Abstract

Understanding the full scope of human impact on wildlife populations requires a framework to assess the population‐level repercussions of nonlethal disturbance. The Population Consequences of Disturbance (PCoD) framework provides such an approach, by linking the effects of disturbance on the behavior and physiology of individuals to their population‐level consequences. Bio‐energetic models have been used as implementations of PCoD, as these integrate the behavioral and physiological state of an individual with the state of the environment, to mediate between disturbance and biological significant changes in vital rates (survival, growth, and reproduction). To assess which levels of disturbance lead to adverse effects on population growth rate requires a bio‐energetic model that covers the complete life cycle of the organism under study. In a density‐independent setting, the expected lifetime reproductive output of a single female can then be used to predict the level of disturbance that leads to population decline. Here, we present such a model for a medium‐sized cetacean, the long‐finned pilot whale (Globicephala melas). Disturbance is modeled as a yearly recurrent period of no resource feeding for the pilot whale female and her calf. Short periods of disturbance lead to the pre‐weaned death of the first one or more calves of the young female. Higher disturbance levels also affect survival of calves produced later in the life of the female, in addition to degrading female survival. The level of disturbance that leads to a negative population growth rate strongly depends on the available resources in the environment. This has important repercussion for the timing of disturbance if resource availability fluctuates seasonally. The model predicts that pilot whales can tolerate on average three times longer periods of disturbance in seasons of high resource availability, compared to disturbance happening when resources are low. Although our model is specifically parameterized for pilot whales, it provides useful insights into the general consequences of nonlethal disturbance. If appropriate data on life history and energetics are available, it can be used to provide management advice for specific species or populations.

Highlights

  • The increase of human activity in the marine environment has led to concern about the effects of disturbance on marine mammals (Halpern et al 2008, DeRuiter et al 2013, Maxwell et al 2013, Fleishman et al 2016, Parsons 2017)

  • Bio-energetic models have been used as implementations of Population Consequences of Disturbance (PCoD), as these integrate the behavioral and physiological state of an individual with the state of the environment, to mediate between disturbance and biological significant changes in vital rates

  • The model predicts that pilot whales can tolerate on average three times longer periods of disturbance in seasons of high resource availability, compared to disturbance happening when resources are low

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Summary

Introduction

The increase of human activity in the marine environment has led to concern about the effects of disturbance on marine mammals (Halpern et al 2008, DeRuiter et al 2013, Maxwell et al 2013, Fleishman et al 2016, Parsons 2017). While the link between disturbance and its (short term) effect on behavior, feeding, and health of individuals is becoming more apparent (Miller 2012, Sivle et al 2012, DeRuiter et al 2013, Christiansen and Lusseau 2015, Friedlaender et al 2016), assessing the (long-term) population consequences is challenging and involves many uncertainties These arise from (among others) the inaccessibility of the marine environment and the species in question, uncertainty about many life-history parameters and processes, the difference in timescale between a disturbance event and its consequences for populations, and the lack of information about behavioral responses

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