A growing practice in fisheries management is the allocation access rights to marine fisheries through individual transferable quota (ITQs) – limits on the amount of fish allocated to individual licences as transferable permits. By establishing an ownership claim over the right to fish and a market for exchange, ITQs are purported to provide a conservation incentive that reduces or eliminates overfishing while increasing economic efficiency. Yet despite enthusiastic support for ITQs as a conservation tool, the connection between ITQs and stewardship remains a theory in need of validation. Where research has found that ITQs outperform non-ITQ fisheries in protecting against overfishing, this has been demonstrated through problematic control groups that cover a wide range of systems including unregulated fisheries. As ITQ systems are a collection of management features, there is a lack of understanding of which attribute is associated with positive outcomes – the I, the T, or the Q. This paper explores this question through a statistical analysis of 150 fisheries from around the world, documenting their changes in fisheries management system (e.g. ITQ, IQ, quota pool, effort-based) and the health of the corresponding fish stocks (e.g. fishing mortality, biomass). The results indicate that a more nuanced view of ITQs and conservation incentives is required as ITQs are neither necessary nor sufficient to deliver positive environmental outcomes. An understanding of ITQs/catch shares and other allocation systems as a combination of design attributes would greatly improve debates surrounding fisheries management.