Would it be possible to do semi-enclosed fish farming, like changing the netting out for a big bag and filtering the input and output water?
It seems like there’s lots of surface area on the sea that is largely not occupied by sea life, and that could reasonably be expanded into for aquaculture to feed the growing population. The sun mostly hits the ocean and becomes heat that drives ocean and weather - could we intercept a fraction of the exergy to drive offshore agriculture?
My understanding is that the issues with fish farming are:
- High parasite and disease load from close quarters
- Antibiotic and pesticide emission managing above
- Escaping fish harming natural habitat
- Pollution from food pellets falling out the bottom
If you could filter and sterilize the input and output water, this would help prevent diseases and parasites entering and leaving the pen. You could also put a drain hose at the bottom and slope the sides into a cone to handle fallen food pellets. There would also be far fewer escaped fish, especially if the pen was double-lined.
You could power the filtration systems with solar panels overtop of the pen.
The farm wouldn’t need to be at the surface if they were enclosed. Make spherical stainless tanks ~50m dia, explosively hydroform at sea, then sink to ~5m below the surface. Keep air headspace above to get neutral buoyancy and keep lightly pressurized for structural strength.
You’d need lights on the inside for circadian rhythm. Probably put a service port at the top and a drain at the bottom for excess feed and animal waste.
There could be hanging chains below the tank for filter feeder animals like mussels and barnacles along with vegetation like kelp to grow on, which could feed off the ejected fish waste. The solar array would also shelter fish and other marine life, creating an offshore reef of sorts.
During storms, the platform and tank could submerge to below the wave base to avoid wave damage.
For service and harvest, the tank could surface and be worked on by a crew entering the top from a ship.
One of my friends looked at semi-enclosed aquaculture as part of a study on the impacts of fish farming! Looks like it’s been considered as an intermediate solution between open net and fully onshore approaches - see Page 21 onwards here: https://cwf-fcf.org/en/resources/research-papers/CRA_13102_Aquaculture_Manual_EN_web.pdf