Approaches to Understanding the Cumulative Effects of Stressors on Marine Mammals (2017) / Chapter Skim
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Marine Mammal Commission funded The Committee developed a Population Consequences of the present study in order to review the understanding of Multiple Stressors (PCoMS) model to provide a conceptual cumulative effects of anthropogenic stressors, including framework for the challenging task of assessing the risks sound, on marine mammals and to identify new approaches associated with aggregate exposures to one kind of stressor, that may improve the ability to estimate cumulative effects.
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The committee will assess current method demonstrate, but the intervening decade has seen an increas ologies used for evaluating cumulative effects and ing number of studies showing the effects of ocean noise on identify new approaches that could improve these individual marine mammals. Under the U.S.
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physiological effects of sound cannot be generalized based While the relationship between the dose of a single on testing of a few species of marine mammals but will stressor and the response of an individual animal is relatively require studies in more individuals of more species. Under straightforward to predict given sufficient data, the addistanding how the physiological effects of sound become per tion of a second stressor can add considerable complexity manent hearing loss requires audiogrametric measurements.
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Note through which cumulative effects arise, and the nature of that this same phenomenon could also occur with aggregate these effects will be difficult to predict. In cases such as this exposure to a single stressor.
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In situations where the current pattern of exposure The influences of multiple stressors on marine mam- to stressors is expected to change in the future beyond the mals might be inferred from studies of other species, such levels currently experienced, such as those caused by changas nonmammalian marine species or terrestrial mammals. es in ocean climate, this approach for studying cumulative However, this can be problematic because marine mammals effects will be inadequate.
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Where possible, the data Establishing baseline values of health indices and their on changes in demography, population size, and the health associations across life history stages in marine mammal of individuals collected in these studies should be used to species will provide critical information for assessing indiimprove estimates of the parameters of the PCoMS model vidual and population health. Cross-sectional sampling and and reduce uncertainty.
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to multiple stressors is an unquestioned reality for marine mammals, the best current approach for management and conservation is to identify which stressor combinations cause ECOSYSTEM-LEVEL EFFECTS the greatest risk. The committee developed a decision tree The committee broadened its review from cumulative that can be used to identify situations where a detailed study effects of stressors on marine mammals to consider how of potential cumulative effects should be given a high priority interactions among stressors may affect entire ecosystems.
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can operate directly as a driver on D (Marine Mammals) and indirectly as a driver on D through the indirect pathway (A to B to D)
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SUMMARY 9 FIGURE S.4 A decision tree for identifying situations where studies of the possible interactions between stressors should be given a high priority when considering the effect of a focal stressor on a population.
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For the current baseline. example, declines in population health indices may indicate The committee recognizes that the state of the science increases in exposure to anthropogenic stressors, but they of cumulative effects has low predictive power compared to may alternatively be caused by an increase in population size regulatory demands to assess these effects.
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