UC Santa Cruz

Human activities are having widespread and pervasive impacts on terrestrial and aquatic ecosystems. In addition to intensifying climate change, from rising sea levels to shifting weather and climate patterns, these impacts are causing habitat degradation and even species extinctions. As a result, assessing the effects of these stressors on ecosystems and dependent wildlife populations is necessary for their management and conservation. This requires a framework to identify vulnerability and, subsequently, tools to quantify impacts that can inform strategies to mitigate negative consequences. For my dissertation, I used qualitative and quantitative approaches to assess the population consequences of disturbance (PCoD) from human and environmental stressors on marine mammal populations. First, I synthesized existing PCoD models developed for marine mammals to provide insights into what contextual factors influence a population’s likelihood and duration of exposure and sensitivity to disturbance (Chapter 1). Then, I added to the existing suite of PCoD models by developing the first stochastic dynamic programming model for humpback whales. With this model, I examined the temporal sensitives of humpback whales to climate- and fishery-driven changes in krill availability on their western Antarctic Peninsula feeding grounds (Chapter 2). Finally, I extended the model to examine the spatial and temporal sensitivities of an endangered population of humpback whales to stressors on their feeding grounds in the California Current Ecosystem (Chapter 3). Overall, a population’s resilience to disturbance largely depended on its life-history traits, the stressor’s characteristics, and the environmental conditions. Stressors had varying effects on a population depending on the type of stressor, the severity of the disturbance, and whether multiple stressors were present. However, impacts to the population could generally be reduced when the overlap between stressors and biologically important areas was minimized, especially during energetically vulnerable and reproductively sensitive times. Finally, stressors had a greater impact on a population when the prey environment was already poor due to natural variability, with effects worsening within the context of a changing climate. Collectively, my dissertation provides a qualitative and quantitative basis for assessing the effects of stressors on population dynamics and comparing different stressor scenarios associated with our expanding offshore footprint.