Approaches to Understanding the
Cumulative Effects of Stressors on
Committee on the Assessment of the Cumulative Effects of Anthropogenic Stressors on Marine Mammals
Ocean Studies Board
Division on Earth and Life Studies
A Report of
THE NATIONAL ACADEMIES PRESS
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This study was supported by the Bureau of Ocean Energy Management, Marine Mammal Commission, National Oceanic and Atmospheric Administration, and the Office of Naval Research. Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any organization or agency that provided support for the project.
International Standard Book Number-13: 978-0-309-44048-6
International Standard Book Number-10: 0-309-44048-3
Digital Object Identifier: https://doi.org/10.17226/23479
Library of Congress Control Number: 2016958819
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Cover art by Jenifer Strachan, “North Atlantic Right Whale.” Mosaics at jeniferstrachan.com.
Suggested citation: National Academies of Sciences, Engineering, and Medicine. 2017. Approaches to Understanding the Cumulative Effects of Stressors on Marine Mammals. Washington, DC: The National Academies Press. doi: https://doi.org/10.17226/23479.
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COMMITTEE ON THE ASSESSMENT OF THE CUMULATIVE EFFECTS OF ANTHROPOGENIC STRESSORS ON MARINE MAMMALS
PETER L. TYACK, Chair, University of St. Andrews, Scotland
HELEN BAILEY, University of Maryland Center for Environmental Science, Solomons
DANIEL E. CROCKER, Sonoma State University, Rohnert Park, California
JAMES E. ESTES, University of California, Santa Cruz
CLINTON D. FRANCIS, California Polytechnic State University, San Luis Obispo
JOHN HARWOOD, University of St. Andrews, Scotland
LORI H. SCHWACKE, Hollings Marine Laboratory (National Oceanic and Atmospheric Administration), Charleston, South Carolina
LEN THOMAS, University of St. Andrews, Scotland
DOUGLAS WARTZOK, Florida International University, Miami
KIM WADDELL, Study Director, Gulf Research Program
STACEE KARRAS, Associate Program Officer, Ocean Studies Board
PAYTON KULINA, Senior Program Assistant, Ocean Studies Board
NICHOLAS MACFARLANE, Mirzayan Fellow, Ocean Studies Board
OCEAN STUDIES BOARD
LARRY A. MAYER, Chair, University of New Hampshire, Durham
E. VIRGINIA ARMBRUST, University of Washington, Seattle
KEVIN R. ARRIGO, Stanford University, California
CLAUDIA BENITEZ-NELSON, University of South Carolina, Columbia
RITA R. COLWELL, University of Maryland, College Park
SARAH W. COOKSEY, State of Delaware, Dover
DAVID HALPERN, Jet Propulsion Laboratory, Pasadena, California
SUSAN E. HUMPHRIS, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
BONNIE J. MCCAY, Rutgers University, New Brunswick, New Jersey
STEVEN A. MURAWSKI, University of South Florida, St. Petersburg
JOHN A. ORCUTT, Scripps Institution of Oceanography, La Jolla, California
H. TUBA ÖZKAN-HALLER, Oregon State University, Corvallis
MARTIN D. SMITH, Duke University, Durham, North Carolina
MARGARET SPRING, Monterey Bay Aquarium, Monterey, California
DOUGLAS WARTZOK, Florida International University, Miami
LISA D. WHITE, University of California, Berkeley, and San Francisco State University
OSB Staff Members
SUSAN ROBERTS, Director
STACEE KARRAS, Program Officer
EMILY TWIGG, Associate Program Officer
PAMELA LEWIS, Administrative Coordinator
ALEXANDRA PHILLIPS, Program Assistant
SHUBHA BANSKOTA, Financial Associate
JAMES HEISS, Postdoctoral Fellow
Assessing the cumulative effects of multiple stressors is a top-priority problem in marine ecology. An important marine policy paper by Rudd (2014) surveyed more than 2,000 ocean scientists and policy makers from nearly 100 countries, asking them to prioritize the most important questions for the ocean environment. Out of 67 questions, the top priority was “How will the individual and interactive effects of multiple stressors (e.g., ocean acidification, anoxia, warming, fishing, and pollution) affect the capacity of marine ecosystems and species to adapt to changing oceans?” The topic of cumulative effects was chosen by the federal agencies that funded this report because assessing cumulative effects has been an important part of U.S. regulations protecting marine mammals since the 1970s, but the approaches used have little predictive value. Marine mammal populations are affected by a large number of natural and anthropogenic stressors. This report was tasked with focusing on sound and other stressors when evaluating cumulative effects on marine mammals. If cumulative effects cannot be accounted for, then unexpected adverse impacts from interactions between stressors pose a risk to marine mammal populations and the marine ecosystems on which people and marine mammals depend.
Assessing cumulative effects is not only important, it is also a problem that has proven nearly impossible to solve. Scientists and managers involved in these assessments confront data gaps concerning the dosages of all stressors to which marine mammals are exposed, and a lack of dose–response functions to predict effects of single stressors. For ethical and practical reasons, there are no studies in marine mammals on interactions between stressors. Studies in other marine organisms show that these stressors often interact, but their cumulative effects are extremely difficult to predict.
The audience intended for this report includes stakeholders, managers, policy makers, and scientists. This report has developed approaches to analyze how stressors exert their effects on individuals, populations, and ecosystems to help guide research on cumulative effects in the future. The report aims to help managers decide when cumulative effects are particularly important, and to help guide decisions about which stressors or combinations of stressors to reduce when this is necessary to protect marine mammal populations.
Recognizing that quantitative prediction of cumulative effects of stressors on marine mammals is not currently possible, this committee developed a conceptual framework for assessing the population consequences of multiple stressors. The framework uses indicators of health that integrate short-term effects of different stressors that affect survival and reproduction. The report explores a variety of methods to estimate health, stressor exposure, and responses to stressors. The committee also developed a decision tree for determining when cumulative effects are particularly important for managing a marine mammal population.
Many stressors that affect marine mammals are themselves affected by larger-scale ecological drivers. For example, ocean climate is an ecological driver that changes the exposure of marine life to the stressors of warming and ocean acidification. Similarly predators, prey, and competitors of marine mammals are potential stressors whose distributions are affected by ecological interactions. The committee explored the use of interaction webs to help ensure that important ecological interactions, including indirect interactions, are included in assessments of cumulative effects.
Cumulative effects must be evaluated in environmental assessments of planned activities, but this evaluation is equally important for selecting management actions once populations or ecosystems are found to be at risk of adverse impacts. In this case, the critical issue is to decide what
combination of stressors to reduce in order to bring the population or ecosystem into a more favorable state. Whatever increases in stressors may have created the risk, the best management action may require reducing a different combination of stressors. For example, if a persistent toxicant increases mortality of a species but cannot be removed from the ocean, the best management action might involve reducing fishing bycatch, which can be controlled. This broadening of management approaches could be a particularly important result of assessing cumulative effects.
Recognizing difficulties with measuring trends in marine mammal populations, the report explores early warning indicators for adverse impacts, including health and population measures. Measures of health that indicate which stressors caused an effect would be particularly useful for managing the effects. The committee hopes that this report may help direct the development of methods to identify when cumulative effects pose a risk of driving a population or ecosystem into an adverse state, and to develop management strategies that can select stressors whose reduction will minimize this risk. The committee recognizes the enormous scientific challenge posed by these two problems, but their importance justifies significant effort to solve them.
This committee met four times and held a workshop in the National Academies of Sciences, Engineering, and Medicine’s Beckman Center in Irvine, California. On behalf of the committee, I would like to thank the speakers invited to the workshop and audience members who shared their insights with the committee. On behalf of the committee, I would also like to thank the study directors who oversaw this report, first Deborah Glickson and then Kim Waddell, and the director of the Ocean Studies Board, Susan Roberts, along with other members of the staff whose contributions were essential for our meetings and development of the report.
Academies reports are designed to address problems that are both important and difficult, but this committee was tasked with a more difficult and broad-ranging problem than I have encountered in previous studies on marine mammals and sound. The committee explored many approaches to evaluating cumulative effects, and, in response to this task, this report is more extensive than the others on marine mammals and sound. The committee members and members of the National Academies staff working on this report not only had to write about and review a large body of information, but were all stretched to work outside of their disciplines. I would like to thank the committee members for their generosity in working together so well to meet the challenge of the statement of task, exploring creative solutions while providing a broad and critical review of the problem of evaluating cumulative effects in marine mammals.
Peter L. Tyack, Chair
Committee on the Assessment of the Cumulative
Effects of Anthropogenic Stressors on Marine Mammals
This report was greatly enhanced by discussions with participants at the committee’s meetings as part of this study. The committee would like to acknowledge, especially, the efforts of those who gave presentations at the committee meetings: Kim Anderson (Oregon State University), Jesse Barber (Boise State University), Steve Beissinger (University of California, Berkeley), Shekhar Bhansali (Florida International University), Tiffini Brookens (Marine Mammal Commission), Mitch Eaton (U.S. Geological Survey), Tim Essington (University of Washington), Jason Gedamke (National Oceanic and Atmospheric Administration), Horst Greczmiel (Council on Environmental Quality), Carrie Kappel (University of California, Santa Barbara), Sara Maxwell (Old Dominion University), Jonna Mazet (University of California, Davis), Jim Price (Bureau of Ocean Energy Management), and Mike Weise (Office of Naval Research).
This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the process. We wish to thank the following individuals for their review of this report:
MICHAEL CASTELLINI, University of Alaska, Fairbanks
ANNA FAIRBROTHER, Exponent EcoSciences
FRANCES GULLAND, Marine Mammal Center
ALAN HASTINGS, University of California, Davis
GARY ISAKSEN, ExxonMobil Exploration Company
CARRIE KAPPEL, National Center for Ecological Analysis and Synthesis
JOHN ORCUTT, Scripps Institution of Oceanography
BRANDON SOUTHALL, Southall Environmental Associates, Inc.
CATHERINE WANNAMAKER, Southern Environmental Law Center
Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the report’s conclusions or recommendations, nor did they see the final draft of the report before the release. The review of this report was overseen by Andrew R. Solow, Woods Hole Oceanographic Institution Senior Scientist, and John Dowling, Harvard University Professor of Neurosciences. They were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.
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