Edible Insects?
Crickets, bumblebees, ants, mealworms, caterpillars...these and myriad more versions thereof are staple foods sold in hotdog-style vendor stalls from Africa to South America to Asia. I researched some facts, it appears insects have nearly the same (or in many cases more) protein, mineral, vitamin levels compared to similiar amounts of beef or poultry, also much less fatty tissue and the costs of rearing are significantly lower. Converting the cattle industry over to bugs would mostly halt deforestation threatening wide swaths of rainforest. Those of you who go "yuck" at the thought should consider there's no colossal difference between (for example) shrimps and grasshoppers: both have feeler antennas, bulbous little eyes, and live within exoskeletons.
In warmer monthes at night it requires little effort to back-light a white cotton sheet with a bit of slack and a billow at the bottom so crawlies are drawn to the brightness of the material and thus easily collected. Kill the bugs by pinching their chubby little cheeks. Then dry them in the sun, or over a fire. Once dry it's easy to crumble them into a non-descript powder so they can be added later to fortify soups and stews. The "effort-to-energy" ratio is very much on the positive side- though not quite so much as shellfish harvesting, but a great deal moreso than, say, plant-harvesting.
If you've ever walked across a flat farm field in summer, you know the thousands of grasshoppers jumping away can be quite the sight so imagine first switching your fields over to organic fertilizers (don't want pesticide toxins), then erecting mesh netting and hiring people to "herd" the hoppers; theoretically tons could be harvested and turned into protein powder/pet food/human cuisine. The only problem for human consumption is the legs must be plucked, so those big greenish 2 inch varieties more common to eastern Canada might be better for quicker processing. There's already some mom & pop cricket farming for pet stores (grow them in warehouses), never tried eating them nor the reputedly very yummy mealworms, only had chocolate covered ants but have heard the crickets/hoppers are very tasty.