Publisher's version, source: <a href=http://doi.org/10.1093/icesjms/fsv199>http://doi.org/10.1093/icesjms/fsv199</a>. | Trends towards a more participatory agenda in policy-relevant science imply that the roles and work tasks of scientists become more multifaceted. In Europe, the increased use of multiannual plans creates a need for fishery scientists to contribute with their expertise in a wide variety of situations. We identify and characterize four roles for scientists as <i>developers</i>, <i>reviewers</i>, <i>judges</i>, and <i>messengers</i> in arenas where management plans are produced and evaluated. Using examples of producing and evaluating management plans for pelagic fish stocks in Europe, we present different scientific roles and how they may intertwine. The examples illustrate that fishery scientists increasingly interact with advisory councils and industry stakeholders when performing roles as developers and messengers. The roles as reviewers and judges are typically affiliated with evaluation processes carried out under the auspices of the marine science and advisory organization International Council for the Exploration of the Sea (ICES). While it may be difficult to separate the roles in practice, we argue that it must be emphasized to be aware of their different requirements to ensure that scientific credibility is not compromised. By asking the question “What hat are you wearing?”, we encourage individual fishery scientists, their employers, and ICES as a network organization of expertise to reflect on roles, affiliations, mandates, and possible consequences of wearing different “hats”.