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It makes sense to me that the best food in an underwater dome complex would be fish. Considering the massive amounts of aquatic life in the vicinity, it could work pretty well.

However, I can't think of how the people would actually catch the fish. They need to be able to breathe, so an airlock leading into a section of ocean wouldn't be useful (assume there is no underwater breathing technology nor submersibles available).

I've thought about some sort of net to catch them, but I'm not sure how the fish could be moved into the dome from there without flooding the place. If there were a way to catch fish on the sea floor (lobsters, crabs, etc.) easily, that would also work.

Assume the technology level when building the domes is that of today, but there will be no communication or supply deliveries from anywhere outside the domes (so nothing that would require extensive maintenance or consume too many non-renewable supplies).

Any ideas?

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    $\begingroup$ Books 'Dark Life' and 'Riptide' by Kat Falls contain underwater houses similar to those you mention, although the technology is higher. I think the idea there is that you exit (or fish, or set traps, or whatever) underneath. Try looking them up; you might get some ideas. $\endgroup$
    – NadiraSpzirglas
    Sep 1, 2019 at 2:52
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    $\begingroup$ What about algae-agriculture instead of fishing? Seems to me a more obvious and efficient (and peaceful) solution to gather food. $\endgroup$
    – ascripter
    Sep 1, 2019 at 10:22
  • $\begingroup$ It's perfectly easy to have a room with portions of the floor open at the bottom to sea, and there, you can fish like normal... $\endgroup$
    – Harper - Reinstate Monica
    Sep 1, 2019 at 20:23

4 Answers 4

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They need to be able to breathe, so an airlock leading into a section of ocean wouldn't be useful

Well, not so much. Freediving is very much a thing, after all, and has been for quite a considerable length of time. People have been able to variously dive to over 100m, swim hundreds of metres and hold their breath for about 10 minutes (probably not all three at once, mind you). You can look back centuries to find traditions of people diving without breathing gear to recover wrecks, pearls or food. Plenty of interesting stuff out there... have a read about ama divers, for example.

Once you're out in the water, spearfishing is a reasonable technique, and one often used in combination with free diving.

So all you really need is a moon pool or fast cycling airlock and a bunch of people willing to practise apnoea.

Now, the issues of diving illness and long term human viability at depth, that's a different matter...

Edit to add some alternative food sources

Remember that whilst fishing can be a very effective source of nutrition, it needn't be the only game in town and alternatives may be easier to arrange.

Shellfish are one good possibility... oysters and mussels are already farmed commercially. They have potentially useful byproducts (shells, pearls) and perform useful ecological services such as removing carbonates from the water and filtering out nutrients that might otherwise cause problems (like poop from fish farming). Mussels can be farmed on a rope, and the whole lot hauled in for harvesting without anyone having to take a dip.

Many varieties of seaweed and other algae can also be farmed if you are high enough in the photic zone for them to thrive. Not just useful for food, but you can use them to make other handy raw materials like fuel or plastic feedstocks. In either case, you don't necessarily need constant hands-on work to get your food, making the logistics of the whole thing much simpler.

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    $\begingroup$ If you can build and use a moon pool, why not just fish from within the dome? I can just picture dozens of people sat on little stools around a huge steel oculus filled with still ocean water, eating sandwiches from paper bags as they wait patiently for a bite. $\endgroup$
    – Joe Bloggs
    Sep 1, 2019 at 10:47
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    $\begingroup$ @JoeBloggs depends on local density of fish and how quickly stocks replenish, probably. You also might not be able to use the moon pool for other moon pooly things, or you risk scaring the fish. $\endgroup$
    – Starfish Prime
    Sep 1, 2019 at 10:50
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    $\begingroup$ Moon-pooly is my new favourite adjective. $\endgroup$
    – Joe Bloggs
    Sep 1, 2019 at 11:27
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    $\begingroup$ @JoeBloggs its no "potatoid", but I try my best. $\endgroup$
    – Starfish Prime
    Sep 1, 2019 at 11:50
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    $\begingroup$ @pipe as a trade good or medium of exchange they're clearly useful. $\endgroup$
    – Starfish Prime
    Sep 1, 2019 at 19:19
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Underwater domes will probably be located deep in the oceans. If you are under one of the major oceanic currents, then all you need is some dynamite.

Find a school of fish far enough from home for a blast to be safe and... well, blast. The fish will all die or be stunned, and they will float to the surface where a ship can gather them. mostly sink to the seafloor where they could be easily picked up (thanks Dubukay for correcting me). The oceanic current will make sure that more fish will eventually pass by.

The advantage of this method is that since water is incompressible, explosions tend to have a far greater blast radius than in air, making fish much easier to catch with explosives than birds or game.

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    $\begingroup$ Actually, this is a fantastic idea because most fish killed by blast fishing actually sink to the seafloor, where they could be easily picked up! Dynamite fishing is the worst. $\endgroup$
    – Dubukay
    Sep 1, 2019 at 4:47
  • $\begingroup$ This would be a pretty cool way of obtaining food, though I'm wondering about the renewable-ness of explosives from underwater. $\endgroup$
    – Radvylf Programs
    Sep 2, 2019 at 20:51
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    $\begingroup$ @RedwolfPrograms use sunlight at the surface to separate sodium from seawater. Throw the chlorine away. When you want a bang, release the sodium back into the seawater. High-school teacher of mine exploded a toilet once with a block of sodium by dropping it in for lulz. $\endgroup$
    – The Square-Cube Law
    Sep 2, 2019 at 20:59
  • $\begingroup$ @Renan You can't just "throw the chlorine away", right? $\endgroup$
    – Radvylf Programs
    Sep 2, 2019 at 22:33
  • $\begingroup$ @RedwolfPrograms if you live underwater you don't nees the planet to have a breathable atmosphere ;) $\endgroup$
    – The Square-Cube Law
    Sep 3, 2019 at 0:39
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Fish traps are a convenient way to catch fishes and other sea creatures.

A fish trap is a trap used for fishing. Fish traps can have the form of a fishing weir or a lobster trap. A typical contemporary trap consists of a frame of thick steel wire in the shape of a heart, with chicken wire stretched around it. The mesh wraps around the frame and then tapers into the inside of the trap. When a fish swims inside through this opening, it cannot get out, as the chicken wire opening bends back into its original narrowness. Contemporary eel traps come in many shapes and sizes and are constructed of many materials. In earlier times, traps were constructed of wood and fiber.

fish trap

Just put a suitable lure into the trap, and when the catch is done, pull the trap into a load-lock which you will evacuate from water before letting human access it.

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    $\begingroup$ Similar items are used to catch crabs and lobster commercially. $\endgroup$
    – Zeiss Ikon
    Aug 31, 2019 at 16:58
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    $\begingroup$ Baiting crab and lobster pots is a particularly nauseating task, even in a good breeze on the deck of a boat. Crabs love their rancid decaying dead stuff. The thought of making that in a confined space is frankly horrifying. $\endgroup$
    – Starfish Prime
    Aug 31, 2019 at 17:57
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    $\begingroup$ Anyway: trapping fish in this way doesn't seem to be very common at sea, probably because the sort of fish you'd want to eat aren't fooled by it. That's not to say it isn't possible, but I wouldn't want to rely on it. $\endgroup$
    – Starfish Prime
    Aug 31, 2019 at 18:00
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    $\begingroup$ (also, thinking more on this, "sea" should be extended to mean "large open bodies of water such as seas or lakes". fish trapping is best done in rivers, but it might be possible in areas with strong underwater currents) $\endgroup$
    – Starfish Prime
    Aug 31, 2019 at 20:20
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Depending on the level of scientific realism you want, it should be possible to enable rod and reel "sport" type fishing activity from your underwater dome (even if the dome itself is kept at surface pressure, i.e. the humans inside aren't "saturation divers" spending long periods at depth pressure.

First, you need a "waldo" type manipulator system. These have existed for decades in deep diving submersibles; in this case, it would be optimized for the movement of the reel crank, a little casting motion, a sensor to feel the line tension (to detect bites). This lets the fisher operate the rod and reel in a "moon pool."

The "moon pool" is a sea-pressure chamber with an opening at the bottom to the sea. In surface vessels, these allow launching submersibles and ROVs from inside the hull, broadening the range of weather conditions for operations. In your colony dome, it provides a pressurized access to a water surface. The rod would be mounted by remote manipulators, or with the moon pool closed and the chamber pumped down to dome pressure.

When all is ready, the pressure is brought up to match the exterior, and the moon pool opened, so that the bait or lure can be cast into the pool and allowed to trail in the outside water. Assuming a continental shelf location (as opposed to abyssal), there is still some outside light, which might be augmented by floodlights outside the dome (to attract fish).

Once the bait is in the water, fishing operation would work much like surface rod and reel ocean fishing. Fish recovered through the moon pool would be stored in live wells (as are used in offshore recreational fishing), which could be sealed and brought inboard to be gradually depressurized (to cut down on exploding fish), before the fish are extracted to be consumed or sold.

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