For more information about the MOCHA project, please contact the project manager Catriona Harris at firstname.lastname@example.org.
Behavioral response studies (BRSs) are experiments aimed at directly quantifying the relationship between potential anthropogenic disturbances and their effect on specific marine mammals. The US Navy is making a substantial investment in BRS studies, aimed at understanding the effect of active sonar on species of concern. Studying these species in ecologically valid settings often requires field experiments. BRS studies are difficult and expensive to conduct, and so sample sizes are necessarily small. Traditional statistical methods for analysis, based on null models and hypothesis testing, do not make best use of the available data, and make it hard to represent accurately the complexity of BRS experimental protocols. With traditional approaches, small sample sizes result in insufficient power for all but the most extreme effects. This creates a risk of biased reporting, where clear responses from the most sensitive species will be publishable, while responses (or lack of responses) from less sensitive species are harder to detect and results are more difficult to interpret and publish. There is therefore a need for analytical approaches where every outcome contributes equally to our understanding.
We formed a working group, supported by two full-time post-doctoral researchers, to develop and implement innovative methods for the analysis of the results from BRSs. The aim was to complement and enhance analyses already taking place as part of each current Navy-funded BRS project. The outputs of this project have substantially enhanced our ability to quantify the response of marine mammal species to navy sonar and other acoustic stimuli, making best use of available data, and providing guidance for future studies.
The overall objective of this project was to develop and implement innovative statistical methodologies for the analysis of behavioral response study data. Our focus was on studies estimating the response to mid-frequency active sonar, but the methods developed are widely applicable. We aimed to maximize the inferences that can be drawn from current and ongoing studies as well as to provide advice on future studies. Advances have been made in close collaboration with those involved in existing BRS projects, using a working group format. This approach has enabled us to complement and enhance the analytical work already being undertaken, as well as to be flexible and incorporate new ideas as they arose in working group sessions.
The project had four specific objectives.
- Improve methods for combining diverse behavioral measures into metrics of behavioral response. Consideration was given to obtaining metrics that can be linked to biological consequences.
- Improve methods for estimating dose-response functions for individual studies. This involved both developing and applying cutting-edge statistical methods, as well as considering which contextual variables in addition to acoustic dose could be incorporated into the analysis.
- Combine information across studies and species, making use of expert biological opinion, to make predictions about taxa and contexts not yet studied. These “meta-analyses” aimed to fully account for differences in methods/protocols between studies
- Based on the above, determine where major uncertainties still lie (for example, through sensitivity analyses), and hence suggest where future experimental effort might be applied most fruitfully.
This research is being financially supported by the United States Office of Naval Research.
Links to other relevant efforts can be found here.