Environment & concept
Every serious environmental objection to salmonid farming — nutrient discharge, escapes, sea lice, chemicals, seabed damage — is an objection to the net. Replace the net with a closed steel wall and the objections do not need to be managed, mitigated or offset. They stop existing.
The concept
It is not a smaller land plant and it is not a better net. It is a third category: a sealed, drainable steel tank that borrows the ocean's physics while refusing its biology.
An open-net pen is a bag of mesh hung in the sea: whatever enters or leaves the fish population moves freely with the current. A closed unit replaces that mesh with a solid marine-steel wall. Nothing crosses it except water that we choose to pump, filter and measure. That single change converts an uncontrolled interaction with the ecosystem into a managed, monitored process.
Unlike a land-based recirculation plant, we do not have to build, chill and re-oxygenate an artificial ocean. The surrounding sea provides volume, stable cold temperature and buoyancy for free. That is why the environmental gains arrive at roughly one kilowatt-hour per kilo produced instead of the five to ten typical of land-based systems.
Intake water is taken from well below the surface layer, where sea lice larvae, algal blooms and surface pollution live. It is filtered before it reaches the fish. The result is stable, clean, pathogen-poor water all year — which is what makes chemical-free farming possible rather than aspirational.
Outflow passes through solids capture before returning to the sea. Sludge, faeces and uneaten feed are collected as a concentrated stream. Instead of dispersing into the seabed, they become feedstock for biogas or fertiliser — the difference between a waste problem and a circular input.
Environmental case
For each issue: what the open net pen does today, and what a closed unit does instead.
Open net
An open pen discharges nitrogen and phosphorus directly into the water column and onto the seabed beneath it.
Closed unit
Solids are captured and removed from the marine environment entirely. Production can grow without adding to Baltic eutrophication — the single constraint that most limits new licences in the region.
Open net
Storms, seal attacks and net wear release farmed fish that interbreed with, and outcompete, wild populations.
Closed unit
A solid steel wall has no mesh to tear. Escape risk is removed by construction, not by procedure — so wild Baltic and Nordic stocks stay genetically intact.
Open net
Delousing means hydrogen peroxide, medicated feed, thermal or mechanical handling — stressful for fish and damaging to surrounding crustaceans and wrasse.
Closed unit
Lice never enter, because the intake sits below their zone. We operate with zero delousing treatments and therefore zero pharmaceutical residue in the sea.
Open net
Organic waste settles under the pen, deoxygenating sediment and killing benthic life.
Closed unit
The captured sludge stream is directed to biogas digestion or processed into agricultural fertiliser, displacing fossil energy and mined phosphorus.
Open net
Low direct energy use, but heavy losses: high mortality and poor feed conversion waste the embedded carbon of every kilo of feed.
Closed unit
Around 1 kWh per kilo on Nordic low-carbon electricity, combined with under 1% mortality, means almost no feed carbon is wasted on fish that never reach the plate.
Open net
Nordic and Baltic countries import the majority of the salmonids they consume, flown and trucked over long distances.
Closed unit
Local production inside each market removes long-haul logistics from the footprint and puts protein supply inside national borders.
Open net
Uses sea space, but degrades the seabed it occupies.
Closed unit
Uses sea space without consuming farmland, groundwater or river abstraction, and the seabed beneath stays clean because nothing settles on it.
Open net
Sediment damage under long-established pen sites can take years to recover after fallowing.
Closed unit
Units are drained, lifted, cleaned and relocated. A decommissioned site leaves essentially no footprint behind — and the steel itself is recyclable at end of life.
Side by side
| Environmental factor | Open net pen | Closed steel unit |
|---|---|---|
| Nutrient discharge to sea | Uncontrolled, continuous | Captured and removed |
| Escape risk | Structural and ongoing | Eliminated by construction |
| Sea lice treatments | Multiple per cycle | None |
| Pharmaceuticals in water | Medicated feed, peroxide | None |
| Cycle mortality | Typically 10-15% | Under 1% |
| Seabed condition beneath | Organic loading, oxygen loss | Unaffected |
| Energy per kilo | Low but wasteful | ~1 kWh, little waste |
| Land and freshwater use | None | None |
| End-of-life footprint | Sediment recovery years | Removable, steel recycled |
Why it matters here
Brackish, shallow, slow to exchange water and already among the most eutrophication-damaged seas in the world. Any model that adds nutrients cannot expand here. A model that adds none can. That is why closed containment is not a premium option in this region — it is the only licensable growth path, and it maps directly onto EU Blue Economy, EMFAF and circular nutrient priorities.