ABSTRACT Non-compliance with fishing regulations is a widespread phenomenon in fisheries worldwide, jeopardizing the recovery of stocks and ecosystem services. There is an urgent need to fill the gaps in our understanding of the scale and nature of illegal fishing in artisanal fisheries, balancing the advances made in industrial fisheries. We explored patterns of fisher compliance with the existing minimum legal size (MLS) regulation in the small-scale benthic fisheries of central Chile. We focus on two of the most conspicuous species (loco Concholepas concholepas and keyhole limpets Fissurella spp.) and comparing two management regimes: management areas (MAs; local name for territorial use rights for fisheries) and open access areas (OAAs; no spatial entry restrictions). We also evaluated the effect of the spatial distribution of MAs, which determines the availability of OAAs on compliance. For both species, we measured the size of individuals in the catch in two consecutive years. We developed an index that accounts for the availability of open access areas per fisher. We found that a) the number of undersized individuals in the catch in OAAs is enormous, b) management regime influences both the median size and fraction of the undersized catch, and c) as the availability of OAAs per fisher decreases, illegal fishing increases, demonstrating the need to manage the levels of effort displacement in designing area-based instruments for management and conservation. Our findings also highlight the need to a) analyze the benefits of area-based instruments at the seascape scale, and b) develop and adapt instruments to prevent illegal fishing.