Dear colleagues, It is with great pleasure that I inform you of this new publication now available in PLOS-One. Please note that there was a problem with figure mislabelling, but the notes are added to the online version to fix this mistake. The updated PDF version from PLOS-One should be available shortly. For any inquiry (including a enhanced PDF version with the correct figure labelling), please contact the first author directly at Lyne.Morissette@globetrotter.net Marine Mammal Impacts in Exploited Ecosystems: Would Large Scale Culling Benefit Fisheries? By Lyne Morissette, Villy Christensen and Daniel Pauly PLOS-One; Sept. 6, 2012 ABSTRACT: Competition between marine mammals and fisheries for marine resources—whether real or perceived—has become a major issue for several countries and in international fora. We examined trophic interactions between marine mammals and fisheries based on a resource overlap index, using seven Ecopath models including marine mammal groups. On a global scale, most food consumed by marine mammals consisted of prey types that were not the main target of fisheries. For each ecosystem, the primary production required (PPR) to sustain marine mammals was less than half the PPR to sustain fisheries catches. We also developed an index representing the mean trophic level of marine mammal's consumption (TLQ) and compared it with the mean trophic level of fisheries' catches (TLC). Our results showed that overall TLQ was lower than TLC (2.88 versus 3.42). As fisheries increasingly exploit lower-trophic level species, the competition with marine mammals may become more important. We used mixed trophic impact analysis to evaluate indirect trophic effects of marine mammals, and in some cases found beneficial effects on some prey. Finally, we assessed the change in the trophic structure of an ecosystem after a simulated extirpation of marine mammal populations. We found that this lead to alterations in the structure of the ecosystems, and that there was no clear and direct relationship between marine mammals' predation and the potential catch by fisheries. Indeed, total biomass, with no marine mammals in the ecosystem, generally remained surprisingly similar, or even decreased for some species. Link to the article in PLOS-One: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0043966