Marine mammals are exposed to multiple stressors, including manmade underwater sound, chemical pollution and interaction with fisheries. Despite progress towards predicting the effect of single stressors on individual marine mammals and populations, existing scientific theory and data cannot predict the cumulative effect of multiple stressors. One particular concern of environmental assessments is the danger of synergistic interactions, where a stressor that has only a mild effect on its own has a strong effect when other stressors are present. However, the critical issue is estimating when the combination of stressors exerts an adverse impact, whether synergistic or not. This is relevant to the Department of Defense (DoD) because DoD submits environmental impact assessments for the potential impact of its activities, particularly use of Navy sonar, on marine mammal populations that are exposed to a wide range of other stressors. The overall goal of this project is to advance understanding of the cumulative effects of multiple stressors on marine mammals. The project's objectives are to: develop quantitative methods to predict behavioral or physiological responses to two or more stressors; apply these approaches in case studies; use the results to help construct a Population Consequences of Multiple Stressors (PCoMS) model for each case study; develop and/or evaluate new technologies to assess adverse health and ecosystem-level effects; and promote information exchange by interacting with researchers and managers working on cumulative effects.

Collecting data from a northern elephant seal to develop Population Consequences of Multiple Stressors (PCoMS) model

Technical Approach

The overall approach for this research program involves an interdisciplinary working group (WG) and several sub-teams, with each sub-team focused on either carrying out a specific case study or evaluating a new technology. This proposal will support the case studies and technology development; the WG, which consists of experts from diverse disciplines that can extend the PCoMS framework, will be supported by a separate proposal. This Strategic Environmental Research and Development Program (SERDP) proposal includes project management to lead the required methodological development, coordinate among case studies, and interact with SERDP and external researchers and managers. The case studies will develop multi-stressor dose-response relationships for the selected species under realistic field conditions, including estimating the effect of interaction between stressors. Case studies are: (1) bottlenose dolphins exposed to chemical stressors – we will test experimentally whether the response of dolphins to vessel approaches depends on how much the chemicals have impacted their health; and (2) right whales – a study to investigate how prey availability interacts with sub-lethal health effects of entanglement, vessel strike and noise. Each of these case studies has excellent data on exposure to and/or effects of stressors, along with estimates of the effects of individual stressors. The key innovation here is the effort to estimate the effects of interactions between multiple stressors. We will explore the new technology of whether epigenetic biomarkers indicating age acceleration can be used to estimate the cumulative effects of multiple stressors on marine mammal health that can influence life-span.


Development of methods to quantify how marine mammals respond to different levels of more than one stressor are essential for predicting cumulative effects. The dolphin case study uses veterinary health assessment to study interactions for stressors that share the same mechanistic pathways for adverse effects. The right whale case study develops methods to study interaction between stressors using health measures suitable for animals unavailable for hands-on health assessment. This latter case study focuses on an endangered species where effects of multiple stressors put it on a path to extinction. Development of methods to estimate interactions between stressors using non-invasive methods is essential for managing their effects in this high priority situation. The research team also propose to explore new biological markers for cumulative physiological effects that can be used with these inaccessible species. This work develops new theory, measures and data for understanding cumulative effects of interacting stressors.