[OANNES Foro] Bottlenose dolphins: decreased foraging efficiency when exposed to human disturbance

[Mario Cabrejos]

Journal of Applied Ecology

Article first published online: 6 OCT 2014

DOI: 10.1111/1365-2664.12337

 


Sex differences in risk perception in deep-diving bottlenose dolphins leads
to decreased foraging efficiency when exposed to human disturbance


1.     John Symons*, Enrico Pirotta and David Lusseau

Institute of Biological and Environmental Sciences, University of Aberdeen,
Aberdeen, UK. E-mail: <mailto:j.symons.12 en aberdeen.ac.uk>
j.symons.12 en aberdeen.ac.uk

 

Summary

1.     Individuals make behavioural decisions by weighing potential
advantages and costs (e.g. increased food intake vs. increased risk of
predation). When animals change their activities in response to a perceived
threat, their energetic input may decline. Marine ecotourism, including
whale and dolphin watching, is growing globally and cetaceans perceive
interactions with tour vessels as a form of risk. Observable behavioural
changes need to be linked to bioenergetic effects to determine the potential
population consequences of this disturbance.

2.     We developed a theoretical optimal dive model for bottlenose dolphins
under three potential types of perceived risk resulting from human
interactions at the surface (decreasing instantaneous risk, increasing
instantaneous risk and no risk). We compared the predictions of these
theoretical models to observed dive cycles of foraging male and female
dolphins in the presence and absence of tour vessels. We used mixture models
to classify dive types and mixed effects models to analyse changes in the
interbreath interval of surface and bottom dives and the frequency of
estimated bottom dives.

3.     Males significantly increased bottom time and performed fewer bottom
dives when boats were present, matching predictions of our theoretical model
for perceived decreasing instantaneous risk. In contrast, females
significantly decreased bottom times and increased the frequency of bottom
dives, matching predictions from the model for perceived increasing
instantaneous risk. Therefore, our empirical results suggest differences in
the perception of risk between sexes.

4.     Synthesis and applications. By comparing theoretical predictions with
observed dive data, our study suggests that boat interactions during
foraging can cause decreased net energy gain over a foraging bout for both
sexes, with females being more impacted. The population under study is
currently listed as critically endangered. Understanding whether these
predicted energetic impacts affect an individual's vital rates will provide
a link to the population-level consequences of this disturbance. Previous
analytical approaches have failed to capture the costs associated with
disturbance during foraging, leading to management recommendations that only
protect animals from increased energetic expenditure. We suggest that the
current management scheme should be revised to include foraging areas in
order to secure the energy intake of animals.

 



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