Abstract Labour exploitation in marine fishing industries has received considerable negative publicity. Yet, is there something specific about marine fishing that makes it highly exploitative? We compare work on purse-seiners catching tuna for canning with work on longliners catching tuna for sashimi. We explain difference through a comparative analysis along three axes: (1) tuna population dynamics, fishing technologies and resource access; (2) industrial organization and governance of global production networks; and their relationships with (3) workplace labour regimes on vessels. The article contributes to labour regime analysis by demonstrating the relative material significance of ecology in shaping labour regimes.