Marine net pen aquaculture raises complex welfare questions about the behavioral needs of fish that evolved to swim vast distances in open ocean environments.
Marine net pen welfare involves fundamental questions about what level of spatial restriction is acceptable for fish that evolved in essentially unlimited ocean space. The behavioral ecology of salmonids involves long migrations, complex habitat use, and ocean-wide foraging - none of which is possible in net pen systems. Whether the welfare costs of this restriction are mitigated by reduced predation pressure, reliable nutrition, and absence of migration challenges is genuinely uncertain. The most honest assessment is that marine net pens impose significant welfare costs from spatial restriction, and improving welfare requires both better net pen design and development of alternative production systems.