchs with differing life histories; the largetooth sawfish (Pristis pristis) and bull shark (Carcharhinus leucas) in the Fitzroy River. In response to increasing environmental temperatures and metabolism across the study period, between-individual repeatability of behaviour varied in sawfish, but not bull sharks. Overall between-individual repeatability of behaviour increased across the study period as sawfish altered their behaviours presumably to mitigate competition. Between-individual repeatability of behaviour decreased across the study period with respect to diurnal activity rhythms, indicating sawfish became less diurnal in their activity use. This may indicate active avoidance of the hottest part of the day and a loss to individuals’ ability to temporally partition the diel cycle, with more overlap in activity apparent in the population. Additionally, individuals showed consistent individual differences in their within-individual repeatability of behaviour. This further supports the hypothesis that individuals of these species exhibit personalities. Ecological pressures such as competition, predation pressure and resource constraints are potential drivers of the formation of personality, both in this system and in general. This study demonstrates that repeatability of behaviour can be studied in the field using acoustic telemetry. Additionally, this approach can be used to understand the effects of environmental change on specialisation in other aquatic ectotherms.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): Environmental and Conservation Sciences
Supervisor(s): Gleiss, Adrian and Byrnes, Evan
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