Declining populations of marine mammals have led to growing concern about their conservation. As a result, a series of specific marine conservation measures have been put in place, such as banning hunting and trading or establishing protected areas. This set of rules, although having restored the populations of some species of marine mammals, have failed to address the biggest threat to their survival, which consists of the bycatch of non-target species. On this question, fisheries law which should address critical issues contains some important protection gaps. This paper seeks to elucidate the efficacy of existing global and regional legal rules in protecting marine mammals, the most endangered marine species, from over-exploitation, with a particular focus on cetaceans. To this aim, the paper explores specific norms developed by global and regional treaties and the European Union (EU) for specific species (whales, seals, small cetaceans) (‘direct protection’). An analysis of the current international and regional legal framework (fisheries law) addressing marine mammal protection less directly is also provided (‘indirect protection’). The paper builds upon the assumption that measures that simply ban hunting or fishing, as envisaged by wildlife law, must be complemented by fisheries law (‘inter-regime linkages’). Paradoxically, indirect protection represented by fisheries law can significantly affect improvement of both fish welfare, which is often neglected, and conservation. The challenge lies in the fact that current fisheries law, in spite of having progressed the field, still fails to provide an adequate response to bycatch problems. A focus on marine mammal law illustrates the problem of fisheries management. In this context, the paper proposes tangible solutions to improve fisheries law and also discusses whether the emerging concept of fish welfare can be an ‘asset’ if included in fisheries rules, contending that welfare issues must necessarily be part of future legal developments.