Extreme Effects of Extreme Disturbances: A Simulation Approach to Assess Population Specific Responses

Abstract

In South Australia, discrete populations of bottlenose dolphins inhabit two large gulfs, where key threats and population estimates have been identified. Climate change, habitat disturbance (shipping and noise pollution), fishery interactions and epizootic events have been identified as the key threats facing these populations. The Population Consequences of Disturbance (PCoD) framework has been developed to understand how disturbances can influence population dynamics. We used population estimates combined with population specific bioenergetics models to undertake a partial PCoD assessment, comparing how the two populations respond to the identified regional threats. Populations were modeled over a 5 year period looking at the influence of each disturbance separately. As expected, the most extreme epizootic and climate change disturbance scenarios with high frequency and intensity had the biggest influence on population trends. However, the magnitude of the effect differed by population, with Spencer Gulf showing a 43% and Gulf St Vincent a 23% decline under high frequency and high impact epizootic scenarios. Epizootic events were seen to have the strongest influence on population trends and reproductive parameters for both populations, followed by climate change. PCoD modeling provides insights into how disturbances may affect different populations and informs management on how to mitigate potential effects while there is still time to act.

A review of bioenergetic modelling for marine mammal populations

“…The most widespread use of dynamic bioenergetic models in the past decade has been in the context (either implicit or explicit) of assessing the long-term consequences of sublethal anthropogenic disturbance on individuals or populations under the PCoD framework, which has included applications to pinnipeds ( Goedegebuure et al, 2018 ; McHuron et al, 2017a , 2018 ), harbour porpoises Phocoena phocoena ( Gallagher et al, 2021a ; Harwood et al, 2020 ; Nabe-Nielsen et al, 2014 ; Nabe-Nielsen et al, 2018 ), delphinids ( Hin et al, 2019 ; New et al, 2013b ; Pirotta et al, 2014 ; Pirotta et al, 2015 , 2020 ; Reed et al, 2020 ; Williams et al, 2006 ), beaked whales ( New et al, 2013a ), baleen whales ( Braithwaite et al, 2015 ; Christiansen and Lusseau, 2015 ; Dunlop et al, 2021 ; Guilpin et al, 2020 ; McHuron et al, 2021 ; Pirotta et al, 2018a , 2019 , 2021 ; Riekkola et al, 2020 ; van der Hoop et al, 2017 ; Villegas-Amtmann et al, 2015 ; Villegas-Amtmann et al, 2017 ), small- to medium-sized odontocetes ( Noren et al, 2017 ) and sperm whales ( Farmer et al, 2018b , 2018a ).…”

Emerging themes in Population Consequences of Disturbance models

“…Understanding how disturbance may affect vital rates such as fecundity and survival can provide valuable insights into a population's response to a disturbance event [ 74 , 92 ] and guide mitigation and management strategies that target important life-history stages (e.g. mating and reproduction) or specific age classes (e.g.…”

“…Future models could be developed for representative populations or species exposed to common disturbance scenarios to investigate broad patterns in population responses to disturbance (e.g. see [ 31 , 92 ]). By identifying population characteristics and other contextual factors that could lead to population-level effects, model findings could be used to further guide decision-making and develop mitigations that target populations most at risk or sensitive to a proposed activity.…”

Abundance and Potential Biological Removal of Common Dolphins Subject to Fishery Impacts in South Australian Waters

“…Apart from fisheries interactions, anthropogenic threats to common dolphins in South Australian waters span a wide range of stressors, including over-exploitation of prey resources, water pollution, diseases, urban and industrial habitat degradation and climate change (Kemper et al, 2016;Robbins et al, 2017). For example, modeling has shown that extreme epizootic events and climate change disturbance scenarios with high frequency and intensity have the biggest influence on population trends of bottlenose dolphins in Spencer Gulf and Gulf St. Vincent (Reed et al, 2020), and these are likely to also pose a threat to common dolphins. Furthermore, there has been no assessment of the potential long-term impacts (e.g., enhanced stress levels, mothercalf separations) that fisheries interactions (e.g., encirclement and release operations in purse seine nets) may have on dolphins, and how this may impact reproductive success and survival rates in the affected populations (Archer et al, 2004;Edwards, 2006;Wade et al, 2007;Cramer et al, 2008).…”