Irish fisheries policy discourse insists that fishing opportunities are a public resource that are managed to ensure that such opportunities are not concentrated into the hands of large fishing interests. Yet, an examination of the ontological assumptions underlying Irish fisheries governance reveals that access to valuable quota-controlled stocks is shaped by historical assumptions that reinforce the worlds or ontological ‘realities’ of larger vessels, while different requirements combine to frustrate the attempts of small-scale vessels to assert a reality that is designed around their differences. Drawing on ethnographic research into small-scale fishing communities in Ireland’s offshore islands, and supported by an emerging theoretical focus on the politics of diverse ontologies, I argue that we need to examine the ontological assumptions underpinning State approaches to fisheries governance to gain a fuller understanding of the on-the-ground implications of the governance arrangements that shape the day-to-day lives of fishing communities in Ireland’s offshore islands. I consider six key ontological assumptions (social-historical, ecological, geographical, technocratic, material and markets-driven) that define these approaches. I focus on two islands-driven fisheries governance initiatives that have challenged these ontological assumptions in their assertion of particular fisheries worlds, and I consider what the State’s response, of retrenchment of the ontological status quo, means for fisheries policy and governance. I conclude that by failing to accommodate diverse ontologies, the State is locked into (re)producing a fisheries seascape that is stifling the exploration of alternative governance possibilities, while privileging institutional arrangements, approaches and practices that do not challenge the ontological status quo.