Net pen design - including cage depth, netting material, predator exclusion and lighting - directly affects salmon welfare. Understanding the welfare implications of net pen design helps set appropriate standards.
Net pen design is a significant but underappreciated welfare lever in salmon aquaculture. The physical environment of the cage - its depth, light regime, current exposure and surface character - shapes every aspect of the salmon's daily experience. Snorkel systems that keep fish away from lice-dense surface water represent a genuine welfare innovation because they reduce lice burden (and treatment frequency) through environmental management rather than chemical or mechanical intervention. Submerged lighting for photoperiod manipulation can affect salmon circadian rhythms and welfare - a poorly understood area requiring more research. Seal-net interactions causing injury to seals attempting to access cages present a dual welfare concern for both salmon and marine mammals.