Fish Net Pen Welfare: Environmental Challenges in Open Water Salmon Farming

Net pen aquaculture exposes salmon to the environmental conditions of the surrounding water body. Understanding how environmental variability affects welfare helps evaluate and improve net pen management.

Key Facts

Open net pen aquaculture uses mesh enclosures anchored in coastal or freshwater environments
Fish in net pens cannot escape environmental conditions including temperature spikes, jellyfish blooms, and oxygen depletion
Jellyfish blooms have caused mass mortality events in Norwegian salmon farms by damaging fish gills
Harmful algal blooms (HABs) produce toxins that cause gill damage and mortality in net pen fish
Sea surface temperature warming from climate change is increasing the frequency of heat stress events
Net pen sites must be carefully selected for water exchange, current patterns, and environmental stability
Semi-enclosed or land-based recirculating aquaculture systems (RAS) eliminate most environmental welfare risks
Lice management in open net pens using chemical treatments has welfare costs for both target and non-target organisms

Welfare Considerations

Net pen aquaculture creates a fundamental welfare challenge: fish cannot escape the water they live in, and that water's quality is determined by environmental conditions beyond the farmer's control. When jellyfish blooms occur, fish cannot swim away from gill-damaging tentacles. When oxygen drops during algal blooms, fish cannot move to better-oxygenated water. When surface temperatures spike in summer, fish cannot seek cooler depths. These environmental insults cause suffering and mortality that cannot be prevented once they occur, only reduced through site selection and early response. The move toward land-based systems that provide complete environmental control eliminates these welfare risks but at significantly higher capital and energy cost. The long-term trajectory of salmon aquaculture welfare likely requires reducing dependence on open environmental systems.

What You Can Do

Support seafood certification standards that include environmental welfare risk assessment for net pen sites
Engage salmon producers about their monitoring and response protocols for environmental welfare events
Support investment in land-based aquaculture systems that eliminate uncontrollable environmental welfare risks
Advocate for net pen siting regulations that require environmental impact and welfare risk assessment
Learn about the environmental welfare risks specific to your regional salmon aquaculture industry
Choose salmon from systems that can demonstrate low frequency of environmental welfare incidents